Crystallization modulation for wide-bandgap perovskites with universal defect passivation toward efficient perovskite/organic tandem photovoltaics

Domain: chemistry
Published: 2026-01-03
Editorial outcome: minor_revision

Abstract
Wide-bandgap (WBG) perovskites with bandgaps exceeding 1.8 eV are suitable for perovskite/organic or multi-junction tandem solar cell (TSC) applications. However, their complex components easily induce hardly controlled phase heterogeneity and defects during the crystallization process. Herein, we propose a multifunctional additive, DL-methionine methylsulfonium chloride, with a unique combination of functional groups to regulate the crystallization thermodynamics and passivate defects of WBG perovskites. Our comprehensive experimental and computational results reveal that the additive synergistically promotes the nucleation kinetics and improves phase homogeneity during the crystallization process, thereby achieving uniform and low-defect perovskite films, significantly suppressing the non-radiative recombination and phase segregation. Consequently, the single-junction 1.83 eV-WBG perovskite solar cells demonstrate a champion power conversion efficiency (PCE) of 20.4% and notably enhanced operational stability. Furthermore, impressive PCEs of 26.0% and 22.1% are achieved for rigid and flexible perovskite/organic TSCs, respectively, showing great promise for pursuing flexible tandem applications.

Introduction
Tandem solar cells (TSCs) represent a promising strategy to surpass the inherent Shockley-Queisser efficiency limit of single-junction photovoltaics1–3. Wide-bandgap (WBG) perovskite solar cells (PSCs), which absorb high-energy photons4, can be effectively coupled with narrow-bandgap (NBG) photovoltaics that utilize near-infrared radiation, such as Si solar cells5,6, NBG PSCs7,8, Cu(In 1−x Ga x )Se 2 (CIGS) solar cells9,10, and organic solar cells (OSCs)9,11, etc. Among these technique combinations, perovskite/organic TSCs are notable for their potential in low-cost solution fabrication and flexible photovoltaic promoting applications12. To optimally match with the commonly used NBG organic active layers (bandgap <1.35 eV)13–15, extensive research has established a higher bandgap of 1.8 eV as the threshold for WBG perovskites3. However, these WBG perovskites composed of more complex components inevitably aggravate the phase heterogeneity of nuclei, resulting in non-uniform morphology and severe defect formation1,16. Notably, the defects, especially the vacancies and interstitials, induce severe non-radiative recombination and are prone to ion migration and accelerating the phase segregation.

Therefore, the WBG (>1.8 eV) PSCs still suffer from severe power conversion efficiency (PCE) loss and poor stability, which undermines the performance of corresponding TSCs4,17,18.

To mitigate the resulting defect-induced issues, numerous strategies have been explored for improving the quality of WBG perovskites from various aspects, including the passivation of the buried interface, surface, bulk, and/or grain boundaries, thereby improving the performance of perovskite/organic TSCs3,6,19–25. For example, the methylamine propionate can passivate the defects at the buried perovskite interface19. Other passivators, such as the cyclohexane 1,4-diammonium diiodide26, can effectively passivate the surface defects and achieve a high PCE of over 26% for the TSCs. Beyond interface treatments, additives can effectively passivate the defects in the bulk phase. For instance, the size-matched ions like thiocyanate ions (SCN−) for filling the halide vacancies11, and oversized cations such as dimethylammonium (DMA⁺) for reinforcing the crystal lattice21 can significantly enhance the stability of WBG perovskites and TSCs. Moreover, the additives with various functional groups, which form strong hydrogen bonds or exhibit high dipole moments, can interact with undercoordinated ions and passivate the defects in the bulk phase, enhancing the efficiency and stability of TSCs22,23. However, few reports focus on regulating the complex precursors-induced heterogeneous nucleation of >1.8 eV WBG perovskites, wherein the diversity of components inevitably induces different growth kinetics that deteriorate morphological homogeneity and dominate defect generation in the resulting perovskite films22. To address this root cause of the phase heterogeneity during crystallization, it is crucial to develop effective strategies that tune the crystallization thermodynamics and maintain a homogeneous nuclei phase from complex components to the final desired >1.8 eV WBG perovskites.

In response to this need, we developed a multifunctional additive, DL-methionine methylsulfonium chloride (MMSC), that combines amino, carboxyl, and methylsulfonium groups to holistically address the aforementioned challenges in WBG perovskites. Its cation (MMS+) acts as a nucleation center by simultaneously forming strong hydrogen bonds with organic FA+ and interacting with other inorganic components, thus increasing the nucleation rate. In addition, the additive can also improve the phase homogeneity during spin-coating and facilitate more uniform crystal growth to produce high-quality perovskite films with reduced defects. Notably, it significantly increases the defect formation energy of both vacancies and interstitials in WBG perovskite, achieving universal defect passivation and thereby suppressing non-radiative recombination and ion migration pathways. As a result, we obtained a champion PCE of 20.4% for 1.83 eV-WBG PSCs, as well as significantly improved stability with a T 80 lifetime of 830 h at maximum power point (MPP) tracking under continuous light illumination in air. When coupled with the OSCs to form the two-terminal tandem devices, we demonstrated impressive PCEs of 26.0% and 22.1% for the rigid and flexible TSCs, respectively, advancing the potential of flexible application of perovskite/organic tandem photovoltaics.

Results
Regulation of the crystallization process with phase homogeneity
To effectively regulate the crystallization thermodynamics of WBG perovskite, we rationally designed the DL-methionine methylsulfonium chloride (MMSC) to act as an additive in FA 0.8 Cs 0.2 PbI 1.6 Br 1.4 perovskite precursor solution (bandgap ~1.83 eV), leveraging its unique multifunctional cation MMS+ (Fig. 1a). The MMSC contains a methylsulfonium terminal group (-S(CH 3 ) 2 ), which is expected to enhance electrostatic interactions with [PbX 6 ] 4− octahedra27, while the amino (-NH 2 ) and carboxyl (-COOH) groups can form strong hydrogen bonds with FA+ cations19,28,29. The strong interactions between MMSC and various components of WBG perovskite were also verified by density functional theory (DFT) calculations (Supplementary Fig. 1)30,31. Therefore, the MMS+ can promote the aggregation of precursors and enhance homogeneous nucleation kinetics22,27,29. Conversely, the additive-free system tends to exhibit uncontrolled nucleation and undesirable phase heterogeneity during crystallization, primarily due to the formation of Br-rich phases with low formation energy barriers4,32. Beyond nucleation regulation, MMSC also enables the invariant growth thermodynamics to achieve a more uniform perovskite morphology, while the phase heterogeneity in the control crystallization process leads to diverse crystal growth rates and non-uniform distribution of crystal grain sizes.

