Ultralong-range exciton transport in submillimeter-scale spherulite film of π-conjugated polymers

Domain: neuroscience
Published: 2026-01-28
Editorial outcome: major_revision

Abstract
Long-range exciton transport in organic semiconductors is essential for the performance of optoelectronic devices. However, solution-processed π-conjugated polymers films typically exhibit short exciton diffusion lengths (<20 nm) due to local imperfections or variations in interchain packing. Here, large-area submillimeter-scale spherulites are achieved by treating the spin-coated polydiarylfluorene film under solvent vapor annealing. The exciton diffusion length, visualized using transient photoluminescence microscopy, is determined to be an average of 186 nm, with a corresponding diffusion coefficient of 0.14 cm2 s-1. Notably, the maximum value of exciton diffusion lengths and diffusion coefficient can reach up to approximately 396 nm and 0.63 cm2 s-1, respectively. Well-ordered hierarchical structure with an outstanding chain alignment in spherulite provides a uniform excitonic energy landscape, enabling ultralong exciton diffusion. The reduced defect density in the spherulite film may result in shallower trap states, facilitating exciton diffusion and radiative recombination. Polymer light-emitting diodes based on submillimeter-scale spherulite films exhibit deep-blue electroluminescence with high brightness (4897 cd m-2) at low current density and good color purity. These findings demonstrate that the long-range ordered spherulite structure can significantly enhance the excitons transport and improve the overall optoelectronic property.

Introduction
Long-range transport of excitons in semiconducting polymer films is highly desirable for solution-processed optoelectronic devices. However, due to the local energetic disorder, imperfection and structural variation, most of the semiconducting polymer films present an extremely short singlet exciton diffusion length (LD) of 5–20 nm1–3. This is significantly shorter than the length (>100 nm) typically observed in single crystals and self-assembled nanostructures, which possess substantial intermolecular electronic coupling and π–π stacking1–8. For instance, single nanofibers from amphiphilic conjugated polymers (oligomer) with well-defined structures, prepared by living crystallization-driven self-assembly, yield efficient exciton diffusion with coefficients ranging from 0.5 to 1.1 cm2 s-1 and LD exceeding 200 nm6,7. However, the complex and precise multi-step preparation of these nanostructures limits their practical applications, and obtaining well-ordered chain alignment in semiconducting polymer films for industrial-scale fabrication remains a significant challenging.

Approaches for constructing well-ordered hierarchical structures, including delicate side-chain engineering and exquisite control of fluid flow during solution coating, have been extensively exploited in organic solar cells and organic field-effect transistors. Regarding polymer light-emitting diodes (PLEDs), a solution-processed emissive layer with a long-range-ordered intermolecular arrangement is essential for improving their efficiency, but is rarely reported, and the impact of structural order and exciton diffusion on optoelectronic performance needs systematic exploration9–11.

As promising candidates for PLEDs, light-emitting π-conjugated polymers (πCPs) are easily solution-processed capacity to manufacture large-area films for solid-state optoelectronic applications12–15. Nevertheless, amorphous films with disordered polymer chain arrangement generally exhibit ubiquitous exciton traps in the form of low-energy defect structures, resulting in severe non-radiative recombination and short-range localization of excitons, which could reduce the photoluminescence quantum efficiency and device performance10. Recently, crystalline organic semiconductors attracted more attentions, as their long-range ordered molecular packing facilitates both charge carrier mobility and the alignment of transition dipole moments16. From this perspective, transforming the conjugated polymer film with interpenetrating and entangled polymer chains into highly crystalline self-assembled nanostructures would theoretically benefit efficient exciton diffusion and light emission properties. However, this approach still faces enormous challenges, due to the presence of ubiquitous structural defects, disorder aggregation and micro-scale grain boundaries17. The performance of high-quality light-emitting devices largely depends on the ability to fabricate ordered crystalline πCPs films that enable long-range exciton transport and diffusion.

Spherulite is the most common characteristic form of large-scale crystallized polymer, typically consisting of fibrillar crystals that grow radially and branch irregularly18, which plays significant roles in material molding and processing, especially for optical materials19,20. Herein, under solvent vapor annealing (SVA) approach, large-area and continuous submillimeter-scale spherulite films were easily obtained from spin-coated films of wide band gap polydiarylfluorene whose side chains were modified by branched 2-ethylhexyl (poly[4-(isooctyl)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(isooctyl)-9,9-diphenylfluoren-2,7-diyl], named as PEODPF) (Fig. 1a). The crystalline film with multi-scale ordering and alignment of polymer chains can effectively suppress the internal defect that potentially acted as exciton traps, rendering the film an ultralong singlet-excitons diffusion length up to ~396 nm and a large diffusion coefficient (D) of ~0.63 cm2 s-1. This submillimeter-scale spherulite presents a deep-blue emission with high-quality color purity, which confirmed their uniform exciton energetic landscape for the potential optoelectronic application.

Results
Growth condition of spherulite
The condensed structure of πCPs in the film state is closely related to the type of side chains. As previously reported, linear side chains at the fourth position of polydiarylfluorene (PODPF) endow the polymer with exceptional backbone planarity (β-conformation), in which the inter-monomer torsion angle approaches 180o, facilitating the film with unique photophysical properties and excellent crystallinity21,22. Herein, the linear side chains of PODPF were replaced by branched side chains to synthesize a series of polymers, named POYDPF, PDODPF, and PEODPF, aiming to minimize aggregation in condensed states and side-chain interdigitation, as well as generating a “flexible random” region during crystallization under SVA (Fig. 1a and Supplementary Fig. 5b). As expected, only crystalline regions but no spherulitic structures were observed in PODPF film (Supplementary Fig. 5a, i), which can be attributed to the strong crystallinity of its linear alkyl chains. Interestingly, POYDPF (Supplementary Fig. 5a, ii) and PDODPF (Supplementary Fig. 5a, iii) with shorter branched side chains can self-assemble into small nuclei, but no complete and regular spherulites formed. In contrast, the PEODPF film with bulky side chain displayed well-defined spherulite morphology, confirmed by the characteristic birefringence and Maltese Cross under the polarized optical microscope (POM) (Fig. 1c, d and Supplementary Fig. 5a, iv). These observations suggest that the formation of spherulites relies on the introduction of bulky branched side chains, which weakens the aggregation between chains and provides more space for crystal nuclei growth, thereby facilitating the formation of highly ordered spherulites. Furthermore, the prominent crystalline ability of PEODPF is proved by the single crystal structure analysis of monomer (Fig. 1b), where the herringbone molecular packing induced by the branched alkyl chains favors the interchain π–π stacking9,23–25. The results simulated by Material Studio (Supplementary Fig. 5d) predicted that the crystal grows along the a-axis direction of crystal cell, further indicating the tendency of fibrillar crystals to grow along the direction of polymer chain axis. Consistent with the polymer spherulite crystallized from viscous melts and solutions at large undercooling, the PEODPF spherulite formed through the SVA approach also involves two stages: (i) primary nucleation and (ii) crystal growth26. As observed in Fig. 1c, nano-crystal nuclei formed spontaneously in the pristine film during the early stages of growth, acting as primary nucleation sites for the subsequent radial growth of spherulites. Then, the primary spherulites appear as sheaves of fibrillar crystals, resembling fan-shaped bundles, which assemble by the orderly packing of the fluorene backbone. These fibrillar crystals continued to grow outward and branch irregularly around the nucleus. As more nanofibres grow together, the size of the spherulite gradually increases, forming boundaries when neighboring spherulites contact each other. Eventually, the film is covered by spherulites ranging in diameter from a few micrometers to hundreds of micrometers, and the size of spherulite can be easily controlled by tuning the environmental temperature of SVA process (Fig. 1d). We counted the average radius of spherulite in PEODPF film grown at different temperatures, and the largest average radius (~200 μm) can be obtained at ~50 °C, suggesting that this temperature is optimal for the growth of spherulite (Fig. 1e and Supplementary Table 1). Additionally, we studied the influence of different solvents on spherulite growth during the SVA process and found that chloroform is the most effective solvent for promoting spherulite formation (Supplementary Fig. 6). The temperature and solvent dependence of spherulite prove that the growth of fibrillar crystals is closely related to chain activity, and a properly saturated solvent vapor atmosphere provides sufficient time for molecular realignment and assembly into highly ordered configurations. It is noteworthy that this type of spherulite undergoes heterogeneous nucleation, self-seeded by polymer crystals, as confirmed by the central images (Fig. 2a).

Morphology and structure characterization
The micromorphology of submillimeter-scale spherulites is systematically explored by the atomic force microscope (AFM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The micromorphology of spherulite center displayed in Fig. 2a and Supplementary Fig. 7a, crystal nucleus and the surrounding bundle-like lamellas are observed, which consisted of irregular nanofibres (Fig. 2b and Supplementary Fig. 7b). Spherulite is composed of cylindrical nanofibres aligned orderly, as evidenced by the cross-section SEM image of film (Fig. 2b and Supplementary Fig. 7d). The width of a single nanofibre is about 42 nm, according to the statistical data shown in Fig. 2c. The degree of polymerization of PEODPF is approximately 88, based on the number-average molecular weight (39.3 kDa), and the length of a fluorene unit is 0.83 nm determined from the single crystal data. Combining the values mentioned above, the extended single chain length of PEODPF is estimated to be about 73 nm, which is twice the width of a single nanofibre in PEODPF spherulites. This indicates that the nanofibres are composed of folded chains that align parallel to the nanofibre growth direction (Fig. 2f). The stacking model of submillimeter-scale spherulite is further investigated by high-resolution electron microscopy (HR-TEM) and selected-area electron diffraction (SAED) characterization in Fig. 2d and Supplementary Fig. 7e. The lattice stripe spacing is about 0.24 nm with an excellent periodic interchain arrangement, which could enhance the exciton diffusion length. Meanwhile, the multiple diffraction spots in the SAED pattern image and grazing incidence wide-angle X-ray scattering (GIWAXS) (Fig. 2e) also further confirm the polycrystalline structure of interchain stacking in PEODPF spherulite film. Along the out-of-plane direction, the diffraction peak (100) at qz of 5.8 and 14.2 nm−1 corresponds to the interchain spacing (d100 = 1.08 and 0.44 nm) in the vertical direction of the edge-on interchain arrangement. Along the in-plane direction, the diffraction peak at 8.8 nm−1 (d001 = 0.71 nm) of qxy is attributed to the periodicity of fluorene monomers. Therefore, combining the GIWAXS results, we illustrated the chain stacking model of the spherulite, including the interchain stacking distance (1.09 nm), the characteristic peak of fluorene (0.71 nm), and the π–π interaction distance (0.44 nm), as shown in Fig. 2f. Generally, the degree of interchain packing order is closely associated with the exciton diffusion as mentioned above. Thus, we inferred that the spherulite film with well-aligned nanofibres will provide a remarkably uniform energy landscape, which may benefit the exciton diffusion with a narrowing of the excitonic density of states. Meanwhile, these uniforms interchain packing also permits an excellent orientation of polymer chain and may further benefit for its transportation of exciton transition dipole moments27,28.

