A passivation–reduction synergistic strategy for achieving efficient and durable inverted perovskite solar cells†

Jingyu Cai, Congcong Tian, Anxin Sun, Jinling Chen, Xiling Wu, Beilin Ouyang, Jiajun Du, Ziyi Li, Rongshan Zhuang, Ran Li, Teng Xue, Tiantian Cen, Kaibo Zhao, Yuyang Zhao, Qianwen Chen and Chun-Chao Chen*
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China. E-mail: c3chen@sjtu.edu.cn

First published on 16th July 2025

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1 Introduction

Metal halide perovskite solar cells (PSCs) have immense commercial potential due to their excellent optoelectronic properties and low manufacturing costs. In recent years, the development of PSCs has made rapid progress. Recently, power conversion efficiencies (PCEs) of over 26.8% have been demonstrated in PSCs with an inverted structure by various interface passivation methods.^1,2 In particular, the interface between the perovskite and electron transport layer (ETL) is considered to be the most problematic interface in inverted PSCs.^3,4 Significant energy loss often occurs at this interface due to iodine defects, resulting in limited PCE and short-lived device stability.⁵ As a result, the current stability of PSCs is still far inferior to that of silicon solar cells.^6,7 To facilitate the commercialization of PSCs, an efficient and durable passivation method for the interface between the perovskite and ETL is highly desirable.

The soft ionic nature of metal halide perovskites leads to a high defect density in the films, with the defect density at the interface being much higher than that in the bulk. This results in severe carrier trapping and non-radiative recombination at the interface, leading to undesirably low voltages in device performance.^8,9 Specifically, due to the instability of Pb–I bonds and the volatilization of iodine components during annealing, the upper surface of perovskite films contains a large number of iodine-related defects, such as iodine vacancies (V_I) and uncoordinated Pb²⁺ defects. Post-treatment with ammonium halides can passivate A-position defects while introducing additional iodine ions to compensate for surface V_I.^10–12 However, the introduction of 2D perovskites results in high exciton binding energy and pronounced quantum confinement effects,^13–16 which hinder carrier transport. To avoid the introduction of 2D phases, anion passivators have attracted growing interest.^17–20 Halides, especially the iodide ion (I⁻), are widely adopted anions, which can fill iodine vacancies and suppress surface defects.^21–24 Wu et al. introduced CdI₂ to compensate for the surface I⁻ ion deficiency, forming stronger Cd–I bonds relative to Pb.²¹ Subsequently, the interfacial charge recombination loss is reduced, yielding an open-circuit voltage of 1.20 V. However, excessive iodide ions can induce interstitial iodine defects,²⁵ while also causing surface composition disorder,²⁶ which impairs device performance and stability. Compared to halide anions, nonhalide anions usually contain groups with lone pair electrons, such as S, O, and F, which have been proven to strongly coordinate with uncoordinated Pb²⁺, thus more effectively filling and passivating iodine vacancy defects. Some typical nonhalide anions include CH₃COO⁻, BF₄⁻, and SCN⁻.^27–29 However, these nonhalide anions usually only bind to a single undercoordinated lead site, with limited binding strength. Therefore, anion passivators that can simultaneously bind to multiple uncoordinated Pb²⁺ sites with stronger passivation capability are worth exploring.

Besides, I⁻ undergoes oxidation reactions under external conditions such as light, thermal stress, and electric fields, generating I₂.^30,31 I₂ has been proven to be highly corrosive, leading to the destruction of the perovskite structure.³² Meanwhile, the generation and volatilization of I₂ cause surface iodine loss and create deep defects such as Pb⁰ on the perovskite surface,^33,34 resulting in the degradation of PSC device performance. The use of reducing agents has been demonstrated to eliminate I₂. For example, benzylhydrazine hydrochloride (BHC)³⁵ and potassium formate (HCOOK)³⁰ have been introduced into the bulk, mitigating I₂-induced film stability issues by reducing I₂ to I⁻. Notably, borohydrides (BH₄⁻) and their derivatives possess broad reducibility^36,37 and have been applied in the inhibition of Sn²⁺ oxidation in tin-lead perovskites,^38,39 but there is currently limited research on their use in reducing I₂. Liu et al.⁴⁰ used potassium borohydride (KBH₄) on a NiO_x substrate, preventing adverse interfacial reactions caused by Ni²⁺ oxidation and reducing the I₂ content within the film, demonstrating the effective reduction of elemental iodine by borohydrides. However, KBH₄ is extremely reactive and flammable, making it unsuitable for large-scale production. At present, no suitable borohydride derivative has been discovered to simultaneously reduce I₂ and provide interfacial passivation for synergistic improvements in PCE and stability.

