Redox-Improved Self-Assembled Monolayers for Inverted Perovskite Solar Cells

Domain: physics
Published: 2025-12-12
Editorial outcome: major_revision

Abstract
Inverted perovskite solar cells (pero-SCs) utilizing nickel oxide (NiO x)/self-assembled monolayer (SAM) as a hole transport layer (HTL) have demonstrated high power conversion efficiency (PCE). However, variations in the valence states of NiO x on the surface create complexity in the growth of a high-quality SAM HTL. To address these challenges, a new SAM molecule MeOF-4SHCz is synthesized and utilized to target the Ni3+-rich regions on the NiO x substrate. A redox reaction occurs at the interface and the oxidation product of MeOF-4SHCz forms a new S−O−Ni bonding at the Ni3+-rich regions. The application of the combined SAMs of MeOF-4SHCz and the regular SAM MeOF-4PACz can improve the overall coverage and uniformity of the SAM layer on NiO x. As a result, the optimized inverted pero-SCs based on this redox-improved (ROI)-SAM HTL of MeOF-4SHCz/MeOF-4PACz = 4:1 (w/w) achieve a high PCE of 26.5% (certified as 26.28%) and improved stability with T 90 > 1000 hours.

Introduction
Interface engineering is a crucial strategy in enhancing the overall performance of perovskite solar cells (pero-SCs), by improving film morphology1, charge carrier dynamics2,3, and reducing interface charge recombination4,5. Particularly, in inverted pero-SCs (or p-i-n pero-SCs), hole transport layer (HTL) at the bottom buried interface plays a critical role in the device performance. Among these HTLs, the self-assembled monolayer (SAM) has recently drawn great attention due to its simple structure, facile fabrication process and superior charge extraction efficiency6–9. A typical SAM molecule consists of a p-type conjugated (such as a carbazole unit) terminal group, an alkyl spacer and an anchoring group10. The terminal group usually determines the energy level and surface wettability of the HTL, while the anchoring group shows significant influence on the resulting SAM coverage on substrate11–15. Anchoring groups with −PO(OH) 2 exhibit higher substrate coverage compared to the alternatives like −COOH and −SO 3H, and are widely used in the molecular design of SAMs16–19.

During the thermal annealing process, these SAM molecules bond to the metal oxide (MO) and form an organized monolayer. Among various metal oxides (MO), nickel oxide (NiO x), a well-known p-type metal oxide, has been widely used as the substrate of the SAM HTL for its exceptional hole transport ability, chemical and thermal stability20. With the application of the magnetron sputtering technology, the fabrication becomes suitable and widely utilized for large-scale production in industry21.

NiO x exhibits strong chemical bonding with SAM22. Meanwhile, the deposition of SAM effectively passivates the defects on the NiO x surface and optimizes the HTL/perovskite interface. Consequently, the combined HTL of NiO x/SAM provides important opportunities for the improvement of the performance of p-i-n pero-SCs. You et al. modified NiO x with hydrogen peroxide and created a more hydroxyl content surface, promoting the SAM anchoring on it22. Zhu et al. reported a SAM MeO-4PADBC in the NiO x/SAM HTL with lowered voltage deficit in the pero-SCs23. Sargent et al. applied the NiO x/SAM HTL into wide-bandgap pero-SCs in all perovskite tandem solar cell and achieved high performance24. However, variations in the valence states of NiO x on the surface create complexity in the growth of a high-quality SAM HTL. Meanwhile, the oxidation reaction caused by high-valent nickel species (Ni3+) in NiO x can accelerate the decomposition of amine halides, detrimentally affecting both device performance and long-term stability25–27.

To simultaneously enhance the quality of the SAM and reduce the intrinsic reactivity of the NiO x surface, comparing with the strategies mentioned above, we aimed to develop a dual-functional interfacial strategy. Given the strong oxidative nature of high-valence nickel species in NiO x, we sought to exploit this property to promote the formation of a more homogeneous SAM layer. Specifically, we envisioned introducing a reducing agent that could react with NiO x to passivate its surface while concurrently functioning as an HTL and facilitating the formation of a high-quality SAM layer.