Photophysical properties
From the absorption spectra of the PEODPF film (Fig. 3a), we observed that the spherulite film (Spherulite) and pristine film (Film) exhibit similar absorption peaks at about 387 nm, attributed to the polyfluorene backbone. Compared with the absorption spectra of Film, Spherulite exhibits a broader spectral profile and a stronger absorption edge at longer wavelength, which could be attributed to their higher order chain packing and the scattered light of their crystalline structure. Raman spectra of spherulite and spin-coated film showed negligible differences, indicating the film crystallization does not alter the backbone planarity of polymer (Supplementary Fig. 8a). Photoluminescence (PL) spectra with fine vibrational structures are observed in Film and Spherulite with peaks both at 434, 462, and 495 nm (0-0, 0-1, and 0-2 vibrational transitions), respectively. Compared to that of the Film, the 0-1 and 0-2 vibrational transitions of the Spherulite are weaker due to the well-ordered chain stacking in the Spherulite. To elucidate the impact of molecular ordering on excitonic behavior, we systematically investigated the radiative and non-radiative recombination dynamics of the spherulite and pristine films. Base on the photoluminescence quantum yield (PLQY, φ) and transient PL decay characteristics (τ), the calculated radiative decay rate (kr) of spherulite film is 7.9×108 s−1, higher than that of pristine film, while the non-radiative decay rate (knr) is 2.2×109 s−1, lower than that of pristine film (Fig. 3b and Supplementary Fig. 8b). The excitation energy-dependent PLQY measurements (Fig. 3c) further reveal that the Spherulite exhibits a higher average PLQY (~40%) than the Film (~30%) and remains stable at high excitation energies, suggesting the ordered stacking structures in spherulites can reduce non-radiative energy losses. This improvement is further confirmed by the analysis of the band gap tail states (EU) by fitting the photothermal deflection spectroscopy (PDS)29. The EU value of spherulite film is 48.1 meV, lower than the 52.9 meV of pristine spin-coated film (Fig. 3d), confirming a reduced trap state density. To further trace the ultrafast exciton decay behavior in Spherulite and Film, the fluence-dependent femtosecond-transient absorption (fs-TA) measurements were performed under pump fluences of 1.5, 3, 5, 10, and 15 μJ cm−2 with 400 nm excitation (Supplementary Fig. 9a, c). The differential absorption (ΔA) spectra from 1 to 200 ps exhibit consistent spectral features across fluences (Supplementary Fig. 9b, d), including the ground state bleach (GSB) peaks at 415 nm for Film and 416 nm for Spherulite, along with stimulated emission (SE) signals at 450 nm. These features are similar to the ΔA spectra previously reported for related polyfluorene derivatives30,31. In Fig. 3e and Supplementary Fig. 10, the normalized SE dynamics are fitted using a tri-exponential function, and the intensity-weighted averaged lifetimes are summarized in Supplementary Table 2. The Spherulite film exhibits a notably longer stimulated emission (SE) lifetime (136 ps) than the amorphous Film (97 ps), suggesting that the ordered molecular packing facilitates exciton diffusion and radiative recombination. Interesting, fluorescence lifetime imaging microscopy (FLIM) reveals that the longer average fluorescence decay time (τm) of spherulite film (470 ps) than that Film (360 ps) (Fig. 3f and Supplementary Fig. 11a), supporting that ordered crystalline domains promote rapid exciton transport and delocalization, thereby reducing exciton trapping and enhancing radiative decay rate, in agreement with the observed enhancement in PLQY. Taken together, these results indicate that enhanced molecular order and suppressed defect states in Spherulite contribute to improved excitonic performance and reduced non-radiative losses. Generally, the crystalline film exhibited intriguing optical anisotropy, which may promote exciton diffusion capacity28,32,33. Thus, we further investigated the anisotropic properties of Film and Spherulite through fluorescence anisotropy imaging microscopy (FAIM) images (Fig. 3g, h). The value of fluorescence anisotropy (r) is defined as:
r = (I|| - GI⊥) / (I|| + 2GI⊥) (1)
where I|| and I⊥ represent the fluorescence intensities polarized parallel and perpendicular to the excitation polarization, respectively. The value of r > 0 indicates emission parallels with the excitation polarization direction, while r < 0 means the emission is perpendicular to the excitation polarization direction. As illustrated in Fig. 3i, the pristine film shows uniform r with values ranging from 0 to 0.2, narrower than the spherulite film that ranges from −0.4 to 0.4. The optical anisotropy is also confirmed by the angle-dependent PL measurement (Supplementary Fig. 11b and Supplementary Fig. 11c). As known, the alignment of chromophores in polymer films significantly affects exciton behavior, energy transfer and luminescence performance, which is crucial for the optoelectronic properties of luminescent polymers34. The higher r value observed in Spherulites suggests its higher ordered chromophores alignment structure, making energy and exciton diffuse easier along the alignment direction. This research indicates that the strong coupling of adjacent chromophores in Spherulite is foreseeable due to their ordered molecular chain packing structure. In addition, their electron energy transfer pathways include intrachain and interchain, with the former involving energy transfer along the backbone between adjacent fluorene conjugated fragments. The latter is achieved through energy hops between spatially coupled chain segments due to the self-folding of molecular chains within the Spherulite. These results demonstrate that the ordered PEODPF chains in spherulite can substantially improve their luminescence efficiency and excited state lifetime, thereby providing the possibility for obtaining long-range exciton transport.

Exciton diffusion length characterization
To further explore the excitonic behaviors in spherulite, transient photoluminescence microscopy (TPLM) is used to visualize their exciton diffusion property35,36. Supplementary Fig. 12 displays a schematic diagram of the TPLM setup. The principle of this method involves exciting the spherulite and collecting signals to reconstruct the temporal and spatial emission intensity distribution, and exciton diffusion is represented by the expansion of the fluorescence emission intensity distribution over decay time. As shown in Fig. 4a, the diameter of the excitation spot (beam center) irradiated on the nanofiber bundles is about 238 nm, covering several single nanofibers. The TPLM images of spherulite shows the PL intensity distribution along the x-scanning direction as a function of decay time (Fig. 4b). Compared to the TPLM image of a single crystal, the spherulite exciton diffusion state is not very obvious, which could be attributed to the emission signal is collected from a branch of not perfectly horizontally aligned nanofibre bundles (Fig. 4a). As a result, it can increase the energetic disorder and local electronic perturbation, and indistinct exciton diffusion in the TPLM image. For further quantitative analysis, we utilize the mean squared displacement (MSD) model to extract the diffusion coefficient (D) from the slope of the time-related variance of the PL intensity distribution σ2int(t), according to Eq. (2)37:
D = σ2int(t) / 2t (2)
Figure 4c shows the time evolution of the singlet exciton MSD in spherulite, which exhibits a good linear relationship in the range of 0–0.3 ns. At longer times t > 0.3 ns, exciton–exciton annihilation (EEA) becomes the dominant process, and together with exciton trapping, reduces the spatial spread of the exciton distribution, leading to a decrease in the calculated MSD values (Supplementary Fig. 14). By performing TPLM measurements on various samples, the statistics of D is established and the average D can be reliably fitted as 0.146 cm2 s−1, with the Dmax of 0.45 ± 0.18 cm2 s−1 (Fig. 4d, Supplementary Fig. 14, and Supplementary Table 3). Combining with the equation LD = √2Dτ, the LD is calculated to be an average of 186.37 nm with a maximum of 331 ± 65 nm. The maximum value of D is still high for semiconductor polymer films, although reported the bundled nanofibres make the exciton diffusivity lower38. The prolonged exciton diffusion length in spherulites proves that the well-ordered polymer chain packing and less defect structures could assist to slow down the exciton deactivation rate and extend the relative luminescent lifetime, which further favors the enhancement of the emission property and excitonic organic electronic devices efficiency.

PLEDs fabrication and characterization
In order to validate the feasibility of this submillimeter-scale spherulite film on multi-layer optoelectronic devices, we constructed PLEDs with the pristine and spherulite film adopted the structure shown in Fig. 5a (the detailed process is depicted in Supplementary Fig. 15a). PLEDs based on film and spherulite show similar electroluminescence (EL) spectral profile with maximum emission peak (λmax) at 436 and 435 nm (0-0 emission), consistent with their PL spectra (Fig. 5b). Besides, the corresponding full width at half maximum (FWHM) are calculated about 54 and 43 nm, indicated the small Huang–Rhys factor induced by the weak interchain charge transfer interaction and aggregation in crystalline structures, similar to the PL spectral and TA analysis mentioned above. Therefore, the Commission Internationale de l'éclairage (CIE) chromaticity coordinates also proves better colorimetric purity of Spherulite-based PLEDs (Fig. 5b). In addition, the PLEDs based on Spherulite are more stable than those of Film, indicating the slight change in different fabrication batching (Supplementary Fig. 15d). Notably, the Spherulite-based PLED shows an angular dependent EL spectrum that the intensity at 462 nm (0-1) increased with increased angle attributed to their polarized property (Fig. 5c). Due to the fact that the λmax (0-0) of Spherulite-based PLED does not vary with angle, the corresponding angular emission intensity distribution of both devices follow the Lambertian profile (Fig. 5d). As shown in Fig. 5e, the spherulite-based PLED achieve the maximum EQE (EQEmax) value of ~1.16% and the maximum current efficiency (CEmax) of ~1.46 cd A−1, which is substantially higher than that of Film-based devices (1.06% and 0.88 cd A−1). According to the EQE equation:
EQE = IQE × ηout = γ × ηr × φ × ηout (3)
where γ is hole/electron recombination efficiency, ηr is exciton formation probability (0.25 for conventional fluorescent emitters), φ is PLQY and ηout represents light out coupling efficiency. When assuming γ=1, ηout=0.2, ηr=0.25, φFilm=0.3, φSpherulite=0.4, the theoretical EQEmax for the Film and Spherulite devices are calculated to be 1.5 and 2.0%, respectively. The measured values are below these due to an unoptimized device architecture. Nonetheless, the higher EQE in the spherulite-based device correlates with its increased PLQY, indicating reduced non-radiative losses and confirming the key role of molecular ordering in suppressing defect-induced quenching and enhancing overall device performance.

Besides, these devices have a similar turn-on voltage at around 5.3 V, and the maximum luminance (Lmax) of spherulite-based PLEDs is 4897 cd m−2, much higher (Enhanced by about 47%) than that of Film-based device (3342 cd m−2), as shown in Supplementary Fig. 15b and Table 1. Then, we counted the Lmax of two types devices fabricated under the same condition, as shown in Fig. 5i. Apparently, the spherulite-based devices have brightness range of 1000–4000 cd m−2, relatively higher than the Film-based devices (1000–2000 cd m−2). Furthermore, the Spherulite-based PLEDs also display a feature of high brightness at low current density, suggesting that the ordered stacked interchain facilitates carrier transport and increases the carrier concentration (Fig. 5f). The carrier mobility tested by the hole/electron-only carrier devices (Supplementary Fig. 15c) reveal that the excellent electrical properties of submillimeter-scale spherulite film, which also confirms the excellent morphology and dense packing of PEODPF nanofibres to ensure the inter-fiber charge transportation.

To reveal the physical processes of the PLEDs, we study the electronic processes during device operation using transient EL (Tr-EL) analysis39. The typical Tr-EL curves consist of four stages: (i) time delay from pulse voltage turn-on to Tr-EL onset; (ii) EL intensity increased to steady-state value; (iii) stable EL intensity when voltage is on; (iv) EL intensity decay after voltage turns off. In Fig. 5g, the Tr-EL intensity of the Film-based device rises and then reaches stability before showing a decaying trend with increasing current density (up to 25 mA cm−2) at a pulse duration time of 40 µs, reflecting exciton–exciton annihilation via singlet-singlet annihilation and singlet-triplet annihilation under high exciton densities, where exciton diffusion is limited and local accumulation becomes significant. Under the same conditions, the EL intensity of the spherulite-based device shows a rising trend with the increase of current density without reaching saturation or decay (Fig. 5h). This behavior is attributed to the low density of the defect structures in spherulite film. Electrons are less prone to defect trapping, which enhances exciton transport and charge mobility, thereby prolonging the recombination process between holes and electrons. Slight enhancement of exciton recombination emission at the plateau state in the Tr-EL curve of Spherulite-based PLED also confirmed the excellent molecular landscape for the transportation of hole and electron injection and transportation, which may reasonably explain their good device efficiency and efficient deep-blue emission. Thus, the ordered stacked interchain arrangement in the spherulite is a feasible strategy to suppress defect formation and exciton utilization rate for achieving high-performance blue light emission.

Methods
Materials
All reagents and catalysts used in this study were purchased from commercial suppliers and used without further purification unless stated otherwise. 2,2’-bipyridine, 1,5-cyclooctadiene (COD), and bis(1,5-cyclooctadiene)nickel (0) [Ni(COD)2] were obtained from Sigma-Aldrich. All other drugs used in the synthesis process were obtained from Adamas-beta. Dimethylformamide (DMF) was dried over calcium hydride (CaH2) and then distilled under a dry nitrogen atmosphere immediately before use. Toluene was dried over sodium (Na) and subsequently distilled under a dry nitrogen atmosphere immediately before use. Anhydrous THF (HPLC grade) was obtained from Solvent Purification Systems (Innovative Technology, Inc.). PEDOT:PSS (Clevios PV P AI 4083) was purchased from Heraeus. The detailed synthesis of PDODPF was provided in the Supplementary Information. The PEODPF, PODPF, and POYDPF used in this paper was synthesized by our previous work.

Preparation of polymer solution, the pristine film (film) and the spherulite film (spherulite)
Polymer solution. The polymer solutions were prepared by dissolving the PEODPF polymer in the chloroform (CF) solvent spontaneously overnight. Various concentrated polymers solution for the spin-coating process is obtained after the heated solution cools to room temperature.

Spin-coated films (Film). Pristine films were spin-casted on quartz or silicon substrates from CF solution (various concentrations) using KW-4A (from the Institute of Micro-electronics of the Chinese Academy of Science) at 1500 for 60 s.

Spherulite films (Spherulite). The spherulite films were prepared by the solvent vapor annealing (SVA) method in Supplementary Fig. 5b. The spin-coated or drop-coated film was placed in a weighing bottle containing chloroform solvent, then the airtight weighing bottle into the oven, setting the oven temperature, and waiting for the chloroform solvent to finish evaporating to get the spherulite film.

