One-pot synthesis of quasi-block fluoropolymers for graded heterojunctions via dual resurfacing

Domain: neuroscience
Published: 2026-04-09
Editorial outcome: minor_revision

Abstract
Graded heterojunctions (GHJs) featuring a gradient donor/acceptor distribution represent an ideal architecture for organic solar cells (OSCs), yet remain challenging to realize. Here, we report a series of fluoropolymers that can form GHJs through surface-energy-driven resurfacing in solution processes. The distinct chemical reactivity of fluorinated versus standard monomers enables the formation of quasi-block copolymers in one-pot polymerization, which rivals the two-step synthesized block copolymer in polymer properties and photovoltaic performance. These fluoropolymers can resurface due to the low-surface-energy fluorinated blocks. During the sequential deposition that small-molecular acceptor solution is cast atop the underlying fluoropolymer film, the acceptor penetrates downwards accompanied by donor resurfacing, consequently generating a vertical donor/acceptor gradient. Moreover, a post-treatment namely fluorous solvent vapor annealing (FSVA) is adopted to further regulate the distribution. The unique solubility of fluoropolymers in fluorous solvents enables fluoropolymers to resurface again, yielding an optimal GHJ to deliver an impressive efficiency of 19.60% in OSCs. Notably, block-containing copolymers achieve superior device performance and more optimal GHJ than the random fluoropolymer, highlighting the importance of monomer sequence. Our findings provide an efficient approach to create GHJs by leveraging surface energy, and also attract attentions to explore the precise structure of copolymers, in particular for fluoropolymers.

Introduction
Heterojunctions comprising two organic semiconductors with cascaded energy levels have been extensively applied in optoelectronics due to their unique merits in accelerating exciton dissociation and enabling ambipolar transporting1-3. In organic semiconductors, excitons (i.e., electron-hole pairs) exhibit strong Coulombic binding energy, necessitating heterojunctions to provide sufficient driving force at the donor-acceptor interfaces for efficient exciton dissociation into free carriers, which it crucial for photoelectric conversion devices such as organic solar cells (OSCs)4, 5. Early planar heterojunctions (PHJs), featuring a bilayer heterojunction placed between two electrodes, wherein the excitons are difficult to reach the interfaces due to limited exciton diffusion lengths and inadequate donor/acceptor interfaces6. Mostly used bulk heterojunctions (BHJs), formed by blend casting donor and acceptor materials7, 8, promote phase separation to create numerous interfaces for effective exciton dissociation but inevitably suffer from charge recombination9-11. Recently, quasi-planar heterojunctions (Q-PHJs) are developed through sequential deposition of donor and acceptor12-14, forming a donor-acceptor mixed layer sandwiched between an acceptor-rich top layer and a donor-rich bottom layer, thereby enhancing ambipolar transport and suppressing charge recombination15, 16. Although Q-PHJs have achieved high efficiencies, there is an urgent need to explore more ideal architectures to further advance OSCs. Graded heterojunctions (GHJs) that features a gradient distribution of donor/acceptor components, combine the short exciton diffusion distances of BHJs with the charge gradient of bilayer heterojunctions. However, it remains challenging to achieve GHJs, particularly through solution processing17-19.

The vertical donor/acceptor distribution in solution-processed heterojunctions is primarily dictated by their intrinsic material properties. Current research efforts predominantly concentrate on leveraging the differential solubility and crystallinity of donor and acceptor materials to modulate vertical phase distribution20-22. However, since both donor and acceptor are composed of similar conjugated structures, their subtle differences are insufficient to confer markedly distinct thermodynamic and kinetic properties during the rapid film-formation process23-25. Surface energy, as an intrinsic material property, is a crucial determinant to impact the stratification of blend films, with components exhibiting lower surface energy tending to spontaneously lift onto the surface during film-forming process26-28. Polyfluoride moieties (e.g., fluoroalkyl chains) are well-known for their capacity to lower surface energy29-32. Nevertheless, their application in controlling donor/acceptor distribution in OSCs remains limited, possibly owing to the miscibility and compatibility issues that emerge from substantial surface energy disparities between donor and acceptor materials33, 34. Block fluoropolymers may present a potential solution to these challenges. In such block copolymers, the fluorine-enriched blocks facilitate surface-energy-driven resurfacing during solution processing, while the other block, with less or no fluorine, maintains acceptable miscibility. Notably, conventional synthetic routes for conjugated block polymers often involve laborious procedures with limited control over block length and sequence precision. Thus, we are inspired to explore a facile approach to synthesize block fluoropolymers, as well as their applications in tuning the donor/acceptor distribution to realize GHJs for OSCs.

In this work, a series of fluoropolymers containing identical monomers but different monomer sequences are designed and prepared. The different chemical reactivity between standard monomer and polyfluorinated monomer helps the resulted copolymers to form quasi-block polymer chains rather than random ones in one-pot polymerization. Notably, the one-pot synthesized qb-PF20 rivals the two-step synthesized block copolymer b-PF20 in both structural precision and optoelectronic performance, while block-containing fluoropolymers outperform the random polymer ra-PF20. In the solution cast, the fluorinated blocks tend to resurface owing to the extra-low surface energy, while the standard blocks ensure the solubility in organic solvent and the miscibility with acceptor. When employing sequential deposition for heterojunction construction, the small-molecule acceptor percolates downwards accompanied by the spontaneous resurfacing of the underlying fluoropolymer. This dual action results in a vertical gradient distribution of donor/acceptor. More importantly, a post-treatment, namely fluorous solvent vapor annealing (FSVA) further elevates the donor due to the selectively solubility of fluoropolymers in the fluorous solvent, consequently providing a more uniform gradient. Based on the optimal GHJ, the corresponding OSCs achieve a power conversion efficiency (PCE) of 19.60% based on the one-step synthesized quasi-block copolymer qb-PF20. This work demonstrates the potential of developing new materials with tailored properties, such as surface energy, to meet the critical requirements of optoelectronic devices.

Results
Synthesis and polymerization kinetics of fluoropolymers

In our previous work, heptafluoroisopropoxyl groups terminated side chains have been demonstrated to reduce surface energy and enhance intermolecular interactions35. Thus, polyfluorinated monomers (D ) containing heptafluoroisopropoxyl groups are introduced into copolymers to reduce surface energy, while standard monomers (D) ensure the solubility and miscibility of the resulted copolymers. The detailed synthetic routes for the monomers are illustrated in Supplementary Fig. 1 and their chemical structures are conclusively verified using nuclear magnetic resonance (NMR) spectra and mass spectra. The copolymers qb-PFX (X = 10, 20, 30, denoting D contents of 10%, 20% , and 30% respectively) are synthesized via one-pot Stille cross-coupling reaction with D , D and the comonomer A (Fig. 1a), while lab-made PM6 (Supplementary Fig. 2) with D and A is prepared as the counterpart. Gel permeation chromatography (GPC) is employed to determine the molecular weight (M ) and polydispersity index (PDI), and the values of as-synthesized fluoropolymers are similar with that of PM6 (Supplementary Fig. 3). Both the qb-PFX series and PM6 exhibit excellent solubility in common organic solvents (e.g., chloroform and chlorobenzene). As expected, the fluoropolymers show slight solubility in fluorous solvents like perfluorotoluene (PFT), whereas PM6 is virtually insoluble (Supplementary Fig. 4).

Notably, the polyfluorinated monomer D exhibits higher reactivity than the common monomer D, which might be attributed to the strong polarization and coordination ability of hepafluoroisopropoxyl groups36, 37. Thus, the existence of D accelerates the polymerization. Taking qb-PF20 as an example, the mixture solution becomes dark red after heating at 80 ℃ for 30 min, whereas the PM6 polymerization under identical conditions appears as an orange solution (Supplementary Fig. 5). To further investigate the distinct polymerization kinetics between qb-PF20 and PM6, parallel reactions are conducted at 80 ℃ with equal-volume aliquots withdrawn at 30, 60, 90 and 120 min for subsequent GPC and NMR characterizations. The GPC elution curves (Supplementary Fig. 6) reveal that PM6 predominantly exhibits monomer signals after 30 min, while qb-PF20 already displays prominent oligomer formation. Notably, monomer signals in qb-PF20 nearly disappears by 120 min, confirming the accelerated polymerization rate for the fluoropolymer. To quantitatively evaluate monomer conversion, 1H NMR measurements are performed on PM6 and qb-PF20 samples at different reaction times using an equimolar amount of 1,4-dibromo-2,5-diiodobenzene as the internal standard. As depicted in Supplementary Figs. 7-9, the progressive decrease in integral ratios of monomer A quantitatively reflects monomer consumption during polymerization, with the fluoropolymer qb-PF20 consistently exhibiting higher monomer conversion rates relative to PM6 throughout the reaction time. Upon extending the reaction to 120 min, monomer signals in qb-PF20 become nearly undetectable with a conversion rate of 0.91, demonstrating the significantly enhanced reaction kinetics imparted by fluorinated monomers. Thus, we speculate this reactivity disparity would influence monomer sequence in polymer chains, i.e., qb-PFX may form as quasi-block copolymers rather than random copolymers. To verify this, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is used to analyze oligomer compositions during the early polymerization stage (80 ℃ for 30 min), with the segments and corresponding molecular mass summarized in Supplementary Fig. 10. As shown in Fig. 1b, the characteristic signals of fluorinated monomer D -based segments including D -A, D -A-D , D -A-D -A and D -A-D -A-D , consistently exhibit higher intensity than corresponding segments only containing the monomer D, suggesting the higher reactivity of D drives preferential polymerization to form fluorine-enriched blocks. Meanwhile, the hybrid segments combining both D and D, like D -A-D and D -A-D-A shows very weak intensity in the early polymerization stage. To further analyze the distribution of D and D segments, preparative GPC is employed to separate oligomers with varying molecular weights. Through systematic optimization of mobile phase, temperature and flow rate, the oligomers and monomers can be separated with the retention time peaks of 37.3 and 44.5 min (Supplementary Fig. 11). The two collected fractions (oligomer-1 and oligomer-2) are characterized by 1H NMR after solvent removal. Although aromatic proton signals of oligomers are difficult to resolve, the relative proportions of D and D segments are determined by comparing integral ratios of the methylene groups connected to thiophene in sidechains and heptafluoroisopropoxyl groups. Notably, oligomer-2 contains a markedly higher proportion of D -containing segments than D-based segments, with an integral ratio of 1:0.28 (Supplementary Fig. 12). As for higher molecular weight oligomer-1, the relative content of D -based segments is further increased, yielding an integral ratio of 1:0.16. These results suggest that the highly reactive D preferentially polymerize to form fluorine-rich blocks with considerable numbers of repeat units, consequently delivering a quasi-block copolymer.

To further elucidate the pivotal role of monomer sequence in determining polymer properties and photovoltaic performance, two well-defined fluoropolymer derivatives, a block copolymer and a random copolymer, are synthesized as control samples. Based on the preliminary data (Supplementary Figs. 13-20 and Supplementary Tables 1-5), qb-PF20 demonstrates balanced physicochemical properties and superior photovoltaic performance among qb-PFX. Thus, the optimal D content 20% is also employed in the block and random copolymers. As illustrated in Fig. 1c-d, the block copolymer (b-PF20) and random copolymer (ra-PF20) are synthesized through controlling monomer addition sequences. To obtain the copolymer b-PF20, 0.2 equivalent (eq) each D and A monomers are initially reacted at 90 ℃ for 2 h to form D -A oligomers, followed by the addition of 0.8 eq each D and A, and then the mixture is heated to 120 ℃ and kept for 24 h. For the copolymer ra-PF20, the polymerization of 0.8 eq each D and A monomers is initiated by heating to 120 ℃, immediately followed by the dropwise addition of 0.2 eq each D and A monomers in 50 min. Since the monomer D shows higher reactivity than D, the dropwise addition of D in the early polymerization stage ensures the fluorinated monomer will randomly and evenly distribute in oligomers to form a random copolymer. Both copolymers exhibited comparable molecular weight to qb-PF20, thereby minimizing the influence of various molecular weight on polymer properties (Supplementary Fig. 21).

Polymer properties of fluoropolymers with distinct monomer sequence

To study the fluorine effect on surface energy, the contact angle measurement of these three copolymers with different monomer sequence is carried out. As shown in Fig. 2a and Supplementary Fig. 22, the surface energies of ra-PF20, qb-PF20, and b-PF20 neat films are calculated according to Wu’s model, as 19.76, 19.20 and 19.03 mN m-1, respectively. As expected, these fluoropolymers exhibit evidently smaller surface energy than PM6 (20.77 mN m-1). Notably, the surface energy of qb-PF20 is comparable to that of b-PF20 but obviously lower than ra-PF20, further confirming qb-PF20 synthesized via one-pot polymerization is a quasi-block copolymer rather than a random copolymer. Moreover, the measured surface energy reflects the overall property of the (quasi-)block copolymer, while the fluorinated block should inherently possess a lower surface energy. As a result, fluorinated blocks can make qb-PF20 and b-PF20 resurface spontaneously during the solution cast to form a stratified film. To verify it, the stratification of ra-PF20, qb-PF20, and b-PF20 neat films is examined using time-of-flight secondary ion mass spectrometry (TOF-SIMS). As illustrated in Fig. 2b, the characteristic (CF ) (CF)O- ion signals of qb-PF20 and b-PF20 exhibit a similar trend featuring with a rapid decline at the initial sputtering stage, which indicates an enrichment of the polyfluorinated moiety in the top layer of these two films. Compared with qb-PF20 and b-PF20, the intensity of (CF ) (CF)O- ion in the random copolymer ra-PF20 is obviously weaker in the top layer because ra-PF20 has a more uniform distribution of polyfluorinated monomers. These results suggest that one-pot synthesized qb-PF20 is predominantly consists of localized fluorinated blocks rather than being uniformly and randomly distributed throughout the polymer chains. More importantly, some studies demonstrated that the fluorinated units and molecules preferentially migrate to the surface owing to their low surface energy26, 28, 38, suggesting these fluorinated blocks accompanied by the whole polymer chain will migrate to the surface during the film-formation process. To evaluate the thermodynamic difference among these copolymers, differential scanning calorimetry (DSC) measurements are conducted on ra-PF20, qb-PF20 and b-PF20 copolymers. As shown in Supplementary Fig. 23, the melting peak of qb-PF20 (328.1 ℃) in the heating scan is closer to that of b-PF20 (329.5 ℃) than ra-PF20 (324.9 ℃), indicating not only the formation of fluorine-containing blocks in qb-PF20 but also a higher packing order and crystallinity in block copolymers.

To study the molecular packing and morphology of these copolymers with different monomer sequences, grazing-incidence wide-angle X-ray diffraction (GIWAXS) and atomic force microscopy (AFM) measurements are conducted, while PM6 is used as control. As shown in the 2D GIWAXS pattern (Supplementary Fig. 24), all polymers exhibit a preferential face-on orientation. The corresponding 1D GIWAXS profiles (Fig. 2c and Supplementary Table 6) reveal π-π stacking peaks at 1.745, 1.761, 1.767 and 1.769 Å-1, corresponding to d-spacings of 3.601, 3.568, 3.556 and 3.552 Å for PM6, ra-PF20, qb-PF20, and b-PF20, respectively. Furthermore, the crystal coherence length (CCL) values representing the crystallinity are calculated, and the values are 21.34, 22.18, 22.80, and 22.62 Å for the respective polymers. These results demonstrate that incorporating polyfluorinated units in the side chains enhances the molecular packing of the relevant copolymers, relative to the original polymer PM6. Furthermore, qb-PF20 achieves ordered packing and high crystallinity comparable to b-PF20, due to the existence of fluorinated blocks. As shown in Fig. 2d and Supplementary Fig. 25, the PM6 neat film exhibits a smooth surface with slimmer domain and a low root-mean-square roughness (R ) of 1.12 nm. In contrast, all fluoropolymers display distinct fibrillar morphologies with increased surface roughness. Notably, the higher R values of qb-PF20 (1.47 nm) and b-PF20 (1.56 nm) relative to ra-PF20 (1.29 nm) suggest that block formation enhances molecular aggregation and serve as crystalline nucleus to promote crystallinity. The optical and electrochemical properties for these copolymers composed of identical monomers but distinct sequences also exhibit sequence-dependent behavior. As shown in Fig. 2e, Supplementary Fig. 26a, and Supplementary Table 7, all polymers exhibit similar absorption profiles featuring two characteristic peaks at around 576 and 616 nm corresponding to 0-1 and 0-0 transitions, respectively. All fluoropolymers exhibit higher 0-0/0-1 peak intensity (A /A ) ratios than PM6 in both solution and solid states. Notably, both qb-PF20 and b-PF20 display marginally higher molecular extinction coefficients and A /A ratios compared to ra-PF20, suggesting the enhancement of molecular packing induced by block formation. Moreover, the block-containing copolymers feature slightly deep HOMO/LUMO energy levels (Fig. 2f and Supplementary Fig. 26b).

Photovoltaic performance of blend-cast OSCs

To systematically assess the impact of monomer sequence on the photovoltaic performance, OSCs are fabricated by employing ra-PF20, qb-PF20, and b-PF20 as donor along BTP-eC9 as acceptor. As shown in current-density-voltage (J-V) characteristic curves (Fig. 3a) and corresponding parameters (Table 1) of the optimized devices, the control PM6:BTP-eC9 exhibits a PCE of 17.91% with an open-circuit voltage (V ) of 0.848 V, a short-circuit current density (J ) of 27.52 mA cm-2, and a fill factor (FF) of 76.74%. In contrast, the fluoropolymer-based devices all display superior PCE with synergistic improvements of photovoltaic parameters. Notably, the qb-PF20:BTP-eC9 device demonstrates a superior PCE of 18.97% to ra-PF20:BTP-eC9 device (18.54%), attributable to synergistic enhancements in V (0.862 V), J (28.05 mA cm-2) and FF (78.47%). The elevated V and J of block-containing copolymer-based device is associated with the suppressed charge recombination and improved charge transport. Remarkably, the qb-PF20:BTP-eC9 device achieves near-identical device efficiency to its block counterpart b-PF20 (19.03%) with comparable photovoltaic parameters, demonstrating that the one-pot synthesized quasi-block copolymer rivals the two-step synthesized block copolymer in photovoltaic performance. External quantum efficiency (EQE) spectra indicate that OSCs based on fluoropolymers exhibit enhanced EQE values compared to the PM6:BTP-eC9 device (Fig. 3b), particularly in the donor absorption region. This improvement is ascribed to optimized packing order and crystallinity induced by fluorinated side-chain incorporation. Furthermore, devices incorporating block-containing copolymers demonstrate superior photoresponse relative to ra-PF20, suggesting more efficient charge transfer and collection. Given the comparable HOMO energy levels of the copolymers yet distinct V in the devices, the electroluminescence external quantum efficiency (EQE ) of devices is measured to quantificationally analyze the energy losses from different contributions. As summarized in Fig. 3c, Supplementary Fig. 27, and Supplementary Table 8, the radiative recombination losses derived from absorption above (∆E ) and below (∆E ) bandgap exhibit minimal variation, suggesting similar charge-transfer state39. Notably, the non-radiative recombination loss (∆E ) values are calculated to be 0.249, 0.245, 0.236, and 0.239 eV for devices based on PM6, ra-PF20, qb-PF20, and b-PF20, respectively. These results demonstrate that the enhanced crystallinity of block-containing copolymers (qb-PF20 and b-PF20) relative to ra-PF20, effectively reduce energy disorder, thereby mitigating energy loss.

To gain deeper insight into the carrier dynamics, the exciton dissociation (P ) and charge collection probabilities (P ) are estimated from the effective voltage (V ) versus photocurrent density (J ) relationship. As shown in Fig. 3d, the devices incorporating fluoropolymers exhibit higher P and P values than PM6-based device. Notably, the qb-PF20 based device demonstrates comparable P and P values to those of b-PF20 counterpart, with both devices exhibiting higher P /P values than ra-PF20 based device. To characterize the charge transport properties, the hole mobility (µ ) and electron mobility (µ ) are determined by space-charge-limited current (SCLC) model. As summarized in Fig. 3e and Supplementary Fig. 28, the µ /µ values are 6.88/7.92×10-4, 7.54/8.69×10-4, 8.03/8.93×10-4, and 8.18/9.07×10-4 cm2 V-1 s-1 for PM6:BTP-eC9, ra-PF20:BTP-eC9, qb-PF20:BTP-eC9, and b-PF20:BTP-eC9 devices, respectively. Notably, the higher and more balanced mobilities of devices employing block-containing copolymers as donors than ra-PF20 counterpart, correlate with the enhanced packing order and improved crystallinity induced by block formation. To investigate the charge recombination behaviors, we examine the dependence of V and J on incident light intensity (P ). The relationships between V /J and P can be expressed as V ∝n(kT/q)ln(P ) and J ∝P α, respectively (where k is the Boltzmann constant, T is the Kelvin temperature, and q is the elementary charge). As shown in Fig. 3f, the slope n values are 1.15, 1.13, 1.07 and 1.08 kT/q and the α values are 0.973, 0.975, 0.982 and 0.980 for PM6:BTP-eC9, ra-PF20:BTP-eC9, qb-PF20:BTP-eC9, and b-PF20:BTP-eC9 devices, respectively. These results demonstrate that devices incorporating block-containing copolymers show progressively reduced trap-assisted and bimolecular recombination, consistent with their enhanced packing order and crystallinity. In summary, the device employing qb-PF20 possesses essentially equivalent carrier dynamics compared with the b-PF20 device, while both systems exhibit superior exciton dissociation, balanced charge transport and suppressed charge recombination relative to the ra-PF20 device. These findings indicate that introducing well-defined block sequences rather than randomly distributed sequences into the copolymer can afford superior optoelectronic properties.

Photovoltaic performance of sequential-deposited OSCs and the effect of FSVA

Based on the above results, the block-containing copolymers qb-PF20 and b-PF20 exhibit the potential to resurface in solution processes, and the one-pot synthesized qb-PF20 rivals the two-step synthesized b-PF20 in photovoltaic performance. Consequently, qb-PF20 is selected as the donor material for the fabrication of graded heterojunctions via sequential deposition (SD). However, the initial SD attempt failed to yield a uniform film (inset of Fig. 4a), resulting in a reduced PCE of 17.84% with a large fluctuation of 1.49%, significantly worse than the benchmark BC-processed devices (a PCE of 18.97% with only 0.33% fluctuation). TOF-SIMS analysis (Fig. 2a) has identified a fluorine-enriched surface in the as-cast qb-PF20 film, which may induce a significant surface-energy disparity between the underlying qb-PF20 and overlying BTP-eC9 that impeded the latter solution infiltration. To address this, perfluorotoluene is employed as a cosolvent for the process of BTP-eC9, due to its selective solubility for polyfluorinated groups and excellent miscibility with chloroform. Adding only 0.5 vol% PFT into the BTP-eC9 solution enables the formation of a high-quality blend film (inset of Fig. 4a). As summarized in Table 1, the fluorous solvent-assisted SD device (defined as SD/FS) with uniform blend films achieved a higher PCE of 19.12% associated with a V of 0.862 V, a J of 28.25 mA cm-2, and an FF of 78.53%. Notably, the organic/fluorous mixed solvent is also applicable in other fluoropolymers. As shown in Supplementary Fig. 29 and Table 1, the SD/FS processed devices for ra-PF20/BTP-eC9 and b-PF20/BTP-eC9 achieve PCEs of 18.71% and 19.07%, respectively. These results further demonstrate that the quasi-block copolymer qb-PF20 rivals the block copolymer b-PF20 in the devices prepared by various methods.