Herein, we designed and synthesized a new SAM molecule 4-(3-fluoro-6-methoxy-9H-carbazol-9-yl)butane-1-thiol (MeOF-4SHCz), which is applied together with (4-(3-fluoro-6-methoxy-9H-carbazol-9-yl)butyl)phosphonic acid (MeOF-4PACz) as a combined HTL28. Due to the reducibility of thiol groups, MeOF-4SHCz can serve as an effective reducing agent to reduce the Ni3+-rich regions on the surface of the NiO x substrate. The oxidation product of 4-(3-fluoro-6-methoxy-9H-carbazol-9-yl)butane-1-sulfonic acid (MeOF-4SACz) could form a new S-O-Ni bond at the Ni3+ region, together with the P-O-Ni bond at the Ni2+ region, improving the overall quality and coverage of SAM on the NiO x substrate. Moreover, the redox reaction causes the reduction of Ni3+ on the NiO x surface and hence lowers the reactivity between the NiO x and perovskite interface, which is beneficial to improving the photovoltaic performance of pero-SCs. As a result, the device based on the redox-improved (ROI)-SAM reaches a higher PCE of 26.5% (certified as 26.28%), and a better stability of T 90 > 1000 h at the maximum power point (MPP) under continuous 1 sun illumination.

Results
Mechanisms for ROI-SAM

The molecular structure of MeOF-4SHCz is presented in Fig. 1a, and the synthesis procedures of MeOF-4SHCz are described in the Methods section. The molecular structures were further confirmed by nuclear magnetic resonance (NMR) spectroscopy as shown in Supplementary Figs. 1-7. To investigate the interaction between the MeOF-4SHCz and the NiO x substrate, X-ray photoelectron spectroscopy (XPS) measurements were performed. We analyzed the XPS spectra to examine the valence states of the elements, and the detailed XPS peak fitting data are listed in Supplementary Tables 1-7. The MeOF-4SHCz SAM was deposited onto the NiO x substrate, before annealing, two distinct peaks were observed in S 2p spectrum at binding energies of 163.2 eV and 164.3 eV, corresponding to the S2− species from thiol groups29. Notably, after annealing at 100 °C for 10 minutes, a new peak appeared in S 2p spectrum at binding energy of 167.5 eV (see Fig. 1b, Supplementary Tables 1 and 2), which is also reported in the previous study on the adsorption of alkyl mercaptan on the NiO x surface30. To determine the oxidation product, we conducted electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) based on the mixture of NiO x nanoparticles and MeOF-4SHCz. The substance with mass-to-charge (m/z) of 350.1 was detected, suggesting the formation of MeOF-4SACz molecules with −SO 3H groups (Supplementary Fig. 8). Therefore, we deduce that the −SH group in MeOF-4SHCz is oxidized by Ni3+ into −SO 3H group, as illustrated by the following chemical equation:

3Ni 2 O 3 + 2R-SH → 6NiO + 2R-SO 3 H (1)

where R represents the 3-fluoro-6-methoxy-9H-carbazol (MeOF-Cz). Based on the above redox reaction, we further synthesized the MeOF-4SACz and measured its XPS spectrum. It exhibits a binding energy of 167.7 eV (Fig. 1c), closely matching the new peak appeared in S 2p spectrum mentioned above. Moreover, for the MeOF-4SHCz treated NiO x film, the existence of −SO 3H groups can also be observed by photo-induced force microscopy (PiFM) (Supplementary Fig. 9). This oxidation process is shown in Fig. 1d. The −SO 3H group generated from oxidation can serve as an additional anchoring group on the NiO x surface.

As MeOF-4SHCz is co-applied with MeOF-4PACz on the NiO x substrate, it is important to investigate the binding preference of each SAM on different Ni species (Ni2+, Ni3+). Therefore, we calculated the reaction energy between SAM and NiO x surface (Fig. 1d, e)31–34. The results show that there is a tridentate bind mode at NiO x surface because of the thermodynamically favorable configuration with the lowest total energy, while a bidentate mode at Ni 2 O 3 surface due to the larger lattice spacing, and this larger lattice spacing limits the interaction between the anchor group and the substrate (Supplementary Fig. 10, Supplementary Tables 3-4). For the MeOF-4PACz, the reaction energy with NiO is −0.80 eV, and that with Ni 2 O 3 is −1.00 eV, indicating no significant preference between the two Ni species. For the MeOF-4SHCz, the reaction energy with NiO is −0.09 eV, which suggests it hardly interacts with Ni2+. However, on Ni 2 O 3 , MeOF-4SHCz preferentially undergoes oxidation with a reaction energy of −5.25 eV, which is significantly lower than that of MeOF-4PACz with Ni 2 O 3 , indicating a much stronger driving force for the reaction of MeOF-4SHCz with Ni 2 O 3 during the self-assembly process. As a result, the MeOF-4SHCz strengthens the binding of the SAM to the Ni3+-rich regions, and improves the quality of the SAM layer on NiO x substrate.