Fabrication of polymer light-emitting diodes (PLEDs)
The PLEDs structure is ITO/PEDOT: PSS (50 nm)/EML/TPBi (23 nm)/LiF (1 nm)/Al (100 nm). The detailed fabrication procedure of PLEDs was described as follows. Before spin-coating, the ITO substrate was cleaned in an ultrasonic bath with detergent, acetone, isopropanol and deionized water, dried in an oven at 120 °C for 2 h, and treated with ultraviolet ozone for 10 min. In the spin-coating procedure, a 40 nm thick PEDOT:PSS was firstly spin-coated (Supplementary Fig. 15a, Step 1) and annealed at 120 °C for 20 min (Supplementary Fig. 15a, Step 2). Then, the emitting layer was spin-coated from CF solution (6 mg mL−1) (Supplementary Fig. 15a, Step 3) and the spherulite films were prepared by the SVA method (Supplementary Fig. 15a, Step 4). Next, Film and Spherulite film annealed at 100 °C for 10 min in a nitrogen-filled glovebox. Finally, the other layers, such as 23 nm TPBi, 1 nm LiF and 100 nm Al, were deposited by thermal evaporating sequentially through a shadow mask at a pressure below 1 × 10−5 mbar. The area of the device was 4 mm2 defined by the overlap between the ITO and Al electrode. The EL spectra were measured using a QE65 Pro (Ocean Optics) spectrometer in air with encapsulated devices. The structure of single carrier devices ITO/PEDOT: PSS/EML/MoO3/Al single carrier devices (hole-only) and ITO/ZnO/EML/TPBi/LiF/Al (electron-only) were prepared.

Characterization
General characterization. Nuclear magnetic resonance (NMR) spectra were recorded using a JEOL NMR spectrometer (JNMECZ400S, 400 MHz, Japan), 1H NMR and 13C NMR spectra were referenced to CDCl3 (1H NMR: 7.26 ppm, 13C NMR: 77.0 ppm). Absorption spectra were measured with a Shimadzu UV-3600 spectrometer at room temperature, and emission spectra were recorded on a Hitachi F-4600 luminescence spectrometer. Nanosecond time-resolved studies were performed with an Edinburgh FLS980 time-correlated single photon-counting (TCSPC). The transient signal was acquired by TCSPC. Raman microscopy was performed using a Renishaw 2000 CCD spectrometer coupled to an Olympus BH-2 confocal microscope, and using the 633 nm line of a He–Ne laser as the excitation source to avoid absorption and resonance effects. The excitation energy-dependent PLQY of spherulite and pristine film samples were determined by a self-made system by combining a laser (MDL-III-375 nm, spot size is ≈0.13 cm2), an optical fiber, a spectrometer, and an integrating sphere. All films were deposited onto quartz substrates through spin-coating.

Grazing incidence wide-angle X-ray scattering (GIWAXS) test. The GIWAXS measurement was performed at the BL14B1 beamline of the Shanghai Synchrotron Radiation Facility (SSRF) using an X-ray with a wavelength of 1.24 Å. The X-ray beam size was ≈0.2 mm × 0.3 mm, as defined by the horizontal and vertical slits.

Film morphology characterization. The polarized optical microscopy (POM) images were performed by NIKON LV100ND. AFM measurement was performed on Park XE-70 atomic force microscopy. Using tapping mode with as little force as possible to collect the topography and phase image of the sample at the same time, the scanning rate was 1 Hz, and the scanning range was 500 nm to 5 μm to obtain the results. The samples were then examined with a field emission SEM (Hitachi, S-4800) at an accelerating voltage of 5 kV. The transmission electron microscope (TEM) observations were performed with an FEI Talos F200X microscope operated at 200 kV. (Point resolution 0.25 nm)

Femtosecond-transient absorption (fs-TA) test. Ultrafast TA spectroscopy was conducted using a Ti:sapphire regenerative amplifier (Libra, Coherent Inc.). The second harmonic of the primary beam at 400 nm or an optical parametric amplifier (OperA Solo, Coherent Inc.) pumped by the regenerative amplifier was used to generate the pump beam. The probe beam was a broadband supercontinuum light source generated by focusing a small portion of the femtosecond laser beam onto either a 5-mm-thick CaF2 plate. The TA signal was then analyzed by a silicon charge-coupled device mounted on a monochromater (Acton 2358, Princeton Instrument) at 1 kHz, enabled by a home-built control board.

Transient photoluminescence microscopies (TPLM) test. Photoexcitation diffusion imaging was performed using a home-built TPLM (Supplementary Fig. 12), a 405 nm picosecond pulsed laser (ALPHA-LAS) with a repetition rate of 10 MHz and pulse width of 25 ps was focused onto the surface of the sample using an objective lens (Olympus, 100X, Apo, 0.95 numerical aperture). Additionally, the single-photon detecting avalanche photodiode (APD) (SPCM-AQRH, dead time of 28 ns) was used to detect the PL, and the APD was connected to timing electronics (PicoQuant PicoHarp 3000). The measurement of time-resolved PL decay was based on the same excitation light path of the home-built TPLM, but the PL signal was collected by leading it out of the TPLM system through a multimode fiber (Thorlabs, ø50 μm, 5 m) with a pair of couplers and collimators (Thorlabs RC08FC-P01) and sending it to another APD (MPD PDM Series 20 μm) that was also attached to the timing electronics (PicoQuant PicoHarp 300), as shown in Supplementary Fig. 13.

Photothermal deflection spectroscopy (PDS) test. The measurement of PDS was based on NANOUPE-PDS-1. The testing scanning range of 350–600 nm. The absorption detection limit of PDS was 0.001%. The thermal deflection solution was 3 M Flourinert.