To reveal the influence of MMSC on the crystallization process of perovskites, in situ photoluminescence (PL) measurements were performed33. For the control sample, an obvious PL emission signal at shorter wavelengths appears at ~27 s, indicating a rapid nucleation of Br-rich phases34. Subsequently, the PL peak gradually redshifts, indicating that iodine was enriched within the nuclei and the composition evolved toward the stoichiometric WBG perovskite (Fig. 1b). In contrast, the PL emission signal for the modified sample exhibits a negligible peak shift and a rapid increase in intensity, indicating direct formation of WBG perovskites with the target composition. We further tracked the evolution of PL intensity at the final peak position during the whole spin-coating process (Fig. 1c). The PL intensity for the control film starts to increase at ~48 s, whereas the modified film exhibits an earlier onset of ~40 s. These results confirm that the introduction of MMSC facilitates the formation of phase-pure perovskite nuclei and suppresses the undesirable phase transition35. Moreover, the final PL intensity for the modified perovskite film is greater than that of the control group, corresponding to the reduced defects, which is also consistent with the higher initial PL intensity in the annealing process (Fig. 1d). During annealing, both samples exhibit a high initial PL intensity followed by a rapid decrease within the first 2 s due to the fast solvent evaporation36. Subsequently, crystal growth and Ostwald ripening lead to a gradual increase in the PL signals. Notably, compared to the control perovskite film, the modified film not only reaches the highest PL intensity earlier (~4 s) but also exhibits a slower intensity decay, indicating prolonged crystal growth of perovskites (Fig. 1e)16,32.

During spin coating, the phase heterogeneity of nuclei in the control film during the initial crystallization process results in variable growth dynamics and thus large variations in final grain size. In contrast, MMSC-induced homogeneity of nuclei ensures a homogeneous growth kinetic, suggesting a more uniform grain size distribution. As shown in Fig. 1f–h, top-view and cross-sectional scanning electron microscopy (SEM) images show the narrower distribution of grain sizes for the MMSC-modified film than the control film (Supplementary Fig. 2), which is primarily caused by the additive-induced uniform crystal growth of the homogeneous nuclei. In addition, the aggregated PbI 2 clusters can be found in the control film, which is probably caused by the additive of Pb(SCN) 2 37, while the modified film exhibits less PbI 2 . Moreover, atomic force microscopy (AFM) tests were performed to assess the uniformity and roughness of perovskite films (Supplementary Fig. 3)38. The root-mean-square (RMS) roughness values for the control and MMSC-modified films are 46.2 and 37.0 nm, respectively, indicating the additive-induced improved morphological uniformity. Further analysis of the wrinkle surfaces indicates that the modified film exhibits lower RMS roughness in both the valley and hill regions, which also suggests a smoother surface morphology.

Changes in crystallographic properties and interactions
To investigate the phase evolution of perovskite films and the effect of the additive, we performed X-ray diffraction (XRD) and grazing incidence wide-angle X-ray scattering (GIWAXS) analyses. XRD patterns (Supplementary Fig. 4a, b) show that both control and MMSC-modified films exhibit similar crystallographic features before annealing. However, after annealing at 100 °C for 15 min, a pronounced PbI 2 diffraction peak appears in the control film, indicating incomplete conversion of precursors. In contrast, MMSC-modified films exhibit a gradual decrease in PbI 2 peak intensity with increasing additive content (Supplementary Fig. 4c, d), demonstrating the ability of the additive to suppress residual PbI 2 formation and promote more complete perovskite crystallization. GIWAXS measurements were further carried out to explore the crystallographic properties of the perovskite surface (Fig. 2a, b and Supplementary Fig. 5). The MMSC-modified film not only displays weaker PbI 2 signals but also exhibits smaller full width at half maximum (FWHM) for the (100), (110), and (111) facets of WBG perovskite, indicating improved crystallinity. In addition, the modification slightly increases the intensity ratios of (100)/(110) and (111)/(110), which is beneficial to the enhanced photovoltaic performance and stability, respectively39,40. Furthermore, the depth-resolved GIWAXS results demonstrate that MMSC reduces the shift of the diffraction peaks, suggesting the alleviated residual stress and suppressed defect formation within the films (Fig. 2c and Supplementary Fig. 6).

DFT calculation of the charge density difference was performed to evaluate the interactions between MMS+ and the WBG perovskite film (Supplementary Fig. 7). Reduced charge densities are observed near the perovskite lattice for both the carboxyl and amido gen groups of the additive, and a noticeable decrease in charge density is also detected around the two methyl groups adjacent to the sulfur atom. The electron densities for different functional groups of the additive decrease when the electron density of unpaired Pb2+ increases, revealing substantial charge transfer between the organic cation and the inorganic octahedra. Notably, despite being separated by a layer of [PbX 6 ] 4− units, charge redistribution is also evident on the hydrogen atoms of FA+ cations, suggesting strong interactions between the additive and the organic components of perovskite. These interactions were further revealed by 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared (FTIR) spectra, and X-ray photoelectron spectroscopy (XPS) measurements (Fig. 2d–i). In the 1H NMR spectra (Fig. 2d), a distinct shift of the N-H bond in FA+ is observed for the additive-perovskite mixture compared to the perovskite, which can be attributed to the hydrogen bond between the lone pair electrons on nitrogen of FA⁺ and the hydrogen atoms of the MMS+19. As shown in the FTIR spectra (Fig. 2e), after incorporating the additive into perovskite, the O-H stretching vibration peak of MMSC shifts from 3433 to 3400 cm−1, while the N-H bending vibration peak of perovskite shifts from 1612 to 1628 cm−1, confirming the formation of the strong O-H…N hydrogen bonds. In addition, the C-S stretching vibration peak of MMS+ shifts from 758 to 747 cm−1, demonstrating a changed bond energy of the methylsulfonium group41. XPS spectra detect the O signal of the carboxyl group in the modified perovskite film, verifying the incorporation of the additive into the perovskite films (Fig. 2f)42. In addition, the additive-induced influences on the perovskite film were also verified through high-resolution XPS measurements. After modification, the Pb 4f peaks shift to lower binding energies (Fig. 2g), consistent with the electron density redistribution observed in the DFT simulations. Shifts toward lower binding energies are also observed for Br and I, suggesting the reduced uncoordinated halide ions and significant passivation effect (Fig. 2h, i)22.

Enhanced photoelectronic properties and phase stability
As the strong interactions between the additive and the perovskite are well established through both DFT calculations and experimental validation, we are convinced that the universal defect passivation effect is another significant advantage of the MMSC (Fig. 3a). The positively charged methylsulfonium group of MMS+ tends to passivate negatively charged defects. Meanwhile, the amino (-NH 2 ) and carboxyl (-COOH) groups at the opposite end of the additive can strongly interact with the unpaired ions and passivate other defects. Notably, the -COOH group can form strong hydrogen bonds with the FA+ and passivate its surrounding defects. To verify the universality of passivation effects, perovskite models with 10 different defects, including all types of vacancies and interstitials, were constructed for the control and modified groups, respectively (Supplementary Fig. 8), and the defect formation energies were compared (Fig. 3b and Supplementary Table 1)43. It can be seen clearly that the additive provides a universal passivation effect for the WBG perovskite.