As the thiol group in MeOF-4SHCz is oxidized to higher valence states, the valence state of the oxidant NiO x also changes. The peak fitting and analysis of Ni in the XPS spectra were performed25,27,35,36. The content of NiO species was calculated to evaluate the Ni2+ content, and the total content of higher valence species was considered as Ni3+ content. The binding energy of different Ni species is listed in Supplementary Table 5. For bare NiO x, as shown in Supplementary Fig. 11 and Supplementary Table 6, the integration results of the peak fitting show that the content of Ni3+ is 78.2%. When MeOF-4SHCz is deposited on NiO x, as shown in Fig. 1f and Supplementary Table 6, the Ni3+ content decreases to 75.3%. This change suggests that the Ni3+ species on the surface is reduced to a lower oxidation state. However, when the regular MeOF-4PACz is deposited on NiO x, the content of Ni3+ remained 78.1% and shows almost no change, which means the −PO(OH) 2 group barely influences the valence state of the NiO x surface. The results also indicate that the −SH groups are more inclined to react with Ni3+ than −PO(OH) 2 groups, which makes MeOF-4SHCz an effective SAM to target the Ni3+-rich region on the NiO x substrate, potentially contributing to a more homogeneous SAM layer. Considering that the reaction mainly occurs at the surface, to further investigate the oxidation of Ni3+ species, Ni 2 O 3 powder was mixed with the MeOF-4SHCz powder and XPS measurements were performed. The results show about 47% of MeOF-4SHCz oxidized to MeOF-4SACz, which confirms the surface oxidative role of the Ni3+ (Supplementary Fig. 12). And this process can be illustrated as Fig. 1g.

Measurements of kinetic process of the SAMs were conducted to characterize the oxidation influence of HTL on the perovskite layer. For simplicity, the MeOF-4PACz SAM is named as “Pristine-SAM”. The X-ray diffraction (XRD) analysis reveals that the perovskite layers coated on the ROI-SAM substrates exhibit a slight decrease in the intensity ratio of the PbI 2 peak to the FAPbI 3 (100) (Fig. 1h). And the tendency is shown in the inset, with the ratio of 0.128 for bare NiO x, 0.103 for the Pristine-SAM, and 0.091 for the ROI-SAM, respectively (Supplementary Table 7). As the three samples have the same perovskite composition, the reduced PbI 2 formation corresponds to a lower loss of ammonium salts, which indicates the less oxidation of I−. We performed additional analyses to directly investigate the interfacial degradation (Supplementary Fig. 13). Specifically, we deposited FAI onto the NiO x layer and the NiO x/MeOF-4SHCz layer, and found the formation of the neutral FA molecule in NiO x/FAI sample. To figure out the chemical transformation, we immersed the sample into anhydrous toluene and performed UV measurement. The UV-vis absorption spectrum shows a peak at ~500 nm, characteristic of molecular iodine, confirming the oxidation of I- during the process. The reaction can be summarized as:

2FAI + NiO x → 2FA + I 2 (2)

However, the NiO x/MeOF-4SHCz sample shows no FA molecule generated. As a result, the deposition of MeOF-4SHCz on NiO x could reduce the reactivity between NiO x and perovskite active layer, thereby suppressing the oxidation of perovskite components and potentially enhancing the long-term stability of the corresponding pero-SCs.

As shown in Fig. 1i and Supplementary Table 8, the addition of MeOF-4SHCz did not affect the binding energy of phosphorus, indicating the −SH group did not cause obvious change to the bonding between −PO(OH) 2 and NiO x layer in the rest Ni2+-rich regions. Eventually, MeOF-4SHCz can serve as an effective reducing agent and effectively reduce the Ni3+-rich regions on the NiO x substrate, which may contribute to a more uniform SAM layer.

