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

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.

Defect formation and phase instability remain critical challenges for perovskite/organic tandem solar cells. Jiang et al. address this by designing an additive to modulate the crystallization thermodynamics of wide-bandgap perovskite, achieving a record efficiency of 22.1% in a flexible cell.

Introduction

Tandem solar cells (TSCs) represent a promising strategy to surpass the inherent Shockley-Queisser efficiency limit of single-junction photovoltaics^1–3. 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 cells^5,6, NBG PSCs^7,8, Cu(In_1−xGa_x)Se₂ (CIGS) solar cells^9,10, 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 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 formation^1,16. Notably, the defects, especially the vacancies and interstitials, induce severe non-radiative recombination and are prone to promoting 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 TSCs^4,17,18.

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 TSCs^3,6,19–25. 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 TSCs^22,23. 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 T₈₀ 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_0.8Cs_0.2PbI_1.6Br_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(CH₃)₂), which is expected to enhance electrostatic interactions with [PbX₆]⁴⁻ octahedra²⁷, while the amino (-NH₂) and carboxyl (-COOH) groups can form strong hydrogen bonds with FA⁺ cations^19,28,29. 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 kinetics^22,27,29. 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 barriers^4,32. 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.

Fig. 1. Regulation of crystallization thermodynamics.

a Scheme diagram of the crystallization regulation. b In-situ PL spectra of the control and MMSC-modified films during spin-coating. c PL intensity tracking at the final peak position in the spin-coating process. d In-situ PL spectra of the control and MMSC-modified films during annealing. e PL intensity tracking in the annealing process. SEM images of the (f) control and (g) MMSC-modified WBG perovskite films. h Cross-sectional SEM images for the control and MMSC-modified perovskite films.

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 PbI₂ clusters can be found in the control film, which is probably caused by the additive of Pb(SCN)₂³⁷, while the modified film exhibits less PbI₂. 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 PbI₂ diffraction peak appears in the control film, indicating incomplete conversion of precursors. In contrast, MMSC-modified films exhibit a gradual decrease in PbI₂ peak intensity with increasing additive content (Supplementary Fig. 4c, d), demonstrating the ability of the additive to suppress residual PbI₂ 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 PbI₂ 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, respectively^39,40. 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).

Fig. 2. Crystallographic properties and strong interactions.

GIWAXS data of the a control and b MMSC-modified perovskite films. c GIWAXS data collected at different grazing incidence angles for the control and MMSC-modified perovskite films. d Liquid-state ¹H-NMR results of FAI, FAI-MMSC mixture, perovskite, perovskite-MMSC mixture, and MMSC. e FTIR data of the perovskite, MMSC, and perovskite-MMSC mixture. XPS data of f O 1s, g Pb 4f, h I 3d, and i Br 3d core energy levels for the control and MMSC-modified perovskite films.

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 amidogen 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 [PbX₆]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 (-NH₂) 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.

Fig. 3. Universal passivation effect and phase stabilization.

a Scheme diagram of the passivation effect for different types of defects in the WBG perovskite. b Formation energies of different defects for the pristine and MMSC-modified perovskite lattices. c PLQY, QFLS, and iV_oc values for the control and MMSC-modified WBG perovskite films. TRPL mapping data for the d control and e MMSC-modified perovskite films. f PL spectra of the perovskite films after light soaking under 1 Sun irradiation using a solar simulator. g Hyperspectral fluorescence microscopy tracking of the control and MMSC-modified WBG perovskite films after laser exposure for different times. The tested area is 150 μm × 150 μm.

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 C₆₀ 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/C₆₀ 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 PbI₂, 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 PbI₂ 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 stability^50,51. 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 (C₆₀)/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 a 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.

Fig. 4. Performance of the rigid and flexible WBG PSCs.

a Illustration of the single-junction WBG PSC. b Champion J-V curves of the control and MMSC-modified rigid PSCs. c SPO data of the control and MMSC-modified rigid PSCs. d EQE spectra and integrated J_sc of the control and MMSC-modified rigid PSCs. e Stability for the unencapsulated control and MMSC-modified rigid PSCs in N₂. The data are derived from 10 PSCs for each condition. The error bars represent standard deviation (SD). f MPP tracking data (ISOS-L-1) for the encapsulated control and MMSC-modified rigid PSCs in air. g Champion J-V curves of the control and MMSC-modified flexible PSCs. h Statistical distribution of the FF × V_oc and PCE for the rigid and flexible WBG PSCs. The box plots display the mean (small squares), median line (solid lines), and 25–75% box limits with 1.5× interquartile range whiskers. i PCEs of single-junction WBG perovskite photovoltaics in this work and other works using perovskites with band gaps over 1.8 eV.

To reveal the intrinsic stability of these devices, we tracked the PCE evolution of devices stored in the N₂ 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 T₈₀ 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/C₆₀/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 N₂ 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 T₈₀ lifetime of TSCs from ~63 h to ~335 h, demonstrating enhanced operational stability consistent with the trend observed in WBG PSCs.