The enhanced photoelectronic properties of MMSC-modified perovskite films further confirm the significant passivation effect of MMSC. The trap densities of perovskite films were calculated using space-charge-limited current (SCLC) measurements, as illustrated in Supplementary Fig. 9. Upon the MMSC modification, the trap-filled limit voltage (V TFL ) decreases dramatically from 0.45 V to 0.34 V, corresponding to a reduction in trap density from 1.32×1016 cm−3 to 9.95×1015 cm−3, which indicates the suppressed defect-assisted non-radiative recombination. The PL quantum yield (PLQY) tests provide further evidence for the passivation effect of MMSC modification (Fig. 3c)44,45. The MMSC modification effectively improves the PLQY of perovskite films from 0.395% to 0.797%, suggesting a significant increase in the quasi-Fermi level splitting (QFLS) from 1.401 eV to 1.419 eV. In addition, for the perovskite films covered with a C 60 layer, the calculated implied open-circuit voltage (iV oc ) increases from 1.356 V to 1.372 V, indicating the suppressed interface non-radiative recombination and enhanced charge extraction. To explore deeper into carrier lifetime in different regions of the wrinkled WBG perovskite films, we conducted time-resolved PL mapping tests (Fig. 3d, e)46. For the control film, the carrier lifetime in the valley region is significantly lower than that in the hill region, while MMSC modification uniformly increases the carrier lifetime across the entire perovskite film, indicating the homogeneity of the passivation effect. Moreover, time-resolved photoluminescence (TRPL) measurements were also performed to evaluate carrier transfer behaviors in the devices (Supplementary Fig. 10)25,47. Compared to the control group, the additive modification increases the lifetime of the glass/post-treated perovskite film (Supplementary Table 2) and decreases the lifetime of the glass/post-treated perovskite/C 60 film (Supplementary Table 3), indicating a notable carrier extraction. UPS tests were also performed to evaluate the effect of the additive on the electronic properties of the perovskite surface (Supplementary Fig. 11). A large amount of PbI 2 , a typical p-type semiconductor, accumulated on the control perovskite film surface, which increases the hole concentration and the work function (WF)48. In comparison, the formation of PbI 2 on the perovskite film surface is suppressed after MMSC modification, resulting in a reduced WF and a more n-type surface, further verifying the enhanced carrier transport behavior49.

To investigate the phase stability of WBG perovskite films, we tracked the PL spectra for the perovskite films under 1-Sun irradiation using a solar simulator (Fig. 3f). The control film exhibits a notable peak shift of ~85 nm over 120 min, whereas the MMSC-modified film shows only a slight red shift of ~40 nm. This may be attributed to the strong passivation effect of the additive, which effectively restricts the formation of vacancies and interstitial ions, thus inhibiting ion migration and enhancing the phase stability50,51. To further explore this behavior, we tracked the control and the MMSC-modified perovskite films using in-situ hyperspectral fluorescence microscopy (Fig. 3g). For the control film, I-rich regions appear within 1 min and rapidly spread across almost the whole area within 3 min. In contrast, the MMSC-modified film shows much slower phase separation, confined to the valley regions, indicating suppressed ion migration and improved phase stability. Changes in PL intensities were also tracked to unveil the recombination and relaxation of carriers under light exposure (Supplementary Fig. 12). For the control film, the PL intensity decreases in the valley region and increases in the hill region, indicating rapid ion aggregation and severe defect formation. In comparison, the MMSC-modified film exhibits an increase in PL intensity after the initial 5 min, suggesting the enhanced phase stability and a light-induced passivation effect52.

Performance of the single-junction WBG PSCs
Single-junction WBG PSCs with a typical structure of ITO/4PADCB/Perovskite/Fullerene(C 60 )/Bathocuproine(BCP)/Ag were fabricated to evaluate the impact of the additive on device performance (Fig. 4a). The champion PCE of the MMSC-modified device reached 20.4% with a stabilized power output (SPO) of 19.7%, which is significantly higher than that of the control groups (19.2% with an SPO of 18.1%) (Fig. 4b, c and Supplementary Table 4). The corresponding external quantum efficiency (EQE) tests were also performed, as shown in Fig. 4d and Supplementary Fig. 13. The integrated J SC results are consistent with the values derived from their J-V tests. The statistical distribution of the J-V parameters is presented in Supplementary Fig. 14, indicating that an appropriate incorporation amount of the additive can dramatically improve the FF, while excessive introduction causes a severe decline in V OC . The plots of V OC versus light intensity reveal a lower slope for the MMSC-modified PSC (Supplementary Fig. 15), and the dark J-V analysis also presents a lower series resistance (R s ) and ideality factor (A) in the MMSC-modified PSC (Supplementary Fig. 16), indicating an inhibited non-radiative recombination in the device32. These findings strongly support that the MMSC modification enables fewer defects and suppresses carrier recombination in the solar cells, contributing to the enhanced device performance.

To reveal the intrinsic stability of these devices, we tracked the PCE evolution of devices stored in the N 2 glove box (Fig. 4e). The unencapsulated MMSC-modified WBG PSCs maintain ~96% of their initial PCE after over 1000 h of storage in the dark, whereas the control devices only retain ~86% under the same conditions. To further reveal the operational stability, MPP tracking tests (ISOS-L-1) were conducted under continuous light soaking for both control and MMSC-modified devices (Fig. 4f and Supplementary Fig. 17). The MMSC-modified WBG PSC exhibits an excellent T 80 lifetime exceeding 830 h, while the control device drops to 80% of its initial efficiency in just ~100 h, demonstrating significantly improved stability with additive modification.

This strategy is also applicable to flexible devices. We fabricated the flexible WBG PSCs by replacing the rigid ITO/glass substrates with the flexible ITO/PET substrates. The MMSC-modified flexible PSCs demonstrate a champion PCE of 18.0% with an SPO of 17.8%, while the control flexible PSCs exhibit a lower champion PCE of 17.1% and an SPO of 17.0% (Fig. 4g, Supplementary Fig. 18a, and Supplementary Table 5). The integrated J SC values derived from EQE measurements are consistent with their J-V curves, which confirms the reliability of PCE measurement (Supplementary Fig. 18b). As shown in the statistical distribution of the J-V parameters for flexible WBG PSCs (Supplementary Fig. 19), the performance improvement induced by additive modification is similar to that of the rigid devices. In addition, on account of the additive-induced lower residual stress of perovskite crystals, an enhanced bending durability is observed for the modified flexible perovskite film (Supplementary Fig. 20). Consequently, after 400 bending cycles with a bending radius of ~10 mm, the MMSC-modified device retained ~95% of the initial PCE, which is higher than the control device (~85%), indicating the improved mechanical stability (Supplementary Fig. 21). Overall, our additive modification strategy significantly enhances both V OC × FF and PCE in rigid and flexible WBG PSCs (Fig. 4h), demonstrating impressive performance among >1.8 eV WBG PSCs in the literature (Fig. 4i and Supplementary Table 6).

Performance of perovskite/organic TSCs
We fabricated the rigid WBG perovskite/organic TSCs with a structure of ITO/4PADCB/perovskite/C 60 /BCP/Au/MoO x /2PACz/organic active layer/PDINN/Ag, and the corresponding cross-sectional SEM image is shown in Fig. 5a. The performance of the rigid single-junction NBG OSC is demonstrated in Supplementary Fig. 22. Notably, the PCE of the MMSC-modified tandem photovoltaics significantly increases from 24.4% to 26.0% as illustrated in Fig. 5b and Supplementary Table 7. Figure 5c shows the EQE spectra of the front cell and the rear cell, aligning with the J SC derived from the J-V curves. The statistical distribution of the J-V parameters for the rigid TSCs indicates that the additive modification can effectively improve the FF and V OC (Supplementary Fig. 23), consistent with their single junction WBG PSCs. The MMSC-modified TSC also demonstrates an SPO of 25.8% even after testing for 600 s, much more stable than that of the control device (21.8%), as shown in Supplementary Fig. 24. After storage in N 2 for ~600 h, the unencapsulated MMSC-modified TSCs maintain ~80% of their initial PCE, while the control TSCs only maintain ~76%, indicating the improved device long-term stability (Fig. 5d). In addition, MPP tracking tests under ISOS-L-1 protocols (Supplementary Fig. 25) indicate that the MMSC modification extended the T 80 lifetime of TSCs from ~63 h to ~335 h, demonstrating enhanced operational stability consistent with the trend observed in WBG PSCs.