In this work, a mild borohydride derivative, sodium triacetoxyborohydride (STAB), was introduced as a reductive anion passivator for post-treatment of perovskite. Density functional theory (DFT) calculations revealed that in the presence of iodine vacancy (V_I) defects, STAB, containing three electron-rich carbonyl groups (CO), simultaneously coordinates with multiple undercoordinated Pb²⁺ defect sites on the perovskite surface. As a result, TAB⁻ achieved higher adsorption energy compared to commonly used anions (I⁻, Br⁻, and Cl⁻), significantly passivating surface iodine vacancy defects. Additionally, the strong reducing B–H bond in STAB can reduce I₂ to I⁻. UV-vis spectra show that the reducing effect of the B–H bond inhibits the generation of oxidative I₃⁻ in FAI and significantly reduces the extraction of I₂ from the perovskite film under light and thermal stress. Meanwhile, the reduction of I₂ in the film by STAB helps to alleviate the surface iodine deficiency and eliminates harmful Pb⁰ byproducts. Therefore, the defect passivation and I₂ reduction effects brought by STAB post-treatment promote less interface recombination loss and a more uniform, high-quality surface. As a result, the inverted PSCs treated by STAB achieved a champion efficiency of 25.85% and a high open-circuit voltage of 1.185 V. Meanwhile, the target devices retained over 90% of their initial PCE after 1000 hours of thermal aging at 85 °C in a N₂ atmosphere or 1000 hours of maximum power point tracking (MPPT) at 65 °C. Moreover, we applied this strategy to narrow-bandgap (1.27 eV) PSCs and increased the PCE from 20.01% to 22.97%, while achieving better thermal stability. This demonstrates the good universality of this strategy for various bandgap perovskite solar cells.

2 Discussion

Fig. 1a shows the molecular structure of STAB. The electrostatic potential (ESP) map of the triacetoxyborohydride anion (TAB⁻) was calculated using density functional theory (DFT) (Fig. 1b) to investigate the charge distribution of this ion. The low potential region of TAB⁻ is located on the O atom of the carbonyl group (CO), indicating that this area is electron-rich, which corresponds to the Lewis basicity of the carbonyl group. The Lewis basicity of the carbonyl group allows it to coordinate with undercoordinated Pb²⁺. Additionally, the H atom of the B–H bond is also electron-rich due to the negative valence state of this hydrogen atom, which is the source of the reducing property of STAB.^37,39 Considering the charged nature of the anion, TAB⁻ will play an important role in passivating the positively charged defects on the perovskite surface. A Pb–I terminated α-FAPbI₃ surface model was constructed, distinguishing between cases with and without iodine vacancies (V_I), to further explore the passivation effect of TAB⁻ on perovskite. Optimized geometrical structures of the TAB⁻ molecule on the surface model with and without iodine vacancies (V_I) are shown in Fig. 1c and d. Calculations show that the adsorption energy (E_a) of TAB⁻ is −2.77 eV in the absence of V_I, while E_a increases to −4.61 eV on the surface with V_I. This indicates that the TAB⁻ anion has a stronger interaction with the positively charged iodine vacancy defects on the perovskite surface. Furthermore, the charge transfer of TAB⁻ was understood through the differential charge density maps in Fig. 1e and f. It is noted that significant charge transfer occurs between the O atom of the carbonyl group on TAB⁻ and the Pb ion on the perovskite surface, attributed to the coordination bond formed between the electron-rich Lewis base and the undercoordinated Pb²⁺ on the surface. However, this charge transfer is more intense on the surface with V_I, corresponding to the higher adsorption energy (as shown in Fig. 1f), proving that V_I defects are less likely to form in the presence of STAB. We calculated the adsorption energies of several commonly used halide anions (Cl⁻, Br⁻, and I⁻) and V_I (Fig. 1g, with the model schematic shown in Fig. S1†), demonstrating the superior V_I suppression ability of TAB⁻, which not only benefits the passivation of surface defects but also helps to mitigate the migration of iodide ions on the surface under light and the formation of I⁰.^41,42 Previous studies have shown that V_I defects, as the main surface defects, can easily induce other defects (such as Pb_I and V_Pb). The formation energies of several common defects (V_I, V_Pb, and Pb_I) in the presence of TAB⁻ were calculated (Fig. 1g). After STAB treatment, the formation energies of these defects significantly increased, indicating that STAB is highly effective in suppressing the formation of surface defects.