Transient electroluminescence (Tr-EL) measurement. The Agilent pulse generator (8114A, 100 V/2 A, rise time < 7 ns) is used to provide rectangular pulse voltages (repetition rate: 1 kHz or 100 Hz, pulse width: 3 or 5 μs) to drive the PLED. Emissions are collected by a Hamamatsu PTM (H10721–20, rise time: 0.57 ns), which is connected to a digital oscilloscope (Agilent DSOX4024A, bandwidth: 200 MHz).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors present a study on long-range exciton transport in π-conjugated polymer (πCP) films treated by solvent thermal annealing (SVA), and investigates their potential for improving exciton diffusion lengths. The authors show significant advancements, including submillimeter-scale spherulite formation, longer exciton diffusion lengths, and enhanced electroluminescence in PLEDs. While the study has a wide range of characterisation methods covered, I regret that I cannot recommend this manuscript for publication in its current form due to the following major concerns:\n1. The authors used photoluminescence quantum yield (PLQY) values in their calculations; however, these values are not explicitly reported in the manuscript or supporting information. The measured PLQY values are essential for the comparison between the spherulite and pristine film samples and to access the reliability of the calculation.\n2. The transient absorption (TA) measurements were measured at an intensity of up to 10 mOD, which is very high for systems with good diffusion lengths, especially in films. Under these conditions, exciton annihilation is very likely happening, making the kinetics faster and the comparison invalid. The authors should perform a fluence-dependent TA series in both the pristine and spherulite films to identify a low-fluence regime where no annihilation occurs. In this regime, the lifetimes should be compared.\n3. Regarding the response time of the experimental setup, the authors should clarify whether the 0-300 ns range, where the diffusion constant is extracted, is within the response time of the system. If so, this time point may not be representative and needs careful consideration.\n4. The authors extracted diffusion data for the first 300 ps despite the reported lifetime of 1.2 ns. However, Figure S7 reveals a negative trend after 300 ps, which is not adequately explained. The authors should provide a clear justification for excluding this part of the data although it is within the life time and address why the trend goes negative.\n5. The Gaussian fits used in the analysis should be included in the Supplementary Information to allow readers to evaluate the robustness of the fitting procedure.\n6. While the manuscript focuses on singlet exciton dynamics, it does not address the potential influence of triplet excitons in the devices. Optical excitation generates 100% singlet excitons, whilst triplet excitons only form via intersystem crossing (ISC). In contrast, electrical excitation directly produces 75% triplet excitons. The rising electroluminescence (EL) intensity trend observed in the spherulite films could be influenced by delayed triplet excitons contributing through triplet-triplet annihilation, especially given the efficient diffusion reported. The authors should discuss the role of triplet excitons in detail.\n7. The authors should compare the PLQY and EQE values, as such a comparison can offer insights into the presence of trap states or dark triplet excitons, which could influence the overall device performance.", "reviewer_2": "This paper presents an innovative method to improve exciton transport in organic semiconductor materials. It involves creating submillimeter-scale spherulite films through solvent vapor annealing (SVA). The authors report substantial enhancements in exciton diffusion length and coefficients within π-conjugated polymer films, which show great promise for optoelectronic applications, especially in polymer light-emitting diodes (PLEDs). The study is well-structured, featuring comprehensive experimental methods, and the results offer valuable insights into how long-range ordered spherulite structures can significantly improve exciton diffusion and optoelectronic properties. This research deepens our understanding of the structural dynamics and performance of organic semiconductor materials. Therefore, this work can be considered for publication after a minor revision by addressing the following comments.\n1. The paper suggests that the introduction of branched side chains, as opposed to linear side chains, leads to the formation of large-sized spherulites. Why does the introduction of branched side chains result in the formation of spherulites, while materials with linear side chains do not form this morphology? A comparative experiment should be conducted to explore this issue.\n2. The description of “solvent vapor annealing” in the paper should be standardized, as there are currently two different expressions being used, such as “solvent thermal annealing”.\n3. In Fig. 3b, why is the absorption edge of the spherulite higher than that of the pristine film?\n4. Page 8, line 27; “We obtained the width of the bandgap tail states (Eu) by fitting the photothermal deflection spectroscopy (PDS). The Eu value of spherulite film is 48.1 meV, lower than the 52.9 meV of pristine spin-coated film (Fig. 3e).” In the PDS test referenced in the paper, the data obtained indicates minimal differences. Might these data potentially contain errors?\n5. Page 10, line 13; “As shown in Fig. 4a, the diameter of excitation spot (beam center) irradiated on the nanofiber bundles is about 238 nm, covering several single nanofibers. ” This paper utilizes a laser with an excitation wavelength of 405 nm to excite the sample. How is the diameter of the light spot determined to be 238 nm? In Fig. S6, what is the role of the flip mirror?", "reviewer_3": "The manuscript studies exciton transport in a conjugated polymer by transient photoluminescence microscopy. Diffusion coefficients reach in the same order of magnitude as those of other reports in literature. Based on a solvent vapour annealing procedure of a spin coated film of branched side-chain modified polydiarylfluorene, the authors demonstrate improved structural order and ehanced exciton diffusivity. When incorporated into polymer light-emitting diodes, these films yield deep-blue electroluminescence with high brightness and improved color purity at low current densities.\nAlthough the manuscript provides a detailed analysis of the structural and photophysical properties of the spherulite films, the core findings are not strikingly novel. The enhancement of exciton diffusion through improved molecular ordering and reduced defects in π-conjugated polymer films is a concept that is established in the literature. While the work confirms these relationships for the specific polymer under study, it does not introduce fundamentally novel insights or processing strategies. I am not sure about the impact of this work. In summary, the study confirms established principles rather than presenting research of great novelty that I would expect for papers in Nature Communications."}, "author_response": "1 Response to reviewers’ comments\n4 treated by solvent thermal annealing (SVA), and investigates their potential for improving exciton\n5 diffusion lengths. The authors show significant advancements, including submillimeter-scale\n6 spherulite formation, longer exciton diffusion lengths, and enhanced electroluminescence in\n8 cannot recommend this manuscript for publication in its current form due to the following major\n9 concerns:\n12 comments, we have carefully corrected all our mistakes and polished the entire manuscript. We\n13 also added extensive experiments to support our assumption and results in this revised manuscript.\n16 1. The authors used photoluminescence quantum yield (PLQY) values in their calculations;\n17 however, these values are not explicitly reported in the manuscript or supporting information. The\n18 measured PLQY values are essential for the comparison between the spherulite and pristine film\n19 samples and to access the reliability of the calculation.\n22 essential for the comparison of between the thin film and the spherulite samples. We sincerely\n23 apologize that only the PLQY values presented in Figure S4b (Page 7) were shown, without\n24 providing the numerical values in the main text. In response to your helpful suggestion, we have\n25 conducted additional experiments, and the updated PLQY data have been incorporated into the\n26 revised manuscript to provide stronger support for our conclusions and improve the overall clarity\n27 and completeness of the study.\n28 (1) We apologize for not clearly expressing the PLQY values in the previous manuscript. Actually,\n29 we measured the PLQY values of Film and Spherulite (22% and 26%, respectively), as shown in\n31\n33 spherulite and pristine film samples were determined by FLS980 Series of Fluorescence\n1 (2) Additionally, during the revision, we supplemented excitation energy-dependent PLQY\n2 measurements to further validate the difference between the spherulite and pristine film samples.\n5 consisting of a 375nm laser (MDL-III-375 nm, spot size is ≈ 0.13 cm2), optical fibers, a\n6 spectrometer and an integrating sphere (Adv. Mater., 1997, 9, 230). All films were deposited onto\n7 quartz substrates through spin-coating. The results show that Spherulite exhibited a significantly\n8 higher average PLQY of approximately 40%, compared to 30% for Film. Moreover, the PLQY of\n11 facilitates exciton diffusion, reduces nonradiative recombination, and enhances radiative decay.\n13 the highly ordered spherulite film enhances photoluminescence quantum efficiency and\n14 luminescence stability.\n15\n19 “Meanwhile, the excitation energy-dependent PLQY measurements (Fig. 3c) show that the\n21 high excitation energies.”\n23 clarify this point on page 4, lines 3-6:\n24 “The excitation energy-dependent PLQY of spherulite and pristine film samples were determined\n25 by a self-made system by combining laser (MDL-III-375 nm, spot size is ≈0.13 cm2), optical\n26 fiber, spectrometer and integrating sphere (Adv. Mater., 1997, 9, 230). All films were deposited\n27 onto quartz substrates through spin-coating.”\n29\n30 2. The transient absorption (TA) measurements were measured at an intensity of up to 10 mOD,\n31 which is very high for systems with good diffusion lengths, especially in films. Under these\n1 conditions, exciton annihilation is very likely happening, making the kinetics faster and the\n2 comparison invalid. The authors should perform a fluence-dependent TA series in both the pristine\n3 and spherulite films to identify a low-fluence regime where no annihilation occurs. In this regime,\n4 the lifetimes should be compared.\n7 correctly pointed out, performing TA measurements at lower fluence regime is essential for\n8 minimizing effects of exciton-exciton annihilation and for better revealing the intrinsic exciton\n9 dynamics. According to your nice suggestions, we supplemented fluence-dependent TA series on\n10 both the pristine (Film) and spherulite (Spherulite) films. However, we sincerely apologize for not\n11 being able to reduce the TA signal intensity below 10 mOD, due to the limitations of the TA\n12 measurement system. At excitation fluence lower than 70 μJ/cm2, the signal-to-noise ratio was too\n13 low, which makes it difficult to extract reliable kinetic data. Therefore, to ensure data quality and\n14 accurate analysis, we chose to perform measurements starting from 70 μJ/cm2, and compared the\n15 excited-state lifetimes under low-fluence regime, as follows:\n16 (1) To further trace the ultrafast exciton decay behavior in Spherulite and Film, the\n17 fluence-dependent femtosecond-transient absorption (fs-TA) technology is performed under pump\n18 fluences of 70, 140, and 280 μJ/cm² with 400 nm excitation (Figure 3a, c). The differential\n19 absorption (ΔA) spectra from 0.2 to 200 ps exhibit consistent spectral features across fluences\n20 (Figure 3b, d), including the ground state bleach (GSB) peaks at 425 nm for Film and 430 nm for\n22 broad positive ΔA signals which peak at 570 nm (Film) and 580 nm (Spherulite), corresponding to\n23 polaron-pairs photoinduced absorption (PA ). These features are similar to the ΔA spectra\nP\n24 previously reported for related polyfluorene derivatives (Sun, C. et al., Adv. Funct. Mater., 2022,\n25 32, 2206723. Virgili, T. et al., J. Mater. Chem., 2010, 20, 519–523.)\n26\n29 photoexcitation at 400 nm. ΔA spectra of the Film (b) and Spherulite films (d) at different time\n30 delays down to 200 ps (0.2 ps, 0.5 ps, 1 ps, 5 ps, 10 ps, 20 ps, 50 ps, 100 ps and 200 ps,\n31 respectively).\n1 (2) Figure 4 presents the normalized SE and PA dynamics of Film and Spherulite under varying\n2 pump fluences (70 μJ/cm2, 140 μJ/cm2, 280 μJ/cm2). The time trace was fitted using a\n3 triexponential function with lifetimes (τ), and amplitudes A. The intensity weighted averaged\ni i\n4 lifetimes were calculated using the formula:\nτ=\n∑Aiτ\ni\n2\n(1)\n∑Aiτi\n5 as summarized in Table 1. For the Film sample, the SE lifetime (Figure 4a) initially increased and\n6 then rapid decay with increasing excitation fluence, indicating the exciton-exciton annihilationat\n7 higher excitation fluence. In contrast, the Spherulite exhibited gradually decreased SE lifetime\n8 with increasing excitation fluence (Figure 4b). However, the decay curves at 70 and 140 μJ/cm2\n9 are nearly constant, suggesting that exciton annihilation is negligible at low fluence. Based on this\n10 observation, we infer that under 70 μJ/cm2, both the pristine film and spherulite film exhibit\n11 minimal exciton-exciton annihilation.\nP\n13 respectively) compared to the Spherulite (7 ps and 48 ps, respectively). The shorter PA\nP\n14 lifetimes in the Spherulite film suggests more efficient carrier extraction and reduced polaron\n15 formation, consistent with a lower density of nonradiative defects. Combined with the increased\n17 defect density effectively suppress traps and polaron-mediated nonradiative losses, enabling\n18 more efficient and faster exciton recombination.\n19\n21 450 nm (b) and 580 nm (e) with three pump fluences of 70 μJ/cm2, 140 μJ/cm2, 280 μJ/cm2. (c)\n23 fluence. (f) Comparison of normalized the TA decay kinetics of Film at 570 nm and Spherulite at\n24 580 nm with 70 μJ/cm2 fluence.\n25\n26\ni) i\n2 and Spherulite.\nTrace Pump\nτ τ τ\n1 2 average\nSample wavelength Fluence A A A τ (ps)\n1 2 3 3\n(ps) (ps) (ps)\n(nm) (μJ/cm2)\n70 0.84 0.58 0.30 2.32 0.16 14.91 10.53\n450 140 1.10 0.67 0.10 0.67 0.11 18.29 13.24\n280 2.69 0.26 0.61 0.04 0.10 11.82 6.79\nFilm\n70 0.47 1.22 0.16 6.39 0.21 102.62 95.79\n570 140 0.59 1.07 0.15 5.13 0.17 66.35 59.28\n280 0.55 0.38 0.34 1.84 0.21 39.20 35.72\n70 1.08 0.25 0.28 1.27 0.25 8.32 6.57\n450 140 0.88 0.16 0.49 0.81 0.28 6.69 5.35\nSpherulit 280 1.13 0.50 0.14 0.23 0.22 5.84 4.14\ne 70 0.49 0.51 0.27 4.65 0.19 54.05 47.74\n580 140 0.35 0.56 0.32 3.02 0.44 46.76 41.72\n280 0.60 0.65 0.21 5.03 0.17 51.56 44.69\n3\n6 been added to the revised manuscript on page 9, lines 10-31:\n7 “To further trace the ultrafast exciton decay behavior in Spherulite and Film, the\n8 fluence-dependent femtosecond-transient absorption (fs-TA) technology is performed under pump\n9 fluences of 70, 140, and 280 μJ/cm² with 400 nm excitation (Fig. S7a, c). The differential\n10 absorption (ΔA) spectra from 0.2 to 200 ps exhibit consistent spectral features across fluences (Fig.