To fully utilize the advantage of the flexibility of both perovskite and organic solar cells, we further fabricated the flexible perovskite/organic TSCs by replacing the rigid glass/ITO substrates with the flexible PET/ITO substrates. Figure 5e and Supplementary Table 8 present the champion J-V curves and photovoltaic parameters of the control and modified flexible TSCs. The MMSC-modified TSCs achieve an impressive PCE of 22.1%, highlighting the significant potential for high-performance rigid and flexible perovskite/organic TSCs (Supplementary Table 9). The performance of the flexible single-junction NBG OSC is shown in Supplementary Fig. 26. The corresponding EQE spectra, SPO results, and statistical distribution of the J-V parameters are shown in Supplementary Figs. 27, 28. In addition, the MMSC-modified flexible TSC maintains ~90% of its initial PCE after 400 bending cycles with a bending radius of ~10 mm, while the control TSC only retains ~82% of its initial PCE (Supplementary Fig. 29). This work not only effectively improves the performance of rigid TSCs but also reveals the feasibility of fabricating high-performance flexible TSCs (Fig. 5f and Supplementary Fig. 30), underscoring the potential for future commercialization of flexible perovskite/organic TSCs.

Methods
Materials
Ethyl alcohol (99.5%), 2-propanol (IPA, 99.5%), ethyl acetate (EA, anhydrous, 99.8%), N, N-dimethylformamide (DMF, 99.8%), and dimethyl sulfoxide (DMSO, ≥99.9%) were purchased from Sigma-Aldrich. Formamidinium iodide (FAI, 99.99%), lead bromide (PbBr 2 , 99.99%), and PEDOT:PSS solution (1.3–1.7 wt% aqueous solution) were purchased from Xi’an Polymer Light Co., Ltd. PbI 2 (99.999%) was purchased from TCI. C 60 (99%) and BCP (99%) were obtained from Xi’an Yuri Solar Co., Ltd. (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl) phosphonic acid (4PADCB) was purchased from Derthon Optoelectronics Materials Science Technology Co., Ltd. MMSC (≥99%) was obtained from Aladdin. Ag was purchased from Zhong Nuo Advanced Material Technology Co., Ltd. The ITO/glass substrates and the flexible ITO/PET substrates were purchased from SYSTEC and Advanced Election Technology Co., Ltd.

Preparation of the perovskite precursor solution
For the preparation of the control FA 0.8 Cs 0.2 PbI 1.6 Br 1.4 precursor solution, CsI, FAI, PbI 2 , PbBr 2 , and Pb(SCN) 2 were mixed with a molar ratio of 0.2:0.8:0.3:0.7:0.01, and dissolved in a mixed solvent (volume ratio of DMSO:DMF = 1:4). For the preparation of the MMSC-modified perovskite solution, different amount of MMSC additive were added into the perovskite solution. Notably, the 1.3 M solution was prepared for the fabrication of WBG PSCs, and the 1 M solution was used for the fabrication of perovskite/organic TSCs.

Fabrication of the WBG PSCs
To fabricate the rigid WBG perovskite solar cells, the glass/ITO substrates were ultrasonically cleaned with detergent, deionized water, and alcohol for 20 min, respectively. Then the substrates were treated with UV light for 20 min. After moving the films into a N 2 -filled glove box, 50 μL of 4PADCB solution (1.5 mmol L−1 in ethyl alcohol) was filtered and spin-coated onto the substrate at 3000 rpm for 30 s, followed by heating at 100 °C for 10 min. Afterward, 100 μL of perovskite precursor solution was spin-coated onto the film at 4000 rpm for 60 s. 350 μL of ethyl acetate was dropped at ~25 s after starting the spin-coating process. Then the films were quickly moved to a hot plate and annealed at 100 °C for 15 min. After cooling down, 20 μL of the mixed post-treatment solution (3 mmol L−1 of PDADI and 0.3 mmol L−1 of PEABr dissolved in IPA) was spin-coated onto the perovskite films at 5000 rpm for 30 s. Afterward, the film was quickly moved to the hot plate and annealed at 100 °C for 10 min. After cooling to room temperature, 25 nm of C 60 and 6 nm of BCP were deposited by evaporation. Finally, 100 nm Ag was thermally evaporated as the electrode. To fabricate the flexible PSCs, the flexible PET/ITO substrates were fixed to the glass with glue. Afterward, all the steps are the same as those for the fabrication of the rigid PSCs.

Fabrication of the OSCs
To fabricate the rigid OSCs, the glass/ITO substrates were ultrasonically cleaned with detergent, deionized water, and alcohol for 20 min, respectively, followed by a UVO treatment for 20 min before use. Afterward, the PEDOT:PSS aqueous solution was spin-coated on the substrate, and then the films were annealed at 150 °C for 15 min. D18: BTP-ec9 with a mass ratio of 1:1.2 was dissolved in trichloromethane with DIB (4.5 mg mL−1), and spin-coated on the film at 3000 rpm for 30 s and annealed at 100 °C for 1 min. Then, PDINN was dissolved in methanol (1.5 mg mL−1) and spin-coated on the organic active layer. Finally, 100 nm of Ag was thermally evaporated through a metal mask. To fabricate the flexible OSCs, the flexible PET/ITO substrates were fixed to the glass with glue. Afterward, all the steps are the same as those for the fabrication of the rigid OSCs.

Fabrication of the perovskite/organic TSCs
The preparation of the structure of glass/ITO/4PADCB/Perovskite/C 60 /BCP is the same as the fabrication of the single-junction WBG PSCs. Then, 1.25 nm of Au was evaporated on the films, followed by depositing 16 nm of MoO x . The 2PACz solution (0.3 mg mL−1 in IPA) was spin-coated on the film at 5000 rpm for 30 s and annealed at 75 °C for 2 min. Afterward, the preparation of the structure of the organic active layer/PDINN/Ag is the same as the fabrication of the single-junction OSCs. To fabricate the flexible TSCs, the flexible PET/ITO substrates were fixed to the glass with glue. Afterward, all the steps are the same as those for the fabrication of the rigid TSCs.

Characterizations of materials
Nuclear magnetic resonance was performed with an NMR spectrometer (Bruker, Avance III HD) using a frequency of 500 MHz. The tested powders were mixed with the (CD 3 ) 2 SO and vibrated at room temperature for 10 min. Grazing Incidence X-ray diffraction (GIXRD) measurements were performed using Xeuss 3.0 SAXS/WAXS (Eiger 2R 1M) with a copper target 8.05 KeV X-ray, and the wavelength was 1.54189 Å (Test environment: Vacuum < 1 mbar). The distance between the detector and the film was 80 mm. The steady-state photoluminescence (PL) was measured by a PL spectroscope (Ocean Insight) with an excitation wavelength of 405 nm. The TRPL mapping tests were performed by a combined equipment (MicroTime100 & FluoTime300) with a tested area of 50 μm × 50 μm.