Fig. 5. Performance of the rigid and flexible perovskite/organic TSCs.

a Cross-sectional SEM image of the rigid perovskite/organic TSC. b Champion J-V curves of the control and MMSC-modified rigid TSCs. c EQE spectra of the front cell and rear cell for the MMSC-modified rigid tandem solar cell. d Long-term storage stability of the unencapsulated rigid TSCs. The data are derived from 12 TSCs. The error bars represent SD. e Champion J-V curves of the control and MMSC-modified flexible TSCs. f PCEs of the rigid and flexible perovskite/organic TSCs in this work and other reports.

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.

Discussion

In summary, we have developed an environmentally friendly additive, DL-methionine methylsulfonium chloride, that simultaneously enables crystallization control, defect passivation, and phase stabilization in WBG perovskite films. Owing to its rationally designed structure incorporating multiple functional groups, the additive can strongly interact with all the raw materials and thereby facilitate homogenous nucleation of target WBG perovskites, which enables uniform crystal growth and ultimately leads to improved morphological homogeneity. In addition, experimental results and DFT calculations further confirm the universal defect passivation capability of the additive, as evidenced by effectively increased formation energies for various defects, leading to reduced trap density, inhibited non-radiative recombination, and extended carrier lifetime. Based on this additive modification, champion PCEs of 20.4% and 18.0% for the rigid and flexible single-junction WBG PSCs are achieved, respectively. The MMSC-modified WBG PSCs also exhibit significantly improved operational stability, with a T₈₀ lifetime of 830 h under the ISOS-L-1 protocol. Moreover, the rigid and flexible perovskite/organic TSCs demonstrate champion PCEs of 26.0% and 22.1%, respectively, along with superior bending stability. These results validate the potential for the application of 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 (PbBr₂, 99.99%), and PEDOT: PSS solution (1.3–1.7 wt% aqueous solution) were purchased from Xi’an Polymer Light Co., Ltd. PbI₂ (99.999%) was purchased from TCI. C₆₀ (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 ZhongNuo 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_0.8Cs_0.2PbI_1.6Br_1.4 precursor solution, CsI, FAI, PbI₂, PbBr₂, 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 N₂-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 C₆₀ 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/C₆₀/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 (CD₃)₂SO and vibrated at room temperature for 10 min. Grazing Incidence X-ray diffraction (GIXRD) measurements were performed using Xeuss 3.0 SAXS/WAXS (Eiger2R 1 M) 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 1.5 G. 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 SnO₂ 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 van der Waals interactions in perovskites, we employed the Grimme DFT-D3 approach with Becke-Johnson damping^56,57. 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:

$$E_{\mathrm{int}}=E_{\mathrm{AB}}-\left(E_{\mathrm{A}}+E_{\mathrm{B}}\right)$$ 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 (Eads) is given as:

$$E_{\mathrm{ads}}=E_{\mathrm{passivated}\mathrm{system}}-E_{\mathrm{clean}\mathrm{surface}}-E_{\mathrm{isolated}\mathrm{passivator}}$$ 2

Where $E_{\mathrm{passivated}\mathrm{system}}$ is the total energy of the perovskite surface with the adsorbed passivator, $E_{\mathrm{clean}\mathrm{surface}}$ is the total energy of the perovskite surface without a passivator, $E_{\mathrm{isolated}\mathrm{passivator}}$ is the total energy of the passivation material in its free state. The defect formation energy is given as:

$$DEF\left(X^q\right)=E\left(X^q\right)-E\left(bulk\right)-\sum _i{n}_i{\mu }_i+q\left(E_F+E_{VBM}+\mathrm{\Delta }V\right)$$ 3

Where $E\left(X^q\right)$ is the total energy of the defect system with charge $q$, $E\left(bulk\right)$ is the total energy of the pristine system, and $n$ and $\mu$ 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 $\mathrm{\Delta }V$ induced by the defect. The charge density difference (Δρ) is calculated using VESTA in conjunction with VASP. The (Δρ) is defined as:

$$\Delta \rho ={\rho }_{system}-\sum {\rho }_{isolatedatoms}$$ 4

Where ${\rho }_{system}$ is the charge density of the fully optimized system. ${\rho }_{isolatedstom}$ is the charge density of the isolated atom (calculated with identical parameters, including spin polarization).

Reporting summary

Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.

Author contributions

T.B., F.H., C.L. (Cheng Li), L.Q., and Y.L. supervised this work. T.B. and R.J. conceived the ideas and designed the experiments. R.J. prepared the films and devices and performed the corresponding basic characterization. Y.Y. performed the hyperspectral fluorescence microscopy tracking tests. K.S. conducted the DFT calculations. X.C. conducted the fabrication and tests of the rigid OSC and TSCs. Q.Z. and C.H. participated in the fabrication and tests of the perovskite films and TSCs. C.J. conducted the GIWAXS and PLQY measurements. Q.K. and Q.Z. participated in the fabrication of the flexible OSC and TSCs and performed the corresponding characterizations. J.G., S.H., C.L. (Chang Liu), S.B., Z.B., and Y.-B.C. provided valuable suggestions for the experiments and manuscript. T.B., R.J., Y.Y., K.S., and X.C. participated in all the data analysis and finished this paper, and all authors reviewed the paper.

Peer review

Peer review information

Nature Communications thanks Yi Hou, Lei Meng, and Yue-Min Xie for their contribution to the peer review of this work. A peer review file is available.

Data availability

All data supporting the results of this study are provided in this article and its supplementary information. Any other information can be requested from the corresponding author. Source data are provided with this paper.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-025-68125-1.