Further detailed characterization studies of the interaction mechanism between STAB and perovskite films were conducted. First, time-of-flight secondary-ion mass spectrometry (ToF-SIMS) depth profiles were performed to clarify the distribution of STAB in perovskite films,⁴³ as shown in Fig. S1.† Since B⁺ accumulated at the surface, this indicates that the anions of STAB are mainly present at the surface of the perovskite. Na⁺, in contrast, was distributed throughout the perovskite film and was enriched both at the surface and at the buried interface.⁴⁴ It has been reported that the presence of Na⁺ in the bulk and at the interfaces suppresses ion migration and reduces hysteresis.^45,46 Then, the detailed spectroscopic tests were conducted to further investigate the interaction between STAB and perovskite components. The FTIR spectra of a series of samples, including STAB powder, STAB + PbI₂ mixture, FAI, and FAI + STAB mixture, were analyzed, as shown in Fig. 2a. After the addition of PbI₂, the CO peak of the CO bond in STAB shifted from 1683.1 cm⁻¹ to 1650.7 cm⁻¹. In addition, the FTIR spectra of the control and STAB-treated perovskite films were measured, as shown in Fig. S3.† The stretching vibration of CO of STAB appeared in STAB-treated perovskite films and shifted from 1683.1 to 1653.7 cm⁻¹. These results indicate a strong interaction between STAB and perovskite, which can be attributed to the coordination of carbonyl oxygen in TAB⁻ with Pb²⁺.⁴⁷ Additionally, the peaks of NH and CH in FAI moved from 3338.5 cm⁻¹ and 1692.5 cm⁻¹ to 3350.2 cm⁻¹ and 1698.4 cm⁻¹, respectively, with the peak of NH shifting to 3350.2 cm⁻¹ after adding STAB (Fig. S4†), which may be attributed to the hydrogen bonding between the highly electronegative oxygen atoms in STAB and FAI. The proton nuclear magnetic resonance (¹H NMR) spectra (Fig. S5†) showed that the chemical shift of N–H in FA⁺ exhibited an upfield shift after mixing with STAB, further confirming the presence of hydrogen bonding. This hydrogen bonding has been proven to stabilize the surface structure, which is beneficial for reducing the generation of V_I.⁷ X-ray Photoelectron Spectroscopy (XPS) tests were performed on perovskite films to elucidate the changes in the chemical environment on the film surface. Fig. S6† shows the signal of B 1s. The presence of boron on the surface of STAB-treated films, which was absent in the control films, indicates that STAB was successfully introduced onto the perovskite surface. As shown in Fig. 2b, the binding energies (BE) corresponding to the Pb 4f_5/2 and Pb 4f_7/2 electronic states in the control film were 143.35 eV and 138.49 eV, respectively. In contrast, the Pb 4f spectrum of the STAB-treated film shifted towards lower binding energy by 0.16 eV, further confirming that undercoordinated Pb²⁺ formed coordination bonds with carbonyl groups, leading to an increase in electron density around Pb. Interestingly, the control film showed two shoulder peaks at 141.72 eV and 136.62 eV, indicating the presence of trace amounts of Pb⁰ on the surface.⁴⁸ Pb⁰ is known as a primary deep defect state that severely degrades the performance and durability of perovskite optoelectronic devices. The peaks of Pb⁰ were eliminated after STAB treatment, indicating that the multi-carbonyl coordination of STAB reduced Pb-based defects in the film.