The significantly different performance of the SD and SD/FS devices prompted an investigation into film formation kinetics using in-situ time-resolved UV-Vis absorption spectroscopy40, 41. The maximum absorption peaks of qb-PF20 and BTP-eC9 are employed as the sign to reflect the molecular packing, and Supplementary Fig. 30 illustrates the change of maximum absorption peaks following the spin-coating time. During the cast of BTP-eC9, the absorption of qb-PF20 changes in different ways depending on solvents for BTP-eC9. When the BTP-eC9 chloroform solution is dropped atop the underlying qb-PF20 film, the maximum peak of qb-PF20 declines to 612 nm initially attributed to solvent-induced swelling of the pre-fabricated film, and then almost equilibrates at 612-613 nm until 0.4 s. In contrast, the deposition of BTP-eC9 in organic/fluorous cosolvent induces a steep decline of qb-PF20 to 608 nm followed by a gradual rise to 614 nm from 0.1-0.4 s. In this period from 0-0.4 s, the underlying qb-PF20 will swell accompanied by the penetration of BTP-eC9. Evidently, the existence of fluorous solvent PFT enhances wettability during the second deposition, promoting qb-PF20 swelling and intermolecular interactions with BTP-eC9. Without PFT, the absorption peak of BTP-eC9 starts to red-shift at 0.4 s and achieves 821 nm at 0.6 s, indicating the molecular aggregation process is around 0.2 s. Meanwhile, the packing of BTP-eC9 costs 0.3 s (from 0.3 to 0.6 s) with the existence of PFT, wherein the prolonged aggregation can facilitate nanoscale phase separation.

Sequential deposition enables the formation of heterojunction with a donor-rich bottom and an acceptor-rich top, which is beneficial to suppress charge recombination between the active layer and carrier transporting layer. However, the significant different surface energy between qb-PF20 and BTP-eC9, combined with rapid solution process causes excessive confinement of the donor and acceptor to the bottom and top, respectively. Although redissolution and vertical redistribution of partial qb-PF20 occur during secondary spin-coating, this self-adjustment only alleviates the unfavorable situation. To achieve optimized gradient distribution of donor and acceptor, we implement a fluorous solvent vapor annealing (FSVA) post-treatment based on our recent findings that polyfluorinated polymers undergo selective molecular reorganization with the help of fluorous solvents35, 42-44. Thus, the vapor of the fluorous solvent PFT is speculated to provide a slight solubility for qb-PF20 and then induce its resurfacing to further regulate vertical donor/acceptor distribution. After the optimizing FSVA post-treatment at 100 ℃ for 3 min (Supplementary Table 9), the device (defined as SD/FS-FSVA) achieves a champion PCE of 19.60% with a V of 0.868 V, a J of 28.42 mA cm-2, and an FF of 79.44% (Fig. 4a and Table 1).

Notably, the FSVA treatment may facilitate the formation of a gradient donor-acceptor distribution to enhance exciton dissociation and mitigate energy loss. EQE spectra demonstrate that SD/FS-FSVA device exhibits enhanced photoresponse relative to SD and SD/FS devices particularly in the donor absorption region (Fig. 4b), suggesting FSVA can enhance packing order of qb-PF20 to facilitate the photon-to-electron conversion. As summarized in Fig. 4c, Supplementary Fig. 31, and Supplementary Table 10, the ∆E values are determined to be 0.240, 0.233, and 0.228 eV for the SD, SD/FS, and SD/FS-FSVA devices, respectively, indicating that FSVA treatment can optimize the donor/acceptor distribution and molecular packing to reduce energy loss. To further demonstrate the effect of FSVA in carrier dynamic behaviors, the exciton dissociation, charge extraction, transport, and recombination are systematically measured for SD, SD/FS, and SD/FS-FSVA devices. As shown in Fig. 4d, SD/FS-FSVA device exhibits P and P values of 97.74% and 89.85%, respectively, which is obviously higher than those of the SD and SD/FS devices, evidencing more efficient exciton dissociation and charge extraction after FSVA post-treatment. Regarding charge transport properties, SD/FS-FSVA devices show higher and more balanced carrier mobilities compare to SD and SD/FS counterparts (Fig. 4e and Supplementary Fig. 32). To validate suppressed charge recombination, the light density-dependence V and J characteristics are measured. As shown in Fig. 4f, the slope n values are 1.10, 1.06, and 1.04 kT/q and the α values are 0.980, 0.988, and 0.991 for SD, SD/FS, and SD/FS-FSVA devices, respectively. These trends unambiguously demonstrate that FSVA post-treatment effectively suppresses both trap-assisted and bimolecular recombination. Briefly, the SD/FS-FSVA device demonstrates significantly improved exciton dissociation and charge transport, minimized energy loss, and suppressed charge recombination, attributes directly linked to its optimized gradient donor-acceptor distribution.

The post-treatment FSVA is also employed in devices based on ra-PF20 and b-PF20 to elucidate the effect of distinct monomer sequences. After many attempts, the optimal FSVA conditions for b-PF20 and ra-PF20 based devices are 90 ℃ for 5 min and 100 ℃ for 5 min, respectively (Supplementary Tables 11-12). The lower processing temperature for b-PF20 and the longer annealing time for ra-PF20 compared to qb-PF20 (100 ℃ for 3 min) can be attributed to their distinct surface fluorine distributions, i.e., polyfluoride moieties are more localized and dispersive in b-PF20 and ra-PF20, respectively. As shown in Supplementary Fig. 33 and Table 1, the SD/FS-FSVA processed b-PF20/BTP-eC9 device achieves a champion PCE of 19.71% with a V of 0.866 V, a J of 28.49 mA cm-2, and an FF of 79.87%. The photovoltaic performance based on b-PF20 and qb-PF20 markedly surpass those of the ra-PF20 based device (18.82%), highlighting the selective efficacy of FSVA treatment on block-containing fluoropolymers. Furthermore, the SD/FS-FSVA method is also more effective for qb-PF20 and b-PF20 in optimizing carrier dynamics (Supplementary Figs. 34-35 and Supplementary Tables 13-14), further confirming the synergetic role of block-containing fluoropolymers and FSVA treatment in optimizing gradient donor-acceptor distribution.

GHJ formation mechanism and universality

Compared with the blend-cast OSCs, the enhancements in photovoltaic performance and carrier dynamics of sequential-deposited devices, in particular the ones with FSVA, can be attributed to the optimal vertical phase distribution. To elucidate the graded heterojunction (GHJ) formation, the surface and depth-dependent properties of qb-PF20/BTP-eC9 blend films are characterized. As presented in Supplementary Fig. 36, the surface energy of the SD/FS-FSVA film (20.41 mN m-1) is significantly lower than that of the SD/FS film (21.34 mN m-1), demonstrating FSVA renders the resurfacing of qb-PF20 that consequently enables secondary regulation of the vertical distribution. The essential role of perfluorotoluene is further investigated by applying conventional organic solvent (toluene) vapor annealing (OSVA) post-treatment to qb-PF20/BTP-eC9 devices (denoted as SD/FS-OSVA). As summarized in Supplementary Table 15, the PCEs of SD/FS-OSVA devices remain inferior to SD/FS-FSVA devices while close to SD/FS devices, suggesting the limited ability of toluene to reorganize fluoropolymer. This performance difference may arise from the preferential dissolution of small-molecule acceptor in toluene over the fluoropolymer, as reflected in the distinct surface energy. Specifically, the SD/FS-OSVA blend film exhibits a surface energy of 21.62 mN m-1 (Supplementary Fig. 36), significantly higher than that of SD/FS-FSVA film and slightly elevated relative to SD/FS films, reaffirming the critical role of fluorous solvent in resurfacing fluoropolymer and optimizing GHJ. Furthermore, the donor/acceptor distribution in the vertical direction is quantitatively analyzed by TOF-SIMS. Depth profiles of CN- (representing the acceptor BTP-eC9) and F- (representing the donor qb-PF20) are shown in Fig. 5a-b. The CN- signal is intensive in the initial sputtering stage, decaying gradually with depth, whereas the F- signal shows an inverse trend that increases progressively during sputtering. In simpler terms, BTP-eC9 content gradually decreases and qb-PF20 content increases from the blend film surface to substrate, illustrating these films are GHJs. To verify the effect of FSVA in manipulating the donor/acceptor distribution, the change slopes of CN- and F- signals over a sputtering time of 0-200 s are fitted and presented in the insets of Fig. 5a-b. Compared to the SD/FS film, the SD/FS-FSVA film exhibits smaller slopes in both CN- and F- profiles, i.e., an optimized GHJ with a more even gradient donor/acceptor distribution, owing to that qb-PF20 continually resurfaces during FSVA treatment. To identify the superiority of block-containing fluoropolymers in GHJ formation, TOF-SIMS measurement is also conducted in the ra-PF20 and b-PF20 based films. As depicted in Supplementary Fig. 37, compared with the qb-PF20 counterpart, the SD/FS-FSVA-processed b-PF20/BTP-eC9 film display similar trends with slightly smaller slopes in both CN⁻ and F⁻ depth profiles, while the slopes of the ra-PF20/BTP-eC9 film is obviously bigger, indicating an inferior gradient distribution in the case of the random copolymer. These results demonstrate that fluorinated blocks with low surface energy can facilitate the resurfacing of polymer donors to realize optimal GHJs.

Besides donor/acceptor distribution, the molecular packing is investigated by in-situ film-depth-dependent light absorption spectroscopy (FLAS). SD/FS and SD/FS-FSVA blend films are sequentially etched by soft plasma and the absorption spectra of the remaining layers are monitored. Absorption difference between the original and remaining film are transformed to reflect the absorption of each etched layer45, 46. As displayed in Fig. 5c and Supplementary Fig. 38, the A /A ratio of qb-PF20 increases from 1.54 to 2.12 after FSVA with enhanced 0-0 peaks in each etched layers, suggesting FSVA improves packing order of the fluoropolymer. Meanwhile, FSVA induces a 3 nm red-shift in qb-PF20 maximum peak, versus only 1 nm for BTP-eC9, indicating preferential reorganization of the fluoropolymer. To further validate this, GIWAXS measurements are performed on SD/FS and SD/FS-FSVA blend films (Supplementary Fig. 39 and Supplementary Table 16). Notably, the SD/FS-FSVA film exhibits reduced d-spacing and increased CCL values relative to the SD/FS film, demonstrating that FSVA treatment enhances packing order and crystallinity. Collectively, these results show that FSVA optimizes the graded heterojunction by regulating vertical donor/acceptor distribution and improving fluoropolymer packing order.

Based on the aforementioned results, the GHJ formation and optimization mechanism is schematically illustrated in Fig. 5d. The fluorinated blocks containing heptafluoroisopropoxyl groups decrease surface energy of fluoropolymers, and then endow them the capability of resurfacing in solution processes. During the sequential deposition, the fluorine-enriched surface increases the difficulty for the percolation of BTP-eC9. To mitigate this issue, the organic/fluorous mixed solvents facilitate BTP-eC9 to successfully percolate into the fluoropolymer mesh, while the fluoropolymer would partially redissolve and resurface during the cast of BTP-eC9. Thus, the first regulation of the vertical distribution is achieved to provide a crude GHJ. Further treating with FSVA, the fluorous solvent penetrates into GHJ and selectively lift the fluoropolymer, realizing the secondary regulation of the gradient distribution. This two-stage resurfacing are driven by extra-low surface energy of fluorinated blocks, whereas the second resurfacing is assisted by the fluorous solvent, ultimately yielding an optimal GHJ with ideal gradient donor/acceptor distribution.

Batch-to-batch reproducibility in OSCs remains a significant challenge due to inevitable variations in M and PDI of polymers. Notably, the synthesis of block-containing copolymers addresses this issue through controlled, stepwise polymerization that forms well-defined blocks, effectively minimizing batch-to-batch variations in device performance. To confirm it, three additional batches of ra-PF20, qb-PF20 and b-PF20 with different M and PDI are synthesized, as detailed in Supplementary Fig. 40 and Supplementary Table 17. These polymers are then associated with BTP-eC9 and fabricate OSCs using the SD/FS-FSVA method to investigate the dependence of PCEs versus copolymer M (Supplementary Fig. 41 and Supplementary Table 18). While all devices exhibit reduced performance with decreasing polymer M , ra-PF20 based devices suffer an obvious decline of PCE (10.4% at M of 25.6 kDa) compared to the best batch. In contrast, all batches qb-PF20 and b-PF20 based devices maintain almost identical V and slightly declined J and FF, resulting in mitigated PCE losses of 7.4% (at M of 24.6 kDa) and 6.8% (at M of 25.7 kDa), respectively. These results demonstrate the superior molecular weight insensitivity of block-containing fluoropolymers compared to random copolymer, highlighting the importance of precise monomer sequence control in optimizing batch-to-batch reproducibility of OSCs. To further evaluate the universality of fluoropolymers and FSVA combined strategy, other representative acceptors L8BO and Y6 are paired with ra-PF20, qb-PF20 and b-PF20 to fabricate both BC and SD/FS-FSVA devices. J-V curves and corresponding photovoltaic parameters are presented in Supplementary Fig. 42 and Supplementary Tables 19-20. Crucially, SD/FS-FSVA devices demonstrate consistently higher PCEs than their BC counterparts across both L8BO and Y6 systems. Notably, qb-PF20/L8BO and b-PF20/L8BO based devices via SD/FS-FSVA method achieve remarkable PCEs of approximately 19.50%. The efficiency improvements prove more pronounced in block-containing copolymers compared to random copolymer, underscoring the superiority and broad applicability of the block fluoropolymer-FSVA synergistic strategy.

Methods
Polymerization of qb-PF20, b-PF20, and ra-PF20

The chemical structure of monomer D are confirmed by NMR spectra and mass spectra (Supplementary Figs. 43-54). The quasi-block copolymer qb-PF20 is synthesized via one-pot polymerization. A mixture of D (25.7 mg, 0.02 mmol), D (75.2 mg, 0.08 mmol), A (76.7 mg, 0.10 mmol), and Pd(PPh ) (4.6 mg, 0.004 mmol) in dry toluene/DMF (5 mL/1 mL) was degassed via three freeze-pump-thaw cycles and refluxed at 120 ℃ for 24 h under inert atmosphere. For the synthesis of block copolymer b-PF20, a two-step polymerization is employed. A mixture of D (25.7 mg, 0.02 mmol), A (15.3 mg, 0.02 mmol), and Pd(PPh ) (4.6 mg, 0.004 mmol) in toluene/DMF was initially reacted at 90 ℃ for 2 h, followed by the addition of D (75.2 mg, 0.08 mmol) and A (61.4 mg, 0.08 mmol), and then the mixture is heated to 120 ℃ and kept for 24 h. For the random copolymer ra-PF20, a mixture of D (75.2 mg, 0.08 mmol), A (61.4 mg, 0.08 mmol), and Pd(PPh ) (4.6 mg, 0.004 mmol) in toluene/DMF was first heated to 120 ℃, immediately followed by the dropwise addition of D (25.7 mg, 0.02 mmol) and A (15.3 mg, 0.02 mmol) in 50 minutes. After the polymerization is completed, the solution was cooled to room temperature and added dropwise into methanol. The precipitate was collected and purified via Soxhlet extraction using methanol, hexane, acetone, chloroform, and chlorobenzene in sequence. The chlorobenzene fractions were concentrated, reprecipitated into methanol, and dried under vacuum overnight to afford qb-PF20, b-PF20, and ra-PF20 copolymers. GPC: qb-PF20: M = 44 kDa, PDI = 2.03; b-PF20: M = 47 kDa, PDI = 2.24; ra-PF20: M = 45 kDa, PDI = 2.00.

General methods

1H NMR and 19F NMR spectra of monomers were measured by a Bruker AV-400 (400 MHz) spectrometers with CDCl solvent. To study the polymerization kinetics, parallel reactions of PM6 and qb-PF20 were conducted at 80 ℃ with equal-volume aliquots withdrawn at 30, 60, 90 and 120 min. To further investigate the oligomer distributions, the molar ratio of D :D is 1:1 and refluxed at 90 ℃ for 30 min and the obtained oligomers were measured by MALDI-TOF mass spectrometry. The preparative GPC was employed to separate the oligomers using tetrahydrofuran at 30 °C with a flow rate of 2.5 mL/min. The molecular weight and distribution were determined by Shimadzu-20A GPC. TOF-SIMS spectra of samples were analyzed by double-beam analysis mode on TOF-SIMS 5-100. DSC measurements were performed on PerkinElmer DSC8500 calorimeter using a heating/cooling rate of 10 °C/min. Absorption spectra were recorded on the UV-2700 spectrophotometer. Cyclic voltammetry measurements of the materials were conducted on a CHI660D electrochemical workstation. AFM images of films were detected by a Bruker Multimode 8. GIWAXS characterizations of films were performed at the BL14B1 beamline of Shanghai Synchrotron Radiation Facility (SSRF). In-situ UV-Vis spectrometer consists of light source, detector and spin coating instrument. The detector collected the absorption spectra during spin-coating of active layer solution. FLAS spectra was obtained upon a spectrometer. In-situ oxygen plasma etching was utilized to extract the depth-dependent absorption spectrum for the active layer.

Device fabrication

The opaque device is fabricated with a conventional structure. The pre-pattern ITO was scrubbed and cleaned sequentially using deionized water, acetone, and isopropanol, and treated by UV-Ozone for 10 min. A thin PEDOT:PSS layer is spin-coated onto the substrates at 5000 rom for 45 s and baked at 150 ℃ for 10 min. Subsequently, the 0.5 mg mL-1 self-assembled monolayer Ph-4PACz in i-PrOH:toluene (0.6:0.4) were spin-coated at 3000 rpm for 45 s with TA at 110 ℃ for 5 min. For BHJ structure prepared by BC method, the polymer and BTP-eC9 are dissolved in chloroform at the polymer concentration of 7.2 mg/mL with 10 mg/mL 1,3,5-trichlorobenzene (TCB) as solid additive, and stirred at 60 ℃ for 4 h. After the active layer is spin-coated, the films were treated by thermal annealing at 100 ℃ for 5 min. Subsequently, the 0.5 mg/mL PNDIT-F3N methanol/acetic acid (0.995/0.005, v/v) solution was spin-coated. Finally, 100 nm Ag was evaporated and deposited as the anode. For SD process devices, the copolymers (qb-PF20, b-PF20, and ra-PF20) and BTP-eC9 are separately dissolved in chlorobenzene and chloroform with the concentration of 10.5 mg/mL and 9.5 mg/mL. To obtain the high-quality blend film, 0.5 vol% PFT is added into acceptor solution. In detail, the donor solution was firstly spin-coated, then the film is left in a vacuum for 5 minutes. Afterwards, the BTP-eC9 solution with 10 mg/mL TCB is further spin-coated to acquire the active layer film. As for the FSVA post-treatment, the fabricated blend films are placed onto a stand in an airtight brown jar and 200 μL PFT was added into the jar, and the brown jar was put onto the hotplate with different annealing temperature and time. After FSVA treatment, the active layers were placed under vacuum for 5 minutes to ensure the removal of fluorous solvent residues.