\n13 broad positive ΔA signals which peak at 570 nm (Film) and 580 nm (Spherulite), corresponding to\n14 polaron-pairs photoinduced absorption (PA ). These features are similar to the ΔA spectra\nP\n15 previously reported for related polyfluorene derivatives. In Fig. 3e and Fig. S8, the normalized SE\n16 and PA dynamics are fitted using a tri-exponential function, and the intensity weighted averaged\n17 lifetimes are summarized in Table S2. For the Film, the SE lifetime initially increased and then\n18 rapid decay at high excitation fluence, suggesting exciton–exciton annihilation, while the PA\nP\n19 lifetime decrease continuously, implying enhanced polaron generation. In contrast, the Spherulite\n20 shows a gradual decrease in SE lifetime with increasing pumping fluence, and nearly constant PA\nP\n21 lifetime, indicating suppressed exciton-polaron interactions. At low excitation fluence, both SE\n22 and PA lifetimes in Spherulite (7 ps and 48 ps, respectively) are shorter than those in Film (11 ps\nP\n23 and 96 ps, respectively), consistent with more efficient carrier extraction and fewer trap-assisted\n24 processes. These results highlight the critical role of molecular ordering in suppressing\n25 trap-assisted and polaron-mediated losses, thereby enhancing exciton recombination efficiency.\n27 fluorescence decay time (τ ) of spherulite film (470 ps) than that Film (360 ps) (Fig. 3f and S9a).\nm\nP\n1 suggests that highly ordered crystalline domains promote rapid exciton transport and\n2 delocalization, thereby reducing exciton trapping and enhancing radiative decay, in agreement\n3 with the observed increase in PLQY. Taken together, these results indicate that enhanced\n4 molecular order and suppressed defect states in Spherulite contribute to improved excitonic\n5 performance and suppressed non-radiative losses. ”\n7 as Fig. S7, Fig. S8 and Table S2, respectively on page 9-10.\n8\n10 this point on page 4, lines 16-21:\n11 “Time-resolved fs-TA spectroscopy is measured by using fs laser (Coherent Astrella), optical\n12 parametric amplifier (Ultrafast Systems Apollo-T) and Helios Pump-Probe System (Ultrafast\n14 1 kHz, 800 nm,7 mJ pulse−1). The pump pulse centered at 400 nm were generate by an optical\n15 parametric amplifier. The vis-light probe pulses (420–780 nm) by focusing an attenuated fraction\n16 of the fundamental 800 nm laser pulses (Coherent Astrella, 800 nm, 1 kHz, 7 mJ pulse−1). The\n17 system provides a time window of up to 8 ns and a time resolution better than 14 fs.”\n18\n20\n21 3. Regarding the response time of the experimental setup, the authors should clarify whether the\n22 0-300 ns range, where the diffusion constant is extracted, is within the response time of the system.\n26 our experimental setup. Photoexcitation diffusion imaging was performed using a home-built\n28 pulse width of 25 ps was focused onto the surface of the sample using an objective lens (Olympus,\n29 100X, Apo, 0.95 numerical aperture). Additionally, the single-photon detecting avalanche\n30 photodiode (APD) (SPCM-AQRH, dead time of 28 ns) was used to detect the PL, and the APD\n31 was connected to timing eletronics (PicoQuant PicoHarp 3000).\n33 resolution of 25 ps, which enables precise detection of the fluorescence dynamics over the\n34 entire analyzed time range. Although the single-photon detector has a dead time of 28 ns, this\n35 parameter affects only the maximum count rate and not the temporal resolution or the validity of\n36 the time rang itself.\n38 the experimental setup’s response and reflects the intrinsic exciton diffusion of the sample.\n41 point on page 4, lines 22-26:\n1 “Photoexcitation diffusion imaging was performed using a home-built TPLM, a 405 nm\n2 picosecond pulsed laser (ALPHALAS) with a repetition rate of 10 MHz and pulse width of 25 ps\n3 was focused onto the surface of the sample using an objective lens (Olympus, 100X, Apo, 0.95\n4 numerical aperture). Additionally, PL was detected using a single-photon detecting avalanche\n5 photodiode (APD) (SPCM-AQRH, dead time of 28 ns), which was connected to a time-correlated\n6 single-photon counting module (PicoQuant PicoHarp 3000).”\n8\n9 4. The authors extracted diffusion data for the first 300 ps despite the reported lifetime of 1.2 ns.\n11 authors should provide a clear justification for excluding this part of the data although it is within\n12 the life time and address why the trend goes negative.\nMSD (t)=σ2(t)-σ2(0) =2Dt (2)\n15 where MSD is the mean-squared displacement, which grows linearly over time, and the diffusion\n16 coefficient (D) is proportional to the swath lope. As shown in our data, the MSD values in the\n17 0-300 ps interval exhibit a clear linear trend, fully consistent with this theoretical model.\n19 although still within the emission lifetime (~1.2 ns), the MSD curve shows a negative trend in\n21 becomes increasing at longer delay times. The recombination of exciton effectively and exciton\n22 trapped that reduces the spatial spread of the exciton distribution, leading to a decrease in the\n23 calculated MSD values.\n26 lines 3-4:\n27 “At longer times t>0.3 ns, the recombination of exciton effectively and exciton trapped that\n28 reduces the spatial spread of the exciton distribution, leading to a decrease in the calculated MSD\n29 values (Fig. S12).”\n31\n32 5. The Gaussian fits used in the analysis should be included in the Supplementary Information to\n33 allow readers to evaluate the robustness of the fitting procedure.\n36 results (including fitted curves, parameters, and r2 values) in the Supplementary Information on\n37 page 13, line 1 as follows:\n38\n39\nD\nD (cm2/s) L (nm)\nD\nModel Gauss Gauss\n𝐴\n𝑦 =𝑦 +( 𝐴 )∗ 𝑒𝑥𝑝{−2∗ 𝑦 =𝑦 +\n0 𝜋 0 𝜋\nEquation 𝑤∗√ 2 ( 𝑤∗√ 2)\n2\n𝑥−𝑥𝑐\n( ) } 𝑥−𝑥𝑐 2\n𝑤 ∗ 𝑒𝑥𝑝{−2∗( ) }\n𝑤\nPlot Relative Frequency Relative Frequency\ny0 0.042±0.042 0.042±0.044\nxc 0.14±0.015 186.62±7.13\nw 0.096±0.022 52.67±14.96\nA 0.078±0.018 39.40±8.78\nReduced\n0.0035 0.0037\nChi-S\nR-Square\n0.988 0.983\n(COD)\nAdj.\n0.951 0.932\nR-Square\n2\n4\n5 6. While the manuscript focuses on singlet exciton dynamics, it does not address the potential\n6 influence of triplet excitons in the devices. Optical excitation generates 100% singlet excitons,\n7 whilst triplet excitons only form via intersystem crossing (ISC). In contrast, electrical excitation\n8 directly produces 75% triplet excitons. The rising electroluminescence (EL) intensity trend\n9 observed in the spherulite films could be influenced by delayed triplet excitons contributing\n10 through triplet-triplet annihilation, especially given the efficient diffusion reported. The authors\n11 should discuss the role of triplet excitons in detail.\n14 electroluminescence (EL) intensity trend could be influenced by delayed triplet excitons\n15 contributing through triplet-triplet annihilation. However, our devices are based on conventional\n16 fluorescent materials, and the emission originates exclusively from singlet excitons. Since no\n17 phosphorescent or thermally activated delayed fluorescence (TADF) materials are involved, triplet\n18 excitons generated under electrical excitation are non-radiative due to spin-forbidden transitions,\n19 and thus do not contribute directly to electroluminescence. Although triplet-triplet annihilation\n20 (TTA) can, in principle, occur in systems with long-lived triplet excitons, it is not expected to\n21 play a significant role in our devices. First, the absence of delayed emission features in transient\n23 the energy level alignment and molecular design typically required to enable efficient TTA\n24 upconversion.\n2 intensity of the Film-based device rises and then reaches stability before showing a decaying trend\n3 with increasing current density (up to 25 mA·cm-2) at a pulse duration time of 40 µs, reflecting\n4 exciton-exciton annihilation via singlet-singlet annihilation and singlet-triplet annihilation under\n5 high exciton densities, where exciton diffusion is limited and local accumulation becomes\n6 significant. Under the same condition, the EL intensity of the Spherulite-based device (Figure 5b)\n7 shows a rising trend with the increase of current density without reaching saturation or decay. This\n8 behavior is attributed to the low density of the defect structures in spherulite film, electrons are\n9 less prone to defect trapping, which enhances exciton transport and charge mobility, thereby\n10 prolonging the recombination process between holes and electrons. These findings are consistent\n11 with the improved excitonic properties of the Spherulite film observed in PLQY and fs-TA\n12 measurements.\n13\n17 lines 14-21:\n18 “In Fig. 5g, the Tr-EL intensity of the Film-based device rises and then reaches stability before\n19 showing a decaying trend with increasing current density (up to 25 mA·cm-2) at a pulse duration\n20 time of 40 µs, reflecting exciton-exciton annihilation via singlet-singlet annihilation and\n21 singlet-triplet annihilation under high exciton densities, where exciton diffusion is limited and\n22 local accumulation becomes significant. Under the same condition, the EL intensity of the\n24 saturation or decay (Fig. 5h). This behavior is attributed to the low density of the defect structures\n25 in spherulite film. Electrons are less prone to defect trapping, which enhances exciton transport\n26 and charge mobility, thereby prolonging the recombination process between holes and electrons.”\n28\n29 7. The authors should compare the PLQY and EQE values, as such a comparison can offer\n30 insights into the presence of trap states or dark triplet excitons, which could influence the overall\n31 device performance.\n33 and EQE of the two types of films. In the experimental conditions, the Film-based device exhibits\n34 a PLQY of 30% and EQE of 0.88%, while the Spherulite-based device shows a PLQY of 40%\nmax\n35 and EQE of 1.16%. According to the EQE equation:\nmax\nEQE = IQE×𝜂 =𝜂×𝜂 ×𝜂×\nout r\n(3)\n𝜂\nout\n1 where γ is hole/electron recombination efficiency, η is exciton formation probability (0.25 for\nr\n2 conventional fluorescent emitters), 𝜂 is PLQY and η is light outcoupling efficiency. When\nout\n3 assuming γ=1, η =0.2, η=0.25, φ =0.3, φ =0.4, the theoretical maximum EQE for the\nout r Film Spherulite max\nmax\n6 these theoretical EQE , primarily due to limitations in our current device structure and\nmax\n7 fabrication process, which is not fully optimized. Nonetheless, this comparison clearly shows that\n8 the higher EQE in the Spherulite-based device correlates well with their increased PLQY, which\n9 results from reduced non-radiative losses, due to a lower density of trap states and suppressed\n10 structural disorder after film crystallization. The improvement in EQE further supports the role of\n11 molecular ordering in suppressing defect-induced quenching and enhancing overall device\n12 performance.\n13\n16 lines 23-30:\nEQE = IQE×𝜂 =𝛾×𝜂 ×𝜑×\nout r\n(3)\n𝜂\nout\n18 where γ is hole/electron recombination efficiency, η is exciton formation probability (0.25 for\nr\n19 conventional fluorescent emitters), 𝜑 is PLQY and η represents light outcoupling efficiency.\nout\nout r Film Spherulite\n21 the Film and Spherulite device are calculated to be 1.5% and 2.0%, respectively. The measured\n22 values are below these due to unoptimized device architecture. Nonetheless, the higher EQE in the\n24 losses and confirming the key role of molecular ordering in suppressing defect-induced quenching\n25 and enhancing overall device performance.\n27\n29 sentences in this revised manuscript. We sincerely hope that our paper can be accepted and\n30 published in Nature Communications.\n2\n4 materials. It involves creating submillimeter-scale spherulite films through solvent vapor\n5 annealing (SVA). The authors report substantial enhancements in exciton diffusion length and\n6 coefficients within π-conjugated polymer films, which show great promise for optoelectronic\n7 applications, especially in polymer light-emitting diodes (PLEDs). The study is well-structured,\n8 featuring comprehensive experimental methods, and the results offer valuable insights into how\n9 long-range ordered spherulite structures can significantly improve exciton diffusion and\n10 optoelectronic properties. This research deepens our understanding of the structural dynamics and\n11 performance of organic semiconductor materials. Therefore, this work can be considered for\n12 publication after a minor revision by addressing the following comments.\n14 comments.\n15\n16 1. The paper suggests that the introduction of branched side chains, as opposed to linear side\n17 chains, leads to the formation of large-sized spherulites. Why does the introduction of branched\n18 side chains result in the formation of spherulites, while materials with linear side chains do not\n19 form this morphology? A comparative experiment should be conducted to explore this issue.\n22 the polymer with exceptional backbone planarity (β-conformation), in which the intermonomer\n23 torsion angle approaches 180o, facilitating the film with unique photophysical properties and\n24 excellent crystallinity (Macromolecules, 2022, 55, 8084−8094). Besides, as mentioned above,\n26 under undercooling (Cell Rep. Phys. Sci., 2020, 1, 100029). However, there are rarely spherulitic\n27 structures observed. Additionally, as your suggestion, under the same conditions, the PODPF film\n28 was explored by the SVA method. Polarized optical microscopy image (Figure 1c) reveal that the\n29 small crystalline domains are formed within the PODPF film, but no spherulite can be observed.\n30\n32 (c) POM image of PODPF film with small crystalline domains.\n34 introduced a branched side-chain at 4-position, named PEODPF, instead of liner-type in PODPF.\n36 and these branched side chains can act as “self-dopants” to disrupt the periodic interchain\n37 arrangement in crystalline processing and leading to the formation of the amorphous nano-region\n1 between single lamella crystalline structures, which further induced the formation of molecular\n2 spherulites. The single crystal structure (Figure 2a) analysis of the branched monomer, which is\n3 herringbone-like arrangement, further verifies that the introduction of the branched side chains\n4 breaks the close packing of the conjugated backbone. In contrast, the monomer with linear side\n5 chains adopts a linear pacing motif in its single crystal structure (Figure 2b).\n6\n10\n11 2. The description of “solvent vapor annealing” in the paper should be standardized, as there are\n12 currently two different expressions being used, such as “solvent thermal annealing”.