Due to the reducing nature of the BH bond in STAB, the inhibition of oxidation of I⁻ by STAB is investigated here. The above result shows that the inhibition of V_I by STAB can block the generation of V_I-mediated I⁰ species.⁴⁹ Therefore, the presence of STAB should be beneficial in suppressing the formation of iodine in the film, thereby improving the film's photostability. To verify this hypothesis, STAB was first added to an IPA solution containing I₂ and left to stand for 5 minutes, observing that the solution changed from dark brown to transparent and colorless (Fig. 2d). FTIR was used to examine the changes in chemical groups after mixing STAB with I₂, as shown in Fig. 2d. The scissoring bending vibration of B–H at 1106 cm⁻¹ disappeared after mixing with I₂,^50,51 proving the role of the reducing B–H bond in STAB in eliminating I₂. Furthermore, FAI was dissolved in IPA solvent and subjected to light aging at 55 °C for two hours. As shown in Fig. 2e, the aged FAI solution showed a new peak at 360 nm,⁴⁰ indicating the oxidation of I⁻ to I₂. In contrast, the FAI solution with added STAB did not show a peak at this position, indicating that STAB could prevent the oxidation of I⁻ under light.^23,30 The I/Pb ratio and Pb⁰ content in the perovskite films were calculated based on XPS (Fig. 2f), and the results showed that the STAB-treated films had a higher I/Pb ratio and less content of Pb⁰. At the same time, the XPS spectra of the I 3d signal (Fig. 2c) shifted (initially at 630.9 and 619.4 eV) to 630.7 and 619.2 eV, respectively. These results indicate that the loss of I⁻ due to the oxidation to I₂ in STAB-treated samples was reduced,⁴⁸ and the by-product Pb⁰ was also reduced.¹⁵ To study the inhibitory effect of STAB on I₂ in perovskite films, two perovskite films (control and STAB-treated) were immersed in toluene under 1 sun continuous illumination and tested for the presence of I₂ produced at different times using UV-vis absorption spectra, as shown in Fig. 2g and h. After 12 hours of illumination, the I₂ absorption peak (∼500 nm) of the control film was significant, attributed to the degradation of the perovskite film during light aging. In contrast, the STAB-treated film showed a weak peak. The intensity of the I₂ absorption peak at different times was statistically analyzed (Fig. 2i). It can be seen that STAB significantly reduced the escape of I₂ from the perovskite film, delaying the degradation of the perovskite film and improving the film's photostability.

The effects of STAB post-treatment on the crystal structure and surface morphology of perovskite films were investigated. The results of Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) and X-ray diffraction (XRD) (Fig. 3a and S7†) both demonstrated that the crystal structure remained unchanged after STAB treatment. The crystallinity slightly improved, which can be attributed to the passivation of under-coordinated Pb defects and post-treatment annealing.^42,52 Additionally, the reduction of PbI₂ was observed in GIWAXS, XRD, and SEM (Fig. 3b). As a photo-unstable substance, the reduction of PbI₂ will benefit the film's tolerance to light.⁵³ The UV-vis absorption spectra of the perovskite film (Fig. S8†) indicated that STAB treatment almost did not alter the bandgap width of the perovskite and had no significant impact on the light absorption properties. Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) were used to study the films (Fig. S9† and 3c). The STAB film showed a lower root mean square roughness (RMS) compared to the control group, decreasing from 21.8 nm to 17.4 nm. Furthermore, the average contact potential difference (CPD) of perovskite films significantly decreased from 50.58 mV to 42.93 mV and became more uniform after STAB treatment (Fig. 3d). These observations indicated that a smoother and more uniform surface is formed by STAB treatment, which could be beneficial for achieving better interfacial contact and promoting efficient interfacial charge extraction.¹¹