Characterizations of devices
The current density-voltage (J-V) tests of devices were performed with a Keithley 2450 source meter with a solar simulator (SS-XRC, Enlitech) that matches AM 1.5G. The light intensity was calibrated to 100 mW cm−2 using a standard reference silicon solar cell. The WBG PSCs were tested using a metal mask with an aperture area of 0.09 cm2, and the OSCs and TSCs were tested using a metal mask with an aperture area of 0.04 cm2. The scan rate for the PSCs and OSCs was 100 mV s−1, and the scan rate for the TSCs was 200 mV s−1. The delay time for the J-V test was 10 ms. The external quantum efficiency (EQE) measurements were performed using a computer-controlled quantum efficiency measuring instrument (QE-R, manufactured by Enlitech). The MPP tracking tests were performed using a multi-channel solar cell stability test system (Wuhan 9IPVKSolar Technology Co., Ltd). For the MPP tracking tests, the BCP layer was substituted with a SnO 2 layer fabricated through atomic layer deposition, and the devices were encapsulated with a glass sheet.

DFT calculations
The DFT calculations in this research were performed using the Vienna ab initio simulation software (VASP)53. To simulate electron exchange-related interactions, the Perdew–Burke–Ernzerhof (PBE) functional was utilized54, and the projector augmented wave (PAW) approach was used for electron-ion–nucleus interactions55. To handle vander Waals interactions in perovskites, we employed the Grimme DFT-D3 approach with Becke-Johnson damping56,57. Geometry optimization was carried out with the Γ-centered 3×3×1 Monkhorst−Pack k-point mesh and the 400 eV plane wave energy cutoff. The geometric structure was regarded as convergent when the energy difference between all ions was smaller than 10−5 eV. The models employed in all calculations were optimized structurally using VASP. We established the defect models based on the optimized perovskite surface model and an adsorbed additive ion on its surface to simulate the effect of adsorbed organic ions on surface defects. The interaction energy (E int ) is given as:
E int = E AB − E A + E B (1)
Where E AB is the total energy of the interacting complex, E A /E B is the energy of the isolated monomers. The adsorption energy (E ads ) is given as:
E ads = E passivated system − E clean surface − E isolated passivator (2)
Where E passivated system is the total energy of the perovskite surface with the adsorbed passivator, E clean surface is the total energy of the perovskite surface without a passivator, E isolated passivator is the total energy of the passivation material in its free state. The defect formation energy is given as:
E DEF Xq = E(Xq) − E(bulk) + n i μ i + q(E F + E VBM + ΔV) (3)
Where E(Xq) is the total energy of the defect system with charge q, E(bulk) is the total energy of the pristine system, and n and μ are the number and the chemical potentials of the species added to or subtracted from the perfect system to form the defect. The last term is the energy associated with the exchange of charges with the electrons’ reservoir (the Fermi level of the system, E F ), referenced to the valence band maximum (E VBM ) of the pristine system, followed by a correction for the electrostatic potential ΔV induced by the defect. The charge density difference (Δρ) is calculated using VESTA in conjunction with VASP. The (Δρ) is defined as:
Δρ = ρ system − ρ isolated atoms (4)
Where ρ system is the charge density of the fully optimized system. ρ isolated atoms is the charge density of the isolated atom (calculated with identical parameters, including spin polarization).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, the authors present a multifunctional additive that regulates crystallization, passivates defects, and enhances phase stability in WBG perovskite films. Their findings reveal that the additive can promote pre-nucleation and uniform nucleation kinetics, resulting in phase-homogeneous crystallization and enhanced morphological uniformity. With additive modification, the WBG PSCs achieve champion PCEs of 20.4% (rigid) and 18.0% (flexible), along with a T80 lifetime of 830 h under ISOS-L-1. Furthermore, the rigid and flexible perovskite/organic tandem solar cells achieve champion PCEs of 26.0% and 22.1%, respectively, while also exhibiting excellent mechanical flexibility. I recommend publication after addressing the issues below.\n1. In Figure 1h, the authors discuss the film uniformity based on cross-sectional SEM images. However, cross-sectional SEM may not reliably reflect the nanoscale uniformity of the perovskite films due to artifacts from sample preparation. The authors are encouraged to provide AFM data to assess the uniformity and roughness of perovskite film.\n2. In Figure 2, the authors used GIWAXS to analyze residual PbI₂ in the films. However, to more comprehensively understand the impact of the additive on film quality, it is recommended to include a detailed comparison of the crystallinity and crystal orientation of the perovskite films before and after additive incorporation.\n3. The UPS results show a reduced work function and more n-type surface after additive incorporation. However, the mechanism by which the additive induces the n-type shift is unclear and requires further clarification. In addition, to further support the claim of efficient carrier extraction and reduced charge recombination, the authors are encouraged to measure the PLQY and iVoc of the perovskite/C₆₀ stack.\n4. In Figure S19, the chemical structures of the OPV materials appear to be incorrect. Please verify and revise accordingly.\n5. Please provide the sum EQE response curve for the tandem device. In Figure 5c, the summed EQE response near 650 nm appears to approach 100%, which requires further clarification.", "reviewer_2": "In the manuscript titled \"Crystallization Modulation for Wide-Bandgap Perovskites with Universal Defect Passivation Toward Efficient Perovskite/Organic Tandem Photovoltaics,\" the authors introduce a multifunctional additive, DL-methionine methylsulfonium chloride, to modulate the crystallization process and properties of wide-bandgap (WBG) perovskites. This strategy contributes to the achievement of efficient WBG perovskite solar cells (PSCs) and perovskite/organic tandem solar cells (TSCs). While the device performance is impressive, some aspects of the manuscript are unclear and are seldom discussed. Therefore, I recommend considering the acceptance of the manuscript after addressing the following concerns:\n1. The authors investigate the detailed interactions between the additive and perovskites using DFT calculations. To further validate these interactions, complementary characterizations such as FTIR and NMR spectroscopy should be conducted.\n2. In the evolution of PL spectra during the spin-coating process, the introduction of the additive appears to accelerate the self-crystallization process of perovskites (Figure 1b,c), while during annealing, the additive-incorporated sample exhibits slower mass transfer and crystal growth (Figure 1d,e). To provide a clearer understanding of how the additive influences the overall perovskite crystallization process, a more detailed analysis of these phenomena is necessary.\n3. The top-view SEM results (Figure 1f-g) suggest that the introduction of the additive reduces the grain size of the perovskites, which could be associated with its impact on the initial crystallization process during spin-coating. A discussion of this phenomenon is required.\n4. The scale bar for the AFM images (Figure S3) should be provided for clarity.\n5. Several subscripts are missing in the supporting figures, such as in Figure S4a-c, Figure S18a-b, and Figure S19a. Please ensure that the entire manuscript and supplementary materials are thoroughly reviewed for completeness.\n6. In the XRD results (Figure S4c), the control film shows a distinct yellow phase peak around 10.8°. However, this signal appears to be absent in the GIWAXS image (Figure 2a). A specific explanation for this discrepancy should be provided.