\n14 position and corrected “solvent thermal annealing” to “solvent vapor annealing”.\n17 lines 5:\n18 “Here, large-area submillimeter-scale spherulite is achieved by treating the spin-coated film of\n19 polydiarylfluorene with solvent vapor annealing (SVA).”\n21\n22 3. In Fig. 3b, why is the absorption edge of the spherulite higher than that of the pristine film?\n25 which could be attributed from their higher order chain packing and the scattered light of their\n26 crystalline structure.\n28\n29 4. Page 8, line 27; “We obtained the width of the bandgap tail states (Eu) by fitting the\n30 photothermal deflection spectroscopy (PDS). The Eu value of spherulite film is 48.1 meV, lower\n31 than the 52.9 meV of pristine spin-coated film (Fig. 3e).” In the PDS test referenced in the paper,\n32 the data obtained indicates minimal differences. Might these data potentially contain errors?\n34 spectroscopy (PDS) results. Although the difference in Urbach energy (Eu) between the spherulite\n35 film (48.1 meV) and the pristine spin-coated film (52.9 meV) may seem small, it is both\n36 reproducible and meaningful. It is important to note that PDS is an extremely sensitive technique,\n1 with a spectral resolution of ~0.1 nm. This high precision allows for accurate detection of subtle\n2 differences in the sub-bandgap absorption edge. The ~5 meV reduction in Eu reflects the amount\n3 of disorder decrease in Spherulite, which is consistent with the enhanced molecular order and\n4 reduced trap states in the spherulite films.\n6\n7 5. Page 10, line 13; “As shown in Fig. 4a, the diameter of excitation spot (beam center) irradiated\n8 on the nanofiber bundles is about 238 nm, covering several single nanofibers.” This paper utilizes\n9 a laser with an excitation wavelength of 405 nm to excite the sample. How is the diameter of the\n10 light spot determined to be 238 nm? In Fig. S6, what is the role of the flip mirror?\n12 focused onto the sample surface with an objective lens (NA=0.95), generating an in-plane\n0\n14\n16 distribution profile across the center of the laser spot (Right) (J. Phys. Chem. Lett. 2022, 13, 7645−\n17 7652).\n18\n20 excitation light path of the home-built TPLM. The flip mirror functions as a beam routing element.\n23\n25 sent out of the TPLM system for TRPL measurement. (This figure has now been added to the\n26 revised Supplementary Information on page 11, line 10.)\n2\n4 sentences in this revised manuscript. We sincerely hope that our paper can be accepted and\n5 published in Nature Communications.\n6\n3 microscopy. Diffusion coefficients reach in the same order of magnitude as those of other reports\n4 in literature. Based on a solvent vapour annealing procedure of a spin coated film of branched\n5 side-chain modified polydiarylfluorene, the authors demonstrate improved structural order and\n6 enhanced exciton diffusivity. When incorporated into polymer light-emitting diodes, these films\n7 yield deep-blue electroluminescence with high brightness and improved color purity at low current\n8 densities.\n10 properties of the spherulite films, the core findings are not strikingly novel. The enhancement of\n11 exciton diffusion through improved molecular ordering and reduced defects in π-conjugated\n12 polymer films is a concept that is established in the literature. While the work confirms these\n13 relationships for the specific polymer under study, it does not introduce fundamentally novel\n14 insights or processing strategies. I am not sure about the impact of this work. In summary, the\n15 study confirms established principles rather than presenting research of great novelty that I would\n16 expect for papers in Nature Communications.\n19 we have corrected all our mistakes and polished the whole manuscript. Meanwhile, we added\n20 many experiments to support our assumption and results in this revised manuscript. Therefore, we\n21 sincerely hoped that you can re-consider our revised manuscript and agree to accept and publish\n22 our work in Nature Communications journal.\n24 migration lengths exceeding 100 nanometers are highly desirable for optoelectronic devices (Jin et\n25 al Science 2018, 360, 897. Andreas T. et al Nature 2015, 523, 196. Russell J. et al Science 2018,\n26 360, 854. Sneyd et al., Sci. Adv., 2021, 7, eabh4232. Shi Y. et al Proc. Natl. Acad. Sci. U.S.A. 2025,\n27 122, e2413850122.) (Figure 1). All these high-quality studies mentioned above are following an\n28 established concept that the exciton transport can be substantially improved in crystalline\n29 materials by reducing energetic disorder and exciton trapping, while also enabling a more\n30 optimized orientation of molecular transition dipole moments (S. R. Forrest et al Adv. Mater., 2010,\n31 22, 1233). Therefore, the ability to easily fabricate the large-scale crystalline π-conjugated\n32 polymer films is key to achieving ultra-long exciton diffusion length for thin-film optoelectronic\n33 devices, yet it has rarely been reported over the past several decades. In this work, we report the\n34 ultra-long exciton diffusion length of ~400 nm achieved in our easily solution-processed,\n35 submillimeter-scale spherulite film of π-conjugated polymer represents a significant advance in\n36 organic electronics, especially for the fabrication of efficient deep-blue PLEDs (Figure 1).\n1\n3\n5 three sections. In this revised manuscript, we have also added many experimental data to further\n6 support our assumptions. We hope that our responses help to clarify the core findings of our study.\n7 (1) Although the manuscript provides a detailed analysis of the structural and photophysical\n8 properties of the spherulite films, the core findings are not strikingly novel. Firstly, we\n9 appreciate the reviewer’s recognition of the detailed analysis of the structural and photophysical\n10 properties of the spherulite films presented in our work. However, we apology any confusion\n11 regarding the core findings related to our manuscript about the structural and photophysical\n12 properties of the spherulite films. To address this, in this revised manuscript, we added extensive\n13 experimental data to better support our conclusions. We would like to highlight the three core\n14 findings as follow: (1) Highly ordered and densely packed interchain arrangement in\n15 submillimeter-scale spherulite film. The lattice stripe spacing is about 0.24 nm with an excellent\n16 periodic interchain arrangement, which could enhance the exciton diffusion length. The diffraction\n17 spots in SAED pattern image also further confirms the outstanding crystalline structure of\n18 interchain stacking in PEODPF spherulite film (Figure 2). (2) Visualization of the crystallization\n19 growth process of π-conjugated polymers. We provide the images of PEODPF spherulites at\n20 various growth stages, accompanied by a schematic illustration of the crystallization growth\n21 model (Figure 3). (3) Ultra-fast exciton behavior in spherulite films. The spherulitic films\n22 exhibit distinct ultrafast exciton behavior, as revealed by transient absorption spectroscopy,\n23 highlighting the impact of ordered molecular packing on excited-state processes. (4) Ultrafast\n24 exciton dynamics and long-range transport. For the first time, ultralong exciton diffusion with a\n25 length of ~400 nm has been observed in submillimeter-scale spherulite films of π-conjugated\n26 polymers, demonstrating exceptional exciton transport properties. In addition, efficient deep-blue\n27 polymer light-emitting diodes based on these crystalline films are also firstly fabricated with an\n28 excellent electroluminescent property.\n1\n3 (c) POM image of PODPF inhomogeneous and discontinuous films with small crystalline\n4 nanodomains. (d) Cross-section scanning electron microscopy (SEM) image of PEODPF\n5 spherulite. (e) TEM selected-area electron diffraction pattern (SAED) of spherulite and the curve\n6 corresponds to SAED red line.\n7\n9 together with schematic illustration of the growth process model (Bottom right corner).\n10\n11 (2) The enhancement of exciton diffusion through improved molecular ordering and reduced\n12 defects in π-conjugated polymer films is a concept that is established in the literature.\n14 molecular ordering and reduced defects in π-conjugated polymer films is a well-established\n15 concept in the literature. We appreciate this insightful comment; it aligns with our findings that an\n16 ordered interchain arrangement with low defect density is beneficial for exciton diffusion.\n18 diffusion lengths (L ) of around 10 nm, due to their energetic disorder (Energy Environ. Sci. 2015,\nD\n19 8, 1867-1888.). In contrast, singlet excitons diffusion lengths in single crystals are known to be\n20 considerably larger (up to 220 nm), which confirms the effectiveness of improved molecular\n21 ordering as noted. More interestingly, nanofibres from amphiphilic conjugated polymers\n22 (oligomers) with a well-defined structure, prepared by living crystallization-driven self-assembly,\n23 yield an efficient exciton diffusion with coefficient of 0.5~1.1 cm2/s and L exceeding 200 nm (Jin\nD\n24 et al., Science 2018, 360, 897-900. Sneyd et al., Sci. Adv., 2021, 7, eabh4232.). However, in these\n25 cases, the materials are generally polydisperse in size and challenges for integration into practical\n26 devices. Therefore, solution-processable films of π-conjugated polymers, capable of transporting\n1 excitons over lengths exceeding 100 nm, are highly desirable for a range of organic optoelectronic\n2 devices. Up to date, our work is the first work to demonstrate ultra-long exciton transport\n3 lengths in solution-processed crystalline film of π-conjugated polymer. Moreover, this is also\n4 the first work to incorporate these easily processed materials, with exciton transport\n5 capacities comparable to the optical absorption depth (>100 nm) into functional electronic\n6 devices. We also believed that realizing this commonly held assumption and concept remains a\n7 significant challenge, which lies at the core of fundamental research in this field.\n8\n10\n11 (3) While the work confirms these relationships for the specific polymer under study, it does\n12 not introduce fundamentally novel insights or processing strategies. We thank you for the\n13 positive comment regarding the clear structure–property relationships demonstrated in our\n14 manuscript. However, we regret any confusion caused in understanding the novelty of our work.\n16 study. (1) Fundamentally novel insights: (i) Precisely control size-tunable submillimeter-scale\n17 spherulite via branched side-chain functionalization. Fully π-conjugated hydrocarbons\n18 polymers (For example: PODPF and PFO) typically self-assembled into polydisperse\n19 multi-dimensional crystalline nanostructures (such as nanowires) due to their strong interchain π-π\n20 interaction, which limits their application in optoelectronic devices. Compared to the linear-type\n21 side chain at 4-position (PODPF), only branched-side chain (PEODPF) can induce the polymer\n22 self-assembled into submillimeter-scale spherulite. This branched side-chain may reduce the\n23 crystallization capacity to cause the formation of amorphous region and induce the formation of\n24 submillimeter-scale spherulite. (ii) Prolonging exciton diffusion length for singlet excitons via\n25 the spherulite processing for optoelectronic application. While we agree with the reviewer that\n26 enhancing exciton diffusion through improved molecular ordering and defects suppression in\n27 π-conjugated polymer films is a known concept in the literature. However, most conjugated\n28 polymers films, even with high crystallization degree, also present short exciton diffusion lengths\n29 (L ) of around ~10 nm. In contrast, the densely interchain structure of our submillimeter-scale\nD\n30 spherulite film support the ultralong exciton diffusion (~400 nm), far beyond previously reported\n1 values for solution-processed films, and even comparable to or exceeding those in single crystals\n2 or oligomeric nanofibers. (2) Novel processing strategies: We developed a facile solvent vapor\n3 annealing (SVA) method to fabricate large-area crystalline films of π-conjugated polymers for\n4 efficient deep-blue PLEDs. To date, long-range exciton diffusion (>100 nm) has only been\n5 observed in highly ordered crystalline organic semiconductors. However, these materials are often\n6 polydisperse and difficult to integrate into practical devices. Our strategy addresses this limitation\n7 by enabling the formation of uniform, device-compatible, crystalline polymer films via a simple\n8 and scalable process. This is the first report of integrating solution-processable polymer\n9 spherulites that support ultralong exciton transport into functional optoelectronic devices.\n10\n12\n14 obtained as follow:\n15 (1) Ultralong exciton diffusion lengths (~400 nm) were observed in large-scale\n16 solution-processed crystalline films. Generally, solution-processable materials capable of\n17 transporting excitons over length exceeding 100 nm are highly desirable for a variety of\n18 light-harvesting and optoelectronic devices. We agree that enhancing molecular ordering and\n19 reducing trap densities are established strategies to improve exciton diffusion and device\n20 performance 1,2. However, our study tackles a challenge in organic optoelectronics by achieving\n21 ultralong exciton diffusion lengths and efficient deep-blue emission in solution-processable\n22 π-conjugated polymer thin films. This remains difficult due to the intrinsic energetic disorder and\n23 weak interchain coupling in most polymers 1,3,4. In contrast to previous studies that focus on single\n24 crystals or supramolecular assemblies with limited processability, we introduce a simple and\n25 scalable approach based on solvent vapor annealing to form submillimetre-scale spherulites with\n26 densely packed nanofibers and strong π-π overlap. This morphology supports singlet exciton\n27 diffusion lengths up to ~396 nm and a diffusion coefficient of ~0.63 cm²·s⁻¹, which are among the\n28 highest reported for π-conjugated polymers under ambient conditions7,8.\n29 (2) Manufacture large-scale crystalline films from π-conjugated polymers via simple and\n30 scalable solvent vapor annealing for optoelectronic applications. Interchain π-π interactions in\n31 polymer semiconductors play a key role in fundamental optoelectronic processes such as charge\n32 transport and exciton dynamics. In particular, interchain π-π stacking significantly influences the\n33 carrier mobility and conductivity of polymer semiconductor films, which are essential for\n34 high-performance optoelectronic devices. A systematic and visual understanding of polymer chain\n35 crystallization is central to polymer physics and provides the foundation for designing\n1 high-performance materials. The development of large-scale crystalline polymer films with\n2 well-defined structures and outstanding properties has therefore attracted increasing attention.