To investigate the passivation effect of STAB, steady-state PL and time-resolved photoluminescence (TRPL) were measured on glass/perovskite samples to study the carrier dynamics of the films. As shown in Fig. 4a and b, the STAB-treated film exhibited significantly enhanced PL intensity compared to the control perovskite film, indicating suppressed non-radiative recombination due to effective passivation of surface defects. TRPL demonstrated that STAB treatment significantly increased the average carrier lifetime (τ_ave) of the perovskite from 546.21 ns to 1725.10 ns (bi-exponential function fitting was applied; detailed parameters are listed in Table S1†), which is consistent with the PL result. To further investigate the effects of STAB on charge transport, a semi-complete device with a glass/perovskite/PCBM structure was prepared. The control sample showed a strong PL peak, while the intensity of the PL peak of the STAB-treated sample was only about 33% of the control sample, indicating fast fluorescence quenching. Meanwhile, the TRPL results showed that the τ₁ of the STAB-treated sample is shorter (14.55 ns) than that of the control sample (18.76 ns), indicating faster charge extraction from the STAB-treated perovskite surface to the PCBM layer.^4,54 At the same time, the τ₂ of the STAB-treated sample is longer than that of the control sample (273.17 ns vs. 223.22 ns), suggesting suppressed non-radiative recombination at the interface. These results demonstrate that STAB promotes electron extraction at the perovskite/PCBM interface and hinders non-radiative recombination within the perovskite.²⁸ The c-AFM tests (Fig. 3e) were conducted to further investigate the charge transport properties of the film surface. The control film had a lower average current, indicating high carrier transport loss.⁵⁵ Moreover, the grain boundaries appeared brighter, suggesting the presence of leakage current.^56,57 After STAB treatment, the average surface current was increased from 2.46 pA to 2.93 pA, and the contrast between grain boundaries and grains was reduced, indicating reduced carrier recombination at the grain boundaries. The frequency distribution of the current is plotted in Fig. 3f. The STAB-treated film showed stronger current signals and a narrower current distribution, indicating that good defect passivation effects enhanced both conductivity and uniformity of the film surface. These results collectively demonstrate the excellent defect passivation and carrier extraction promotion capabilities of STAB.

UPS (Ultraviolet Photoelectron Spectroscopy) was used to study how STAB affects the surface band structure of perovskite films. Fig. 4g shows the secondary electron cut-off edge and the Fermi edge for both the control and STAB-treated films. The STAB-treated film has a slightly lower work function (WF) of 4.15 eV compared to the control's 4.17 eV, which aligns with the lower surface potential measured by KPFM. Based on the film's bandgap (1.55 eV) from absorption spectra, the full band alignment was calculated, as shown in Fig. 4i. The STAB film has an E_F (Fermi level) further away from the valence band minimum (VBM) (1.26 eV vs. 1.12 eV), indicating stronger n-type surface characteristics. Additionally, the conduction band minimum (CBM) of the STAB-treated film is −3.86 eV, closer to the LUMO of PCBM (−3.92 eV) than the control's −3.74 eV, suggesting better band-alignment compatibility. These findings are consistent with earlier PL (photoluminescence) and TRPL (time-resolved photoluminescence) studies, showing the significant effect of STAB treatment to obtain a high-quality surface with suppressed non-radiative recombination and enhanced electron extraction.