\n7. It appears that the additive has a significant impact on the MPP stability of WBG PSCs. I am curious whether this advantage extends to the MPP stability in perovskite/organic TSCs as well.", "reviewer_3": "In this manuscript, the author introduces a novel additive, DL-methionine methylsulfonium chloride, which simultaneously modulates the crystallization thermodynamics and provides comprehensive defect passivation for wide-bandgap perovskites. As a result of improved phase homogeneity and enhanced phase stability, excellent performance was realized in both rigid and flexible perovskite/organic tandem solar cells. This manuscript provides a useful strategy for crystallization modulation in wide-bandgap perovskite. I recommend publication after revisions.\n1. Since methylsulfonium is a positively charged group, it is recommended to include a “+” sign in its abbreviation to clearly indicate its cationic character.\n2. The manuscript uses various terms to refer to the control and experimental groups. For experimental groups, such as “target sample”, “modified group”, “modified sample”, and “target film”. It is recommended to standardize these terms throughout the manuscript to avoid confusion and improve clarity.\n3. The nitrogen atom in the amine group possesses lone pair electrons, allowing it to act as a hydrogen bond acceptor and form hydrogen bonds with the hydrogen atoms of the ammonium group. This interaction should be considered when interpreting the 1H NMR spectrum.\n4. It is recommended to employ infrared spectroscopy to better elucidate the interactions and coordination mechanisms between various functional groups of the additive and the perovskite.\n5. The authors mention the application of this strategy in flexible devices. It might be helpful if the authors could consider providing the impact of this strategy on the mechanical stability of flexible single-junction WBG PSCs under bending or stretching conditions.\n6. If the hole transport layer is deposited by thermal evaporation, it is more accurate to denote it as “MoOₓ” rather than “MoO₃”, unless characterization have definitively confirmed the presence of a pure MoO₃ phase.\n7. The authors claim that the rigid and flexible perovskite/organic TSCs demonstrate champion PCEs of 26.0% and 22.1% respectively, along with superior bending stability. As a high performance is claimed, a certificate would be needed to verify the performance.\n8. The storage stability data of the perovskite/organic TSCs in N2 is insufficient to demonstrate the operational stability of TSCs under operational conditions. It is strongly recommended to present more related stability test results."}, "author_response": "Response to Reviewers\n(Black type: Reviewer’s comments; Blue type: Our response; Yellow highlight: Revisions)\nResponse to Reviewer #1\nReviewer #1:\nComments:\nIn this manuscript, the authors present a multifunctional additive that regulates crystallization, passivates\ndefects, and enhances phase stability in WBG perovskite films. Their findings reveal that the additive can\npromote pre-nucleation and uniform nucleation kinetics, resulting in phase-homogeneous crystallization and\nenhanced morphological uniformity. With additive modification, the WBG PSCs achieve champion PCEs of\n20.4% (rigid) and 18.0% (flexible), along with a T80 lifetime of 830 h under ISOS-L-1. Furthermore, the\nrigid and flexible perovskite/organic tandem solar cells achieve champion PCEs of 26.0% and 22.1%,\nrespectively, while also exhibiting excellent mechanical flexibility. I recommend publication after addressing\nthe issues below.\nResponse: We appreciate the reviewer’s valuable comments. We have carefully read through them. Below,\nwe provide our point-by-point responses along with additional experimental results and appropriate\nmodifications in our revised manuscript. For your convenience, the major changes we have made in the\nmanuscript and the supporting information are marked in yellow.\n1. In Figure 1h, the authors discuss the film uniformity based on cross-sectional SEM images. However,\ncross-sectional SEM may not reliably reflect the nanoscale uniformity of the perovskite films due to artifacts\nfrom sample preparation. The authors are encouraged to provide AFM data to assess the uniformity and\nroughness of perovskite film.\nResponse: We thank the reviewer for this comment. We provided additional AFM analysis in the\nsupplementary information of the AFM data to evaluate the uniformity and surface roughness of the\nperovskite films in the supplementary information. To further explore the wrinkle morphology of the wide-\nbandgap perovskite, we further analyzed the valley region and hill region, respectively. The experimental\nresults indicate that the MMSC-modified film exhibits lower RMS roughness in the whole region, as well as\nin both the valley and hill regions, demonstrating the improved nanoscale uniformity.\nPage 5, line 137 of our revised manuscript.\nMoreover, atomic force microscopy (AFM) tests were performed to assess the uniformity and roughness of\nperovskite films (Figure S3)[38]. The root-mean-square (RMS) roughness values for the control and MMSC-\nmodified films are 46.2 and 37.0 nm, respectively, indicating the additive-induced improved morphological\nuniformity. Further analysis of the wrinkle surfaces indicates that the modified film exhibits lower RMS\nroughness in both the valley and hill regions, which also suggests a smoother surface morphology.\nPage 6, line 78 of our revised supplementary information.\n[... AFM data and figures omitted for brevity ...]\n2. In Figure 2, the authors used GIWAXS to analyze residual PbI in the films. However, to more\n2\ncomprehensively understand the impact of the additive on film quality, it is recommended to include a\ndetailed comparison of the crystallinity and crystal orientation of the perovskite films before and after\nadditive incorporation.\nResponse: We thank the reviewer for this comment. To more comprehensively evaluate the impact of the\nadditive on film quality by using GIWAXS tests, we provided the corresponding 1D GIWAXS profiles and\na detailed comparison of the crystallinity and crystal orientation of the perovskite films before and after\nadditive incorporation, as suggested.\nPage 5, line 151 of our revised manuscript.\nGIWAXS measurements were further carried out to explore the crystallographic properties of the perovskite\nsurface (Figure 2a-b and Figure S5). The MMSC-modified film not only displays weaker PbI signals but\n2\nalso exhibits smaller full width at half maximum (FWHM) for the (100), (110), and (111) facets of WBG\nperovskite, indicating the improved crystallinity. In addition, the modification slightly increases the intensity\nratios of (100)/(110) and (111)/(110), which is beneficial to the enhanced photovoltaic performance and\nstability, respectively[39, 40]. Furthermore, the depth-resolved GIWAXS results demonstrate that MMSC\nreduces the shift of the diffraction peaks, suggesting the alleviated residual stress and suppressed defect\nformation within the films (Figures 2c and Figure S6).\nPage 8, line 100 of our revised supplementary information.\n[... GIWAXS data and figures omitted for brevity ...]\n3. The UPS results show a reduced work function and more n-type surface after additive incorporation.\nHowever, the mechanism by which the additive induces the n-type shift is unclear and requires further\nclarification. In addition, to further support the claim of efficient carrier extraction and reduced charge\nrecombination, the authors are encouraged to measure the PLQY and iVoc of the perovskite/C₆₀ stack.\nResponse: We thank the reviewer for this comment. We added the discussion of the mechanism of the n-type\nshift in the revised manuscript. In addition, we also supplemented the PLQY and iV data of the\noc\nperovskite/C₆₀ stack to further support the claim of efficient carrier extraction and reduced charge\nrecombination.\nPage 7, line 218 of our revised manuscript.\nUPS tests were also performed to evaluate the effect of the additive on the electronic properties of the\nperovskite surface (Figure S11). A large amount of PbI , a typical p-type semiconductor, accumulated on the\n2\ncontrol perovskite film surface, which increased the hole concentration and the work function (WF)[48]. In\ncomparison, the formation of PbI on the perovskite film surface is suppressed after MMSC modification,\n2\nresulting in a reduced WF and a more n-type surface, further verifying the enhanced carrier transport behavior.