\n4 crystalline films of fully π-conjugated polymers via solution processing remains challenging, often\n5 resulting in randomly distributed nanostructures, such as nanoparticles and nanowires. In this\n6 work, we introduce a simple approach based on solvent vapour annealing to form\n7 submillimetre-scale spherulites with densely packed nanofibers and strong π–π overlap.\n9 investigate the structure-property relationships within Spherulite films. Therefore, we are very\n10 happy about your comment that a detailed analysis of the structural and photophysical properties\n11 of the spherulite films is provided in this manuscript.\n12 (3) High performance deep-blue PLED based on large-scale crystalline film. As discussed\n13 above, the key performance parameters of OLEDs include color purity, emission uniformity, EL\n14 spectral stability, and efficiency, all of which are closely associated with the morphology of active\n15 emission layers. Importantly, the improved molecular ordering leads to a substantial enhancement\n16 in photoluminescence quantum yield (PLQY) from 30% (amorphous film) to 40% (spherulite),\n17 accompanied by a notable enhancement in external quantum efficiency (EQE) from 0.88% to\n18 1.16%. Finally, polymer light-emitting diodes (PLEDs) based on the large-area Spherulite films\n19 present a stable and efficient deep-blue electroluminescence behavior (Brightness: 4897 cd·m-2\n20 and EQE: 1.16%), enhanced about 47% and 32% compared to spin-coated ones, due to their low\n21 defect density, also confirmed their uniform exciton energetic landscape for the potential\n22 optoelectronic application. While the concept of ordering-induced exciton transport is established,\n23 its application to deep-blue emitting and solution-processed polymer devices is rare due to\n24 challenges in achieving long-range order without compromising emission properties. Our findings\n25 demonstrate that controlled crystallization in π-conjugated polymers can simultaneously enhance\n26 exciton transport, PLQY, and device quantum efficiency, offering a viable route toward achieving\n27 high-efficiency photon output in blue-emitting OLED devices at low driving voltages.\n1\n3\n5 optoelectronic applications. However, organic semiconductor films typically exhibit exciton\n6 diffusion lengths (L ) on the order of tens of nanometers, which are most obstacles to limit their\nD\n7 practical optoelectronic applications. Even extremely short L is evaluated about ~10 nm in the\nD\n8 fully π-conjugated polymers (FπCPs), due to their energetic disorder in solid state. Therefore, low\n9 energetic disorder and strong π-orbital overlap in the crystalline structure can enable more\n10 efficient exciton transport and diffusion. The ability to achieve highly ordered hierarchical\n11 structures with dense interchain π-orbital overlap in solution-processed πCPs films remains a core\n12 challenge in the development of organic optoelectronics. In this work, we demonstrate\n13 ultralong-range exciton diffusion (maximum value: ~396 nm) in large-area ordered\n14 submillimeter-scale spherulite films of π-conjugated polydiarylfluorene, enabling high brightness\n15 and narrowband deep-blue polymer light-emitting diodes (PLEDs). These self-assembled\n16 nanofibers, with molecular-scale diameters, efficiently transport singlet excitons at ambient\n17 conditions over distances exceeding hundreds of nanometers. Large-area submillimeter-scale\n18 spherulite are easily manufactured via solvent vapor annealing (SVA), which consisted of a series\n19 of nanowires with a length of ~3.0 μm and width of ~40 nm. More interestingly, the polymer\n20 chains exhibit an extremely dense and periodic packing along the nanofibers within the spherulite,\n21 thereby facilitating excellent interchain π-orbital overlap that enhance exciton and energy transfer.\n23 structure that effectively suppressed the formation of defect-trapping sites, leading to long-range\n24 exciton diffusion (up to ~396 nm) and an extremely large diffusion coefficient (~0.63 cm2/s).\n26 electroluminescence (Brightness: 4897 cd·m-2 and EQE: 1.16%), enhanced about 47% and 32%,\n1 respectively, compared to spin-coated ones. This improvement is attributed to the low defect\n2 density and confirms the uniform exciton energetic landscape for the potential optoelectronic\n3 applications. In a word, we believed that our solution-processed submillimeter-scale spherulite\n4 films present an ultralong exciton diffusion length (L ) and a large diffusion coefficient in\nD\n5 π-conjugated polymers, owing to their high degree of molecular order and strong intra/interchain\n6 π-orbital overlap. In contrast to the work by Jin (Science 2018, 360, 897.) and Andreas T. Haedler\n7 (Nature 2015, 523, 196.), which relied on structurally complex nanofibers and supramolecular\n8 assemblies, our submillimeter-scale spherulite film can be easily manufactured a simple\n9 solution-processing method, making them highly suitable for optoelectronic device applications..\n11 nanoscience and nanotechnology, polymer science and flexible optoelectronics. The topic and\n12 unique conclusions of this work meet with the research scope of “Nature Communications”.\n13\n15 1. Tessler, N., Preezant, Y., Rappaport, N. & Roichman, Y. Charge transport in disordered\n16 organic materials and its relevance to thin‐film devices: A tutorial review. Adv. Mater. 21,\n17 2741–2761 (2009).\n18 2. Yao, Z.-F., Wang, J.-Y. & Pei, J. Controlling morphology and microstructure of conjugated\n19 polymers via solution-state aggregation. Prog. Polym. Sci. 136, 101626 (2023).\n20 3. Congreve, D. N. et al. External quantum efficiency above 100% in a singlet-exciton-fission–\n21 based organic photovoltaic cell. Science 340, 334–337 (2013).\n22 4. Bolinger, J. C., Traub, M. C., Adachi, T. & Barbara, P. F. Ultralong-range polaron-induced\n23 quenching of excitons in isolated conjugated polymers. Science 331, 565–567 (2011).\n24 5. Jin, X.-H. et al. Long-range exciton transport in conjugated polymer nanofibers prepared by\n25 seeded growth. Science 360, 897–900 (2018).\n26 6. Haedler, A. T. et al. Long-range energy transport in single supramolecular nanofibres at room\n27 temperature. Nature 523, 196–199 (2015).\n28 7. Mikhnenko, O. V., Blom, P. W. M. & Nguyen, T.-Q. Exciton diffusion in organic\n29 semiconductors. Energy Environ. Sci. 8, 1867–1888 (2015).\n30 8. Giannini, S. et al. Exciton transport in molecular organic semiconductors boosted by transient\n31 quantum delocalization. Nat. Commun. 13, 2755 (2022).\n33\n35 corrected the errors in this revised manuscript. We sincerely hoped that our work can be\n36 accepted and published in Nature Communications journal.\n38 ------------------------------------\n41 through my Author Centre.\n43 iamwhuang@njupt.edu.cn or by fax at (+86) 25 8586 6999.\n5 \"Program of Global Experts\" Distinguished Professor\n6 \"Changjiang Scholar\" Chair Professor\n10 9 Wenyuan Road, Nanjing 210023, China"}, {"round": 2, "reviewer_comments": {"reviewer_1": "Please find the new Reviewers Comments attached in a Word document as direct answers to the Authors' individual answers (green: new Reviewer comment).", "reviewer_2": "All the comments have been addressed, the reviewer suggests the manuscript can be accepted."}, "author_response": "Answers to Reviewer 1:\n1.1 The transient absorption (TA) measurements were measured at an intensity of up to 10 mOD,\nwhich is very high for systems with good diffusion lengths, especially in films. Under these\nconditions, exciton annihilation is very likely happening, making the kinetics faster and the\ncomparison invalid. The authors should perform a fluence-dependent TA series in both the pristine\nand spherulite films to identify a low-fluence regime where no annihilation occurs. In this regime,\nthe lifetimes should be compared.\n1.2 Reviewer comment: the energy is still very high for materials with good diffusion. TA is\ncommonly measurable at least at 10 µJ/cm2 or until a fluence where no fluence-dependence\nis visible anymore. However, there is still a fluence dependence with 70 µJ/cm2, so the\nauthors should record traces of fluences where no fluence dependence is visible and compare\nthe kinetics at those fluences.\nResponse: Thank you for your kind comments and suggestions.\nWe sincerely thank the reviewer for this valuable comment and for highlighting the importance of\navoiding exciton–exciton annihilation and for better revealing the intrinsic exciton dynamics in\ntransient absorption (TA) measurements. Following your suggestion, we systematically\ninvestigated the fluence-dependent excited-state dynamics of both the pristine (Film) and\nspherulite (Spherulite) films using a self-built fs-TA spectrometer, ensuring that the TA signal\nintensity remained below 10 mOD.\n(1) Fluence-dependent TA spectra: TA measurements were conducted under pump fluences of\n1.5, 3, 5, 10, and 15 µJ/cm² with 400 nm excitation (Figure 1a, c). The differential absorption (ΔA)\nspectra recorded from 1 to 200 ps exhibit consistent spectral features across all fluences (Figure 1b,\nd), including the ground state bleach (GSB) peaks at 415 nm (Film) and 416 nm (Spherulite), as\nwell as the stimulated emission (SE) signals at 450 nm. These features are consistent with\npreviously reported for related polyfluorene derivatives (Sun, C. et al., Adv. Funct. Mater. 2022,\n32, 2206723. Virgili, T. et al., J Mater Chem 2010, 20, 519–523.).\nFigure 1. TA analysis of films. TA contour plots of the Film (a) and Spherulite films (c) under\npump fluences of 1.5, 3, 5, 10, and 15 μJ/cm2 using photoexcitation at 400 nm. ΔA spectra of the\nFilm (b) and Spherulite films (d) at different time delays down to 200 ps (1 ps, 5 ps, 10 ps, 20 ps,\n50 ps, 100 ps and 200 ps, respectively).\n(2) Kinetic analysis and low-fluence regime identification: Figure 2 presents the normalized SE\ndynamics of Film and Spherulite under varying pump fluences (1.5, 3, 5, 10, and 15 μJ/cm2). as\nsummarized in Table 1. As shown in Figure 2a and b, the normalized SE decay kinetic of both\nFilm and Spherulite overlap well at 1.5, 3 and 5 μJ/cm2, indicating that the system operates within\nthe linear excitation regime, where the exciton–exciton annihilation is negligible below ≈ 5 µJ/cm2.\nSince the signal-to-noise ratio at 1.5 µJ/cm2 was relatively low, and a slightly decay acceleration\nwas observed at 5 µJ/cm2, therefore, we selected the data collected at 3 µJ/cm2 as the\nrepresentative fluence for lifetime comparison. The decay curves were fitted using a\ntri-exponential function, and intensity-weighted average lifetimes (τ) were calculated the\nfollowing formula and summarized in Table 1.\n(1)\nwhere τ and A stand for lifetimes and amplitudes.\ni i\nAs displayed in Figure 2c, the Spherulite film exhibits a notably longer SE lifetime (136 ps) than\nthe amorphous Film (97 ps), suggesting that the ordered molecular packing promotes exciton\ndiffusion and radiative recombination.\nThese results, together with the increased PLQY and prolonged PL lifetimes observed in\nSpherulite, demonstrate that improved molecular order and reduced defect density\neffectively suppress nonradiative traps, facilitating more efficient exciton delocalization and\nradiative decay.\nFigure 2. Normalized the TA decay kinetics of Film (a), and Spherulite at 450 nm (b) with five\npump fluences of 1.5, 3, 5, 10, and 15 μJ/cm2. (c) Comparison of normalized the TA decay\nkinetics of Film and Spherulite at 450 nm with 3 μJ /cm2 pump fluence.\nTable 1. Results of the multi-exponential decay fits the lifetimes (τ and amplitudes (A) of Film\ni) i\nand Spherulite.\nTrace wavelength Pump Fluence\nSample A τ (ps) A τ (ps) A τ (ps) τ (ps)\n1 1 2 2 3 3 average\n(nm) (μJ/cm2)\n1.5 0.26 3.25 0.38 78.70 0.37 78.68 77.61\n3 0.27 5.49 0.60 103.05 0.10 37.81 97.30\nFilm 450 5 0.17 4.07 0.29 23.58 0.54 109.30 99.41\n10 0.15 7.01 0.54 108.65 0.39 30.24 94.23\n15 0.47 4.28 0.16 21.48 0.55 89.57 82.21\n1.5 0.18 8.65 0.39 98.19 0.39 98.20 96.40\n3 0.12 9.03 0.48 36.37 0.45 161.79 135.84\nSpherulite 449 5 0.17 2.76 0.45 31.91 0.47 132.97 113.23\n10 0.10 4.75 0.43 20.31 0.54 80.60 69.99\n15 0.32 9.51 0.15 20.11 0.55 66.02 58.62\nAdded to the revised manuscript:\nThe above results and discussion have been incorporated into the revised manuscript (page 9, lines\n10–31):\n“To further trace the ultrafast exciton decay behavior in Spherulite and Film, the\nfluence-dependent femtosecond-transient absorption (fs-TA) measurements were performed under\npump fluences of 1.5, 3, 5, 10, and 15 μJ/cm2 with 400 nm excitation (Fig. S7a, c). The\ndifferential absorption (ΔA) spectra from 1 to 200 ps exhibit consistent spectral features across\nfluences (Fig. S7b, d), including the ground state bleach (GSB) peaks at 415 nm for Film and\n416 nm for Spherulite, along with stimulated emission (SE) signals at 450 nm. These features are\nsimilar to the ΔA spectra previously reported for related polyfluorene derivatives. In Fig. 3e and\nFig. S8, the normalized SE dynamics are fitted using a tri-exponential function, and the intensity\nweighted averaged lifetimes are summarized in Table S2. The Spherulite film exhibits a notably\nlonger stimulated emission (SE) lifetime (136 ps) than the amorphous Film (97 ps), suggesting\nthat the ordered molecular packing facilitates exciton diffusion and radiative recombination.\nInteresting, fluorescence lifetime imaging microscopy (FLIM) reveals that the longer average\nfluorescence decay time (τ ) of spherulite film (470 ps) than that Film (360 ps) (Fig. 3f and S9a),\nm\nsupporting that ordered crystalline domains promote rapid exciton transport and delocalization,\nthereby reducing exciton trapping and enhancing radiative decay rate, in agreement with the\nobserved enhancement in PLQY. Taken together, these results indicate that enhanced molecular\norder and suppressed defect states in Spherulite contribute to improved excitonic performance and\nreduced non-radiative losses.”\nSupplementary additions:\nThe corresponding figures and data have been added to the revised Supplementary Information:\nFigure 1, Figure 2 and Table 1 mentioned above have now been added to the revised\nSupplementary Information as Fig. S7, Fig. S8 and Table S2, respectively on page 9-10.\nThe experimental description of TA measurements has also been added to the revised\nSupplementary Information to clarify this point on page 4, lines 16-21:\n“Ultrafast TA spectroscopy was conducted using a Ti: sapphire regenerative amplifier (Libra,\nCoherent Inc.). The second harmonic of the primary beam at 400 nm or an optical parametric\namplifier (OperA Solo, Coherent Inc.) pumped by the regenerative amplifier was used to generate\nthe pump beam. The probe beam was a broadband supercontinuum light source generated by\nfocusing a small portion of the femtosecond laser beam onto either a 5 mm-thick CaF plate.\nThe\n(Acton 2358, Princeton Instrument) at 1 kHz enabled by a home-built control board.”