Device characterization

The J-V curves of devices were tested under AM 1.5 G illumination (100 mW cm-2) by a Keithley 2420 Source-Meter together with a 300 W Xe lamp solar simulator (Enlitech SS-F5-3A). The EQE spectra was acquired on an Enlitech EQE system (Enlitech QE-M110) with a monochromator and 75 W Xe lamp and checked with a calibrated Si diode. The details of other measurements related to device dynamic behaviors are shown in the Supplementary Information. V equals the the applied bias minus the voltage where photocurrent is zero, and J represents the current density differences between illumination and dark. At a sufficiently high V , it is assumed that all excitons are dissociated into free charges, and the photogenerated current reaches the maximum saturation (J ). The P and P of the devices were calculated from the J /J values under short-circuit condition and maximum power output conditions, respectively. SCLC measurements were carried out using hole-only and electron-only device with the configurations of ITO/PEDOT:PSS/Active layer/MoO /Ag and ITO/ZnO/Active layer /PNDIT-F3N/Ag. Subsequently, the carrier mobilities in active layers were determined by fitting the dark current of hole/electron-only devices to the SCLC model. A digital source meter (Keithley 2400) and a picoammeter (Keithley 6482) were utilized for the EQE measurements. The former was applied to inject electric current into the solar cells to emit the photons, which will be collected using a Si diode and form electric current that can be measured by the latter.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "There are numerous interests to develop ideal heterojunction morphology, the graded heterojunctions (GHJ) with a gradient distribution of donor and acceptor materials are of high interest. In this work, the authors proposed a new method to realize GHJs by employing block fluoropolymers, which simultaneously possess the extra-low surface energy and the suitable compatibility. The increased chemical reactivity of fluorinated monomers compared with conventional monomers facilitates the synthesis of block copolymers in the one-pot reaction. By leveraging the extra-low surface energy of polyfluoride blocks, the polymer is able to resurface in the solution processes, while the standard blocks ensure the miscibility with acceptor materials. As the result, a crude GHJ is achieved during the sequential deposition, attributed to the resurfacing of the fluoropolymer and the permeation downwards of the small-molecule acceptor BTP-eC9. Meanwhile, the authors also found out a post-treatment, defined as fluorous solvent vapor annealing (FSVA) in this work, can further resurface the donor due to the unique solubility of fluoropolymers in fluorous solvents. Based on the dual-resurfacing of the fluoropolymer, an optimized GHJ is achieved to provide an over 19% efficiency in binary organic solar cells. Moreover, the resurfacing processes and the essential role of FSVA are thoroughly investigated by various measurements, such as TOF-SIMS and in-situ absorption spectra.\nOverall, I think this work provides an innovative and efficient approach to realize GHJs through developing new block fluoropolymers with the extra-low surface energy and selective response to the fluorous solvent post-treatment, and will be helpful for advancing organic solar cells as well as other thin-film devices in organic optoelectronics. Thus, I would recommend its publication in Nature Communications after following revisions.\n(1) The gradient distribution of donor and acceptor is expected to suppress the charge recombination and decline the energy loss. Thus, the relevant performance of BHJ-based devices should be measured to compare with the GHJ-based devices.\n(2) The optimal GHJ structure is able to facilitate the charge transport to improve the performance. I suggest that the mobilities of device with different heterojunction should be measured to illustrate the advantages of GHJ.\n(3) Fluorous solvent is used twice in this work. Is there fluorous solvent residue inside or on the surface of the blend film after adding perfluorotoluene in acceptor solution or FSVA treatment? Would it affect the photovoltaic properties?\n(4) For the FSVA-treated devices, whether the conditions would affect the device performance, like changing processing temperature or time?\n(5) Page 11, the authors claimed the FF is significantly declined when increasing the fluorinated monomer content to 30% owing to the increased miscibility challenge. However, the χ values of PF-20/BTP-eC9 and PF-30/BTP-eC9 are close in Table S3. Other factors such as film morphology is expected to rationalize that.\n(6) In Fig. 3e and Fig. S16, the FSVA is recognized to improve the packing order and crystallinity of fluoropolymer. And other stronger evidences are recommended to be provided.\n(7) The universality of a new strategy is essential for its extension. This work only adopts an acceptor BTP-eC9 for verifying the effect of the fluoropolymers and FSVA, and other representative acceptors should be considered.", "reviewer_2": "In this manuscript, He et al. synthesized a series of fluoropolymers that can self-organize into graded heterojunctions. The fluorinated blocks with extra-low surface energy endow the fluoropolymers with capability of resurfacing in solution process. During the sequential deposition (SD) that the small molecular acceptor solution is cast atop the underlying fluoropolymer film, the acceptor penetrates downwards accompanied by the resurfacing of the donor, consequently forming a donor/acceptor gradient in the vertical direction. This manuscript lacks novelty, does not make significant contributions to advancing this field or appeal to a broader audience, and can't be published in Nature Communications. Below are detailed comments:\n1. The authors previously reported incorporation of heptafluoroisopropoxyl groups into polymers (Adv. Mater. 2024, 36, 2404824), achieving a PCE of 19.09% in BHJ OSCs using post-treatment denoted as fluorous solvent vapor annealing (FSVA). In this work, the authors designed and synthesized three polymers which exhibited even lower device performance (PCEs of 18.16-18.65% in BHJ devices). What is the motivation behind designing these polymers? Although a PCE of 19.24% in SD-FS-FSVA device was achieved through post-treatment FSVA used in above paper, these methods such as SD and FSVA have already been reported.\n2. Although graded heterojunctions (GHJs) are expected to suppress charge recombination compared to traditional heterojunctions (BHJs), the device structure presented here does not represent real GHJs.\n3. The authors should provide more detailed explanations regarding why the performance of GHJ devices surpassed that of BHJ devices, including investigations of exciton diffusion, exciton dissociation, charge transport, and charge recombination characteristics.\n4. Which has a longer exciton diffusion length, PF-20 or BTP-eC9? If it's BTP-eC9, introducing heptafluoroisopropoxyl groups into the BTP-eC9 to form a pure phase could potentially enhance performance.\n5. The statement “all polymers showcase similar profiles with two featured absorption peaks at around 575 and 615 nm corresponding to the 0-0 and 0-1 transitions respectively” should be corrected to “575 and 615 nm corresponding to the 0-1 and 0-0 transitions”.\n6. In Figure 3b, why does the wavelength of PF-20 decrease from 0 to 0.1 s?\n7. In Figure 3c and 3d, before 250 s, the intensity of CN- and F- is almost unchanged, which indicates that the donor/acceptor content remains unchanged until 250 s? What is the corresponding thickness at 250 s? What is the thickness for the uniform gradient distribution part? Moreover, why does the F intensity gradually decrease following sputtering?\n8. In SI, MS and 13C NMR data of all new small molecules should be provided, and 1H NMR and 13C NMR data of all new polymers should be provided.", "reviewer_3": "In this manuscript, the authors present design of block fluoropolymers with low surface energy for sequential deposition to optimize charge separation and transport in organic solar cells (OSCs). By regulating the self-aggregation behavior of fluorinated polymers, they showed the surface energy of the fluorinated polymers can be modified. Additionally, the incorporation of fluorinated additives incorporation is proposed t enable the small molecular acceptor solution to penetrate downward during casting, forming a vertical donor/acceptor gradient heterojunction. In the device side, using a fluorinated solvent annealing (FSVA) was shown to further optimize the vertical donor/acceptor gradient distribution. As a result, the authors achieved a good power conversion efficiency of 19.24% in OSCs. The manuscript presents a novel approach for regulating the vertical donor/acceptor distribution, supported by relative comprehensive data and analysis. The paper needs to address a few key missing issues then can be considered for publication in Nature Communications.\nThe following issues should be carefully addressed:\n1. From Figure 1 in the manuscript, it can be observed that each type of monomer is present, although the segments composed of fluorinated monomers are slightly more abundant. Therefore, this is more like a conventional random copolymer rather than the block polymer as claimed by the authors. The authors should provide a reasonable explanation for this.\n2. The authors used TOF-SIMS to study the (CF3)2(CF)O- distribution in the PF-20 neat film, stating, \"Taking PF-20 as an example, the ion (CF3)2(CF)O- signal rapidly declines at the initial sputtering stage and then tends to equilibrium, suggesting the top layer of the neat film is enriched with the polyfluoride moiety (Fig. 2a).\" They then concluded, \"This indicates DF is predominantly confined to some blocks, rather than being uniformly and randomly distributed throughout the polymer chains.\" This conclusion is not rigorous. The TOF-SIMS results can only determine the macroscopic distribution of molecules and cannot infer the distribution of (CF3)2(CF)O- within the polymer chains. Therefore, it is still difficult to agree with the authors' concept of a block polymer.\n3. On page 10, the statement, \"Relative to PM6, the PF-X polymers exhibit slightly low HOMO/LUMO levels, which are related with the strong electron withdrawing ability of the heptafluoroisopropoxyl groups,\" is not entirely accurate. In fact, the reduction in the HOMO energy levels of the PF-X polymers is a result of the combined effects of both the heptafluoroisopropoxyl groups and the chlorine atoms.\n4. The authors’ 2024 AM paper reported PF-7 polymer with polyfluoride. What if you mix PM6 and PF-7 polymers at different ratio, and compare with the “block copolymer”?\n5. On page 13, the authors claim “However, BTP-eC9 hardly percolates through the PF-2- mesh during the fast solution process, ….” This is not necessarily true, considering the solvents are CB for polymer and CF for acceptor, which are both good solvents for the polymers. Earlier reports do not support clear sharp heterojunction formation when using CF for SD process. The authors need to provide strong evidence for the SD processed GHJ formation of control and the “block copolymer” cases, with surface energy difference.\n6. In Figures S21 and S23, the integration of the hydrogen atoms on the aromatic ring should be 2, not 1. The authors are requested to correct this.\n7. How universal is the strategy reported in the manuscript? Has it been applied to other acceptor molecular systems? If not, relevant data should be provided to demonstrate its broader applicability."}, "author_response": "Response to Reviewers’ Comments\nReviewer #1 (Remarks to the Author):\nThere are numerous interests to develop ideal heterojunction morphology, the graded\nheterojunctions (GHJ) with a gradient distribution of donor and acceptor materials are of high\ninterest. In this work, the authors proposed a new method to realize GHJs by employing block\nfluoropolymers, which simultaneously possess the extra-low surface energy and the suitable\ncompatibility. The increased chemical reactivity of fluorinated monomers compared with\nconventional monomers facilitates the synthesis of block copolymers in the one-pot reaction.\nBy leveraging the extra-low surface energy of polyfluoride blocks, the polymer is able to\nresurface in the solution processes, while the standard blocks ensure the miscibility with\nacceptor materials. As the result, a crude GHJ is achieved during the sequential deposition,\nattributed to the resurfacing of the fluoropolymer and the permeation downwards of the small-\nmolecule acceptor BTP-eC9. Meanwhile, the authors also found out a post-treatment, defined\nas fluorous solvent vapor annealing (FSVA) in this work, can further resurface the donor due\nto the unique solubility of fluoropolymers in fluorous solvents. Based on the dual-resurfacing\nof the fluoropolymer, an optimized GHJ is achieved to provide an over 19% efficiency in binary\norganic solar cells. Moreover, the resurfacing processes and the essential role of FSVA are\nthoroughly investigated by various measurements, such as TOF-SIMS and in-situ absorption\nspectra.\nOverall, I think this work provides an innovative and efficient approach to realize GHJs through\ndeveloping new block fluoropolymers with the extra-low surface energy and selective response\nto the fluorous solvent post-treatment, and will be helpful for advancing organic solar cells as\nwell as other thin-film devices in organic optoelectronics. Thus, I would recommend its\npublication in Nature Communications after following revisions.\n1\n(1) The gradient distribution of donor and acceptor is expected to suppress the charge\nrecombination and decline the energy loss. Thus, the relevant performance of BHJ-based\ndevices should be measured to compare with the GHJ-based devices.\nResponse: We appreciate the reviewer for this insightful suggestion. Notably, the synergy of\nblock-containing fluoropolymers and FSVA treatment facilitates the formation of gradient\ndonor/acceptor distribution. Compared to bulk heterojunctions (BHJs), graded heterojunctions\n(GHJs) can effectively reduce energy loss. To demonstrate this, the EQE spectra are measured\nEL\nfor BC and SD/FS-FSVA devices based on ra-PF20, qb-PF20, and b-PF20 copolymers. As\nshown in Fig. R1 and Table R1, the non-radiative recombination loss (∆E ) values for SD/FS-\nb-PF20, respectively. The total energy losses particularly ∆E in SD/FS-FSVA devices are\n3\nsignificantly lower than those of BC devices in all copolymers (0.245, 0.236, and 0.239 eV for\nra-PF20, qb-PF20, and b-PF20 based devices, respectively), directly contributing to the\nenhanced V . Detailed EQE spectra and corresponding parameters of energy losses are\noc EL\nprovided in Supplementary Fig. S19 and S26a, and Table S8 and S13. The relevant description\nin the main text and Supplementary Information have been rephrased as follows:\n“Given the comparable HOMO energy levels of the copolymers yet distinct V in the devices,\noc\nthe electroluminescence external quantum efficiency (EQE ) of devices is measured to\nEL\nquantificationally analyze the energy losses from different contributions. As summarized in Fig.\n3c, Supplementary Fig. S19, and Table S8, the radiative recombination losses derived from\nabsorption above (∆E ) and below (∆E ) bandgap exhibit minimal variation, suggesting similar\n1 2\ncharge-transfer states38. Notably, the non-radiative recombination loss (∆E ) values are\n3\ncalculated to be 0.249, 0.245, 0.236, and 0.239 eV for devices based on PM6, ra-PF20, qb-\nPF20, and b-PF20, respectively. These results demonstrate that the enhanced crystallinity of\nblock-containing copolymers (qb-PF20 and b-PF20) relative to ra-PF20, effectively reduce\nenergy disorder, thereby mitigating energy loss.”\n2\n“Relative to BC-processed devices, the SD/FS-FSVA devices with gradient donor-acceptor\ndistributions can effectively reduce energy loss. As shown in Supplementary Fig. S26a and\nTable S13, the ∆E values for SD/FS-FSVA devices based on ra-PF20, qb-PF20, and b-PF20\n3\nare calculated as 0.240, 0.228, and 0.232 eV, respectively. These reduced energy losses\ncompared to BC processed devices in all copolymers directly contribute to the enhanced V in\noc\nSD/FS-FSVA devices.”\nFig. R1 | EQE spectra of (a) BC and (b) SD/FS-FSVA processed devices based on ra-PF20,\nEL\nqb-PF20, and b-PF20 copolymers.\nTable R1 | Detailed parameters of energy losses for BC and SD/FS-FSVA processed devices.\nMethod Polymers\n(eV)(a) (eV) (eV) (eV𝑆𝑆𝑆𝑆) (eV)(b) (eV)(c) (eV)(d)\n𝐸𝐸𝑔𝑔 𝑉𝑉𝑜𝑜𝑜𝑜 𝐸𝐸𝑙𝑙𝑜𝑜𝑙𝑙𝑙𝑙 𝑉𝑉𝑜𝑜𝑜𝑜 ∆𝐸𝐸1 ∆𝐸𝐸2 ∆𝐸𝐸3\nra-PF20 1.394 0.852 0.542 1.131 0.263 0.034 0.245\nBC qb-PF20 1.392 0.862 0.530 1.130 0.262 0.032 0.236\nb-PF20 1.391 0.860 0.531 1.129 0.262 0.030 0.239\nra-PF20 1.394 0.856 0.538 1.131 0.263 0.035 0.240\nSD/FS-FSVA qb-PF20 1.392 0.868 0.524 1.130 0.262 0.034 0.228\nb-PF20 1.391 0.866 0.525 1.130 0.261 0.032 0.232\n(a) E is determined from the derivatives of the EQE curve. (b) ΔE is the voltage loss due to the charge transfer\ng 1\n(CT) state, which is calculated by ΔE = E -E . (c) ΔE is the voltage loss due to the radiative recombination,\n1 g CT 2\nwhich is calculated by ΔE = E -V -ΔE . (d) ΔE is the voltage loss due to the non-radiative recombination,\nwhich is calculated by ΔE = −(kT/q)ln(EQE ).\n3\n(2) The optimal GHJ structure is able to facilitate the charge transport to improve the\nperformance. I suggest that the mobilities of device with different heterojunction should be\nmeasured to illustrate the advantages of GHJ.\nResponse: We appreciate the reviewer for the constructive suggestions. The SD/FS-FSVA\nprocessing method effectively promotes the formation of gradient donor/acceptor distribution\nin active layer. To highlight the charge transport advantages of GHJs over BHJs, the hole\nmobility (µ ) and electron mobility (µ ) of both BC and SD/FS-FSVA processed devices are\nh e\ndetermined using space-charge-limited current (SCLC) model. As shown in Fig. R2 and Table\nR2, all SD/FS-FSVA treated devices exhibit significantly higher and more balanced carrier\nmobilities compare to BC-processed devices. For instance, the qb-PF20/BTP-eC9 device\nprocessed by SD/FS-FSVA achieves µ /µ values of 8.81/9.53×10-4 cm2 V-1 s-1, notably higher\nh e\nthan the BC device (µ /µ values of 8.03/8.93×10-4 cm2 V-1 s-1), indicating the superiority of\nh e\nGHJ than BHJ in charge transport properties. Notably, devices employing qb-PF20 and b-PF20\nas donors show higher and more balanced mobilities compared to ra-PF20 counterpart,\ncorrelate with the enhanced packing order and improved crystallinity induced by block\nformation. Furthermore, the SD/FS-FSVA method is more effective for qb-PF20 and b-PF20\nin charge transport, further confirming the synergetic role of block-containing fluoropolymers\nand FSVA in optimizing the gradient donor/acceptor distribution. Detailed charge mobility data\nare provided in Supplementary Fig. S20 and S27, and Table S14. The relevant description in\nthe main text and Supplementary Information have been rephrased as follows:\n“To characterize the charge transport properties, the hole mobility (µ ) and electron mobility\nh\n(µ ) are determined by space-charge-limited current (SCLC) model. As summarized in Fig. 3e\ne\nand Supplementary Fig. S20, the µ /µ values are 6.88/7.92×10-4, 7.54/8.69×10-4, 8.03/8.93×10-\nh e\n4, and 8.18/9.07×10-4 cm2 V-1 s-1 for PM6:BTP-eC9, ra-PF20:BTP-eC9, qb-PF20:BTP-eC9,\nand b-PF20:BTP-eC9 devices, respectively. Notably, the higher and more balanced mobilities\nof devices employing block-containing copolymers as donors than ra-PF20 counterpart,\n4\ncorrelate with the enhanced packing order and improved crystallinity induced by block\nformation.”\n“Regarding charge transport properties, SD/FS-FSVA treated devices show higher and more\nbalanced carrier mobilities compare to BC-processed counterparts (Supplementary Fig. S27).”\nFig. R2 | Fitting J-V curves of BC processed (a) hole-only and (b) electron-only devices; and\nSD/FS-FSVA processed (c) hole-only and (d) electron-only devices by SCLC models.\nTable R2 | Charge mobilities of OSC devices with different active layers prepared by BC and\nSD/FS-FSVA methods.\nMethod Polymers (10-4 cm2 V-1 s-1) (10-4 cm2 V-1 s-1) /\nra-PF20 𝜇𝜇ℎ 7.54 𝜇𝜇𝑒𝑒 8.69 𝜇𝜇1𝑒𝑒.1𝜇𝜇5ℎ\nBC qb-PF20 8.03 8.93 1.11\nb-PF20 8.18 9.07 1.11\nra-PF20 7.89 9.04 1.15\nSD/FS-FSVA qb-PF20 8.81 9.53 1.08\nb-PF20 9.12 9.76 1.07\n5\n(3) Fluorous solvent is used twice in this work. Is there fluorous solvent residue inside or on\nthe surface of the blend film after adding perfluorotoluene in acceptor solution or FSVA\ntreatment? Would it affect the photovoltaic properties?\nResponse: We thank the reviewer for highlighting this point. During the sequential deposition\n(SD) process and FSVA treatment, the fluorous solvent (perfluorotoluene) may penetrate into\nthe blend films. According to our experience, trace residues of the fluorous solvent remain in\nthe films, which could slightly affect the spin-coating of the electron transport layer (PNDIT-\nF3N) and the resulting photovoltaic properties. To mitigate the impact of the fluorous solvent,\nthe blend films are placed under vacuum for 5 minutes after FSVA treatment. This step ensures\nthe removal of solvent residues prior to spin-coating PNDIT-F3N. The description in the\nMethods section has been revised as follows:\n“After FSVA treatment, the active layers were placed under vacuum for 5 minutes to ensure\nthe removal of fluorous solvent residues.”\n(4) For the FSVA-treated devices, whether the conditions would affect the device performance,\nlike changing processing temperature or time?\nResponse: We thank the reviewer for highlighting this aspect. The processing conditions of\nFSVA treatment including temperature and vapor annealing time that affect device performance\nare carefully optimized. As shown in Fig. R3, the device efficiency for SD/FS-FSVA processed\nqb-PF20/BTP-eC9 initially increases with rising temperature and annealing time, but declines\nat excessive time and temperature due to the severe phase separation. This yields an optimal\nFSVA condition of 100 ℃ for 3 min. Significantly, the optimal FSVA conditions differ for ra-\nPF20, qb-PF20, and b-PF20 systems, attributed to the distinct surface and optoelectronic\nproperties of these fluoropolymers. After many attempts, the optimal FSVA conditions for b-\nPF20 and ra-PF20 based devices are 90 ℃ for 5 min and 100 ℃ for 5 min, respectively\n(Supplementary Tables S11-12). The lower processing temperature for b-PF20 and the longer\n6\nannealing time for ra-PF20 compared to qb-PF20 (100 ℃ for 3 min) can be attributed to their\ndistinct surface fluorine distributions, i.e. polyfluoride moieties are more localized and\ndispersive in b-PF20 and ra-PF20, respectively. Detailed photovoltaic parameters are provided\nin Supplementary Table S9 and S11-S12. The relevant description in the main text have been\nrephrased as follows:\n“The post-treatment FSVA is also employed in devices based on ra-PF20 and b-PF20 to\nelucidate the effect of distinct monomer sequences. After many attempts, the optimal FSVA\nconditions for b-PF20 and ra-PF20 based devices are 90 ℃ for 5 min and 100 ℃ for 5 min,\nrespectively (Supplementary Tables S11-12). The lower processing temperature for b-PF20 and\nthe longer annealing time for ra-PF20 compared to qb-PF20 (100 ℃ for 3 min) can be attributed\nto their distinct surface fluorine distributions, i.e. polyfluoride moieties are more localized and\ndispersive in b-PF20 and ra-PF20, respectively.”\nTable R3 | Photovoltaic performance of SD/FS-FSVA devices based on qb-PF20/BTP-eC9\nwith different FSVA treatment conditions.\nFSVA Condition V (V) J (mA cm-2) FF (%) PCE (%)\noc sc\n90 ℃, 1 min 0.874 27.89 77.86 18.98 (18.56 0.39)\n90 ℃, 3 min 0.870 28.05 78.63 19.19 (18.75 0.48)\n±\n90 ℃, 5 min 0.870 28.23 79.51 19.53 (19.09 0.46)\n±\n100 ℃, 1 min 0.870 27.96 78.95 19.20 (18.77±0.45)\n100 ℃, 3 min 0.868 28.42 79.44 19.60 (19.17 0.41)\n±\n100 ℃, 5 min 0.862 28.56 78.87 19.42 (18.88 0.50)\n±\n110 ℃, 1 min 0.866 28.13 79.24 19.30 (18.92±0.38)\n110 ℃, 3 min 0.860 28.35 78.44 19.12 (18.62 0.49)\n±\n110 ℃, 5 min 0.860 28.69 77.66 19.16 (18.56 0.55)\n±\n±\n(5) Page 11, the authors claimed the FF is significantly declined when increasing the fluorinated\nmonomer content to 30% owing to the increased miscibility challenge. However, the χ values\n7\nof PF-20/BTP-eC9 and PF-30/BTP-eC9 are close in Table S3. Other factors such as film\nmorphology is expected to rationalize that.\nResponse: We sincerely appreciate the reviewer’s insightful comments. As demonstrated in\nSupplementary Fig. S11 and Table S4, the fill factor (FF) exhibited a notable decline from\n78.84% to 76.30% upon increasing the fluorinated monomer content from 20% to 30%.\nThis reduction could potentially arise from enhanced phase separation within the active layer.\nTo elucidate this hypothesis, atomic force microscopy (AFM) images are measured to characterize\nthe blend film morphologies. As illustrated in Fig. R3, all blend films exhibit distinct fibrillar\nmorphologies, with root-mean-square roughness (R ) of 1.07, 1.26 and 1.65 nm for qb-\nq\nPF10:BTP-eC9, qb-PF20:BTP-eC9 and qb-PF30:BTP-eC9, respectively. Notably, the qb-\nPF30:BTP-eC9 blend film manifests markedly coarser fiber domains and higher R compared\nq\nto qb-PF20:BTP-eC9. These observations corroborate the occurrence of intensified phase\nseparation at higher fluorination levels, which may contribute to the observed FF deterioration.