\nIn comparison, the formation of PbI on the perovskite film surface is suppressed after MMSC modification,\n2\nresulting in a reduced WF and a more n-type surface, further verifying the enhanced carrier transport\nbehavior[49].\nPage 7, line 203 of our revised manuscript.\nThe PL quantum yield (PLQY) tests provide further evidence for the passivation effect of MMSC\nmodification (Figure 3c)[44, 45]. The MMSC modification effectively improved the PLQY of perovskite films\nfrom 0.395% to 0.797%, suggesting a significant increase in the quasi-Fermi level splitting (QFLS) from\n1.401 eV to 1.419 eV. In addition, when the C layer was deposited on top of these perovskite films, the\n60\ncalculated implied open-circuit voltage (iV ) increased from 1.356 V to 1.372 V, indicating the suppressed\noc\ninterface non-radiative recombination and enhanced charge extraction.\nPage 22, line 606 of our revised manuscript.\n[... Figure 3 description omitted ...]\n4. In Figure S19, the chemical structures of the OPV materials appear to be incorrect. Please verify and revise\naccordingly.\nResponse: We thank the reviewer for this comment. We sincerely apologize for our drawing mistakes in the\nmolecular structures. We updated the correct molecular structures in Figure S22 in the revised supplementary\ninformation.\nPage 25, line 175 of our revised supplementary information.\n[... Figure S22 description omitted ...]\n5. Please provide the sum EQE response curve for the tandem device. In Figure 5c, the summed EQE response\nnear 650 nm appears to approach 100%, which requires further clarification.\nResponse: We thank the reviewer for this comment. We sincerely apologize for the confusion caused in the\nprevious version. The updated data with summed EQE response is provided in the revised manuscript and\nsupplementary information.\n[... Figure R1 and S27 descriptions omitted ...]\nResponse to Reviewer #2\nReviewer #2:\nComments:\nIn the manuscript titled \"Crystallization Modulation for Wide-Bandgap Perovskites with Universal Defect\nPassivation Toward Efficient Perovskite/Organic Tandem Photovoltaics,\" the authors introduce a\nmultifunctional additive, DL-methionine methylsulfonium chloride, to modulate the crystallization process\nand properties of wide-bandgap (WBG) perovskites. This strategy contributes to the achievement of efficient\nWBG perovskite solar cells (PSCs) and perovskite/organic tandem solar cells (TSCs). While the device\nperformance is impressive, some aspects of the manuscript are unclear and are seldom discussed. Therefore,\nI recommend considering the acceptance of the manuscript after addressing the following concerns:\nResponse: We appreciate the reviewer’s valuable comments. We have carefully read through them. Below,\nwe provide our point-by-point responses along with additional experimental results and appropriate\nmodifications in our revised manuscript. For your convenience, the major changes we have made in the\nmanuscript and the supporting information are marked in yellow.\n1. The authors investigate the detailed interactions between the additive and perovskites using DFT\ncalculations. To further validate these interactions, complementary characterizations such as FTIR and NMR\nspectroscopy should be conducted.\nResponse: We thank the reviewer for this comment. We provided the FTIR and NMR spectroscopy data to\nfurther validate the interactions between the additive and perovskite in the revised manuscript.\nPage 6, line 168 of our revised manuscript.\nThese interactions were further revealed by 1H nuclear magnetic resonance (1H NMR), Fourier transform\ninfrared (FTIR) spectra, and X-ray photoelectron spectroscopy (XPS) measurements (Figure 2d-i). In the 1H\nNMR spectra (Figure 2d), a distinct shift of the N-H bond in FA+ was observed for the additive-perovskite\nmixture compared to the perovskite, which can be attributed to the hydrogen bond between the lone pair\nelectrons on nitrogen of FA⁺ and the hydrogen atoms of the ammonium group[27]. As shown in the FTIR\nspectra (Figure 2e), after incorporating the additive into perovskite, the O-H stretching vibration peak of\nMMSC shifted from 3433 to 3400 cm-1, while the N-H bending vibration peak of perovskite shifted from\n1612 to 1628 cm-1, confirming the formation of the strong O-H…N hydrogen bonds. In addition, the C-S\nstretching vibration peak of MMS+ shifted from 758 to 747 cm-1, demonstrating a changed bond energy of\nthe methylsulfonium group[41].\nPage 21, line 599 of our revised manuscript.\n[... Figure 2 description omitted ...]\n2. In the evolution of PL spectra during the spin-coating process, the introduction of the additive appears to\naccelerate the self-crystallization process of perovskites (Figure 1b, c), while during annealing, the additive-\nincorporated sample exhibits slower mass transfer and crystal growth (Figure 1d, e). To provide a clearer\nunderstanding of how the additive influences the overall perovskite crystallization process, a more detailed\nanalysis of these phenomena is necessary.\nResponse: We thank the reviewer for this comment. We provided a more detailed analysis and a clearer\nunderstanding of these phenomena in the revised manuscript.\nPage 4, line 113 of our revised manuscript.\nFor the control sample, an obvious PL emission signal at shorter wavelengths appears at ~27 s, corresponding\nto the nucleation of secondary Br-rich phases[34], which reflects the undesirable phase heterogeneity and\ncomplex phase transition (Figure 1b). In contrast, the modified sample exhibits only a small peak shift and\nweaker Br-rich phase signals, indicating that the MMSC modification improved the phase homogeneity of\nperovskites during nucleation.\nPage 4, line 123 of our revised manuscript.\nDuring annealing, both samples exhibit a high initial PL intensity followed by a rapid decrease within the\nfirst 2 s due to the fast solvent evaporation[36]. Subsequently, crystal growth and Ostwald ripening lead to a\ngradual increase in the PL signals.\n3. The top-view SEM results (Figure 1f-g) suggest that the introduction of the additive reduces the grain size\nof the perovskites, which could be associated with its impact on the initial crystallization process during spin-\ncoating. A discussion of this phenomenon is required.\nResponse: We thank the reviewer for this comment. We provided a more detailed discussion of this\nphenomenon in the revised manuscript.\nPage 4, line 129 of our revised manuscript.\nDuring spin coating, the phase heterogeneity of nuclei in the control film during the initial crystallization\nprocess results in variable growth dynamics and thus large variations in final grain size. In contrast, MMSC-\ninduced homogeneity of nuclei ensures a homogeneous growth kinetic, suggesting a more uniform grain size\ndistribution.\n4. The scale bar for the AFM images (Figure S3) should be provided for clarity.\nResponse: We thank the reviewer for this comment. We provided the scale bars for the AFM images in the\nrevised supplementary information.\n[... AFM data omitted ...]\n5. Several subscripts are missing in the supporting figures, such as in Figure S4a-c, Figure S18a-b, and Figure\nS19a. Please ensure that the entire manuscript and supplementary materials are thoroughly reviewed for\ncompleteness.\nResponse: We thank the reviewer for this comment. We have provided the corresponding subscripts in the\nrevised supplementary information.\n[... Note sections omitted ...]\n6. In the XRD results (Figure S4c), the control film shows a distinct yellow phase peak around 10.8°.\nHowever, this signal appears to be absent in the GIWAXS image (Figure 2a). A specific explanation for this\ndiscrepancy should be provided.\nResponse: We thank the reviewer for this comment. The GIWAXS measurement (Figure 2a) was conducted\nusing Xeuss 3.0 SAXS/WAXS (Eiger2R 1M) with a small incident angle of only 0.5° in the grazing-incidence\ngeometry, which is sensitive to detecting the crystallographic properties of the perovskite surface rather than\nthe deep position in the bulk phase. In contrast, the XRD test was performed by Empyrean in traditional\nmode, which can characterize the crystallographic properties of the bulk perovskite thin film. The peak\naround 10.8° in the XRD data indicates the existence of non-photoactive phases in the control film (Nat. Rev.