\nThank you for your comments and suggestions again.\n2. The authors extracted diffusion data for the first 300 ps despite the reported lifetime of 1.2 ns.\nHowever, Figure S7 reveals a negative trend after 300 ps, which is not adequately explained. The\nauthors should provide a clear justification for excluding this part of the data although it is within\nthe life time and address why the trend goes negative.\nResponse: We thank you for this important comment.\nOur extracted diffusion data analysis is based on the following model:\nMSD (t)=σ2(t)-σ2(0) =2Dt (2)\nwhere MSD is the mean-squared displacement, which grows linearly over time, and the diffusion\ncoefficient (D) is proportional to the swsth lope. As shown in our data, the MSD values in the\n0-300 ps interval exhibit a clear linear trend, fully consistent with this theoretical model.\nAccordingly, we selected the 0-300 ps region of the MSD data to fitting D. Beyond 300 ps,\nalthough still within the emission lifetime (~1.2 ns), the MSD curve shows a negative trend in\nFigure S7. This deviation arises from exciton-exciton recombination and traps on defect, that\nbecomes increasing at longer delay times. The recombination of exciton effectively and exciton\ntrapped that reduces the spatial spread of the exciton distribution, leading to a decrease in the\ncalculated MSD values.\nRevision:\nThis explanation has now been added to the revised manuscript to clarify this point on page 11,\nlines 13-14:\n“At longer times t>0.3 ns, the recombination of exciton effectively and exciton trapped that\nreduces the spatial spread of the exciton distribution, leading to a decrease in the calculated MSD\nvalues (Fig. S12).”\nThank you for your comments and suggestions again.\nReviewer comment: should exciton-exciton annihilation now already be before 300 ps?\nResponse: We thank the reviewer for this important question.\nIn our TPLM measurements, the excitation fluence was 11 μJ/cm2. Under these conditions,\nexciton-exciton annihilation (EEA) is indeed expected to occur, consistent with the TA data.\nPrevious reports on polyfluorene (PFO) films have shown that EEA processes typically occur\nwithin the first ~15 ps (Paul E. Shaw. et al., Adv. Funct. Mater. 2010, 20, 155-161). Therefore,\nsome degree of EEA may exist during the first 300 ps at high fluences. However, as shown in our\ndata, the MSD values in the 0-300 ps interval exhibit a clear linear trend, suggesting that\nalthough EEA may exist in this timescale, its contribution in this regime is minor compared\nto radiative recombination. The radiative decay dominates the exciton dynamics within this\ntime window, resulting in an overall increase in MSD. At longer times (t > 300 ps), a\ndecrease in intensity is observed, indicating EEA becomes more significant, and combined\nwith defect-assisted trapping, it suppresses exciton migration and leads to the observed\nnegative MSD trend.\nRevision:\nThis explanation has now been added to the revised manuscript to clarify this point on page 12,\nlines 3-4:\n“At longer times t>0.3 ns, exciton–exciton annihilation (EEA) becomes the dominant process, and\ntogether with exciton trapping, reduces the spatial spread of the exciton distribution, leading to a\ndecrease in the calculated MSD values (Fig. S12).”\nWe appreciate the reviewer’s careful reading and constructive feedback, which has helped us\nclarify the interpretation of the diffusion analysis.\n5. The Gaussian fits used in the analysis should be included in the Supplementary Information to\nallow readers to evaluate the robustness of the fitting procedure.\nResponse: Thank you for the reminder.\nWe apologize for the missing information and have now added the full set of Gaussian fitting\nresults (including fitted curves, parameters, and r2 values) in the Supplementary Information on\npage 13, line 1 as follows:\nTable S4. The parameters of Gaussian fits Diffusion coefficient (D) and Diffusion length (L ).\nD\nD (cm2/s) L (nm)\nD\nModel Gauss Gauss\n𝐴 𝑥−𝑥𝑐 2 𝐴 𝑥−𝑥𝑐 2\nEquation 𝑦=𝑦 +( )∗ 𝑒𝑥𝑝{−2∗( ) } 𝑦=𝑦 +( )∗ 𝑒𝑥𝑝{−2∗( ) }\n0 𝜋 𝑤 0 𝜋 𝑤\n𝑤∗√ 𝑤∗√\n2 2\nPlot Relative Frequency Relative Frequency\ny0 0.042±0.042 0.042±0.044\nxc 0.14±0.015 186.62±7.13\nw 0.096±0.022 52.67±14.96\nA 0.078±0.018 39.40±8.78\nReduced Chi-S 0.0035 0.0037\nR-Square (COD) 0.988 0.983\nAdj. R-Square 0.951 0.932\nThank you for your comments and suggestions again.\nReviewer comment: Thank you for adding the fit results, however, I meant the actual fit\ncurves in front of the data, so that the reader can evaluate if the gaussian fits are good fits for the\ndata.\nResponse: We sincerely appreciate your valuable comment. We realized that our initial\ndescription was not sufficiently clear. In the revised version, we have now included both the\noriginal data (Table 2) and the processed frequency distribution data (Table 3) to provide a more\nintuitive presentation of the Gaussian fitting procedure. Following examples in similar works1–4,\nwe performed frequency histogram analyses to obtain the diffusion coefficient (D) and diffusion\nlength (L ) distributions, summarized in Tables 3 and 4.\nD\nBased on these data, we constructed the bar charts shown in Figure 4, where the x-axis represents\nthe interval centers and the y-axis corresponds to the relative frequencies derived from Table 3.\nThe experimental data points are plotted together with the Gaussian fit curves, showing only small\ndeviations, which confirms the good consistency between the data and the fitting results. For D,\nthe 0.1~0.2 bin exhibits the highest frequence (8 out of 12 samples, 66.67%), and the fitted mean\nvalue (fitted parameter xc, Table 4) is 0.14 ± 0.015 cm2/s. Similarly, L values are most frequently\nD\ndistributed within the 150~200 interval (7 out of 12 samples, 58.33%), and the fitted mean (xc) is\n186.62 ± 7.13 nm. The corresponding relative frequence distribution curves are displayed in\nFigure 4, with the fitted mean values are also inset for clarity.\nWe apologize for this oversight and appreciate your careful attention.\nTable 2. Summary of D and L for different samples at different locations.\nD\nSpherulite D (cm2/s) L (nm)\nD\n1 0.4566±0.1813 331.03±65.73\n2 0.2108±0.0670 224.92±35.75\n3 0.0948±0.0438 150.81±34.82\n4 0.1477±0.1265 188.00±80.66\n5 0.1778±0.1209 206.56±70.26\n6 0.1126±0.0448 164.39±32.72\n7 0.1433±0.0391 185.45±25.32\n8 0.1733±0.0492 203.93±28.97\n9 0.1231±0.0669 171.89±46.69\n10 0.1616±0.0714 196.91±43.50\n11 0.1217±0.0629 170.87±44.21\n12 0.0928±0.0639 149.21±51.40\nMean values 0.14±0.015 186.62±7.13\nTable 3. The processed frequency distribution data of D and L .\nD\nInterval Interval Cumulative Relative Frequency\nCount\nCenter range Count (%)\n0.05 0.0~0.1 2 2 16.67\n0.15 0.1~0.2 8 10 66.67\nDiffuse coefficient\n0.25 0.2~0.3 1 11 8.33\n(D, cm2/s)\n0.35 0.3~0.4 0 11 0\n0.45 0.4~0.5 1 12 8.33\n125 100~150 1 1 8.33\nDiffuse 175 150~200 7 8 58.33\nlength 225 200~250 3 11 25\n(L D , nm) 275 250~300 0 11 0\n325 300~350 1 12 8.33\nTolal - - 12 - 100\nTable 4. The parameters of Gaussian fits Diffusion coefficient (D) and Diffusion length (L ).\nD\nD (cm2/s) L (nm)\nD\nModel Gauss Gauss\n𝐴 𝑥−𝑥𝑐 2 𝐴 𝑥−𝑥𝑐 2\nEquation 𝑦=𝑦 +( )∗ 𝑒𝑥𝑝{−2∗( ) } 𝑦=𝑦 +( )∗ 𝑒𝑥𝑝{−2∗( ) }\n0 𝜋 𝑤 0 𝜋 𝑤\n𝑤∗√ 𝑤∗√\n2 2\nPlot Relative Frequency Relative Frequency\ny0 0.042±0.042 0.042±0.044\nxc 0.14±0.015 186.62±7.13\nw 0.096±0.022 52.67±14.96\nA 0.078±0.018 39.40±8.78\nReduced\n0.0035 0.0037\nChi-S\nR-Square\n0.988 0.983\n(COD)\nAdj.\n0.951 0.932\nR-Square\nFigure 4. Relative frequency distribution curves of (a) diffusion coefficient (D) and (b) diffusion\nlength (L ) from Table 2. The mean value (xc), derived from the dashed fitted curve, is labeled in\nD\nthe figure.\nRevision:\nThe corresponding data have been added to the revised Supplementary Information: Table 2,\nTable 3 and Table 4 mentioned above have now been added to the revised Supplementary\nInformation as Table S3, Table S4 and Table S5, respectively on page 13-14.\nThe experimental description of relative frequency distribution analysis has also been added to\nclarify this point in the revised Supplementary Information on page 14, lines 2-7:\n“To more intuitively illustrate the diffusion coefficients (D) and diffusion length (L ), we\nD\nperformed frequence histogram analyses summarized in Table S3 and Table S4, following\nexamples in similar works1–4. For D, the 0.1~0.2 bin exhibits the highest frequence (8 out of 12\nsamples, 66.67%), and the fitted mean value (fitted parameter xc, Table S5) obtained from the\nGaussian fit is 0.14 ± 0.015 cm2/s. Similarly, L values are most frequently distributed within the\nD\n150~200 interval (7 out of 12 samples, 58.33%), and the fitted mean (xc) is 186.62 ± 7.13 nm. The\ncorresponding relative frequence distribution curves are displayed in Fig. 4d, e, with the fitted\nmean values are also inset for clarity.”\nReferences\n1. Cai, Y. et al. Vertically optimized phase separation with improved exciton diffusion enables\nefficient organic solar cells with thick active layers. Nat. Commun. 13, 2369 (2022).\n2. Sneyd, A. J. et al. Efficient energy transport in an organic semiconductor mediated by transient\nexciton delocalization. Sci. Adv. 7, eabh4232 (2021).\n3. Li, M. et al. Acceleration of radiative recombination for efficient perovskite LEDs. Nature 630,\n631–635 (2024).\n4. Wang Yongshuai et al. Highly fluorescent semiconducting two-dimensional conjugated\npolymer films achieved by side-chain engineering showing large exciton diffusion length. CCS\nChem. 5, 2366–2377 (2022).\nThank you again for your insightful suggestion, which helped us significantly improve the clarity\nand completeness of our analysis.\nFinally, thank you very much for your thoughtful comments and suggestions. We have corrected\nall issues in this revised manuscript and sincerely hope that our paper will be accepted and\npublished in Nature Communications.\n------------------------------------\nAll changes to the manuscript have been highlighted. The revised manuscript, Supporting\nInformation, and a list of changes & our responses to the referees’ comments have been submitted\nthrough my Author Centre.\nShould you have any other questions or queries, please kindly contact me by e-mail at\niamwhuang@njupt.edu.cn or by fax at (+86) 25 8586 6999.\nThank you very much.\nWith best wishes.\nSincerely yours,\nProfessor Wei HUANG\nAcademician of China Academy of Sciences\n\"Program of Global Experts\" Distinguished Professor\n\"Changjiang Scholar\" Chair Professor\nDirector-General\nState Key Laboratory of Flexible Electronics (LoFE)\nNanjing University of Posts & Telecommunications\nFax: +86 25 5813 9988;\nTel: +86 25 5813 9001.\nE-mail: iamwhuang@njupt.edu.cn./iamdirector@fudan.edu.cn"}, {"round": 3, "reviewer_comments": {"reviewer_1": "The authors have carefully addressed the reviewers comments. From my last round of comments, two of the three points have now been fully addressed: the low-fluence TA measurements and the clarification regarding exciton-exciton annihilation before 300 ps.\nHowever, one comment remains unresolved: the Gaussian fit curves are still not shown directly overlaid on the raw diffusion data so that readers can visually assess the fit and confirm that the Gaussian model is appropriate. This should be a straightforward figure update, but essential for transparency. Once this final point is addressed, I am satisfied with the revision and can recommend the manuscript for publication."}, "author_response": "Response: We thank the reviewer for their careful evaluation and for highlighting this important issue. We regret that our previous response did not clearly convey our intent.\nIn the earlier version of the manuscript, statistical analyses of the exciton diffusion length (L ) and\nD\ndiffusion coefficient (D) were performed based on twelve datasets, and Gaussian functions were\napplied to fit the corresponding frequency distributions, to obtain average values (L =186.62 ±\nD\n7.13 nm, D=0.14 ± 0.015 cm2/s). This approach was initially adopted to facilitate data\nvisualization, consistent with related reports (e.g., Fig. 1). However, we acknowledge that, given\nthe relatively small sample size, such fitting may introduce bias and therefore lacks of sufficient\nstatistical rigor.\nFigure 1. Similar to data treatment in the other papers (Li, M. et al., Nature, 2024, 630, 631-635; Cai, Y.\net al., Nat. Commun. 2022, 13, 2369; Wang, Y. et al., CCS Chem. 2023, 5, 2366-2377).\nTo avoid potential misinterpretation and in line with the editor’s recommendation that “For all\ndata presented in a plot, chart or other visual representation, ensure that individual data points\nare shown when possible, and always for n ≤ 10. The format shows data distribution clearly\n(e.g. dot plots, box-and-whisker plots)”, we have revised the data presentation. Specifically, box\nplots are now employed to display the distributions of the exciton diffusion length and diffusion\ncoefficient, as shown in the Figure 2. The average values were recalculated after excluding the\nhighest and lowest data points (L =186.37 nm, D=0.146 cm2/s). The results remain consistent\nD\nwith the previously reported values and do not alter the analysis or the conclusions of this work.\nTherefore, to ensure transparency and physical accuracy, the revised Figure 2 now directly\ndisplays the experimental data. As shown, the diffuse coefficients are mainly distributed in the\nrange of 0.1~0.2 cm2/s, while the corresponding diffusion lengths are primarily concentrated in the\nrange of 150~200 nm.\nFigure 2. Statistical distribution of the diffuse coefficient (D, green) and diffusion length (L , bule) of\nD\nbundles nanofibers (Data are presented as mean values ± s.d. n=12).\nThank you again for your insightful suggestion, which helped us significantly improve the clarity\nand completeness of our analysis.\nFinally, we thank the reviewers and editors again for their thoughtful comments and constructive\nfeedback. We have corrected all issues in this revised manuscript and sincerely hope that our\npaper will be accepted and published in Nature Communications.\n------------------------------------\nAll changes to the manuscript have been highlighted. The revised manuscript, Supporting\nInformation, and a list of changes & our responses to the referees’ comments have been submitted\nthrough my Author Centre.\nShould you have any other questions or queries, please kindly contact me by e-mail at\niamwhuang@njupt.edu.cn or by fax at (+86) 25 8586 6999.\nThank you very much.\nWith best wishes.\nSincerely yours,\nProfessor Wei HUANG\nAcademician of China Academy of Sciences\n\"Program of Global Experts\" Distinguished Professor\n\"Changjiang Scholar\" Chair Professor\nDirector-General\nState Key Laboratory of Flexible Electronics (LoFE)\nNanjing University of Posts & Telecommunications\nFax: +86 25 5813 9988;\nTel: +86 25 5813 9001.\nE-mail: iamwhuang@njupt.edu.cn./iamdirector@fudan.edu.cn"}]

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