Distribution of SAM in devices

Kelvin probe force microscopy (KPFM) was employed to examine the potential distribution of SAM on the NiO x layer. As illustrated in Fig. 2a and b, the sample with ROI-SAM displays a more uniform potential distribution with a smaller standard deviation than that of the sample with the Pristine-SAM, with 22.6 mV for Pristine-SAM and 14.5 mV for ROI-SAM, which suggests that the ROI-SAM exhibits a more uniform SAM layer37. Additionally, the conductive atomic force microscopy (c-AFM) demonstrates that the ROI-SAM sample (root mean square roughness (RMS) equals 0.134 nA) has a more uniform distribution than the Pristine-SAM sample (RMS = 0.197 nA) as shown in Fig. 2c, d. The results indicate that MeOF-4SHCz additive effectively improves the SAM uniformity on the NiO x substrate, which is favorable for the charge transfer in the corresponding pero-SCs. Meanwhile, the contact potential difference (CPD) of the ROI-SAM HTL is 274.2 mV, slightly lower than that (339.2 mV) of the Pristine-SAM sample (Fig. 2a, b), indicating that the ROI-SAM HTL has a deeper Fermi level with improved electron-blocking capability. Additionally, we performed conductivity measurements on both ROI-SAM and Pristine-SAM samples (Supplementary Fig. 14). The conductance showed a negligible change from 0.451 S to 0.439 S, indicating that the surface reaction had little impact on the bulk conductivity. Ultraviolet photoelectron spectroscopy (UPS) measurements were conducted to further confirm the energy level of the HTLs (Supplementary Fig. 15), with the data shown in Supplementary Table 9. The work function calculated from UPS curves of ROI-SAM sample is 5.38 eV, slightly higher than the Pristine-SAM sample of 5.31 eV, which is consistent with the CPD data.

To understand the self-assembly process of the Pristine-SAM and ROI-SAM systems, we performed molecular dynamics simulations to reveal the interaction between MeOF-4PACz and MeOF-4SHCz on the NiO x substrate during self-assembly38. The detailed kinetic processes are presented in Supplementary Figs. 16 and 17. From 20 ps to 100 ps, phosphate groups tend to form clusters due to hydrogen-bond interactions, leading to aggregation in the solution. After introducing MeOF-4SHCz with thiol groups, the dispersion of phosphate groups improves, and the number of clusters decreases at equilibrium, this improvement in solution dispersion facilitates uniform adsorption on the substrate. With the incorporation of MeOF-4SHCz, the SAM precursor solution also exhibits improved homogeneity, as shown in Fig. 2e and f, which is beneficial to the homogeneity of the formation of the SAM. When annealing, MeOF-4SHCz undergoes oxidation to form –SO 3H groups, which anchor onto the NiO x substrate and function as part of the HTL, improving the overall quality of the SAM layer.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was performed to study the spatial distribution of the SAM in the device (Fig. 2g). The perovskite precursor was dissolved in DMF/NMP=6:4 (v/v) to diminish trace DMSO in perovskite film, and the sulfur content is entirely attributed to the −SO 3H group in the SAM. When conducting the TOF-SIMS measurement, the −SO 3H group is detected as SO 3−. It was concentrated at the same depth as PO 3− (see Supplementary Fig. 18) and remains resistant to washing and the annealing of the perovskite precursor solution, which suggests the bonding of the −SO 3H on the NiO x substrate. Moreover, the SO 3− lateral distribution driven by the redox reaction is found to be uniform, which also confirms the overall coverage of the SAM on the NiO x.

Optoelectronic properties of the SAM layer and Perovskite films

To investigate the charge recombination properties and charge-carrier dynamics at the buried perovskite interface, we measured steady-state photoluminescence (PL) spectra (Fig. 3a) and time-resolved photoluminescence (TRPL) (Fig. 3b, Supplementary Fig. 19 and Supplementary Table 10). The perovskite film coated on the ROI-SAM (ROI-SAM sample) exhibits higher PL intensity compared to that on the Pristine-SAM HTL (Pristine-SAM sample), indicating the reduced non-radiative charge recombination. The TRPL spectrum of NiO x/ROI-SAM displays a longer decay time (73.1 ns) compared to that (37.0 ns) of the Pristine-SAM sample, which suggests reduced non-radiative charge recombination loss at the interface39,40. Space charge limited current (SCLC) technique was employed to characterize the defect density41 (Fig. 3c). The trap-filled-limit voltage (V TFL) extracted from the ROI-SAM sample is 0.29 V and smaller than that (0.33 V) of the Pristine-SAM sample, which means a lower trap density. This reduction is likely due to the higher quality of the buried SAM layer, which facilitates better crystallization and growth of the perovskite film, thereby reducing interfacial defects, consistent with the observations from the decay time of TRPL spectrum.