\nDetailed AFM data are provided in Supplementary Fig. S12. The relevant description in the\nSupplementary Information have been rephrased as follows:\n“As shown in Supplementary Fig. S12, all blend films exhibit distinct fibrillar morphologies,\nwith R of 1.07, 1.26 and 1.65 nm for qb-PF10:BTP-eC9, qb-PF20:BTP-eC9 and qb-PF30:BTP-\nq\neC9, respectively. Notably, the qb-PF30:BTP-eC9 blend film manifests markedly coarser fiber\ndomains and higher R compared to qb-PF20:BTP-eC9. These observations corroborate the\nq\noccurrence of intensified phase separation at higher fluorination levels, which may contribute\nto the observed FF deterioration.”\nPF30:BTP-eC9 blend films.\n(6) In Fig. 3e and Fig. S16, the FSVA is recognized to improve the packing order and\ncrystallinity of fluoropolymer. And other stronger evidences are recommended to be provided.\nResponse: We thank the reviewer for the constructive advice. As shown in Fig. 5c and\nSupplementary Fig. S30 in the revised manuscript (Fig. 3e and Supplementary Fig. S16 in the\nprevious version), the A /A ratio of qb-PF20 after FSVA treatment is significantly higher\n0-0 0-1\nthan that of the pristine one with enhanced 0-0 peaks in each etched layer. This indicates that\nFSVA treatment improves the packing order and crystallinity of the fluoropolymer. To further\nvalidate it, GIWAXS measurements are performed to evaluate the crystallization behavior of\nqb-PF20/BTP-eC9 blend films before and after FSVA. As shown in 2D GIWAXS images (Fig.\nR4), both blend films maintain preferential face-on orientation, with slightly enhanced intensity\nafter FSVA treatment. Analysis of 1D GIWAXS profiles and summarized data (Supplementary\nTable S15) reveals that the π-π packing peak of the SD/FS-FSVA blend film is located at 1.775\nÅ-1, higher than that of the SD/FS blend film (1.763 Å-1), indicating a smaller d spacing and\nπ-π\n9\ntighter π-π packing. Furthermore, the CCL values of SD/FS and SD/FS-FSVA blend films are\ncalculated to be 23.27 and 24.91 Å, respectively. These results convincingly demonstrate that\nthe FSVA post-treatment improves the packing order and crystallinity of blend films, thereby\nenhancing photovoltaic performance. Detailed GIWAXS data are provided in Supplementary\nFig. S31 and Table S15. The description in the main text have been rephrased as follows:\n“To further validate this, GIWAXS measurements are performed on SD/FS and SD/FS-FSVA\nblend films (Supplementary Fig. S31 and Table S15). Notably, the SD/FS-FSVA film exhibits\nreduced d-spacing and increased CCL values relative to the SD/FS film, demonstrating that\nFSVA treatment enhances packing order and crystallinity. Collectively, these results show that\nFSVA optimizes the graded heterojunction by regulating vertical donor/acceptor distribution\nand improving fluoropolymer packing.”\nFig. R4 | 2D GIWAXS images and 1D GIWAXS profiles of SD/FS and SD/FS-FSVA blend\nfilms.\n(7) The universality of a new strategy is essential for its extension. This work only adopts an\nacceptor BTP-eC9 for verifying the effect of the fluoropolymers and FSVA, and other\nrepresentative acceptors should be considered.\nResponse: We sincerely appreciate the reviewer for the insightful suggestions. To evaluate the\nuniversality of the combined strategy involving block-containing fluoropolymers and SD/FS-\nFSVA processing, other representative acceptors L8BO and Y6 are paired with ra-PF20, qb-\nPF20, and b-PF20 polymer donors to fabricate both BC and SD/FS-FSVA devices. As shown\n10\nin Fig. R5 and Table R4-5, SD/FS-FSVA devices demonstrate consistently higher PCEs than\ntheir BC counterparts across both L8BO- and Y6-based systems. Notably, SD/FS-FSVA\nprocessed qb-PF20/L8BO and b-PF20/L8BO devices achieve remarkable PCEs of\napproximately 19.50%, significantly surpassing that of BC-processed copolymers:L8BO\ndevices (ca. 18.70%). In Y6-based systems, the PCE enhancements also reach 0.7% in SD/FS-\nFSVA devices. Furthermore, the efficiency improvements prove more pronounced in block-\ncontaining copolymers (qb-PF20 and b-PF20) compared to random copolymer (ra-PF20),\nunderscoring the superiority and broad applicability of the block fluoropolymer-FSVA\nsynergistic strategy. Detailed J-V curves and photovoltaic parameters are presented in\nSupplementary Fig. 32 and Table S16-17. The description in the main text has been rephrased\nas follows:\n“To evaluate the universality of fluoropolymers and FSVA combined strategy, other\nrepresentative acceptors L8BO and Y6 are paired with ra-PF20, qb-PF20 and b-PF20 to\nfabricate both BC and SD/FS-FSVA devices. J-V curves and corresponding photovoltaic\nparameters are presented in Supplementary Fig. S32 and Tables S16-17. Crucially, SD/FS-\nFSVA devices demonstrate consistently higher PCEs than their BC counterparts across both\nL8BO and Y6 systems. Notably, qb-PF20/L8BO and b-PF20/L8BO based devices via SD/FS-\nFSVA method achieve remarkable PCEs of approximately 19.50%. The efficiency\nimprovements prove more pronounced in block-containing copolymers compared to random\ncopolymer, underscoring the superiority and broad applicability of the block fluoropolymer-\nFSVA synergistic strategy.”\n(a-b) L8BO and (c-d) Y6.\nTable R4 | Photovoltaic parameters of BC and SD/FS-FSVA processed OSCs employing\nL8BO as the acceptor materials.\nMethod Polymers V (V) J (mA cm-2) FF (%) PCE (%)\noc sc\nra-PF20 0.880 26.48 78.63 18.32 (17.94 0.37)\nBC qb-PF20 0.886 26.75 79.14 18.76 (18.44 0.30)\n±\nb-PF20 0.884 26.94 78.65 18.73 (18.36 0.36)\n±\nra-PF20 0.884 26.78 78.34 18.54 (18.22±0.35)\nSD/FS-FSVA qb-PF20 0.892 27.24 80.13 19.47 (19.16 0.42)\n±\nb-PF20 0.890 27.47 79.86 19.52 (18.30 0.41)\n±\n±\nas the acceptor materials.\nMethod Polymers V (V) J (mA cm-2) FF (%) PCE (%)\noc sc\nra-PF20 0.846 27.20 76.14 17.52 (17.14 0.34)\nBC qb-PF20 0.852 27.56 76.69 18.01 (17.72 0.35)\n±\nb-PF20 0.850 27.64 76.43 17.95 (17.56 0.38)\n±\nra-PF20 0.850 27.45 76.63 17.87 (17.51±0.35)\nSD/FS-FSVA qb-PF20 0.858 27.94 77.78 18.65 (18.30 0.41)\n±\nb-PF20 0.856 28.03 78.02 18.72 (18.38 0.36)\n±\n±\nIn this manuscript, He et al. synthesized a series of fluoropolymers that can self-organize into\ngraded heterojunctions. The fluorinated blocks with extra-low surface energy endow the\nfluoropolymers with capability of resurfacing in solution process. During the sequential\ndeposition (SD) that the small molecular acceptor solution is cast atop the underlying\nfluoropolymer film, the acceptor penetrates downwards accompanied by the resurfacing of the\ndonor, consequently forming a donor/acceptor gradient in the vertical direction. This\nmanuscript lacks novelty, does not make significant contributions to advancing this field or\nappeal to a broader audience, and can't be published in Nature Communications.\nResponse: We sincerely appreciate the reviewer’s recognition of realizing a donor/acceptor\ngradient in the vertical direction, by leveraging the dual-resurfacing of fluoropolymers with low\nsurface energy. Regarding the advancement over previous works, the novelty of our work\nfocuses on two distinct fields: 1) obtaining quasi-block copolymers via one-pot polymerization\nin polymer chemistry; and 2) achieving graded heterojunctions (GHJs) by leveraging the\nintrinsic properties of materials in photovoltaic devices.\nAs for the precise structure of the one-pot synthesized polymers, we agree with the\nReviewer that the previous manuscript employing three copolymers namely qb-PFX with\ndifferent fluorinated monomer contents did not fully elucidate our objectives. In the revised\nversion, we introduce two additional polymer derivatives with defined structures as controls:\na block copolymer (b-PF20) and a random copolymer (ra-PF20), as shown in Fig. R6. The\nrevised manuscript denotes more efforts to comparing the distinctions of these three copolymers\nb-PF20, qb-PF-20 and ra-PF20. Through systematic investigation (as seen in the response to\nReviewer #3, Question 1), we demonstrate that the one-pot synthesized qb-PF20 achieves\ncomparable structural precision and optoelectronic performance to the two-step synthesized\nblock copolymer b-PF20. This confirms that qb-PF20 is a quasi-block copolymer rather than a\nrandom copolymer. Based on the defined structure of polymers, the critical relationship\n14\nbetween monomer sequence and polymer properties/device performance is unraveled in the\nrevised manuscript. We believe these findings are quite helpful in the community, with the\nincreasing use of terpolymers in organic electronics, which are often mistakenly considered as\nrandom polymers. We thank the Reviewer for the insightful suggestions, that help us to clarify\nour contribution in material design and synthesis.\nThe development of GHJs represents a significant evolution in OSC architecture,\nprogressing from bilayer planar heterojunctions (PHJs) to bulk heterojunctions (BHJs), and\nmore recently to quasi-planar heterojunctions (Q-PHJs), all aimed at optimizing the vertical\ndonor/acceptor distribution. Thus, GHJs with a gradient donor-acceptor distribution is believed\nto further advance the OSC performance by simultaneously facilitating charge transport and\nsuppressing recombination. While previous reports have achieved GHJs primarily through\nvacuum thermal evaporation or other complex processes, our work demonstrates a\nbreakthrough solution-processing approach that capitalizes on intrinsic material properties—\nspecifically surface energy control. Although we acknowledge that the current GHJ\nmorphology could be further optimized, our methodology represents a substantial step forward.\nMore importantly, we have demonstrated in the revised manuscript that the formation of GHJs\nis resulted from the synergy of fluorinated block and fluorous-solvent-based treatment,\nconsequently providing new insights in the synergistic innovation between material design and\ndevice engineering.\nTherefore, we are confident that the revisions based on the Reviewers’ suggestions have\nfully addressed all concerns while further strengthening the novelty and impact of this work.\nThe refined manuscript now presents clear distinctions from existing literatures through its\ninnovative approaches to one-pot quasi-block copolymer synthesis and solution-processed GHJ\nformation.\nPF20, and c ra-PF20.\nBelow are detailed comments:\n1. The authors previously reported incorporation of heptafluoroisopropoxyl groups into\npolymers (Adv. Mater. 2024, 36, 2404824), achieving a PCE of 19.09% in BHJ OSCs using\npost-treatment denoted as fluorous solvent vapor annealing (FSVA). In this work, the authors\ndesigned and synthesized three polymers which exhibited even lower device performance\n(PCEs of 18.16-18.65% in BHJ devices). What is the motivation behind designing these\npolymers? Although a PCE of 19.24% in SD-FS-FSVA device was achieved through post-\ntreatment FSVA used in above paper, these methods such as SD and FSVA have already been\nreported.\nfluorinated sidechains. As shown in Fig. R7, the PF7 polymer in our previous AM paper was\ndesigned as a D-A alternating copolymer with asymmetric sidechains featuring terminal\nheptafluoroisopropoxyl groups, where these uniformly distributed fluorinated moieties\nenhanced the donor-acceptor interaction via fluorine-induced non-covalent bonds. In this work,\nthe PF20-series terpolymers represent a distinct molecular design, incorporating 20% D\nF\nmonomers with dual heptafluoroisopropoxyl-terminated sidechains to precisely tune surface\nenergy properties. Here, the fluorinated monomer plays a fundamentally different role by\nenabling the formation of block-like polymer chains—where the low-surface-energy\nfluorinated blocks make polymer resurface during solution-processing process while the\nstandard blocks maintain solution processability and component miscibility. This comparison\nhighlights that although both systems utilize heptafluoroisopropoxyl groups, they differ\nsubstantially in (1) monomer architecture: asymmetric vs symmetric, (2) polymer chain\nconfiguration: alternating vs quasi-block, and (3) primary functional mechanism: enhancing\nmolecular interaction vs controlling surface energy, demonstrating our progressive\nunderstanding of fluorinated polymer design for OSCs. Significantly, the revised manuscript\nalso includes additional experiments demonstrating that GHJ formation arises from the synergy\nof fluorinated blocks and fluorous solvent treatment. By the way, the PCE is further boosted to\n19.60% for the quasi-block polymer in this work, after the optimization of interface layer.\nFig. R7 | Chemical structure of PF7 in Adv. Mater. 2024, 36, 2404824.\n17\n2. Although graded heterojunctions (GHJs) are expected to suppress charge recombination\ncompared to traditional heterojunctions (BHJs), the device structure presented here does not\nrepresent real GHJs.\nResponse: We sincerely appreciate the reviewer’s insightful comment regarding the GHJ. In\nthis work, the TOF-SIMS measurements of characteristic ions are employed to analyze the\ndonor/acceptor distribution in the vertical direction. Specifically, CN- (representing the\nacceptor BTP-eC9) and F- (representing the donor qb-PF20) are selected as characteristic ions\nto represent the donor and acceptor materials. As shown in Fig. R8, The CN- signal decays\ngradually with depth, whereas the F- signal shows an inverse trend that increases progressively\nduring sputtering. In simpler terms, BTP-eC9 content gradually decreases and qb-PF20 content\nincreases from the blend film surface to substrate, illustrating these films have a gradient\ndonor/acceptor distribution. Compared to the SD/FS film (-85 and 13.6 for CN- and F-,\nrespectively), the SD/FS-FSVA film exhibits smaller slopes in both CN- and F- profiles (-52.7\nand 3.84 for CN- and F-, respectively), i.e., an optimized GHJ with a more even gradient\ndonor/acceptor distribution, owing to that qb-PF20 continually resurfaces during FSVA\ntreatment. We have confessed that the GHJ morphology in this work can be further optimized,\nwhile this still represents a foundational step toward ideal GHJs. We are pursuing refined\nmaterial design and device engineering to realize a better GHJ in future studies.\nFig. R8 | TOF-SIMS depth profiles of (a) CN- (representing the acceptor BTP-eC9) and (b) F-\n(representing the donor qb-PF20) distributions in SD/FS and SD/FS-FSVA films\n18\n3. The authors should provide more detailed explanations regarding why the performance of\nGHJ devices surpassed that of BHJ devices, including investigations of exciton diffusion,\nexciton dissociation, charge transport, and charge recombination characteristics.\nResponse: We sincerely appreciate the reviewer for the insightful suggestions. As shown in\nFig. 5g in the revised manuscript, the two-stage resurfacing of block-containing fluoropolymers\ndriven by their intrinsic extra-low surface energy and the fluorous solvent based post-treatment,\nrespectively, ultimately yielding an optimal GHJ with ideal donor-acceptor gradient distribution.\nTo further demonstrate the superiority of GHJs over BHJs, carrier dynamics including exciton\ndissociation, charge extraction, transport, and recombination are systematically investigated for\nBC and SD/FS-FSVA devices with ra-PF20, qb-PF20, and b-PF20 as donors (Table R6). The\nexciton dissociation (P ) and charge collection probabilities (P ) are estimated from the\ndiss coll\neffective voltage (V ) versus photocurrent density (J ) relationship. As shown in Fig. R9,\neff ph\nall SD/FS-FSVA devices exhibit higher P and P values than BC devices, evidencing more\ndiss coll\nefficient exciton dissociation and charge extraction. To further investigate the charge\nrecombination behaviors, the dependence of V and J on incident light intensity (P ) are\noc sc light\nmeasured. The relationships between V /J and P can be expressed as V n(kT/q)ln(P )\noc sc light oc light\nand J P α, respectively (where k is the Boltzmann constant, T∝ is the Kelvin\nsc light\ntemperatu∝re, and q is the elementary charge). As shown in Fig. R10, the slope n value and\nexponent α value of SD/FS-FSVA devices are closer to 1 than those of BC devices, indicating\nsuppressed trap-assisted and bimolecular recombination. To characterize the charge transport\nproperties, the hole mobility (µ ) and electron mobility (µ ) are determined by space-charge-\nh e\nlimited current (SCLC) model. As summarized in Fig. R2 and Table R2, all SD/FS-FSVA\ntreated devices exhibit significantly higher and more balanced carrier mobilities compare to\nBC-processed devices. Similar to BC processed devices, SD/FS-FSVA devices with block-\ncontaining PF20 (qb-PF20 and b-PF20) also outperform ra-PF20 counterpart, correlate with\nthe enhanced packing order and improved crystallinity induced by block formation.\nin carrier dynamics, further confirming the synergetic role of block-containing fluoropolymers\nand FSVA treatment in optimizing the gradient donor/acceptor distribution. Detailed carrier\ndynamic data are provided in Fig. 3d-f, Supplementary Fig. S20 and S26-27, and\nSupplementary Table S14. The relevant description in the main text and Supplementary\nInformation have been rephrased as follows:\n“To gain deeper insight into the carrier dynamics, the exciton dissociation (P ) and charge\ndiss\ncollection probabilities (P ) are estimated from the effective voltage (V ) versus photocurrent\ncoll eff\ndensity (J ) relationship. As shown in Fig. 3d, the devices incorporating fluoropolymers\nph\nexhibit higher P and P values than PM6-based device. Notably, the qb-PF20 based device\ndiss coll\ndemonstrates comparable P and P values to those of b-PF20 counterpart, with both devices\ndiss coll\nexhibiting higher values than ra-PF20 based device. To characterize the charge transport\nproperties, the hole mobility (µ ) and electron mobility (µ ) are determined by space-charge-\nh e\nlimited currrent (SCLC) model. As summarized in Fig. 3e and Supplementary Fig. S20, the\nµ /µ values are 6.88/7.92×10-4, 7.54/8.69×10-4, 8.03/8.93×10-4, and 8.18/9.07×10-4 cm2 V-1 s-1\nh e\nfor PM6:BTP-eC9, ra-PF20:BTP-eC9, qb-PF20:BTP-eC9, and b-PF20:BTP-eC9 devices,\nrespectively. Notably, the higher and more balanced mobilities of devices employing block-\ncontaining copolymers as donors than ra-PF20 counterpart, correlate with the enhanced\npacking order and improved crystallinity induced by block formation. To investigate the charge\nrecombination behaviors, we examine the dependence of V and J on incident light intensity\noc sc\n(P ). The relationships between V /J and P can be expressed as V n(kT/q)ln(P ) and\nlight oc sc light oc light\nJ P α, respectively (where k is the Boltzmann constant, T is the Ke∝lvin temperature, and\nsc light\nq i∝s the elementary charge). As shown in Fig. 3f, the slope n values are 1.15, 1.13, 1.07 and\n1.08 kT/q and the α values are 0.973, 0.975, 0.982 and 0.980 for PM6:BTP-eC9, ra-PF20-\neC9, qb-PF20:BTP-eC9, and b-PF20:BTP-eC9 devices, respectively. These results demonstrate\nthat devices incorporating block-containing copolymers show progressively reduced trap-\n20\nassisted and bimolecular recombination, consistent with their enhanced packing order and\ncrystallinity. In summary, the device employing qb-PF20 possesses essentially equivalent\ncarrier dynamics compared with the b-PF20 device, while both systems exhibit superior exciton\ndissociation, balanced charge transport and suppressed charge recombination relative to the ra-\nPF20 device. These findings indicate that introducing well-defined block sequences rather than\nrandomly distributed sequences into the copolymer can afford superior optoelectronic\nproperties.”\n“To further demonstrate the superiority of SD/FS-FSVA method over BC, carrier dynamics\nincluding exciton dissociation, charge extraction, transport, and recombination are\nsystematically investigated for SD/FS-FSVA devices based on ra-PF20, qb-PF20, and b-PF20\n(Supplementary Table S14). As shown in Supplementary Fig. S26b, all SD/FS-FSVA devices\nexhibit higher P and P values than BC devices, evidencing more efficient exciton\ndiss coll\ndissociation and charge extraction. Furthermore, the slope n value and exponent α value of\nSD/FS-FSVA devices are closer to 1 than those of BC devices (Supplementary Fig. S26c-d),\nindicating suppressed charge recombination. Regarding charge transport properties, SD/FS-\nFSVA treated devices show higher and more balanced carrier mobilities compare to BC-\nprocessed counterparts (Supplementary Fig. S27). Similar to BC processed devices, SD/FS-\nFSVA devices with block-containing PF20 donors also outperform ra-PF20 systems, which\ncorrelates with the enhanced packing order and crystallinity induced by block formation.\nSignificantly, the SD/FS-FSVA method is also more effective for qb-PF20 and b-PF20 in\noptimizing carrier dynamics, further confirming the synergetic role of block-containing\nfluoropolymers and FSVA treatment.”\neff\nra-PF20, qb-PF20, and b-PF20.\nFig. R10 | Light intensity depends on V and J for (a) BC and (b) SD/FS-FSVA devices based\noc sc\non ra-PF20, qb-PF20, and b-PF20.\nTable R6 | Carrier dynamics of OSC devices with different copolymers prepared by BC and\nSD/FS-FSVA methods.\nMethod Copolymers P P n (10-4 cm2 (10-4 cm2\ndiss coll 𝜇𝜇ℎ 𝜇𝜇𝑒𝑒\nV-1 s-1) V-1 s-1)\n𝛼𝛼\nra-PF20 96.81% 87.69% 1.13 0.975 7.54 8.69\nBC qb-PF20 97.20% 88.89% 1.07 0.982 8.03 8.93\nb-PF20 97.32% 89.21% 1.08 0.980 8.18 9.07\nra-PF20 97.43% 88.73% 1.11 0.979 7.89 9.04\nSD/FS-FSVA qb-PF20 97.74% 89.85% 1.04 0.991 8.81 9.53\nb-PF20 97.91% 90.28% 1.04 0.992 9.12 9.76\n22\n4. Which has a longer exciton diffusion length, PF-20 or BTP-eC9? If it's BTP-eC9, introducing\nheptafluoroisopropoxyl groups into the BTP-eC9 to form a pure phase could potentially\nenhance performance.\nResponse: We sincerely appreciate the reviewer’s insightful comment. Small-molecule\nacceptors (SMAs) typically exhibit longer exciton diffusion lengths than polymer donors due\nto their stronger molecular packing and lower energy disorder. Recent studies demonstrated\nthat introducing fluorinated units, such as trifluoromethyl (CF ) groups, into small-molecule\n3\nacceptors enhances dipole moments and dielectric constants, thereby reducing exciton binding\nenergy and improving charge transport (Energy Environ. Sci. 2025, 18, 4982-4995). On this\nbasis, we hypothesize that incorporating heptafluoroisopropoxyl groups into BTP-eC9 may\nsimilarly enhance the dielectric constant and phase purity, leading to improved exciton\ndissociation, enhanced charge transport, and suppressed charge recombination. Additionally,\npolyfluorinated units can reduce surface energy, facilitating precise control over the vertical\nphase distribution of donor and acceptor materials. However, it is also notably that the existence\nof polyfluorinated groups significantly changes the solubility, miscibility, and compatibility of\nthe relevant materials, especially for small molecules, raising the challenges of solution\nprocessability and high-quality film formation (Angew. Chem. Int. Ed. 2023, 62, e202213869;\nJ. Mater. Chem. A 2022, 10, 8837). These issues must be carefully addressed before\npolyfluorinated photovoltaic materials can be effectively employed to fine-tune donor/acceptor\ngradient distributions and enhance device performance. As helpfully suggested by the Reviewer,\nwe plan to systematically design polyfluorinated acceptors by carefully modulating both the\ntype and number of fluorinated moieties. This future study will aim to achieve an optimal\nbalance of fluorine-related effects, including noncovalent interactions, optoelectronic\nproperties, morphological control, and component compatibility. We believe this fluorination\napproach will provide valuable insights for advancing organic photovoltaic materials, and we\nintend to pursue this as an important follow-up investigation.\n23\n5. The statement “all polymers showcase similar profiles with two featured absorption peaks at\naround 575 and 615 nm corresponding to the 0-0 and 0-1 transitions respectively” should be\ncorrected to “575 and 615 nm corresponding to the 0-1 and 0-0 transitions”.\nResponse: We thank the reviewer for highlighting this. This statement has been corrected, and\nwe have thoroughly check and correct the mistakes in the revised manuscript. The revised\ncontent in the Supplementary Information has been rephrased as follows.\n“As depicted in Supplementary Fig. S6 and Table S1, all polymers showcase similar profiles\nwith two featured absorption peaks at around 575 and 615 nm corresponding to the 0-1 and 0-\n0 transitions, respectively, illustrating the qb-PFX polymers have almost identical optical\nbandgap.”\n6. In Figure 3b, why does the wavelength of PF-20 decrease from 0 to 0.1 s?