\nChem., 2023, 7(7): 462-479; Adv. Funct. Mater., 2025, 35(12), 2417493; Energy Environ. Sci., 2022, 15(9),\n3862-3876.), while the MMSC can inhibit the formation of such undesirable phases. However, according to\nthe GIWAXS data in Figure 2a, this signal is absent for both the control and MMSC-modified films,\nsuggesting the non-photoactive phases are likely to form in the bulk phase of the control perovskite films\ninstead of their surface. We provide the analysis of this phenomenon in the revised supplementary information.\nPage 7, line 97 of our revised supplementary information.\nA non-photoactive phase peak around 10.8° is observed for the control film, while the MMSC can inhibit the\nformation of this undesirable phase.\n7. It appears that the additive has a significant impact on the MPP stability of WBG PSCs. I am curious\nwhether this advantage extends to the MPP stability in perovskite/organic TSCs as well.\nResponse: We thank the reviewer for this comment. We conducted the MPP tracking tests for the TSCs to\nshow the additive-induced enhanced operational stability for tandem photovoltaic.\nPage 9, line 294 of our revised manuscript.\nIn addition, MPP tracking tests under ISOS-L-1 protocols (Figure S25) indicate that the MMSC modification\nextended the T lifetime of TSCs from ~63 h to ~335 h, demonstrating enhanced operational stability\n80\nconsistent with the trend observed in WBG PSCs.\nPage 28, line 187 of our revised supplementary information.\n[... Figure S25 description omitted ...]\nResponse to Reviewer #3\nReviewer #3:\nComments:\nIn this manuscript, the author introduces a novel additive, DL-methionine methylsulfonium chloride, which\nsimultaneously modulates the crystallization thermodynamics and provides comprehensive defect\npassivation for wide-bandgap perovskites. As a result of improved phase homogeneity and enhanced phase\nstability, excellent performance was realized in both rigid and flexible perovskite/organic tandem solar cells.\nThis manuscript provides a useful strategy for crystallization modulation in wide-bandgap perovskite. I\nrecommend publication after revisions.\nResponse: We appreciate the reviewer’s valuable comments. We have carefully read through them. Below,\nwe provide our point-by-point responses along with additional experimental results and appropriate\nmodifications in our revised manuscript. For your convenience, the major changes we have made in the\nmanuscript and the supporting information are marked in yellow.\n1. Since methylsulfonium is a positively charged group, it is recommended to include a “+” sign in its\nabbreviation to clearly indicate its cationic character.\nResponse: We thank the reviewer for this comment. We included a “+” sign in the related abbreviation in the\nrevised version.\n[... Page references and text changes omitted ...]\n2. The manuscript uses various terms to refer to the control and experimental groups. For experimental groups,\nsuch as “target sample”, “modified group”, “modified sample”, and “target film”. It is recommended to\nstandardize these terms throughout the manuscript to avoid confusion and improve clarity.\nResponse: We thank the reviewer for this comment. We apologize for the confusion caused by inconsistent\nterms in the previous version of the manuscript. To avoid any confusion and improve clarity, we use“MMSC-\nmodified” to refer to the experimental group, and all the corresponding revisions are marked in yellow in the\nrevised manuscript.\n3. The nitrogen atom in the amine group possesses lone pair electrons, allowing it to act as a hydrogen bond\nacceptor and form hydrogen bonds with the hydrogen atoms of the ammonium group. This interaction should\nbe considered when interpreting the 1H NMR spectrum.\nResponse: We thank the reviewer for this comment. We add a more detailed discussion of the mechanisms\nof forming hydrogen bonds when interpreting the 1H NMR spectrum in the revised manuscript.\n[... Page references and text changes omitted ...]\n4. It is recommended to employ infrared spectroscopy to better elucidate the interactions and coordination\nmechanisms between various functional groups of the additive and the perovskite.\nResponse: We thank the reviewer for this comment. In the revised manuscript, we performed the infrared\nspectroscopy to better elucidate the interactions and coordination mechanisms between various functional\ngroups of the additive and the perovskite.\n[... Page references and text changes omitted ...]\n5. The authors mention the application of this strategy in flexible devices. It might be helpful if the authors\ncould consider providing the impact of this strategy on the mechanical stability of flexible single-junction\nWBG PSCs under bending or stretching conditions.\nResponse: We thank the reviewer for this comment. In the revised version, we evaluate the mechanical\nstability of flexible single-junction WBG PSCs under bending conditions. After 400 bending cycles with a\nbending radius of ~10 mm, the modified device retained ~95% of its initial PCE, compared to ~85% for the\ncontrol device, demonstrating the improved mechanical stability.\n[... Page references and text changes omitted ...]\n6. If the hole transport layer is deposited by thermal evaporation, it is more accurate to denote it as “MoOₓ”\nrather than “MoO₃”, unless characterization has definitively confirmed the presence of a pure MoO₃ phase.\nResponse: We thank the reviewer for this comment. In the revised manuscript, we used the “MoOₓ” rather\nthan “MoO₃” to more accurately denote the corresponding hole transport layer.\n[... Page references and text changes omitted ...]\n7. The authors claim that the rigid and flexible perovskite/organic TSCs demonstrate champion PCEs of 26.0%\nand 22.1% respectively, along with superior bending stability. As a high performance is claimed, a certificate\nwould be needed to verify the performance.\nResponse: We thank the reviewer for this comment. Due to the unavailable slots from the accredited\ncertification institutions and the difficulty in encapsulating TSCs without efficiency degradation, we failed\nto achieve a certification for our TSCs. In this work, the WBG PSCs were fabricated at Wuhan University of\nTechnology and then sent to Qingdao University to deposit the organic solar cells to complete the two-\nterminal perovskite/organic TSCs preparation. To address the concern about the efficiency of our TSCs raised\nby the reviewer, we further collaborated with Dr. Jianhong Gao (associate professor at Wuhan Institute of\nTechnology), whose research focuses on organic solar cells, to fabricate the TSCs using our WBG PSCs. And\nwe demonstrated similar results for both the rigid and flexible TSCs, thus confirming the consistency and\nreproducibility of our fabrication method and device performance. Our work is to present an effective strategy\nfor regulating the crystallization thermodynamics of wide-bandgap (WBG) perovskite and demonstrate the\nreliability of their applications on perovskite/organic TSCs, rather than claim a record-level efficiency of\nperovskite/organic TSCs in the field. We hope the reviewer would view our efforts in a favorable light and\nfind the third-party device results useful for supporting the device performance.\n[... Figure R2 description omitted ...]\n8. The storage stability data of the perovskite/organic TSCs in N2 is insufficient to demonstrate the\noperational stability of TSCs under operational conditions. It is strongly recommended to present more\nrelated stability test results.\nResponse: We thank the reviewer for this comment. We conducted the MPP tracking tests for the\nencapsulated TSCs under ambient air to present more related stability test results under operational conditions.\nThe MMSC-modified TSC also exhibits enhanced operational stability compared to its counterpart.\n[... Page references and text changes omitted ...]"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revision has addressed my concerns. I am pleased with the author's response and endorse the publication of their work in its current form.", "reviewer_2": "My concerns have been adequately addressed. Nevertheless, I recommend that the authors provide a more detailed discussion of my second concern regarding the evolution of the PL spectra to perovskite phase purity.", "reviewer_3": "The authors have addressed the issues and I recommend publication of the manuscript in current form."}, "author_response": ""}]

Decision letter