The nanosecond transient absorption (TA) spectra measurements were also conducted to investigate the exciton dissociation and recombination dynamics of different HTLs (Fig. 3d, Supplementary Fig. 20). A pump wavelength of 488 nm was used to selectively excite the film. As shown in the 2D spectra in Fig. 3e, f, both samples exhibit similar transient absorption features. Between 520 nm and 720 nm, a broad excited state absorption (ESA) peak centered at 540 nm was observed. We then compared the transient kinetics at the wavelength of 540 nm42,43, as shown in Fig. 3g. The ROI-SAM-based film exhibited a rapid decay before 0.1 μs, likely due to the more effective charge extraction, which decreases the number of charge carriers in the perovskite film. After 1 μs, this curve decays more slowly than that of the Pristine-SAM sample.

Moreover, PL mapping of the ROI-SAM HTL exhibits a more uniform PL emission (Fig. 3h, i), which is likely contributing to the improved buried interface. We further investigated the morphology of the perovskite layer using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Compared to the film coated on Pristine-SAM, the ROI-SAM-based film exhibits larger grains (Supplementary Fig. 21), and reduced RMS (Supplementary Fig. 22). These results also confirm that, after using ROI-SAM as HTL, the perovskite layer exhibits a more uniform morphology, which is beneficial to the interfacial contact and improves the device performance.

Photovoltaic performance of the p-i-n pero-SCs

We fabricated devices and studied the photovoltaic performance of pero-SCs utilizing the Pristine-SAM or ROI-SAM as HTLs. The device structure of the pero-SCs studied in this work is shown in the cross-sectional SEM image in Fig. 4a, with the architecture of ITO/NiO x/SAM/perovskite/C 60/BCP/Ag [ITO, indium tin oxide; BCP, 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline]. The concentration of MeOF-4SHCz in the ROI-SAM solution was optimized to be 0.25 mg·mL−1, and the concentration of MeOF-4PACz is 1 mg·mL−1 (weight ratio of MeOF-4SHCz/MeOF-4PACz is 1:4). The effect of the MeOF-4SHCz concentration on photovoltaic performance parameters of the pero-SCs is presented and compared in Supplementary Fig. 23. It is shown that the PCE of the pero-SCs based on the ROI-SAM increases with the MeOF-4SHCz concentration rising from 0 to 0.25 mg·mL−1. However, as the MeOF-4SHCz concentration is further increased to 0.5 mg·mL−1, the device performance declines, which is likely due to the hindered bonding between MeOF-4PACz and NiO x by excessive MeOF-4SHCz.

The current density (J)–voltage (V) characteristic curves of pero-SCs under forward and reverse scans are illustrated in Fig. 4b. The optimized ROI-SAM based devices show an improved J sc of 26.6 mA·cm−2, V oc of 1.18 V and FF of 84.5% in comparison with the Pristine-SAM based devices showing the slightly lower J sc of 26.4 mA cm−2, V oc of 1.15 V and FF of 83.2%, leading to an enhanced PCE from 25.3% for the Pristine-SAM based devices to 26.5% for the ROI-SAM based devices (Supplementary Table 11, certified PCE of 26.28%, Supplementary Fig. 24). The steady-state PCEs of the pero-SCs using Pristine-SAM or ROI-SAM as HTLs were 25.5% and 25.9%, respectively, as shown in Fig. 4c. In addition, the J sc value from the external quantum efficiency (EQE) measurements was integrated to be 24.7 mA·cm−2 for the Pristine-SAM based devices and 25.0 mA·cm−2 for the ROI-SAM based devices, as shown in Fig. 4d. The statistical device parameters are illustrated in Fig. 4e, which indicates that the ROI-SAM based devices show good reproducibility, likely due to the improved uniformity of the buried SAM layer.

The charge transfer dynamics in the pero-SCs were investigated by transient photocurrent (TPC) measurement44 (Fig. 4f). The photocurrent delay time of the device based on ROI-SAM is 0.8 μs and smaller than that (1.5 μs) of the Pristine-SAM, suggesting more effective charge carrier extraction. In Supplementary Fig. 25, the exponential factor (α) of ROI-SAM device obtained from the slope of the logarithmic J and logarithmic light intensity is closer to 1, suggesting better charge transport and reduced recombination of ROI-SAM HTL.