\nResponse: We thank the reviewer for highlighting this point. Supplementary Fig. S19b-c in the\nrevised manuscript (Fig. 3b in the previous version) illustrates the evolution of maximum\nabsorption peaks of qb-PF20 and BTP-eC9 following the spin-coating time, characterized by\nin-situ time-resolved UV-Vis absorption spectroscopy. In this study, the sequential deposition\nmethod is employed to fabricate SD, SD/FS, and SD/FS-FSVA devices. The initial wavelength\nof qb-PF20 (at 0 s) corresponds to the maximum absorption peak of the pre-fabricated polymer\nneat film. During the second spin-coating step of BTP-eC9, the absorption peak of qb-PF20\nchanges in different ways depending on the solvents for BTP-eC9. Upon casting the BTP-eC9\nsolution onto the qb-PF20 film, the SD unfolds in three stages: (1) The solvent firstly induces\nswelling of the pre-fabricated neat fluoropolymer film; (2) Following polymer gelation, BTP-\neC9 rapidly permeates into the cavities of the polymer gel, forming a molecular-level D-A\nmixture; (3) With solvent evaporation, phase-separation between the donor and acceptor occurs\nand form the heterojunction morphology (Adv. Energy Mater. 2024, 10.1002/aenm.202403162).\nNotably, the polymer state transitions from the solid film to a swollen solution state in the first\n24\nstage, leading to a wavelength decrease from 0 s to 0.1 s. To highlight this, the description in\nthe main text has been revised as follows:\n“When the BTP-eC9 chloroform solution is dropped atop the underlying qb-PF20 film, the\nmaximum peak of qb-PF20 declines to 612 nm initially attributed to solvent-induced swelling\nof the pre-fabricated film, and then almost equilibrates at 612-613 nm until 0.4 s”\n7. In Figure 3c and 3d, before 250 s, the intensity of CN- and F- is almost unchanged, which\nindicates that the donor/acceptor content remains unchanged until 250 s? What is the\ncorresponding thickness at 250 s? What is the thickness for the uniform gradient distribution\npart? Moreover, why does the F- intensity gradually decrease following sputtering?\nResponse: We appreciate the reviewer for highlighting this important point. As shown in Fig.\nR8, especially the zoom-in pictures over a sputtering time of 0-200 s, the CN- signal is decaying\ngradually with depth, whereas the F- signal shows an inverse trend that increases progressively\nduring sputtering. In simpler terms, BTP-eC9 content gradually decreases and qb-PF20 content\nincreases from the blend film surface to substrate, which is the reason that we consider these\nheterojunctions as GHJs. To verify the effect of FSVA in manipulating the donor/acceptor\ndistribution, the change slopes of CN- and F- signals are fitted and presented in the insets of Fig.\nR6. Compared to the SD/FS film (-85 and 13.6 for CN- and F-, respectively), the SD/FS-FSVA\nfilm exhibits smaller slopes in both CN- and F- profiles (-52.7 and 3.84 for CN- and F-,\nrespectively), i.e., an optimized GHJ with a more even gradient donor/acceptor distribution,\nowing to that qb-PF20 continually resurfaces during FSVA treatment.\nTo correlate sputtering time with film thickness, we measure the thicknesses of SD/FS and\nSD/FS-FSVA processed qb-PF20/BTP-eC9 blend films using a Filmetrics Profilm 3D Optical\nStep Profiler (Fig. R11). The thicknesses are determined to be 110 nm and 116 nm for the\nSD/FS and SD/FS-FSVA films, respectively. We assume that the ion beam intensity remained\nconstant during TOF-SIMS measurements, so the sputtering rate (thickness per unit time) is\n25\nuniform for both samples. Since the ion signals terminate at approximately 295 s, the thickness\ncorresponding to 250 s of sputtering is approximately estimated to be 93.2 nm (SD/FS) and\n98.3 nm (SD/FS-FSVA), respectively. The transition point where the CN- signal shifts from\nslow to rapid decay occurs at 210 s, corresponding to the thickness of the uniform gradient\nregion, which are approximately 83.0 nm and 87.5 nm for SD/FS and SD/FS-FSVA blend films,\nrespectively. However, the inherent errors of TOF-SIMS renders this calculation is quasi-\nempirical, and also highlights the need to develop more precise methods for vertical phase\ncharacterization in future. Regarding the decrease in F- intensity after 250 s, this reflects the\nsputtering process penetrating the thin interface between the active layer and the substrate,\nultimately reaching the substrate.\nFig. R11 | Thicknesses of SD/FS and SD/FS-FSVA processed qb-PF20/BTP-eC9 blend films.\n8. In SI, MS and 13C NMR data of all new small molecules should be provided, and 1H NMR\nand 13C NMR data of all new polymers should be provided.\nResponse: We appreciate the reviewer for highlighting this point. The MS and 13C NMR data\nof the new small molecules, along with the 1H NMR and 19F NMR data of the polymers,\nhave\nbeen measured and are provided in Supplementary Figs. S34, S37, S39, S41, S44, and S45.\nHowever, the signal-to-noise ratio in the 13C NMR of the polymers is too low to provide\nmeaningful data, due to their high molecular weight.\nIn this manuscript, the authors present design of block fluoropolymers with low surface energy\nfor sequential deposition to optimize charge separation and transport in organic solar cells\n(OSCs). By regulating the self-aggregation behavior of fluorinated polymers, they showed the\nsurface energy of the fluorinated polymers can be modified. Additionally, the incorporation of\nfluorinated additives incorporation is proposed to enable the small molecular acceptor solution\nto penetrate downward during casting, forming a vertical donor/acceptor gradient\nheterojunction. In the device side, using a fluorinated solvent annealing (FSVA) was shown to\nfurther optimize the vertical donor/acceptor gradient distribution. As a result, the authors\nachieved a good power conversion efficiency of 19.24% in OSCs. The manuscript presents a\nnovel approach for regulating the vertical donor/acceptor distribution, supported by relative\ncomprehensive data and analysis. The paper needs to address a few key missing issues then can\nbe considered for publication in Nature Communications.\nThe following issues should be carefully addressed:\n1. From Figure 1 in the manuscript, it can be observed that each type of monomer is present,\nalthough the segments composed of fluorinated monomers are slightly more abundant.\nTherefore, this is more like a conventional random copolymer rather than the block polymer as\nclaimed by the authors. The authors should provide a reasonable explanation for this.\nResponse: We sincerely appreciate the reviewer for this insightful comment. We agree with\nthe Reviewer that the original data with only three copolymers (namely qb-PF20 in the revised\nmanuscript) cannot fully demonstrate the formation of (quasi-)block polymers. To solve this,\nwe synthesize two control polymers with defined structures in the revised manuscript. As shown\nin Fig. R6, a block copolymer b-PF20 and a random copolymer ra-PF20 are prepared by\ncontrolling the addition sequence of monomers.\n3 2\nfluoropolymer films (inset: 3D depth mapping of (CF ) (CF)O- distribution in qb-PF20);\n3 2\nc 1D\nGIWAXS images. d AFM height images. e Normalized absorption spectra. f Energy level\ndiagram.\nFurthermore, the basic polymer properties of fluoropolymers (ra-PF20, qb-PF20, and b-\nPF20) with different monomer sequences including surface properties, film morphology,\nmolecular packing, optical and electrochemical properties are systematically investigated.\nAs\ndepicted in Fig. R12a, the surface energies of b-PF20, qb-PF20, and ra-PF20 neat films are\ncalculated according to Wu’s model, as 19.03, 19.20 and 19.76 mN m-1, respectively. Notably,\nthe surface energy of qb-PF20 is comparable to that of b-PF20 but obviously lower than ra-\nPF20. As illustrated in TOF-SIMS results (Fig. R12b), the characteristic (CF ) (CF)O- ion\n3 2\nsignals of qb-PF20 and b-PF20 exhibit a similar trend featuring with a rapid decline at the initial\nsputtering stage, which indicates an enrichment of the polyfluorinated moiety in the top layer\nof these two films. In contrast, the intensity of (CF ) (CF)O- ion in the random copolymer ra-\n3 2\nPF20 is obviously weaker, because ra-PF20 has a more uniform distribution of polyfluorinated\nmonomers. These results suggest that qb-PF20 synthesized via one-pot polymerization is\n28\npredominantly consists of localized fluorinated blocks rather than being uniformly and\nrandomly distributed throughout the polymer chains. GIWAXS results demonstrate that qb-\nPF20 achieves packing order and crystallinity comparable to b-PF20, while slightly superior to\nthose of ra-PF20 (Fig. R12c). AFM images reveals that the higher R values of qb-PF20 and b-\nq\nPF20 relative to ra-PF20 suggest that block formation enhances molecular aggregation and\nserve as crystalline nucleus to promote high domain purity (Fig. R12d). The optical and\nelectrochemical properties for these copolymers composed of identical monomer but distinct\nsequences are similar (Fig. R12e-f). These results demonstrate that the one-pot synthesized\nquasi-block copolymer exhibits comparable polymer properties to the two-step synthesized\nblock copolymer.\nFig. R13 | J-V curves of a BC processed PM6:BTP-eC9, ra-PF20:BTP-eC9, qb-PF20:BTP-\neC9, and b-PF20:BTP-eC9 devices and b SD/FS-FSVA processed ra-PF20/BTP-eC9, qb-\nPF20/BTP-eC9, and b-PF20/BTP-eC9 devices.\nApart from the polymer properties, the photovoltaic performance based on ra-PF20,\nqb-\nPF20, and b-PF20 are also measured in both BC and SD/FS-FSVA devices. As shown in Fig.\nR13a, the BC processed qb-PF20:BTP-eC9 device (18.97%) achieves near-identical device\nefficiency to its block counterpart (19.03%) with comparable photovoltaic parameters, with\noutperforming ra-PF20:BTP-eC9 device (18.54%). These results indicate that introducing well-\ndefined block sequences rather than randomly distributed sequences into the copolymer can\n29\nafford superior optoelectronic performance. To elucidate the synergy of block-containing\nfluoropolymers and SD/FS-FSVA method, the SD/FS-FSVA devices based on ra-PF20, qb-\nPF20, and b-PF20 are also fabricated and measured. As shown in Fig. R13b, the SD/FS-FSVA\nprocessed b-PF20/BTP-eC9 achieves a champion PCE 19.71%, markedly surpassing ra-PF20\nbased device (18.82%). Notably, the comparable efficiency of SD/FS-FSVA processed qb-\nPF20/BTP-eC9 (19.60%) further corroborates our one-pot synthesized PF20 preferentially\nforms blocks rather than random monomer distributions. Furthermore, the SD/FS-FSVA\nmethod is also more effective for qb-PF20 and b-PF20 in optimizing carrier dynamics (Fig. R1-\n2 and R9-10), further confirming the synergetic role of block-containing fluoropolymers and\nFSVA treatment in optimizing gradient donor-acceptor distribution.\nThe formed fluorinated blocks endow extra-low surface energy, driving whole polymer\nchain resurfacing during solution processes. During sequential deposition, the resurfacing merit\nmake the fluoropolymer move upwards accompanied by the BTP-eC9 percolates downwards,\nconsequently regulating the donor/acceptor distribution to form a crude GHJ. With the help of\nFSVA treatment, the perfluorotoluene penetrates the blend film to enable the fluoropolymer to\nresurface again. Based on this dual resurfacing of the fluoropolymers, an optimal GHJ is\neventually realized. To identify the superiority of block-containing fluoropolymers in GHJ\nformation, TOF-SIMS measurement is also conducted in the ra-PF20 and b-PF20 based films.\nCompared with the qb-PF20 counterpart, the SD/FS-FSVA-processed b-PF20/BTP-eC9 film\ndisplay similar trends with slightly smaller slopes in both CN⁻ and F⁻ depth profiles, while the\nslopes of the ra-PF20/BTP-eC9 film is obviously bigger, indicating an inferior gradient\ndistribution in the case of the random copolymer. These results demonstrate that fluorinated\nblocks with low surface energy can facilitate the resurfacing of polymer donors to realize\noptimal GHJs. Importantly, the similar change trend observed in qb-PF20 relative to b-PF20\nfurther confirms that comparable surface and depth-dependent properties can be achieved via\n30\none-pot polymerization. The combined strategy also exhibits universality in other\nrepresentative acceptor systems such as L8BO and Y6 (Fig. R5 and Table R4-5).\nIn the revised manuscript, we systematically investigate the influence of fluoropolymers\nwith distinct monomer sequences (ra-PF20, qb-PF20 and b-PF20) on conjugated polymer\nproperties, photovoltaic performance and GHJ formation. In summary, the one-pot synthesized\nqb-PF20 rivals the two-step synthesized b-PF20 in both structural precision, surface and depth-\ndependent properties, optoelectronic performance and GHJ optimization, further confirming\nthe formation of quasi-block fluoropolymer during one-pot polymerization rather than random\none. To clarify it, the polymers synthesized in one-pot reaction is consider as quasi-block\ncopolymers in the revised version rather than block copolymers in the previous version.\n2. The authors used TOF-SIMS to study the (CF ) (CF)O- distribution in the PF-20 neat film,\n3 2\nstating, “Taking PF-20 as an example, the ion (CF ) (CF)O- signal rapidly declines at the initial\n3 2\nsputtering stage and then tends to equilibrium, suggesting the top layer of the neat film is\nenriched with the polyfluoride moiety (Fig. 2a).” They then concluded, “This indicates D is\nF\npredominantly confined to some blocks, rather than being uniformly and randomly distributed\nthroughout the polymer chains.” This conclusion is not rigorous. The TOF-SIMS results can\nonly determine the macroscopic distribution of molecules and cannot infer the distribution of\n(CF ) (CF)O- within the polymer chains. Therefore, it is still difficult to agree with the authors'\n3 2\nconcept of a block polymer.\nResponse: We appreciate the reviewer for highlighting this important point. This conclusion in\nthe original manuscript is derived through proof by contradiction. If heptafluoroisopropoxyl\ngroups are uniformly distributed in the polymer chain, the neat film is expected to be uniform,\nand thus the ion (CF ) (CF)O- signal intensity is similar from the top to the bottom. However,\n3 2\nthe real situation is the (CF ) (CF)O- ion signal of qb-PF20 rapidly declines at the initial\n3 2\nsputtering stage and then tends to equilibrium, so we speculated fluorinated moieties are\n31\nenriched in part of polymer chains, i.e., forming blocks. As pointed by the Reviewer, we agree\nthat the TOF-SIMS cannot be used to directly reflect the distribution of heptafluoroisopropoxyl\ngroups within the polymer chains. Therefore, two copolymers with defined-structures are\nsynthesized in the revised version for comparison, which eventually demonstrates the one-pot\nsynthesized qb-PF20 is a quasi-block polymer rather than a random polymer (details in the\nresponse to Question 1). The relevant description in the main text have been rephrased as\nfollows.\n“To verify it, the stratification of ra-PF20, qb-PF20, and b-PF20 neat films is examined using\ntime-of-flight secondary ion mass spectrometry (TOF-SIMS). As illustrated in Fig. 2b, the\ncharacteristic (CF ) (CF)O- ion signals of qb-PF20 and b-PF20 exhibit a similar trend featuring\n3 2\nwith a rapid decline at the initial sputtering stage, which indicates an enrichment of the\npolyfluorinated moiety in the top layer of these two films. Compared with qb-PF20 and b-PF20,\nthe intensity of (CF ) (CF)O- ion in the random copolymer ra-PF20 is obviously weaker in the\n3 2\ntop layer, because ra-PF20 has a more uniform distribution of polyfluorinated monomers. These\nresults suggest that one-pot synthesized qb-PF20 is predominantly consists of localized\nfluorinated blocks rather than being uniformly and randomly distributed throughout the\npolymer chains.”\n3. On page 10, the statement, “Relative to PM6, the PF-X polymers exhibit slightly low\nHOMO/LUMO levels, which are related with the strong electron withdrawing ability of the\nheptafluoroisopropoxyl groups,” is not entirely accurate. In fact, the reduction in the HOMO\nenergy levels of the PF-X polymers is a result of the combined effects of both the\nheptafluoroisopropoxyl groups and the chlorine atoms.\nResponse: We appreciate the reviewer for the invaluable advice. We agree with the Reviewer\nthat the synergetic effect of chlorine substitution and branched fluorination in the side chains\n32\ngives rise to the deeper HOMO and LUMO energy levels of qb-PFX. The relevant description\nin the Supplementary Information has been rephrased as follows:\n“With increasing D , the HOMO and LUMO energy levels of qb-PFX polymers continuously\nF\ndownshifted. Moreover, the slightly lower HOMO/LUMO levels of qb-PFX relative to PM6 (-\n5.52/-3.63 eV) are related with the synergetic role of branched fluorination in sidechains and\nchlorine substitution and favorable to enhance the open-circuit voltage (V ).”\noc\n4. The authors’ 2024 AM paper reported PF7 polymer with polyfluoride. What if you mix PM6\nand PF-7 polymers at different ratio, and compare with the “block copolymer”?\nResponse: We sincerely appreciate the reviewer’s insightful comment. As seen in the response\nto Reviewer #2, Question 1, the PF7 in previous AM paper and PF20 herein differ substantially\nin (1) monomer architecture: asymmetric vs symmetric, (2) polymer chain configuration:\nalternating vs quasi-block, and (3) primary functional mechanism: enhancing molecular\ninteraction vs controlling surface energy. Meanwhile, as suggested by the Reviewer,\nthe\ncomparation between copolymer and polymer blends (PF7:PM6) might provide some new\ninsights. We first compare the surface energy differences of qb-PF20 and the PF7:PM6 blends.\nAs shown in Fig. R14, the surface energies of qb-PF20 and PF7:PM6 films are determined to\nbe 19.20 and 19.93 mN m-1, respectively. Notably, despite containing heptafluoroisopropoxyl\nside chains in PF7, the PF7:PM6 blends still shows relatively higher surface energy. This\ndifference suggests that simple blending cannot achieve the same fluorine-enriched surface\ncharacteristics as the block copolymer architecture of qb-PF20, which is crucial for effective\nGHJ formation via the combined block-containing fluoropolymers and SD/FS-FSVA method.\nTo further investigate the differences between qb-PF20 and PF7:PM6 blends in\nphotovoltaic performance, the BC and SD/FS-FSVA devices are both fabricated. As shown in\nFig. R15 and Table R7, the BC processed PF7:PM6:BTP-eC9 device (18.94%) achieves similar\nPCE to qb-PF20:BTP-eC9 device (18.97%), which may be attributed to their similar\n33\nphotoelectric properties. However, the PCE of SD/FS-FSVA processed PF7:PM6/BTP-eC9\ndevice (19.19%) is obviously lower than qb-PF20/BTP-eC9 device (19.60%), clearly\ndemonstrating the limited effectiveness of SD/FS-FSVA processing method for blended\nsystems. This can be rationalized by the fact that PF7 can resurface in solution processes due\nto its low surface energy while cannot induce whole polymer blends PF7 and PM6 to resurface.\nThese results further confirm the synergetic advantages of block-containing fluoropolymers in\nGHJ optimization and device performance enhancement, compared to blending polymers.\nFig. R14 | Contact angles and surface energies of PF7:PM6 and qb-PF20 films.\nFig. R15 | J-V curves of (a) BC and (b) SD/FS-FSVA processed devices based on qb-PF20 and\nPF7:PM6 polymers.\nPF20 and PF7:PM6 polymers.\nMethod Polymer V (V) J (mA cm-2) FF (%) PCE (%)\noc sc\nqb-PF20 0.862 28.05 78.47 18.97 (18.60 0.32)\nBC\nPF7:PM6 0.860 28.14 78.28 18.94 (18.55±0.28)\nqb-PF20 0.868 28.42 79.44 19.60 (19.17±0.41)\nSD/FS-FSVA\nPF7:PM6 0.862 28.35 78.51 19.19 (18.82 0.36)\n±\n±\n5. On page 13, the authors claim “However, BTP-eC9 hardly percolates through the PF-20\nmesh during the fast solution process, ….” This is not necessarily true, considering the solvents\nare CB for polymer and CF for acceptor, which are both good solvents for the polymers. Earlier\nreports do not support clear sharp heterojunction formation when using CF for SD process.\nThe authors need to provide strong evidence for the SD processed GHJ formation of control and the\n“block copolymer” cases, with surface energy difference.\nResponse: We sincerely appreciate the reviewer’s insightful comment. Indeed, chloroform (CF)\nis also the good solvent for polymers such as PM6 and PF20. As correctly noted, BTP-eC9\ndissolved in CF can also percolate into the underlying qb-PF20 neat films, albeit to a lesser\nextent compared to BTP-eC9 in CF/PFT mixed solvent. The key issue lies in the donor-acceptor\nmiscibility and compatibility, which are affected by the lower surface energy and fluorine-\nenriched surface of qb-PF20 compared to control polymer PM6. This repulsive force may\nhinder the formation of mixed donor-acceptor phases between the donor-rich bottom and\nacceptor-rich top regions. Consequently, the SD processed blend film behaves like a planar\nheterojunction, where the donor and acceptor are excessively confined to the bottom and top\nlayers, respectively. To verify this, we measure the surface energies of SD processed PM6/BTP-\neC9 and qb-PF20/BTP-eC9 blend films. As shown in Fig. R16, the surface energies are\ndetermined to be 21.93 mN m-1 and 23.17 mN m-1 for these two blend films, respectively. Since\n35\nthe surface energy presents a sequence BTP-eC9 > PM6 > qb-PF20, the higher surface energy\nof the SD-processed qb-PF20/BTP-eC9 blend film indicates a higher acceptor content at its\nsurface compared to the PM6/BTP-eC9 counterpart. These results confirm that BTP-eC9 in CF\nsolvent has difficulty in forming completely mixed donor-acceptor phases with qb-PF20.\nThe description in the main text has been revised as follows:\n“However, the significant different surface energy between qb-PF20 and BTP-eC9,\ncombined\nwith rapid solution process causes excessive confinement of the donor and acceptor to the\nbottom and top, respectively.”\nFig. R16 | Contact angles and surface energies of SD processed PM6/BTP-eC9 and qb-\nPF20/BTP-eC9 blend films.\n6. In Figures S21 and S23, the integration of the hydrogen atoms on the aromatic ring should\nbe 2, not 1. The authors are requested to correct this.\nResponse: We thank the reviewer for highlighting this point. The integration of hydrogen atoms\nis revised in Supplementary Figs. S36 and S40.\n36\n7. How universal is the strategy reported in the manuscript? Has it been applied to other\nacceptor molecular systems? If not, relevant data should be provided to demonstrate its broader\napplicability.\nResponse: We sincerely appreciate the reviewer for the insightful suggestions. As same as the\nQuestion 7 of the Reviewer #1, to further evaluate the universality of the combined strategy\ninvolving block-containing fluoropolymers and SD/FS-FSVA processing, other representative\nacceptors L8BO and Y6 are paired with ra-PF20, qb-PF20, and b-PF20 polymer donors to\nfabricate both BC and SD/FS-FSVA devices. As shown in Fig. R5 and Table R4-5, SD/FS-\nFSVA devices demonstrate consistently higher PCEs than their BC counterparts across both\nL8BO- and Y6-based systems. The efficiency improvements prove more pronounced in block-\ncontaining copolymers compared to random copolymer, underscoring the superiority and broad\napplicability of the block fluoropolymer-FSVA synergistic strategy. Detailed J-V curves and\nphotovoltaic parameters are presented in Supplementary Fig. 32 and Table S16-17. The\ndescription in the main text has been rephrased as follows:\n“To evaluate the universality of fluoropolymers and FSVA combined strategy, other\nrepresentative acceptors L8BO and Y6 are paired with ra-PF20, qb-PF20 and b-PF20 to\nfabricate both BC and SD/FS-FSVA devices. J-V curves and corresponding photovoltaic\nparameters are presented in Supplementary Fig. S32 and Tables S16-17. Crucially, SD/FS-\nFSVA devices demonstrate consistently higher PCEs than their BC counterparts across both\nL8BO and Y6 systems. Notably, qb-PF20/L8BO and b-PF20/L8BO based devices via SD/FS-\nFSVA method achieve remarkable PCEs of approximately 19.50%. The efficiency\nimprovements prove more pronounced in block-containing copolymers compared to random\ncopolymer, underscoring the superiority and broad applicability of the block fluoropolymer-\nFSVA synergistic strategy.”\nReviewer #2 (Remarks to the Author):\nThe authors have highlighted two main innovations: 1) obtaining quasi-block copolymers via\none-pot polymerization; and 2) achieving graded heterojunctions (GHJs) by leveraging the\nintrinsic properties of materials in photovoltaic devices. However, the work lacks sufficient\nnovelty for Nature Communications. The primary reason for this insufficiency is the lack of\nnovelty in material design: the employed heptafluoroisopropoxyl groups strategy has been\npreviously reported (Adv. Mater. 2024, 36, 2404824), and the use of a one-pot method for\nsynthesizing conjugated block copolymers is standard practice and cannot constitute an\ninnovation (Angew. Chem. Int. Ed. 2023, 62, e202308267).\nResponse: We sincerely appreciate the reviewer’s recognition our achievement of graded\nheterojunctions (GHJs). It’s well-known GHJs presents an ideal architecture for organic solar\ncells; however, their realization via solution processing has remained elusive. This work\nestablishes a practical paradigm for achieving that goal.