Given the improved performance of STAB-modified films, we built inverted (p–i–n) perovskite solar cells (PSCs) to test the effect of STAB post-treatment on device performance. The device structure is FTO/MeO-4PACz/perovskite/STAB/PCBM/BCP/Ag (Fig. 5a). The STAB concentration was first optimized for the best results. Fig. 5b shows that 1 mg ml⁻¹ is the optimal concentration, offering the highest average efficiency and reproducibility. Higher concentrations (2 mg ml⁻¹) can lead to excessive STAB deposition at the interface, hindering charge transport. The J–V curves in both reverse and forward scanning directions were measured under standard AM 1.5G sunlight. Fig. 5c and Table S2† display the J–V curves and photovoltaic parameters of the best-performing control and STAB-treated devices. The champion STAB-treated device achieved a PCE of 25.85%, which was significantly higher than the 22.21% of the control device. Notably, the open-circuit voltage (V_OC) increased from 1.122 V to 1.185 V, and the hysteresis index (HI) improved dramatically, dropping from 4.23% to 1.81%. This is due to the ability of STAB to suppress iodine vacancies and passivate undercoordinated Pb²⁺ ions, thus reducing ion migration. The introduction of Na⁺ can also contribute to the reduction of hysteresis.²³ Due to better film quality and charge extraction, the short-circuit current density (J_SC) increased from 24.90 mA cm⁻² to 25.25 mA cm⁻², and the fill factor (FF) also improved from 79.50% to 86.36%. The integrated current density from the EQE (External Quantum Efficiency) spectrum (Fig. 5d) matched the J_SC value at 25.08 mA cm⁻², confirming the accuracy of J–V testing. Fig. 5e shows the results of the steady-state power output (SPO) test. The control device's steady-state PCE is 21.53%, while the champion device achieves a steady-state PCE of 25.47%. Meanwhile, the device with a large area (1.028 cm²) achieved a PCE of 24.39%, a V_OC of 1.179 V, a J_SC of 25.06 mA cm⁻², and an FF of 82.55% (Fig. S10†). The improved performance of the device at a larger scale can be attributed to the uniformity of the perovskite surface passivated by the STAB treatment, demonstrating the potential of this method for large-area fabrication. To demonstrate the method's versatility, STAB treatment was also applied to tin–lead perovskite solar cells with a 1.27 eV bandgap. The PCE of inverted devices based on Cs_0.25FA_0.75Pb_0.5Sn_0.5I₃ increased from 20.02% to 22.97%, with a J_SC of 32.74 mA cm⁻², consistent with EQE results (Fig. S11 and S12,† photovoltaic parameters in Table S3†). The performance enhancement can be attributed to STAB's reducibility, which prevents oxidation of Sn and I components, and its excellent defect passivation of iodine vacancies.³⁹ The 20 tested devices also showed that STAB-treated ones had the narrowest efficiency distribution, indicating high reproducibility (Fig. S13†). The 1.27 eV device treated with STAB exhibited a more stable photocurrent output of 30.04 mA cm⁻² within 300 s, as shown in Fig. S15.† These results highlight STAB's universal effectiveness as a reducible anion passivator in enhancing device performance for both 1.55 eV and 1.27 eV bandgap perovskite solar cells.

Then, a series of performance characterization studies were conducted to explore the mechanisms behind the excellent optoelectronic performance. First, dark-state J–V testing was performed. The devices based on STAB exhibited lower dark current (Fig. 5f, ESI†) compared to the control group. The saturated dark current density J₀ decreased by approximately one order of magnitude (from 1.18 × 10⁻⁵ mA cm⁻² to 1.03 × 10⁻⁶ mA cm⁻²), indicating that shallow-level defects were significantly suppressed.⁵⁸ Next, transient photovoltage (TPV) and transient photocurrent (TPC) were used to investigate the recombination dynamics of the devices (Fig. 5g and h). After STAB treatment, the photovoltage lifetime increased significantly (from 794.64 ns to 1020.28 ns), which demonstrates good agreement with the improved photovoltaic performance due to defect passivation.⁵⁹ Meanwhile, the photocurrent lifetime decreased significantly (from 499.13 ns to 103.28 ns), indicating faster carrier extraction in the STAB-treated devices.⁶⁰ Additionally, the dependence of V_OC on light intensity was tested in the range of 10–100 mW cm⁻². The light intensity (I) and V_OC follow the following equation:

Here, n represents the ideality factor, which can be obtained through linear fitting of V_OC-lnI. As shown in Fig. 5i, the n value of the STAB device obtained after linear fitting is 1.17, significantly lower than the 1.43 of the control group. This indicates that defect-assisted recombination is suppressed in PSCs.⁵ Similarly, the dependence of J_SC on light intensity was measured (Fig. S15†). The results show that the slope of the STAB device is 0.995, higher than the 0.932 of the control group, indicating reduced monomolecular recombination in the STAB-treated device. These results manifest that STAB as an anion passivator can provide a strong surface defect passivation effect, significantly improving the photovoltaic performance of the device.