Besides the increased efficiency, we evaluated the long-term operational stability of the encapsulated device by tracking the maximum power point (MPP) under 1 sun illumination at 25 °C and 30% relative humidity (Fig. 4g). The ROI-SAM based devices retained 90% of their initial efficiency (T 90) after about 1000 hours. In contrast, the Pristine-SAM based control devices maintained 81% of their initial PCE under the same conditions, while the unmodified NiO x-based devices exhibited the T 80 around 600 hours, which shows the enhanced stability of the ROI-SAM-based devices. We then conducted thermal tests at 85 °C under N 2 atmosphere. The ROI-SAM devices showed improved thermal tolerance (T 90 > 576 h) compared to the control (T 90 ~ 72 h) and Pristine-SAM (T 90 ~ 312 h) devices (Supplementary Fig. 26). The improved long-term efficiency is attributed to the improved SAM layer and better interfacial contact with the perovskite active layer, and the decomposition of perovskite caused by the oxidation of Ni3+ can be mitigated. These results indicate that the ROI-SAM HTL with weight ratio of MeOF-4SHCz/MeOF-4PACz=1:4 is an effective strategy for enhancing the operational stability of p-i-n pero-SCs.

Methods
Materials

Cesium iodide (CsI, 99.9%), dimethyl formamide (DMF, anhydrous) and dimethyl sulfoxide (DMSO, anhydrous) were purchased from Sigma-Aldrich. Formamidinium iodide (FAI, 99.5%), methylammonium iodide (MAI, 99.5%), lead iodide (PbI 2, 99.9%), lead chloride (PbCl 2, 99.9%), 1,3-Propyldiammonium diiodide (PDADI) and C 60 were purchased from Xi’an Yuri Solar Co. All materials were used as received without further purification. ITO substrates were purchased from Suzhou Shangyang Solar Technology Co.

Synthesis of MeOF-4PACz

MeOF-4PACz was obtained in our laboratory as published previously.

Synthesis of MeOF-4SHCz

Supplementary Fig. 1 shows the synthetic route of MeOF-4SHCz, and it was synthesized by the following steps. MeOF-4C-Br (500 mg, 1.432 mmol) and thiourea (163.6 mg, 2.149 mmol) were dissolved in EtOH (20 mL) in a two-neck round-bottom flask. The mixture was refluxed at 80 °C for 20 h under argon protection. Subsequently, an aqueous solution of KOH (4.9 g in 7 mL H₂O) was added into the flask and the resulting mixture was refluxed for another 9 h. After cooling to room temperature, HCl was added to adjust the pH of the solution to 4. The mixture was then extracted with dichloromethane (50 mL × 3) and the organic phase was purified by column chromatography on silica gel using dichloromethane/petroleum ether (1/3, v/v) as the eluent. As a result, a white powder of MeOF-4SHCz (212 mg, 49% yield) was obtained. 1H NMR (400 MHz, DMSO-d 6) δ 7.98 (dd, J = 9.4, 2.6 Hz, 1H), 7.75 (d, J = 2.5 Hz, 1H), 7.60–7.48 (m, 2H), 7.27 (td, J = 9.1, 2.6 Hz, 1H), 7.12 (dd, J = 9.0, 2.6 Hz, 1H), 4.36 (t, J = 7.0 Hz, 2H), 3.85 (s, 3H), 2.52-2.42 (m, 2H), 2.21 (t, J = 7.8 Hz, 1H), 1.82 (p, J = 7.1 Hz, 2H), 1.53 (p, J = 7.3 Hz, 2H). 13C NMR (101 MHz, DMSO-d 6) δ 157.77, 155.47, 153.51, 137.44, 136.32, 122.78, 122.68, 122.48, 122.44, 116.08, 113.74, 113.49, 110.81, 110.73, 110.64, 106.52, 106.28, 103.99, 56.17, 56.10, 42.46, 40.63, 40.42, 40.21, 40.00, 39.79, 39.58, 39.37, 31.28, 27.85, 27.76, 26.57, 23.95. ESI-FTICR-MS, Calcd for C 17 H 18 FNOS (M-H)-: 302.10149 Found: 302.10237.