\nWe also thank the reviewer for the insightful observation regarding the fluorinated\npolymer design. While both the PF20-series terpolymers in this work and the PF7 polymer in\nour previous AM paper incorporate heptafluoroisopropoxyl groups in sidechains, their\nmolecular design concepts and intended purposes are fundamentally distinct. The\nfluoropolymer PF7 represents a donor-acceptor alternating polymer with asymmetric\nsidechains, where uniformly distributed fluorinated moieties serve to enhance intermolecular\ninteractions through fluorine-induced non-covalent bonds. In contrast, the current PF20\ncopolymers with different monomer sequences are terpolymers that incorporate 20% D\nF\nmonomers with dual heptafluoroisopropoxyl-terminated sidechains. In such block-containing\ncopolymers, the fluorine-enriched blocks facilitate surface-energy-driven resurfacing during\nsolution processing, while the other blocks with less fluorine maintain solution processability\nand component miscibility. The fluorine-enriched surface formed intrinsically in these\n1\n(quasi-)block copolymers enables precise regulation of vertical donor/acceptor phase\ndistribution for GHJ formation. Thus, the fluoropolymer design in this work differs\nsignificantly from PF7 in terms of monomer architecture, polymer chain sequences, and\nprimary functional mechanisms, demonstrating our continued advancement in understanding\nfluorinated polymer design for high-performance organic solar cells.\nWe also sincerely appreciate the reviewer’s insightful observation regarding one-pot\npolymerization of conjugated block copolymers (CBCs). Traditional one-pot synthesis of CBCs\nfor single-component OSCs typically involves direct addition of acceptor monomers into pre-\npolymerized donor blocks, which often leads to random arrangement in the polymer chains. To\naddress this issue, the cited paper (Angew. Chem. Int. Ed. 2023, 62, e202308267) developed a\ntwo-pot polymerization to precisely manipulate the sequence length and distribution regularity\nof polymer donor/acceptor-block. This two-pot process involves first preparing D18-blocks\nwith carefully controlled pre-polymerization time, followed by their subsequent addition to\nseparately pre-polymerized PYIT-blocks, and the combined solution undergoes stirring for\nanother 24 h to yield final CBCs. Comparatively, our qb-PF20 synthesis employs a distinct one-\npot method, which leverages the differential chemical reactivity between polyfluorinated\nmonomers and standard monomers to form quasi-block polymer chains. This one-pot\npolymerization does not require secondary addition of monomers, which occurs through a facile\nsingle-step process where all monomers and catalysts are blended simultaneously, offering\nadvantages over both above-mentioned traditional one-pot and two-pot polymerization in terms\nof operational complexity and batch-to-batch reproducibility. In summary, our work presents\nsignificant conceptual and methodological advances, developing innovative approaches to one-\npot quasi-block copolymer synthesis and solution-processed GHJ formation for optoelectronic\nfield.\nOther questions:\n2\n1. Regarding the quasi-block copolymer synthesis via the one-pot method: Clarify the batch-\nto-batch reproducibility of polymers synthesized by one-pot method. Additionally, as the\nauthors claim the structural precision achieved with one-pot synthesis is comparable to that of\nthe two-pot method, elucidate how this structural precision was characterized?\nResponse: We sincerely appreciate the reviewer for this insightful comment. The batch-to-\nbatch reproducibility of conjugated polymers critically influences the material properties and\ndevice performance consistency. In this work, the block copolymer b-PF20 is synthesized via\na two-step polymerization, where the D and A monomers are pre-polymerized to form\nF\nfluorinated segment, and followed by the addition of D and A monomers. This sequential\napproach ensures the formation of well-defined blocks through precise control of monomer\nincorporation. Similarly, our one-step synthesized qb-PF20 exploits the differential reactivity\nof fluorinated and conventional monomers to promote the preferential polymerization of D\nF\nand A monomers and form fluorine-rich blocks with considerable numbers of repeat units,\ndelivering a quasi-block copolymer. This one-pot method achieves stepwise polymerization\ncomparable to conventional two-pot polymerization, enabling the formation of well-defined\nblocks to minimize compositional variations and improve batch-to-batch reproducibility. To\naccess the molecular weight (M ) of quasi-block copolymer on device performance, three\nn\nadditional qb-PF20 batches with M of 24.6, 33.2 and 39.4 kDa are synthesized (Fig. R1a).\nn\nThese polymers are associated with BTP-eC9 and fabricate OSCs using the SD/FS-FSVA\nmethod. As shown in Fig. R1b and Table R1, even the batch at the lowest M (24.6 kDa) still\nn\nmaintain almost identical V and slightly declined J and FF, resulting in a PCE of 18.15%.\noc sc\nThe PCE deviation is only 7.4% compared to the best batch (19.60%). These results confirm\nthe excellent M insensitivity of quasi-block fluoropolymers. In the revised manuscript, we\nn\nfurther compare the batch-to-batch reproducibility of ra-PF20, qb-PF20 and b-PF20 based\ndevices, highlighting the critical role of monomer sequence control for achieving reproducible\nOSC performance.\nFSVA processed qb-PF20/BTP-eC9 devices with different polymer M .\nn\nTable R1. Photovoltaic parameters of SD/FS-FSVA processed qb-PF20/BTP-eC9 devices with\ndifferent polymer M .\nn\nCopolymers M (kDa) V (V) J (mA cm-2) FF (%) PCE (%)\nn oc sc\n24.6 0.862 27.58 76.36 18.15 (17.87±0.31)\n33.2 0.865 27.95 77.45 18.72 (18.34±0.33)\nqb-PF20\n39.4 0.868 28.27 78.72 19.32 (18.91±0.39)\n44.4 0.868 28.42 79.44 19.60 (19.17±0.41)\nAs for the structural precision, the directly characterizations of internal monomer\nsequences and distributions in conjugated polymers remain a worldwide challenge. To\ninvestigate the structural characteristics (random or block) of our qb-PF20 copolymer, we\nintroduce two structurally distinct copolymers as controls through controlling the monomer\naddition sequences. The block copolymer b-PF20 is prepared via a sequential two-step\npolymerization, where the fluorinated monomers are pre-polymerized before initiating\npolymerization of conventional monomers. The synthesis of random copolymer ra-PF20\n4\nemploys gradual fluorinated monomers addition within 50 min during early polymerization\nstages of conventional monomers, ensuring the randomly distribution of fluorinated monomers\nin polymer chains. These deliberately designed copolymers would exhibit distinct\nphysicochemical properties and device performance. Through systematic comparison of ra-\nPF20, qb-PF20 and b-PF20 in polymer properties, GHJ formation and final photovoltaic\nperformance, the structural tendency and monomer sequences of one-pot synthesized qb-PF20\ncan be confirmed. As evidenced in the manuscript and Supplementary Information, the one-pot\nsynthesized qb-PF20 exhibits comparable properties in surface, morphological and depth-\ndependent properties, BC- and SD-processed device performance and GHJ formation to the\ntwo-step synthesized b-PF20, suggesting that qb-PF20 is predominantly consist of localized\nfluorinated blocks rather than being randomly distributed throughout the polymer chains.\n2. The sequential deposited GHJ has demonstrated high photovoltaic performance. What\nadvantages does the GHJ achieved through complex material synthesis and device optimization\nin this work offer?\nResponse: We sincerely appreciate the reviewer’s insightful recognition regarding the\nadvantages of our graded heterojunction (GHJ) approach. Our work demonstrates a novel two-\nstage resurfacing process enabled by both the intrinsic low surface energy of fluoropolymers\nand fluorous solvent vapor annealing (FSVA) post-treatment, which ultimately yield an optimal\nGHJ with donor-acceptor gradient distribution. Compared to conventional bulk heterojunctions\n(BHJs), this GHJ structure significantly reduces charge recombination and energy loss,\nimproves exciton dissociation and charge collection efficiency, and achieves more balanced\ncarrier mobilities (Supplementary Table S14), thereby acquiring an improvement in\nphotovoltaic performance. Notably, our work demonstrates advances in both polymer synthesis\nand processing method for GHJ formation and optimization. In polymer synthesis, our one-pot\nsynthesized qb-PF20 achieves comparable polymer properties, photovoltaic performance, and\nfacile method to obtain block-containing copolymers. Furthermore, the similar GHJ structure\nis hardly realized and typically require complex processes such as nanoimprint lithography\n(Adv. Funct. Mater. 2023, 33, 2209152) and vacuum thermal evaporation (Chem. Mater. 2017,\n29, 389). Unlike existing complex methods, our approach leverages the self-resurfacing\nproperties of quasi-block copolymers during solution processing and a simple FSVA post-\ntreatment for GHJ formation, which is still a simple solution processing method even use the\nsequential deposition. These combined advantages in polymer synthesize, processing simplicity\nand device performance represent a substantial step forward for GHJs. In summary, we\ndemonstrate a breakthrough solution-processing approach that capitalizes on intrinsic material\nproperties and facile FSVA treatment for GHJ formation and optimization.\nReviewer #3 (Remarks to the Author):\nReading the major revision version of the submission, I think the authors addressed the\ncomments well. It is now a much better-quality article. It can be accepted in my opinion.\nResponse: We thank the reviewer for the positive comment.\nReviewer #4 (Remarks to the Author):\nFollowing the first round of revisions, Z. He et al. have significantly improved the quality\nof the manuscript by addressing reviewers’ concerns and queries. The authors achieve a champion\nPCE of 19.6%, which approaches state-of-the-art for OPV. However, there are additional areas\nof the manuscript that require additional experimentation and clarification before it could be\nconsidered for publication. These are detailed in the comments below.\nComments:\n1. The authors claim that the coloration of the polymerization reaction (orange versus red)\nfor\nPM6 versus qb-PF20 indicates a faster polymerization rate; however, this could be due to\ndifferences in solubility in the polymerization solvent (toluene/DMF) and\nprecipitation/aggregation of the qb-PF20 compared to PM6. In order to support the claim that\nqb-PF20 has a faster polymerization rate, the authors must perform NMR kinetics experiments\nthat quantitatively assess monomer conversion with respect to polymerization time.\nResponse: We sincerely appreciate the reviewer for this insightful advice. To investigate the\npolymerization kinetics of PM6 and qb-PF20, parallel polymerization reactions are conducted\nat 80 ℃ with equal-volume aliquots withdrawn at 30, 60, 90 and 120 minutes for subsequent\nGPC and NMR characterizations. As shown in Fig. R2, the peaks at ca. 10.06 min corresponds\nto the monomer signals (D, D and A), which gradually decreases with polymerization time\nF\nwhile new signals emerge below 10 min, indicating monomer-to-polymer conversion. Notably,\nPM6 predominantly exhibits monomer signals at 80 °C for 30 minutes, while qb-PF20 already\nshows distinct oligomer signals, demonstrating significantly accelerated reaction kinetics for\nthe fluoropolymer. Moreover, the monomer signals in qb-PF20 nearly disappears and the\npolymer peak shifts to 7.4 min after 120 minutes of polymerization, confirming that the\nincorporation of fluorinated monomers significantly enhances the monomer conversion rates.\nFig. R2. GPC elution curves of (a) PM6 and (b) qb-PF20 at different reaction time (80 ℃).\nTo further quantitatively evaluate monomer conversion, 1H NMR measurements are\nperformed on PM6 and qb-PF20 samples at different reaction times using an equimolar amount\n7\nof 1,4-dibromo-2,5-diiodobenzene as the internal standard. As shown in Fig. R3-4, the\ncharacteristic proton signals at 8.05 ppm and 7.08 ppm correspond to internal standard (H )\nand\na\nmonomer BDD-2Br (H ), respectively. As the polymerization proceeds, the BDD-2Br couples\nb\nwith the distannly monomers to form the conjugated backbone, where the electron density\naround the thiophene hydrogen atoms (H ) becomes increasingly delocalized due to extended\nb\nπ-conjugation, resulting in a downfield chemical shift. Thus, the progressive decrease in\nintegral ratios of BDD-2Br quantitatively reflects monomer consumption during\npolymerization. As summarized in Fig. R5, the fluoropolymer qb-PF20 consistently exhibits\nhigher monomer conversion rates relative to PM6 throughout the reaction time. Upon extending\nthe reaction to 120 minutes, monomer signals in qb-PF20 become nearly undetectable with a\nconversion rate of 0.91, demonstrating the significantly accelerated polymerization kinetics\nimparted by fluorinated monomers. Detailed GPC and NMR data are added in Supplementary\nFig. S5-8. The relevant description in the main text has been rephrased as follows:\n“To further investigate the distinct polymerization kinetics between qb-PF20 and PM6,\nparallel\nreactions are conducted at 80 ℃ with equal-volume aliquots withdrawn at 30, 60, 90 and 120\nmin for subsequent GPC and NMR characterizations. The GPC elution curves (Supplementary\nFig. S5) reveal that PM6 predominantly exhibits monomer signals after 30 min, while qb-PF20\nalready displays prominent oligomer formation. Notably, monomer signals in qb-PF20 nearly\ndisappears by 120 min, confirming the accelerated polymerization rate for the fluoropolymer.\nTo quantitatively evaluate monomer conversion, 1H NMR measurements are performed on\nPM6 and qb-PF20 samples at different reaction times using an equimolar amount of 1,4-\ndibromo-2,5-diiodobenzene as the internal standard. As depicted in Supplementary Fig. S6-8,\nthe progressive decrease in integral ratios of monomer A quantitatively reflects monomer\nconsumption during polymerization, with the fluoropolymer qb-PF20 consistently exhibiting\nhigher monomer conversion rates relative to PM6 throughout the reaction time. Upon extending\nthe reaction to 120 min, monomer signals in qb-PF20 become nearly undetectable with a\n8\nconversion rate of 0.91, demonstrating the significantly enhanced reaction kinetics imparted by\nfluorinated monomers.”\nFig. R3. 1H NMR spectra of PM6 at different reaction time (80 ℃). The characteristic proton\nsignals at 8.05 ppm and 7.08 ppm correspond to internal standard (H ) and BDD-2Br (H ),\na b\nrespectively.\n2. The authors must revise the section on the MALDI analyses. While the MALDI spectra is\nuseful in detailing the molecular weight distribution of the polymers, the claim that the higher\npeak intensity correlates to a greater quantity of D oligomers is incorrect. Quantitative analysis\nF\nof polymers using MALDI is known to be unreliable due to uncertainties in ionization\nefficiency and ionization suppression (see refs: J. Vanderspikken et al. Macromolecules, 2024,\n57, 7138-7155; C. Wesdemiotis et al. Mass. Spectrom. Rev. 2024, 43, 427-476). It is advised\nthe authors use GPC or NMR to estimate the molecular weight distribution of the oligomeric\nspecies.\nResponse: We appreciate the reviewer for highlighting this important point. We agree with the\nreviewer that the MALDI-TOF data can only provide semi-quantitative analysis of oligomer\ndistribution. The characteristic signals of fluorinated monomer (D ) containing segments\nF\nexhibit significantly higher intensities compared to corresponding conventional monomer (D)\ncontaining segments, indicating the preferential formation of fluorine-based blocks with\nconsiderable numbers of repeat units. Moreover, the GPC and NMR analysis of PM6 and qb-\nPF20 at different reaction times demonstrate the D can accelerate the polymerization kinetics\nF\n(Figs. R2-5), which also benefits quasi-block oligomer formation during early polymerization\n11\nstages. To further verify this, the preparative GPC (pre-GPC) is employed to separate\noligomeric species with varying molecular weights. After systematic optimization of mobile\nphase, temperature and flow rate, tetrahydrofuran (THF) is identified as the optimal mobile\nphase, enabling effective separation of oligomers and monomers at 30 °C with a flow rate of\n2.5 mL/min. As shown in Fig. R6, the polymer and monomer peaks are located at 37.3 and 44.5\nmin, respectively, while the fractions with GPC signals below 40 min show the absence of\nmonomer species confirmed by NMR. Furthermore, oligomers with distinct molecular weights\nand segment compositions are also collected (the inset of Fig. R6). To analyze the content of\nD and D segments in these oligomers, the two collected fractions (oligomer-1 and oligomer-\nF\n2) are characterized by 1H NMR measurement after solvent removal by rotary evaporation. The\nrelative proportions of D and D segments are determined by comparing integral ratios of the\nF\nmethylene groups connected to thiophene in sidechains (H ’, 2.79 ppm) and\nc\nheptafluoroisopropoxyl groups (H ’, 4.01 ppm). As shown in Fig. R7, oligomer-2 exhibits\na\nsignificantly more D -containing segments than D-based segments with an integral ratio of\nF\n1:0.28. In oligomer-1 with higher molecular weight, D -based segments further increase,\nF\nyielding an integral ratio of 1:0.16. These results demonstrate that the highly reactive D\nF\npreferentially polymerizes into fluorine-rich blocks with substantial repeat units, consequently\nforming a quasi-block copolymer. The MALDI-TOF analyses are revised, and detailed pre-\nGPC and 1H NMR data are presented in Supplementary Fig. S10-11. The relevant description\nin the main text has been rephrased as follows:\n“As shown in Fig. 1b, the characteristic signals of fluorinated monomer D -based segments\nF\nincluding D -A, D -A-D , D -A-D -A and D -A-D -A-D , consistently exhibit higher intensity\nF F F F F F F F\nthan corresponding segments only containing the monomer D, suggesting the higher reactivity\nof D drives preferential polymerization to form fluorine-enriched blocks. Meanwhile, the\nF\nhybrid segments combining both D and D, like D -A-D and D -A-D-A shows very weak\nF F F\nintensity in the early polymerization stage. To further analyze the distribution of D and D\nF\n12\nsegments, preparative GPC is employed to separate oligomers with varying molecular weights.\nThrough systematic optimization of mobile phase, temperature and flow rate, the oligomers and\nmonomers can be separated with the retention time peaks of 37.3 and 44.5 min (Supplementary\nFig. S10). The two collected fractions (oligomer-1 and oligomer-2) are characterized by 1H\nNMR after solvent removal. Although aromatic proton signals of oligomers are difficult to\nresolve, the relative proportions of D and D segments are determined by comparing integral\nF\nratios of the methylene groups connected to thiophene in sidechains and heptafluoroisopropoxyl\ngroups. Notably, oligomer-2 contains a markedly higher proportion of D -containing segments\nF\nthan D-based segments, with an integral ratio of 1:0.28 (Supplementary Fig. S11). As for higher\nmolecular weight oligomer-1, the relative content of D -based segments is further increased,\nF\nyielding an integral ratio of 1:0.16. These results suggest that the highly reactive D\nF\npreferentially polymerize to form fluorine-rich blocks with considerable numbers of repeat\nunits, consequently delivering a quasi-block copolymer.”\nFig. R6. Preparative GPC elution curves of oligomers in the early polymerization stage (inset:\nthe photos of collected oligomer solutions).\n4.01, 2.92 and 2.80 ppm correspond to the methylene groups connected to\nheptafluoroisopropoxyl groups (H ’), thiophene in D sidechains (H ’) and thiophene in D\na F b\nsidechains (H ’), respectively.\nc\n3. The authors use surface energy to support the claim that a quasi-block copolymer was\nsynthesized. Yet, the difference between the polymers is <1 mN/m. This technique does not\nprovide conclusive results to support this claim. The authors must provide more extensive\nstructural analysis including NMR (1H-NMR and DOSY) and DSC to assert that block or quasi-\nblock copolymers have been synthesized relative to random.\nResponse: We sincerely appreciate the reviewer's insightful advice. In response, the 1H-NMR\nand DSC measurements are performed on the ra-PF20, qb-PF20 and b-PF20 copolymers. As\n14\nshown in Fig. R8, because the low signal-to-noise ratio of the NMR spectra for polymers, the\n1H-NMR results exhibit minimal differences among random, quasi-block and block copolymers,\nmaking it challenging to distinguish their structures. However, the GPC and NMR analyses of\nPM6 and qb-PF20 at different reaction times demonstrate that the fluorinated monomers can\nsignificantly accelerate polymerization kinetics (Fig. R2-5), which benefits quasi-block\ncopolymer formation during the early polymerization stages. More importantly, 1H NMR\ncharacterizations of the separated oligomers obtained via pre-GPC confirms the formation of\nfluorine-enriched blocks with considerable numbers of repeat units (Fig. R6-7). These results\nillustrate that the one-step synthesized qb-PF20 exploits the differential reactivity of fluorinated\nand conventional monomers to promote the preferential polymerization of D and A monomers\nF\nand form fluorine-rich blocks, delivering a quasi-block copolymer. To further study the\nstructural and thermodynamic differences between random copolymer and quasi-block/block\ncopolymers, DSC curves of ra-PF20, qb-PF20 and b-PF20 are recorded. As shown in Fig. R9,\nthe melting peaks in the heating process appear at 324.9 and 329.5 ℃ for ra-PF20 and b-PF20,\nrespectively, suggesting higher packing order and crystallinity in block copolymers. Notably,\nthe melting peak of qb-PF20 (328.1 ℃) is closer to that of b-PF20 than ra-PF20, indicating the\nformation of quasi-blocks in fluoropolymers. These results further demonstrate that the one-pot\nsynthesized quasi-block copolymer exhibits comparable properties to the two-step synthesized\nblock copolymer. Detailed DSC and NMR results are provided in Supplementary Fig. S22 and\nFig. S53. The relevant description in the main text has been rephrased as follows:\n“To evaluate the thermodynamic difference among these copolymers, differential scanning\ncalorimetry (DSC) measurements are conducted on ra-PF20, qb-PF20 and b-PF20 copolymers.\nAs shown in Supplementary Fig. S22, the melting peak of qb-PF20 (328.1 ℃) in the heating\nscan is closer to that of b-PF20 (329.5 ℃) than ra-PF20 (324.9 ℃), indicating not only the\nformation of fluorine-containing blocks in qb-PF20 but also a higher packing order and\ncrystallinity in block copolymers.”\ntetrachloroethane at 80 ℃.\nFig. R9. DSC curves of ra-PF20, qb-PF20 and b-PF20 in the heating process.\n16\n4. To support the ToF-SIMS analysis, the authors must provide literature support or additional\nexperimentation to support the claim that the qb-PF20 and b-PF20 perfluoro blocks migrate to\nthe film surface during fabrication. Did the authors compare solvent vapor annealing using\ntoluene with perfluorotoluene? This would provide a more conclusive analysis and greater\nsupport for the role of fluorinated solvent additives.\nResponse: We sincerely appreciate the reviewer’s valuable advice. As demonstrated by\nreported works in the OSC field, the incorporation of fluorinated moieties into organic\nmolecules can significantly reduce their surface energy for the regulation of vertical phase\ndistribution. Wei et al. (J. Mater. Chem. A. 2022, 10, 8837) introduced trifluoroalkyl groups\nonto the pyrrole unit of Y-series non-fullerene acceptors and found that the fluorinated alkyl\nchains effectively lowered the surface energy and promoted favorable vertical phase separation.\nMore importantly, Huang et al. (Angew. Chem. Int. Ed. 2023, 62, e202213869) developed an\nasymmetric acceptor EH-C F containing polyfluoroalkyl chains that exhibits ultralow surface\n8 17\nenergy, enabling self-migrating to the top surface of the active layer. By employing EH-C F\n8 17\nas a third component, a favorable vertical morphology featuring an upper acceptor-enriched\nthin layer and a lower undisturbed bulk heterojunction layer was achieved. Recently, we\nsynthesized two low-surface-energy acceptors (F6CB and F6CN) by incorporating\npolyfluorinated moiety into their central cores (Chem. Eng. J. 2025, 524, 168750). When\nblended with conventional acceptor, these fluorinated acceptors spontaneously enriched at the\nfilm surface during spin-coating, creating a cascaded vertical donor/acceptor distribution\nthrough surface-energy-driven self-stratification. These studies collectively demonstrate that\nfluorinated units and molecules preferentially migrate to the surface during solution processing,\nwhich strongly supports our finding that block-containing fluoropolymers similarly migrate to\nthe film surface during sequential deposition. These valuable references are added in the revised\nmanuscript and the relevant description in the main text has been rephrased as follows:\n17\n“More importantly, some studies demonstrated that the fluorinated units and molecules\npreferentially migrate to the surface owing to their low surface energy26, 28, 38, suggesting these\nfluorinated blocks accompanied by the whole polymer chain will migrate to the surface during\nthe film-formation process.”