The stability of the devices was evaluated under different settings. First, the unpackaged devices were placed on a hot plate at 85 °C in the dark to study their thermal stability. As shown in Fig. 6a, the performance of the control device deteriorated rapidly, with the PCE decreasing to 61.98% of its initial value after 1000 hours. In contrast, the STAB-treated device retained 92.31% of its initial PCE after 1000 hours, showing significantly improved thermal stability. Fig. 6c displays the cross-sectional SEM images of the control and STAB-treated devices after heat aging at 85 °C for 10 days. Many voids can be seen in the control device, which could be attributed to the loss of components in the perovskite film during heat aging.²⁰ In contrast, the STAB-treated device remained more intact than the control films, which is consistent with the efficiency trend. Moreover, the maximum power point tracking (MPPT) test was performed under continuous one sun illumination in N₂ at 65 ± 5 °C to estimate the photostability of the devices. As shown in Fig. 6b, the STAB device retained 90.21% of its initial efficiency after 1000 hours of MPPT, while the control device retained only 70.52% of its initial efficiency after 600 hours, indicating a significant improvement in the photostability of the STAB device. Additionally, the humidity stability of the device was enhanced, owing to a more hydrophobic surface (Fig. S17 and S18†). The stability gain of the device under light and heat conditions comes from STAB inhibiting the generation of V_I and hindering the conversion of I⁻ to I₂, thereby preventing the degradation of the perovskite film. Furthermore, the 1.27 eV Sn–Pb solar cells were also subjected to 85 °C thermal aging, and it was found that STAB significantly enhanced the thermal stability of the 1.27 eV Sn–Pb device (Fig. 6d). The STAB-treated 1.27 eV devices retained 81.2% of its initial efficiency after 600 hours of thermal aging, while the control device only retained 41.9%. Overall, these results highlight the universal enhancement of the stability of inverted PSCs by the STAB post-treatment method due to the management of iodine vacancy defects and reduction ability towards I₂.

3 Conclusion

We demonstrate an anionic passivator, STAB, which achieves the preparation of highly efficient and stable PSCs through the defect passivation of iodine vacancies and the reducibility for surface iodine management. The multiple carbonyl groups in STAB can interact with undercoordinated Pb²⁺ on the surface and inhibit the formation of iodine vacancy defects. This significantly improves the surface quality of the perovskite film, leading to fewer interfacial recombination losses and enhanced carrier extraction. Meanwhile, the reducibility of the B–H bond in STAB prevents the oxidation of I⁻ in the perovskite surface, inhibiting the generation of I₂ and improving the stability of the perovskite film under light and thermal stress. As a result, the champion STAB-treated device achieved a high PCE of 25.85%, with a V_OC of 1.185 eV. Moreover, the STAB-treated PSCs retained over 90% of their initial PCE after 1000 hours of thermal aging or 800 hours of maximum power point tracking. Furthermore, introducing STAB onto the narrow-bandgap perovskite (1.27 eV) surface also resulted in a significantly improved PCE (from 20.01% to 22.97%) and enhanced thermal stability. This study highlights the potential of surface iodine management strategies based on anionic passivators in improving the performance and long-term stability of PSCs, providing new insights for developing efficient and durable inverted PSCs with different bandgaps for commercial applications.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Author contributions

J. Cai: conceptualization, validation, methodology, investigation, data curation, formal analysis, visualization, and writing – original draft. C. Tian, A. Sun and J. Chen: investigation, methodology and data curation. X. Wu and B. Ouyang: investigation and data curation. J. Du, Z. Li, and R. Zhuang: investigation and validation. R. Li and T. Xue: investigation and validation. T. Cen, K. Zhao, Y. Zhao and Q. Chen: investigation. C.-C. Chen: conceptualization, writing – review & editing, supervision, project administration and funding acquisition.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This research was partly funded by the National Natural Science Foundation of China (52350610264) and the Natural Science Foundation of Shanghai (22ZR1428200). The authors acknowledged the Instrumental Analysis Center of Shanghai Jiao Tong University for providing SEM, AFM, UPS, and XPS measurements. The authors acknowledged the support from the staff at beamline BL16B1 of the Shanghai Synchrotron Radiation Facility (SSRF) for the GIWAXS measurement.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5ta04007h

This journal is © The Royal Society of Chemistry 2025