Synthesis of MeOF-4SACz

Supplementary Fig. 2 shows the synthetic route of MeOF-4SACz, and it was synthesized by the following steps. Sodium hydride (71 mg, 3.04 mmol) was carefully added to a solution of MeOF core (500 mg, 2.33 mmol) in 30 mL of anhydrous THF at 0 °C. After stirring for 1 h, 1,4-butanesultone (414 mg, 3.04 mmol) was added and the reaction mixture was refluxed for 24 h. The resulting solid was recovered by filtration and washed with acetone repeatedly to afford product as a slightly yellow powder (0.66 g, 81% yield). 1H NMR (400 MHz, DMSO-d 6) δ 7.96 (dd, J = 9.4, 2.6 Hz, 1H), 7.74 (d, J = 2.5 Hz, 1H), 7.62-7.50 (m, 2H), 7.25 (td, J = 9.2, 2.6 Hz, 1H), 7.11 (dd, J = 8.9, 2.6 Hz, 1H), 4.34 (t, J = 7.1 Hz, 2H), 3.85 (s, 3H), 2.48–2.40 (m, 2H), 1.80 (p, J = 7.3 Hz, 2H), 1.65-1.53 (m, 2H). 13C NMR (101 MHz, DMSO-d 6) δ 157.73, 155.42, 153.46, 137.46, 136.36, 122.71, 122.62, 122.42, 122.38, 116.06, 113.70, 113.46, 110.88, 110.80, 110.71, 106.44, 106.20, 103.98, 56.19, 56.11, 51.55, 42.90, 40.61, 40.41, 40.29, 40.20, 39.99, 39.78, 39.57, 39.36, 28.43, 23.19. ESI-FTICR-MS, Calcd for C 17 H 17 FNO 4 S (M-H)-: 351.09406 Found: 350.08696.

Device fabrication

The patterned ITO glass substrates were sonicated with detergent, deionized water, acetone and isopropanol for 30 min sequentially. After the ultraviolet ozone treatment for 30 min, NiO x (15 mg·mL−1) were spin-coated on the substrate at 3,000 rpm for 30 s and annealed at 150 °C for 15 minutes in the ambient air. Then the controlled condition (1 mg·mL−1 MeOF-4PACz) and target condition (1 mg·mL−1 MeOF-4PACz and 0.25 mg·mL−1 MeOF-4SHCz) solutions were spin-coated on NiO x at 3,000 rpm for 30 s and then annealed in inert gas at 100 °C for 10 min respectively. Cs 0.05 FA 0.9 MA 0.05 PbI 3 was prepared according to the stoichiometric ratio with solvent of DMSO:DMF (v/v = 1/5) as the perovskite precursor, with excessive 5% PbCl 2 and MAI addition. The 1.8 M perovskite precursor solution was spin-coated at 5,000 rpm for 30 s with an acceleration of 5,000 rpm s−1 and at the 15 s, 800 μL diethyl ether poured onto the substrate. The perovskite films were annealed at 100 °C for 30 min in the N 2 atmosphere. 0.5 mg mL−1 PDADI was spin-coated at 5,000 rpm for 30 s and then annealed at 100 °C for 10 min. Finally, C 60 (30 nm)/BCP (8 nm)/Ag (100 nm) were deposited by thermal evaporation under a pressure of 2 × 10-6 torr. The devices were controlled by a mask with an area of 0.09 cm2 during the J-V measurement.

Characterization of SAM and perovskite films

The 1H and 13C nuclear magnetic resonance spectroscopy was recorded on Bruker AVANCE 400 MHz spectrometer at 300 K. Chemical shifts (δ) are reported relative to tetramethylsilane (TMS) as an internal standard. High-resolution mass spectra were recorded on a Bruker solariX Fourier-transform ion cyclotron resonance mass spectrometer (FTICR-MS) equipped with an electrospray ionization (ESI) source operating in negative-ion mode. Fourier-transform Infrared (FTIR) Spectroscopy was recorded on Bruker VERTEX 70v, and UV-Vis absorption spectra were obtained on PerkinElmer Lambda 1050+.

X-ray Photoelectron spectroscopy (XPS) data and Ultraviolet photoelectron spectroscopy (UPS) were measured by Kratos AXIS ULTRA DLD spectrometer. Nonmonochromatic HeI (21.22 eV) source was used as an excitation source. Gold was used as reference. The bias voltage applied during the test is -9 V. X-ray diffraction (XRD) was measured with PANalytical Empyrean X-ray diffractometer with Cu Kα radiation at the scan rate of 2° min−1.