\nWe also sincerely appreciate the reviewer’s insightful suggestion. In response, we employ\nconventional organic solvent (toluene) vapor annealing (OSVA) as a post-treatment for qb-\nPF20/BTP-eC9 devices (denoted as SD/FS-OSVA) under various processing conditions. As\nsummarized in Table R2, the device efficiency of SD/FS-OSVA devices initially improves with\nrising temperature but declines beyond an optimal point (100 ℃, 3 min), mirroring the trend\nobserved for SD/FS-FSVA devices. The OSVA treated qb-PF20/BTP-eC9 devices achieves a\nrespectable PCE of 19.04% associated with a V of 0.864 V, a J of 28.12 mA cm-2, and an FF\noc sc\nof 78.36%. Notably, the PCE and photovoltaic parameters of SD/FS-OSVA devices remain\ninferior to SD/FS-FSVA devices while close to the device treated by thermal annealing,\nsuggesting the toluene solvent vapor cannot selectively reorganize the fluoropolymer to induce\nthe secondary vertical phase separation required for GHJ optimization. The performance\ndifferences may arise from the preferential dissolution of small-molecule acceptor in toluene\nrather than the fluoropolymer, as reflected in the distinct surface energy of blend films.\nSpecifically, the SD/FS-OSVA blend film exhibits a surface energy of 21.62 mN m-1 (Fig. R10),\nsignificantly higher than that of SD/FS-FSVA film (20.41mN m-1) and slightly elevated\ncompared to SD/FS film (21.34 mN m-1). These results demonstrated that the toluene SVA\ntreatment tend to redistribute the acceptor without effectively lifting the fluoropolymer. Thus,\nthe device performance and surface energy reaffirm the critical role of fluorous solvent\n(perfluorotoluene) in resurfacing fluoropolymer and optimizing GHJ. Detailed photovoltaic\nperformance and surface energy data are provided in Supplementary Fig. S35 and Table S15.\nThe relevant description in the main text has been rephrased as follows:\n18\n“The essential role of perfluorotoluene is further investigated by applying conventional organic\nsolvent (toluene) vapor annealing (OSVA) post-treatment to qb-PF20/BTP-eC9 devices\n(denoted as SD/FS-OSVA). As summarized in Supplementary Table S15, the PCEs of SD/FS-\nOSVA devices remain inferior to SD/FS-FSVA devices while close to SD/FS devices,\nsuggesting the limited ability of toluene to reorganize fluoropolymer. This performance\ndifference may arise from the preferential dissolution of small-molecule acceptor in toluene\nover the fluoropolymer, as reflected in the distinct surface energy. Specifically, the SD/FS-\nOSVA blend film exhibits a surface energy of 21.62 mN m-1 (Supplementary Fig. S35),\nsignificantly higher than that of SD/FS-FSVA film and slightly elevated relative to SD/FS\nfilms, reaffirming the critical role of fluorous solvent in resurfacing fluoropolymer and\noptimizing GHJ.”\nTable R2. Photovoltaic parameters of SD/FS-OSVA processed qb-PF20/BTP-eC9 devices\nwith different treatment conditions.\nOSVA Condition V (V) J (mA cm-2) FF (%) PCE (%)\noc sc\n90 ℃, 3 min 0.866 27.94 78.03 18.88 (18.35±0.42)\n100 ℃, 3 min 0.864 28.12 78.36 19.04 (18.71±0.37)\n110 ℃, 3 min 0.860 28.23 77.12 18.72 (18.23±0.46)\nFig. R10. Contact angles and surface energies of SD/FS, SD/FS-FSVA and SD/FS-OSVA\nprocessed qb-PF20/BTP-eC9 blend films.\n19\n5. Polymer batch-to-batch variation is a common issue with polymer solar-cells. The authors\nmust address the batch-to-batch reproducibility for the block/quasi-block copolymer synthesis\nrelative to random copolymer synthesis.\nResponse: We sincerely appreciate the reviewer’s insightful comment regarding batch-to-batch\nreproducibility of polymers. For a conjugated polymer, the batch-to-batch variations in\nmolecular weight (M ) and polydispersity index (PDI) critically influence their process-\nn\ndependent material properties and device performance consistency. In this work, the PF20\npolymers with distinct monomer sequences are synthesized through controlling the addition\nsequence and time. Specifically, the b-PF20 copolymer is synthesized via a two-step\npolymerization, where the D and A monomers are pre-polymerized to form fluorinated\nF\nsegment, and followed by the addition of D and A monomers. This method ensures the\nformation of well-defined blocks through precise control of monomer incorporation. The one-\nstep synthesized qb-PF20 exploits the differential reactivity of fluorinated and conventional\nmonomers to promote the preferential polymerization of D and A monomers and form\nF\nfluorine-rich blocks with considerable numbers of repeat units, delivering a quasi-block\ncopolymer. Both methods enable controlled and stepwise polymerization to form blocks that\nensures superior batch-to-batch reproducibility through minimizing compositional variations.\nIn contrast, the synthesis of ra-PF20 employs employs gradual D and A monomers addition\nF\nwithin 50 min during early polymerization stages of D and A monomers. Since the fluorinated\nmonomers have higher reactivity, the dropwise addition of D ensures the randomly distribution\nF\nof fluorinated monomer in oligomers to form a random copolymer. The stochastic incorporation\nof fluorinated polymers at varying reaction stages, coupled with their competitive\ncopolymerization with diverse D-A containing blocks, leads to substantial sequence\nheterogeneity in the resulting oligomers, ultimately compromising the synthetic reproducibility\nbetween batches. More Significantly, the improved molecular packing order and higher\ncrystallinity observed in block-containing fluoropolymers (qb-PF20 and b-PF20) compared to\n20\nthe ra-PF20, may render their photovoltaic performance less sensitivity to polymer M .\nTo\nn\nconfirm it, we further synthesized three additional batches of ra-PF20, qb-PF20 and b-PF20\nwith different molecular weight and PDI, as detailed in Fig. R11 and Table R3. These\ncopolymers are then associated with acceptor BTP-eC9 and fabricate OSCs using SD/FS-FSVA\nmethod to investigate the dependence of PCEs versus polymer M .\nn\nFig. R11. Molecular weight and polydispersity index of ra-PF20, qb-PF20 and b-PF20 across\ndifferent batches.\nTable R3. Molecular weight data of ra-PF20, qb-PF20 and b-PF20 across different batches.\nBatch M (kDa) M (kDa) PDI\nn w\nra-PF20-1 25.6 57.4 2.24\nra-PF20-2 32.2 65.5 2.03\nra-PF20-3 39.1 86.5 2.21\nqb-PF20-1 24.6 44.7 1.82\nqb-PF20-2 33.2 63.1 1.90\nqb-PF20-3 39.4 79.6 2.02\nb-PF20-1 25.7 49.6 1.93\nb-PF20-2 34.4 64.6 1.88\nb-PF20-3 41.6 87.2 2.10\nPF20/BTP-eC9, qb-PF20/BTP-eC9 and b-PF20/BTP-eC9 devices with different copolymer M\nn\nare presented in Fig. R12 and Table R4. While all devices exhibit reduced performance with\ndecreasing polymer M , ra-PF20 based devices suffer an obvious decline of PCE (10.4% at M\nn n\nof 25.6 kDa) compared to the best batch. Notably, all batches qb-PF20 and b-PF20 based\ndevices maintain almost identical V , slightly declined J and FF, and afford mitigated PCE\noc sc\nlosses of 7.4% (at M of 24.6 kDa) and 6.8% (at M of 25.7 kDa), respectively. These\nn n\nresults demonstrate the superior molecular weight insensitivity of block-containing\nfluoropolymers compared to random copolymer, highlighting the importance of precise\nmonomer sequence control in optimizing batch-to-batch reproducibility of OSCs. Detailed\nmolecular weight data,\nJ-V curves and photovoltaic parameters are provided in Supplementary\nFigs. S39-40 and Tables S17-18. The relevant description in the main text has been rephrased\nas follows:\n“Batch-to-batch reproducibility in OSCs remains a significant challenge due to inevitable\nvariations in molecular weight (M ) and polydispersity index (PDI) of polymers. Notably, the\nn\nsynthesis of block-containing copolymers addresses this issue through controlled, stepwise\npolymerization that forms well-defined blocks, effectively minimizing batch-to-batch\nvariations in device performance. To confirm it, three additional batches of ra-PF20, qb-PF20\nand b-PF20 with different M and PDI are synthesized, as detailed in Supplementary Fig. S39\nn\nand Table S17. These polymers are then associated with BTP-eC9 and fabricate OSCs using\nthe SD/FS-FSVA method to investigate the dependence of PCEs versus copolymer M\nn\n(Supplementary Fig. S40 and Table S18). While all devices exhibit reduced performance with\ndecreasing polymer M , ra-PF20 based devices suffer an obvious decline of PCE (10.4% at M\nn n\nof 25.6 kDa) compared to the best batch. In contrast, all batches qb-PF20 and b-PF20 based\ndevices maintain almost identical V and slightly declined J and FF, resulting in mitigated\noc sc\nPCE losses of 7.4% (at M of 24.6 kDa) and 6.8% (at M of 25.7 kDa), respectively. These\nn n\nresults demonstrate the superior molecular weight insensitivity of block-containing\n22\nfluoropolymers compared to random copolymer, highlighting the importance of precise\nmonomer sequence control in optimizing batch-to-batch reproducibility of OSCs.”\nFig. R12. J-V curves of SD/FS-FSVA processed (a) ra-PF20/BTP-eC9, (b) qb-PF20/BTP-eC9\nand (c) b-PF20/BTP-eC9 with different copolymer M . (d) Dependence of PCEs versus M .\nn n\nTable R4. Photovoltaic parameters of SD/FS-FSVA processed OSCs based on ra-PF20, qb-\nPF20 and b-PF20 with different M .\nn\nCopolymers M (kDa) V (V) J (mA cm-2) FF (%) PCE (%)\nn oc sc\n25.6 0.844 26.97 74.12 16.87 (16.53±0.31)\n32.2 0.850 27.46 76.10 17.76 (17.35±0.43)\nra-PF20\n39.1 0.853 27.84 77.23 18.34 (17.95±0.37)\n44.7 0.856 28.12 78.18 18.82 (18.39±0.40)\n24.6 0.862 27.58 76.36 18.15 (17.87±0.31)\n33.2 0.865 27.95 77.45 18.72 (18.34±0.33)\nqb-PF20\n39.4 0.868 28.27 78.72 19.32 (18.91±0.39)\n44.4 0.868 28.42 79.44 19.60 (19.17±0.41)\n23\n25.7 0.860 27.65 77.27 18.37 (17.94±0.38)\n34.4 0.860 27.92 78.38 18.82 (18.45±0.33)\nb-PF20\n41.6 0.864 28.31 79.32 19.40 (19.01±0.44)\n47.0 0.866 28.49 79.87 19.71 (19.23±0.45)\n24"}, {"round": 2, "reviewer_comments": {"reviewer_2": "The authors have highlighted two main innovations: 1) obtaining quasi-block copolymers via one-pot polymerization; and 2) achieving graded heterojunctions (GHJs) by leveraging the intrinsic properties of materials in photovoltaic devices. However, the work lacks sufficient novelty for Nature Communications. The primary reason for this insufficiency is the lack of novelty in material design: the employed heptafluoroisopropoxyl groups strategy has been previously reported (Adv. Mater. 2024, 36, 2404824), and the use of a one-pot method for synthesizing conjugated block copolymers is standard practice and cannot constitute an innovation (Angew. Chem. Int. Ed. 2023, 62, e202308267).\nOther questions:\n1. Regarding the quasi-block copolymer synthesis via the one-pot method: Clarify the batch-to-batch reproducibility of polymers synthesized by one-pot method. Additionally, as the authors claim the structural precision achieved with one-pot synthesis is comparable to that of the two-pot method, elucidate how this structural precision was characterized?\n2. The sequential deposited GHJ has demonstrated high photovoltaic performance. What advantages does the GHJ achieved through complex material synthesis and device optimization in this work offer?", "reviewer_3": "Reading the major revision version of the submission, I think the authors addressed the comments well. It is now a much better-quality article. It can be accepted in my opinion.", "reviewer_4": "[Note from the Editor: Reviewer #4 was asked to look over the response given to Reviewer #1]\nFollowing the first round of revisions, Z. He et al. have significantly improved the quality of the manuscript by addressing reviewers’ concerns and queries. The authors achieve a champion PCE of 19.6%, which approaches state-of-the-art for OPV. However, there are additional areas of the manuscript that require additional experimentation and clarification before it could be considered for publication. These are detailed in the comments below.\nComments:\n1. The authors claim that the coloration of the polymerization reaction (orange versus red) for PM6 versus qb-PF20 indicates a faster polymerization rate; however, this could be due to differences in solubility in the polymerization solvent (toluene/DMF) and precipitation/aggregation of the qb-PF20 compared to PM6. In order to support the claim that qb-PF20 has a faster polymerization rate, the authors must perform NMR kinetics experiments that quantitatively assess monomer conversion with respect to polymerization time.\n2. The authors must revise the section on the MALDI analyses. While the MALDI spectra is useful in detailing the molecular weight distribution of the polymers, the claim that the higher peak intensity correlates to a greater quantity of Df oligomers is incorrect. Quantitative analysis of polymers using MALDI is known to be unreliable due to uncertainties in ionization efficiency and ionization suppression (see refs: J. Vanderspikken et al. Macromolecules, 2024, 57, 7138-7155; C. Wesdemiotis et al. Mass. Spectrom. Rev. 2024, 43, 427-476). It is advised the authors use GPC or NMR to estimate the molecular weight distribution of the oligomeric species.\n3. The authors use surface energy to support the claim that a quasi-block copolymer was synthesized. Yet, the difference between the polymers is <1 mN/m. This technique does not provide conclusive results to support this claim. The authors must provide more extensive structural analysis including NMR (1H-NMR and DOSY) and DSC to assert that block or quasi-block copolymers have been synthesized relative to random.\n4. To support the ToF-SIMS analysis, the authors must provide literature support or additional experimentation to support the claim that the qb-PF20 and b-PF20 perfluoro blocks migrate to the film surface during fabrication. Did the authors compare solvent vapor annealing using toluene with perfluorotoluene? This would provide a more conclusive analysis and greater support for the role of fluorinated solvent additives.\n5. Polymer batch-to-batch variation is a common issue with polymer solar-cells. The authors must address the batch-to-batch reproducibility for the block/quasi-block copolymer synthesis relative to random copolymer synthesis."}, "author_response": "Response to Reviewers’ Comments and Revisions\nReviewer #2 (Remarks to the Author):\nThe authors have highlighted two main innovations: 1) obtaining quasi-block copolymers via\none-pot polymerization; and 2) achieving graded heterojunctions (GHJs) by leveraging the\nintrinsic properties of materials in photovoltaic devices. However, the work lacks sufficient\nnovelty for Nature Communications. The primary reason for this insufficiency is the lack of\nnovelty in material design: the employed heptafluoroisopropoxyl groups strategy has been\npreviously reported (Adv. Mater. 2024, 36, 2404824), and the use of a one-pot method for\nsynthesizing conjugated block copolymers is standard practice and cannot constitute an\ninnovation (Angew. Chem. Int. Ed. 2023, 62, e202308267).\nResponse: We sincerely appreciate the reviewer’s recognition our achievement of graded\nheterojunctions (GHJs). It’s well-known GHJs presents an ideal architecture for organic solar\ncells; however, their realization via solution processing has remained elusive. This work\nestablishes a practical paradigm for achieving that goal.\nWe also thank the reviewer for the insightful observation regarding the fluorinated\npolymer design. While both the PF20-series terpolymers in this work and the PF7 polymer in\nour previous AM paper incorporate heptafluoroisopropoxyl groups in sidechains, their\nmolecular design concepts and intended purposes are fundamentally distinct. The\nfluoropolymer PF7 represents a donor-acceptor alternating polymer with asymmetric\nsidechains, where uniformly distributed fluorinated moieties serve to enhance intermolecular\ninteractions through fluorine-induced non-covalent bonds. In contrast, the current PF20\ncopolymers with different monomer sequences are terpolymers that incorporate 20% D\nF\nmonomers with dual heptafluoroisopropoxyl-terminated sidechains. In such block-containing\ncopolymers, the fluorine-enriched blocks facilitate surface-energy-driven resurfacing during\nsolution processing, while the other blocks with less fluorine maintain solution processability\nand component miscibility. The fluorine-enriched surface formed intrinsically in these\n1\n(quasi-)block copolymers enables precise regulation of vertical donor/acceptor phase\ndistribution for GHJ formation. Thus, the fluoropolymer design in this work differs\nsignificantly from PF7 in terms of monomer architecture, polymer chain sequences, and\nprimary functional mechanisms, demonstrating our continued advancement in understanding\nfluorinated polymer design for high-performance organic solar cells.\nWe also sincerely appreciate the reviewer’s insightful observation regarding one-pot\npolymerization of conjugated block copolymers (CBCs). Traditional one-pot synthesis of CBCs\nfor single-component OSCs typically involves direct addition of acceptor monomers into pre-\npolymerized donor blocks, which often leads to random arrangement in the polymer chains. To\naddress this issue, the cited paper (Angew. Chem. Int. Ed. 2023, 62, e202308267) developed a\ntwo-pot polymerization to precisely manipulate the sequence length and distribution regularity\nof polymer donor/acceptor-block. This two-pot process involves first preparing D18-blocks\nwith carefully controlled pre-polymerization time, followed by their subsequent addition to\nseparately pre-polymerized PYIT-blocks, and the combined solution undergoes stirring for\nanother 24 h to yield final CBCs. Comparatively, our qb-PF20 synthesis employs a distinct one-\npot method, which leverages the differential chemical reactivity between polyfluorinated\nmonomers and standard monomers to form quasi-block polymer chains. This one-pot\npolymerization does not require secondary addition of monomers, which occurs through a facile\nsingle-step process where all monomers and catalysts are blended simultaneously, offering\nadvantages over both above-mentioned traditional one-pot and two-pot polymerization in terms\nof operational complexity and batch-to-batch reproducibility. In summary, our work presents\nsignificant conceptual and methodological advances, developing innovative approaches to one-\npot quasi-block copolymer synthesis and solution-processed GHJ formation for optoelectronic\nfield.\nOther questions:\n2\n1. Regarding the quasi-block copolymer synthesis via the one-pot method: Clarify the batch-\nto-batch reproducibility of polymers synthesized by one-pot method. Additionally, as the\nauthors claim the structural precision achieved with one-pot synthesis is comparable to that of\nthe two-pot method, elucidate how this structural precision was characterized?\nResponse: We sincerely appreciate the reviewer for this insightful comment. The batch-to-\nbatch reproducibility of conjugated polymers critically influences the material properties and\ndevice performance consistency. In this work, the block copolymer b-PF20 is synthesized via\na two-step polymerization, where the D and A monomers are pre-polymerized to form\nF\nfluorinated segment, and followed by the addition of D and A monomers. This sequential\napproach ensures the formation of well-defined blocks through precise control of monomer\nincorporation. Similarly, our one-step synthesized qb-PF20 exploits the differential reactivity\nof fluorinated and conventional monomers to promote the preferential polymerization of D\nF\nand A monomers and form fluorine-rich blocks with considerable numbers of repeat units,\ndelivering a quasi-block copolymer. This one-pot method achieves stepwise polymerization\ncomparable to conventional two-pot polymerization, enabling the formation of well-defined\nblocks to minimize compositional variations and improve batch-to-batch reproducibility. To\naccess the molecular weight (M ) of quasi-block copolymer on device performance, three\nn\nadditional qb-PF20 batches with M of 24.6, 33.2 and 39.4 kDa are synthesized (Fig. R1a).\nn\nThese polymers are associated with BTP-eC9 and fabricate OSCs using the SD/FS-FSVA\nmethod. As shown in Fig. R1b and Table R1, even the batch at the lowest M (24.6 kDa) still\nn\nmaintain almost identical V and slightly declined J and FF, resulting in a PCE of 18.15%.\noc sc\nThe PCE deviation is only 7.4% compared to the best batch (19.60%). These results confirm\nthe excellent M insensitivity of quasi-block fluoropolymers. In the revised manuscript, we\nn\nfurther compare the batch-to-batch reproducibility of ra-PF20, qb-PF20 and b-PF20 based\ndevices, highlighting the critical role of monomer sequence control for achieving reproducible\nOSC performance.\nFSVA processed qb-PF20/BTP-eC9 devices with different polymer M .\nn\nTable R1. Photovoltaic parameters of SD/FS-FSVA processed qb-PF20/BTP-eC9 devices with\ndifferent polymer M .\nn\nCopolymers M (kDa) V (V) J (mA cm-2) FF (%) PCE (%)\nn oc sc\n24.6 0.862 27.58 76.36 18.15 (17.87±0.31)\n33.2 0.865 27.95 77.45 18.72 (18.34±0.33)\nqb-PF20\n39.4 0.868 28.27 78.72 19.32 (18.91±0.39)\n44.4 0.868 28.42 79.44 19.60 (19.17±0.41)\nAs for the structural precision, the directly characterizations of internal monomer\nsequences and distributions in conjugated polymers remain a worldwide challenge. To\ninvestigate the structural characteristics (random or block) of our qb-PF20 copolymer, we\nintroduce two structurally distinct copolymers as controls through controlling the monomer\naddition sequences. The block copolymer b-PF20 is prepared via a sequential two-step\npolymerization, where the fluorinated monomers are pre-polymerized before initiating\npolymerization of conventional monomers. The synthesis of random copolymer ra-PF20\n4\nemploys gradual fluorinated monomers addition within 50 min during early polymerization\nstages of conventional monomers, ensuring the randomly distribution of fluorinated monomers\nin polymer chains. These deliberately designed copolymers would exhibit distinct\nphysicochemical properties and device performance. Through systematic comparison of ra-\nPF20, qb-PF20 and b-PF20 in polymer properties, GHJ formation and final photovoltaic\nperformance, the structural tendency and monomer sequences of one-pot synthesized qb-PF20\ncan be confirmed. As evidenced in the manuscript and Supplementary Information, the one-pot\nsynthesized qb-PF20 exhibits comparable properties in surface, morphological and depth-\ndependent properties, BC- and SD-processed device performance and GHJ formation to the\ntwo-step synthesized b-PF20, suggesting that qb-PF20 is predominantly consist of localized\nfluorinated blocks rather than being randomly distributed throughout the polymer chains.\n2. The sequential deposited GHJ has demonstrated high photovoltaic performance. What\nadvantages does the GHJ achieved through complex material synthesis and device optimization\nin this work offer?\nResponse: We sincerely appreciate the reviewer’s insightful recognition regarding the\nadvantages of our graded heterojunction (GHJ) approach. Our work demonstrates a novel two-\nstage resurfacing process enabled by both the intrinsic low surface energy of fluoropolymers\nand fluorous solvent vapor annealing (FSVA) post-treatment, which ultimately yield an optimal\nGHJ with donor-acceptor gradient distribution. Compared to conventional bulk heterojunctions\n(BHJs), this GHJ structure significantly reduces charge recombination and energy loss,\nimproves exciton dissociation and charge collection efficiency, and achieves more balanced\ncarrier mobilities (Supplementary Table S14), thereby acquiring an improvement in\nphotovoltaic performance. Notably, our work demonstrates advances in both polymer synthesis\nand processing method for GHJ formation and optimization. In polymer synthesis, our one-pot\nsynthesized qb-PF20 achieves comparable polymer properties, photovoltaic performance, and\nfacile method to obtain block-containing copolymers. Furthermore, the similar GHJ structure\nis hardly realized and typically require complex processes such as nanoimprint lithography\n(Adv. Funct. Mater. 2023, 33, 2209152) and vacuum thermal evaporation (Chem. Mater. 2017,\n29, 389). Unlike existing complex methods, our approach leverages the self-resurfacing\nproperties of quasi-block copolymers during solution processing and a simple FSVA post-\ntreatment for GHJ formation, which is still a simple solution processing method even use the\nsequential deposition. These combined advantages in polymer synthesize, processing simplicity\nand device performance represent a substantial step forward for GHJs. In summary, we\ndemonstrate a breakthrough solution-processing approach that capitalizes on intrinsic material\nproperties and facile FSVA treatment for GHJ formation and optimization.\nReviewer #3 (Remarks to the Author):\nReading the major revision version of the submission, I think the authors addressed the\ncomments well. It is now a much better-quality article. It can be accepted in my opinion.\nResponse: We thank the reviewer for the positive comment.\nReviewer #4 (Remarks to the Author):\nFollowing the first round of revisions, Z. He et al. have significantly improved the quality\nof the manuscript by addressing reviewers’ concerns and queries. The authors achieve a champion\nPCE of 19.6%, which approaches state-of-the-art for OPV. However, there are additional areas\nof the manuscript that require additional experimentation and clarification before it could be\nconsidered for publication. These are detailed in the comments below.\nComments:\n1. The authors claim that the coloration of the polymerization reaction (orange versus red)\nfor\nPM6 versus qb-PF20 indicates a faster polymerization rate; however, this could be due to\ndifferences in solubility in the polymerization solvent (toluene/DMF) and\nprecipitation/aggregation of the qb-PF20 compared to PM6. In order to support the claim that\nqb-PF20 has a faster polymerization rate, the authors must perform NMR kinetics experiments\nthat quantitatively assess monomer conversion with respect to polymerization time.\nResponse: We sincerely appreciate the reviewer for this insightful advice. To investigate the\npolymerization kinetics of PM6 and qb-PF20, parallel polymerization reactions are conducted\nat 80 ℃ with equal-volume aliquots withdrawn at 30, 60, 90 and 120 minutes for subsequent\nGPC and NMR characterizations. As shown in Fig. R2, the peaks at ca. 10.06 min corresponds\nto the monomer signals (D, D and A), which gradually decreases with polymerization time\nF\nwhile new signals emerge below 10 min, indicating monomer-to-polymer conversion. Notably,\nPM6 predominantly exhibits monomer signals at 80 °C for 30 minutes, while qb-PF20 already\nshows distinct oligomer signals, demonstrating significantly accelerated reaction kinetics for\nthe fluoropolymer. Moreover, the monomer signals in qb-PF20 nearly disappears and the\npolymer peak shifts to 7.4 min after 120 minutes of polymerization, confirming that the\nincorporation of fluorinated monomers significantly enhances the monomer conversion rates.\nFig. R2. GPC elution curves of (a) PM6 and (b) qb-PF20 at different reaction time (80 ℃).\nTo further quantitatively evaluate monomer conversion, 1H NMR measurements are\nperformed on PM6 and qb-PF20 samples at different reaction times using an equimolar amount\n7\nof 1,4-dibromo-2,5-diiodobenzene as the internal standard. As shown in Fig. R3-4, the\ncharacteristic proton signals at 8.05 ppm and 7.08 ppm correspond to internal standard (H )\nand\na\nmonomer BDD-2Br (H ), respectively. As the polymerization proceeds, the BDD-2Br couples\nb\nwith the distannly monomers to form the conjugated backbone, where the electron density\naround the thiophene hydrogen atoms (H ) becomes increasingly delocalized due to extended\nb\nπ-conjugation, resulting in a downfield chemical shift. Thus, the progressive decrease in\nintegral ratios of BDD-2Br quantitatively reflects monomer consumption during\npolymerization. As summarized in Fig. R5, the fluoropolymer qb-PF20 consistently exhibits\nhigher monomer conversion rates relative to PM6 throughout the reaction time. Upon extending\nthe reaction to 120 minutes, monomer signals in qb-PF20 become nearly undetectable with a\nconversion rate of 0.91, demonstrating the significantly accelerated polymerization kinetics\nimparted by fluorinated monomers. Detailed GPC and NMR data are added in Supplementary\nFig. S5-8. The relevant description in the main text has been rephrased as follows:\n“To further investigate the distinct polymerization kinetics between qb-PF20 and PM6,\nparallel\nreactions are conducted at 80 ℃ with equal-volume aliquots withdrawn at 30, 60, 90 and 120\nmin for subsequent GPC and NMR characterizations. The GPC elution curves (Supplementary\nFig. S5) reveal that PM6 predominantly exhibits monomer signals after 30 min, while qb-PF20\nalready displays prominent oligomer formation. Notably, monomer signals in qb-PF20 nearly\ndisappears by 120 min, confirming the accelerated polymerization rate for the fluoropolymer.\nTo quantitatively evaluate monomer conversion, 1H NMR measurements are performed on\nPM6 and qb-PF20 samples at different reaction times using an equimolar amount of 1,4-\ndibromo-2,5-diiodobenzene as the internal standard. As depicted in Supplementary Fig. S6-8,\nthe progressive decrease in integral ratios of monomer A quantitatively reflects monomer\nconsumption during polymerization, with the fluoropolymer qb-PF20 consistently exhibiting\nhigher monomer conversion rates relative to PM6 throughout the reaction time. Upon extending\nthe reaction to 120 min, monomer signals in qb-PF20 become nearly undetectable with a\n8\nconversion rate of 0.91, demonstrating the significantly enhanced reaction kinetics imparted by\nfluorinated monomers.”\nFig. R3. 1H NMR spectra of PM6 at different reaction time (80 ℃). The characteristic proton\nsignals at 8.05 ppm and 7.08 ppm correspond to internal standard (H ) and BDD-2Br (H ),\na b\nrespectively.\n2. The authors must revise the section on the MALDI analyses. While the MALDI spectra is\nuseful in detailing the molecular weight distribution of the polymers, the claim that the higher\npeak intensity correlates to a greater quantity of D oligomers is incorrect. Quantitative analysis\nF\nof polymers using MALDI is known to be unreliable due to uncertainties in ionization\nefficiency and ionization suppression (see refs: J. Vanderspikken et al. Macromolecules, 2024,\n57, 7138-7155; C. Wesdemiotis et al. Mass. Spectrom. Rev. 2024, 43, 427-476). It is advised\nthe authors use GPC or NMR to estimate the molecular weight distribution of the oligomeric\nspecies.\nResponse: We appreciate the reviewer for highlighting this important point. We agree with the\nreviewer that the MALDI-TOF data can only provide semi-quantitative analysis of oligomer\ndistribution. The characteristic signals of fluorinated monomer (D ) containing segments\nF\nexhibit significantly higher intensities compared to corresponding conventional monomer (D)\ncontaining segments, indicating the preferential formation of fluorine-based blocks with\nconsiderable numbers of repeat units. Moreover, the GPC and NMR analysis of PM6 and qb-\nPF20 at different reaction times demonstrate the D can accelerate the polymerization kinetics\nF\n(Figs. R2-5), which also benefits quasi-block oligomer formation during early polymerization\n11\nstages. To further verify this, the preparative GPC (pre-GPC) is employed to separate\noligomeric species with varying molecular weights. After systematic optimization of mobile\nphase, temperature and flow rate, tetrahydrofuran (THF) is identified as the optimal mobile\nphase, enabling effective separation of oligomers and monomers at 30 °C with a flow rate of\n2.5 mL/min. As shown in Fig. R6, the polymer and monomer peaks are located at 37.3 and 44.5\nmin, respectively, while the fractions with GPC signals below 40 min show the absence of\nmonomer species confirmed by NMR. Furthermore, oligomers with distinct molecular weights\nand segment compositions are also collected (the inset of Fig. R6). To analyze the content of\nD and D segments in these oligomers, the two collected fractions (oligomer-1 and oligomer-\nF\n2) are characterized by 1H NMR measurement after solvent removal by rotary evaporation. The\nrelative proportions of D and D segments are determined by comparing integral ratios of the\nF\nmethylene groups connected to thiophene in sidechains (H ’, 2.79 ppm) and\nc\nheptafluoroisopropoxyl groups (H ’, 4.01 ppm). As shown in Fig. R7, oligomer-2 exhibits\na\nsignificantly more D -containing segments than D-based segments with an integral ratio of\nF\n1:0.28. In oligomer-1 with higher molecular weight, D -based segments further increase,\nF\nyielding an integral ratio of 1:0.16. These results demonstrate that the highly reactive D\nF\npreferentially polymerizes into fluorine-rich blocks with substantial repeat units, consequently\nforming a quasi-block copolymer. The MALDI-TOF analyses are revised, and detailed pre-\nGPC and 1H NMR data are presented in Supplementary Fig. S10-11. The relevant description\nin the main text has been rephrased as follows:\n“As shown in Fig. 1b, the characteristic signals of fluorinated monomer D -based segments\nF\nincluding D -A, D -A-D , D -A-D -A and D -A-D -A-D , consistently exhibit higher intensity\nF F F F F F F F\nthan corresponding segments only containing the monomer D, suggesting the higher reactivity\nof D drives preferential polymerization to form fluorine-enriched blocks. Meanwhile, the\nF\nhybrid segments combining both D and D, like D -A-D and D -A-D-A shows very weak\nF F F\nintensity in the early polymerization stage. To further analyze the distribution of D and D\nF\n12\nsegments, preparative GPC is employed to separate oligomers with varying molecular weights.\nThrough systematic optimization of mobile phase, temperature and flow rate, the oligomers and\nmonomers can be separated with the retention time peaks of 37.3 and 44.5 min (Supplementary\nFig. S10). The two collected fractions (oligomer-1 and oligomer-2) are characterized by 1H\nNMR after solvent removal. Although aromatic proton signals of oligomers are difficult to\nresolve, the relative proportions of D and D segments are determined by comparing integral\nF\nratios of the methylene groups connected to thiophene in sidechains and heptafluoroisopropoxyl\ngroups. Notably, oligomer-2 contains a markedly higher proportion of D -containing segments\nF\nthan D-based segments, with an integral ratio of 1:0.28 (Supplementary Fig. S11). As for higher\nmolecular weight oligomer-1, the relative content of D -based segments is further increased,\nF\nyielding an integral ratio of 1:0.16. These results suggest that the highly reactive D\nF\npreferentially polymerize to form fluorine-rich blocks with considerable numbers of repeat\nunits, consequently delivering a quasi-block copolymer.”\nFig. R6. Preparative GPC elution curves of oligomers in the early polymerization stage (inset:\nthe photos of collected oligomer solutions).\n4.01, 2.92 and 2.80 ppm correspond to the methylene groups connected to\nheptafluoroisopropoxyl groups (H ’), thiophene in D sidechains (H ’) and thiophene in D\na F b\nsidechains (H ’), respectively.\nc\n3. The authors use surface energy to support the claim that a quasi-block copolymer was\nsynthesized. Yet, the difference between the polymers is <1 mN/m. This technique does not\nprovide conclusive results to support this claim. The authors must provide more extensive\nstructural analysis including NMR (1H-NMR and DOSY) and DSC to assert that block or quasi-\nblock copolymers have been synthesized relative to random.\nResponse: We sincerely appreciate the reviewer's insightful advice. In response, the 1H-NMR\nand DSC measurements are performed on the ra-PF20, qb-PF20 and b-PF20 copolymers. As\n14\nshown in Fig. R8, because the low signal-to-noise ratio of the NMR spectra for polymers, the\n1H-NMR results exhibit minimal differences among random, quasi-block and block copolymers,\nmaking it challenging to distinguish their structures. However, the GPC and NMR analyses of\nPM6 and qb-PF20 at different reaction times demonstrate that the fluorinated monomers can\nsignificantly accelerate polymerization kinetics (Fig. R2-5), which benefits quasi-block\ncopolymer formation during the early polymerization stages. More importantly, 1H NMR\ncharacterizations of the separated oligomers obtained via pre-GPC confirms the formation of\nfluorine-enriched blocks with considerable numbers of repeat units (Fig. R6-7). These results\nillustrate that the one-step synthesized qb-PF20 exploits the differential reactivity of fluorinated\nand conventional monomers to promote the preferential polymerization of D and A monomers\nF\nand form fluorine-rich blocks, delivering a quasi-block copolymer. To further study the\nstructural and thermodynamic differences between random copolymer and quasi-block/block\ncopolymers, DSC curves of ra-PF20, qb-PF20 and b-PF20 are recorded. As shown in Fig. R9,\nthe melting peaks in the heating process appear at 324.9 and 329.5 ℃ for ra-PF20 and b-PF20,\nrespectively, suggesting higher packing order and crystallinity in block copolymers. Notably,\nthe melting peak of qb-PF20 (328.1 ℃) is closer to that of b-PF20 than ra-PF20, indicating the\nformation of quasi-blocks in fluoropolymers. These results further demonstrate that the one-pot\nsynthesized quasi-block copolymer exhibits comparable properties to the two-step synthesized\nblock copolymer. Detailed DSC and NMR results are provided in Supplementary Fig. S22 and\nFig. S53. The relevant description in the main text has been rephrased as follows:\n“To evaluate the thermodynamic difference among these copolymers, differential scanning\ncalorimetry (DSC) measurements are conducted on ra-PF20, qb-PF20 and b-PF20 copolymers.\nAs shown in Supplementary Fig. S22, the melting peak of qb-PF20 (328.1 ℃) in the heating\nscan is closer to that of b-PF20 (329.5 ℃) than ra-PF20 (324.9 ℃), indicating not only the\nformation of fluorine-containing blocks in qb-PF20 but also a higher packing order and\ncrystallinity in block copolymers.”\ntetrachloroethane at 80 ℃.\nFig. R9. DSC curves of ra-PF20, qb-PF20 and b-PF20 in the heating process.\n16\n4. To support the ToF-SIMS analysis, the authors must provide literature support or additional\nexperimentation to support the claim that the qb-PF20 and b-PF20 perfluoro blocks migrate to\nthe film surface during fabrication. Did the authors compare solvent vapor annealing using\ntoluene with perfluorotoluene? This would provide a more conclusive analysis and greater\nsupport for the role of fluorinated solvent additives.\nResponse: We sincerely appreciate the reviewer’s valuable advice. As demonstrated by\nreported works in the OSC field, the incorporation of fluorinated moieties into organic\nmolecules can significantly reduce their surface energy for the regulation of vertical phase\ndistribution. Wei et al. (J. Mater. Chem. A. 2022, 10, 8837) introduced trifluoroalkyl groups\nonto the pyrrole unit of Y-series non-fullerene acceptors and found that the fluorinated alkyl\nchains effectively lowered the surface energy and promoted favorable vertical phase separation.\nMore importantly, Huang et al. (Angew. Chem. Int. Ed. 2023, 62, e202213869) developed an\nasymmetric acceptor EH-C F containing polyfluoroalkyl chains that exhibits ultralow surface\n8 17\nenergy, enabling self-migrating to the top surface of the active layer. By employing EH-C F\n8 17\nas a third component, a favorable vertical morphology featuring an upper acceptor-enriched\nthin layer and a lower undisturbed bulk heterojunction layer was achieved. Recently, we\nsynthesized two low-surface-energy acceptors (F6CB and F6CN) by incorporating\npolyfluorinated moiety into their central cores (Chem. Eng. J. 2025, 524, 168750). When\nblended with conventional acceptor, these fluorinated acceptors spontaneously enriched at the\nfilm surface during spin-coating, creating a cascaded vertical donor/acceptor distribution\nthrough surface-energy-driven self-stratification. These studies collectively demonstrate that\nfluorinated units and molecules preferentially migrate to the surface during solution processing,\nwhich strongly supports our finding that block-containing fluoropolymers similarly migrate to\nthe film surface during sequential deposition. These valuable references are added in the revised\nmanuscript and the relevant description in the main text has been rephrased as follows:\n17\n“More importantly, some studies demonstrated that the fluorinated units and molecules\npreferentially migrate to the surface owing to their low surface energy26, 28, 38, suggesting these\nfluorinated blocks accompanied by the whole polymer chain will migrate to the surface during\nthe film-formation process.”\nWe also sincerely appreciate the reviewer’s insightful suggestion. In response, we employ\nconventional organic solvent (toluene) vapor annealing (OSVA) as a post-treatment for qb-\nPF20/BTP-eC9 devices (denoted as SD/FS-OSVA) under various processing conditions. As\nsummarized in Table R2, the device efficiency of SD/FS-OSVA devices initially improves with\nrising temperature but declines beyond an optimal point (100 ℃, 3 min), mirroring the trend\nobserved for SD/FS-FSVA devices. The OSVA treated qb-PF20/BTP-eC9 devices achieves a\nrespectable PCE of 19.04% associated with a V of 0.864 V, a J of 28.12 mA cm-2, and an FF\noc sc\nof 78.36%. Notably, the PCE and photovoltaic parameters of SD/FS-OSVA devices remain\ninferior to SD/FS-FSVA devices while close to the device treated by thermal annealing,\nsuggesting the toluene solvent vapor cannot selectively reorganize the fluoropolymer to induce\nthe secondary vertical phase separation required for GHJ optimization. The performance\ndifferences may arise from the preferential dissolution of small-molecule acceptor in toluene\nrather than the fluoropolymer, as reflected in the distinct surface energy of blend films.\nSpecifically, the SD/FS-OSVA blend film exhibits a surface energy of 21.62 mN m-1 (Fig. R10),\nsignificantly higher than that of SD/FS-FSVA film (20.41mN m-1) and slightly elevated\ncompared to SD/FS film (21.34 mN m-1). These results demonstrated that the toluene SVA\ntreatment tend to redistribute the acceptor without effectively lifting the fluoropolymer. Thus,\nthe device performance and surface energy reaffirm the critical role of fluorous solvent\n(perfluorotoluene) in resurfacing fluoropolymer and optimizing GHJ. Detailed photovoltaic\nperformance and surface energy data are provided in Supplementary Fig. S35 and Table S15.\nThe relevant description in the main text has been rephrased as follows:\n18\n“The essential role of perfluorotoluene is further investigated by applying conventional organic\nsolvent (toluene) vapor annealing (OSVA) post-treatment to qb-PF20/BTP-eC9 devices\n(denoted as SD/FS-OSVA). As summarized in Supplementary Table S15, the PCEs of SD/FS-\nOSVA devices remain inferior to SD/FS-FSVA devices while close to SD/FS devices,\nsuggesting the limited ability of toluene to reorganize fluoropolymer. This performance\ndifference may arise from the preferential dissolution of small-molecule acceptor in toluene\nover the fluoropolymer, as reflected in the distinct surface energy. Specifically, the SD/FS-\nOSVA blend film exhibits a surface energy of 21.62 mN m-1 (Supplementary Fig. S35),\nsignificantly higher than that of SD/FS-FSVA film and slightly elevated relative to SD/FS\nfilms, reaffirming the critical role of fluorous solvent in resurfacing fluoropolymer and\noptimizing GHJ.”\nTable R2. Photovoltaic parameters of SD/FS-OSVA processed qb-PF20/BTP-eC9 devices\nwith different treatment conditions.\nOSVA Condition V (V) J (mA cm-2) FF (%) PCE (%)\noc sc\n90 ℃, 3 min 0.866 27.94 78.03 18.88 (18.35±0.42)\n100 ℃, 3 min 0.864 28.12 78.36 19.04 (18.71±0.37)\n110 ℃, 3 min 0.860 28.23 77.12 18.72 (18.23±0.46)\nFig. R10. Contact angles and surface energies of SD/FS, SD/FS-FSVA and SD/FS-OSVA\nprocessed qb-PF20/BTP-eC9 blend films.\n19\n5. Polymer batch-to-batch variation is a common issue with polymer solar-cells. The authors\nmust address the batch-to-batch reproducibility for the block/quasi-block copolymer synthesis\nrelative to random copolymer synthesis.\nResponse: We sincerely appreciate the reviewer’s insightful comment regarding batch-to-batch\nreproducibility of polymers. For a conjugated polymer, the batch-to-batch variations in\nmolecular weight (M ) and polydispersity index (PDI) critically influence their process-\nn\ndependent material properties and device performance consistency. In this work, the PF20\npolymers with distinct monomer sequences are synthesized through controlling the addition\nsequence and time. Specifically, the b-PF20 copolymer is synthesized via a two-step\npolymerization, where the D and A monomers are pre-polymerized to form fluorinated\nF\nsegment, and followed by the addition of D and A monomers. This method ensures the\nformation of well-defined blocks through precise control of monomer incorporation. The one-\nstep synthesized qb-PF20 exploits the differential reactivity of fluorinated and conventional\nmonomers to promote the preferential polymerization of D and A monomers and form\nF\nfluorine-rich blocks with considerable numbers of repeat units, delivering a quasi-block\ncopolymer. Both methods enable controlled and stepwise polymerization to form blocks that\nensures superior batch-to-batch reproducibility through minimizing compositional variations.\nIn contrast, the synthesis of ra-PF20 employs employs gradual D and A monomers addition\nF\nwithin 50 min during early polymerization stages of D and A monomers. Since the fluorinated\nmonomers have higher reactivity, the dropwise addition of D ensures the randomly distribution\nF\nof fluorinated monomer in oligomers to form a random copolymer. The stochastic incorporation\nof fluorinated polymers at varying reaction stages, coupled with their competitive\ncopolymerization with diverse D-A containing blocks, leads to substantial sequence\nheterogeneity in the resulting oligomers, ultimately compromising the synthetic reproducibility\nbetween batches. More Significantly, the improved molecular packing order and higher\ncrystallinity observed in block-containing fluoropolymers (qb-PF20 and b-PF20) compared to\n20\nthe ra-PF20, may render their photovoltaic performance less sensitivity to polymer M .\nTo\nn\nconfirm it, we further synthesized three additional batches of ra-PF20, qb-PF20 and b-PF20\nwith different molecular weight and PDI, as detailed in Fig. R11 and Table R3. These\ncopolymers are then associated with acceptor BTP-eC9 and fabricate OSCs using SD/FS-FSVA\nmethod to investigate the dependence of PCEs versus polymer M .\nn\nFig. R11. Molecular weight and polydispersity index of ra-PF20, qb-PF20 and b-PF20 across\ndifferent batches.\nTable R3. Molecular weight data of ra-PF20, qb-PF20 and b-PF20 across different batches.\nBatch M (kDa) M (kDa) PDI\nn w\nra-PF20-1 25.6 57.4 2.24\nra-PF20-2 32.2 65.5 2.03\nra-PF20-3 39.1 86.5 2.21\nqb-PF20-1 24.6 44.7 1.82\nqb-PF20-2 33.2 63.1 1.90\nqb-PF20-3 39.4 79.6 2.02\nb-PF20-1 25.7 49.6 1.93\nb-PF20-2 34.4 64.6 1.88\nb-PF20-3 41.6 87.2 2.10\nPF20/BTP-eC9, qb-PF20/BTP-eC9 and b-PF20/BTP-eC9 devices with different copolymer M\nn\nare presented in Fig. R12 and Table R4. While all devices exhibit reduced performance with\ndecreasing polymer M , ra-PF20 based devices suffer an obvious decline of PCE (10.4% at M\nn n\nof 25.6 kDa) compared to the best batch. Notably, all batches qb-PF20 and b-PF20 based\ndevices maintain almost identical V , slightly declined J and FF, and afford mitigated PCE\noc sc\nlosses of 7.4% (at M of 24.6 kDa) and 6.8% (at M of 25.7 kDa), respectively. These\nn n\nresults demonstrate the superior molecular weight insensitivity of block-containing\nfluoropolymers compared to random copolymer, highlighting the importance of precise\nmonomer sequence control in optimizing batch-to-batch reproducibility of OSCs. Detailed\nmolecular weight data,\nJ-V curves and photovoltaic parameters are provided in Supplementary\nFigs. S39-40 and Tables S17-18. The relevant description in the main text has been rephrased\nas follows:\n“Batch-to-batch reproducibility in OSCs remains a significant challenge due to inevitable\nvariations in molecular weight (M ) and polydispersity index (PDI) of polymers. Notably, the\nn\nsynthesis of block-containing copolymers addresses this issue through controlled, stepwise\npolymerization that forms well-defined blocks, effectively minimizing batch-to-batch\nvariations in device performance. To confirm it, three additional batches of ra-PF20, qb-PF20\nand b-PF20 with different M and PDI are synthesized, as detailed in Supplementary Fig. S39\nn\nand Table S17. These polymers are then associated with BTP-eC9 and fabricate OSCs using\nthe SD/FS-FSVA method to investigate the dependence of PCEs versus copolymer M\nn\n(Supplementary Fig. S40 and Table S18). While all devices exhibit reduced performance with\ndecreasing polymer M , ra-PF20 based devices suffer an obvious decline of PCE (10.4% at M\nn n\nof 25.6 kDa) compared to the best batch. In contrast, all batches qb-PF20 and b-PF20 based\ndevices maintain almost identical V and slightly declined J and FF, resulting in mitigated\noc sc\nPCE losses of 7.4% (at M of 24.6 kDa) and 6.8% (at M of 25.7 kDa), respectively. These\nn n\nresults demonstrate the superior molecular weight insensitivity of block-containing\n22\nfluoropolymers compared to random copolymer, highlighting the importance of precise\nmonomer sequence control in optimizing batch-to-batch reproducibility of OSCs.”\nFig. R12. J-V curves of SD/FS-FSVA processed (a) ra-PF20/BTP-eC9, (b) qb-PF20/BTP-eC9\nand (c) b-PF20/BTP-eC9 with different copolymer M . (d) Dependence of PCEs versus M .\nn n\nTable R4. Photovoltaic parameters of SD/FS-FSVA processed OSCs based on ra-PF20, qb-\nPF20 and b-PF20 with different M .\nn\nCopolymers M (kDa) V (V) J (mA cm-2) FF (%) PCE (%)\nn oc sc\n25.6 0.844 26.97 74.12 16.87 (16.53±0.31)\n32.2 0.850 27.46 76.10 17.76 (17.35±0.43)\nra-PF20\n39.1 0.853 27.84 77.23 18.34 (17.95±0.37)\n44.7 0.856 28.12 78.18 18.82 (18.39±0.40)\n24.6 0.862 27.58 76.36 18.15 (17.87±0.31)\n33.2 0.865 27.95 77.45 18.72 (18.34±0.33)\nqb-PF20\n39.4 0.868 28.27 78.72 19.32 (18.91±0.39)\n44.4 0.868 28.42 79.44 19.60 (19.17±0.41)\n23\n25.7 0.860 27.65 77.27 18.37 (17.94±0.38)\n34.4 0.860 27.92 78.38 18.82 (18.45±0.33)\nb-PF20\n41.6 0.864 28.31 79.32 19.40 (19.01±0.44)\n47.0 0.866 28.49 79.87 19.71 (19.23±0.45)\n24"}]

Decision letter