Photo-induced force microscopy (PiFM) results were acquired using a Vista Scope microscope from Molecular Vista, inc., from Songshan Lake Materials Laboratory. All PiFM experiments were excited by a pulsed quantum cascade laser (Block Engineering) with a gap-free narrow band tunable wave number of 760-1950 cm−1. The spectral line width is ~2 cm−1 with a wavenumber resolution of 0.5 cm−1. The PiFM experiment here was operated at the sideband excitation with the laser-frequency modulated at f m = f 1-f 0, where f 0 is the first mechanical eigenmode resonances of the cantilever that is used for PiF signal detection, while f 1 denotes the second ones recorded for the AFM topography of the sample. The probe is a Pt-coated tip with a resonant frequency of ~350 kHz (PPP-NCHPt-MB, Nanosensors). The atomic force microscopy, Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (c-AFM) images were obtained by Bruker ICON2-SYS.

TOF-SIMS analysis was performed on a TOF-SIMS-M6 spectrometer (ION-TOF GmbH, Münster, Germany) equipped with a 30 keV Bi 3+ primary ion gun pulsed at 10 kHz (mass range: 0 – 563 Da). An argon gas cluster ion source (GCIB, 10 kV, 5 nA) was employed as sputter gun. Negative ion spectra were calibrated by O-, OH-, C 2-, C 2H-, and Cl-, etc. An electron flood gun for charge neutralization was applied throughout the experiments. The scan sputter area was 400 × 400 μm2 and the analysis area was 200 × 200 μm2. Data were processed by ION-TOF SurfaceLab software (Version 7.4, ION-TOF GmbH) by signal of corresponding ions or fragment ions. To better resolve the SAM signal in TOF-SIMS, perovskite films with reduced thickness were prepared by diluting the perovskite precursor solution. To visualize the SAM layer more clearly, the perovskite precursor solution was diluted to form a thinner perovskite film.

Steady-state photoluminescence (PL) spectra were carried out with Horiba Jobin Yvon system. The excitation wavelength was set to 490 nm, and the final spectra were obtained by averaging three scans. The films tested in time-resolved photoluminescence (TRPL) were excited by a 485 nm pulse laser with a repetition frequency of 500 kHz provided by a picosecond pulsed diode laser (FLS980, Edinburgh Instruments Ltd). PL mapping experiments were undertaken by using a confocal laser scanning microscopy (CLSM, Leica STELLARIS 8, Germany) with a 40x object lens. Perovskite films were excited with a Diode laser (488 nm), and the photoluminescence were collected from 600-700 nm.

Nanosecond transient absorption spectrometer was composed of a regenerative-amplified Ti:sapphire laser system (Coherent) and EOS pump-probe system (Ultrafast Systems). The regenerative-amplified Ti: sapphire laser system (Legend Elite-1K-HE, center wavelength of 800 nm, pulse duration of 25 fs, pulse energy of 4 mJ, repetition rate of 1 kHz) was seeded with a mode-locked Ti: sapphire laser system (Vitara) and pumped with a Nd:YLF laser (Evolution 3). The output 800 nm fundamental of the amplifier was split into two beam pulses. The main part of the fundamental beam went through the optical parametric amplifiers (TOPAS-C), whose output light was set as the pump light with wavelength of 488 nm and chopped by a mechanical chopper operating at frequency of 500 Hz. Probe light was generated from an EOS (Ultrafast Systems) apparatus, produced in a diode-laser-pumped photonic crystal fiber, and electronically delayed relative to the pump pulse with a digital delay generator. Data acquisition was performed using the EOS software package from Ultrafast Systems. The pump was spatially and temporally overlapped with the probe beam on the sample.

Surface and cross-sectional morphology of the films and devices were examined by scanning electron microscopy (SEM, Hitachi S-4800). For the cross-sectional image, the sample was coated with ca. 1 nm-thick gold using sputter to enhance the conductivity.

Characterization of devices

The light intensity was calibrated to be 100 mW·cm−2 by an SRC-2020 reference cell (traceable to NREL). The current density-voltage (J–V) curves of the perovskite solar cells were measured using a Keysight B2901A Source-Meter, with the scanning voltage from 1.22 V to -0.2 V in 20 mV step and delay time of 1 ms. The device area is confined to 0.09 cm2 by a mask. The measurements were performed in a glove box filled with nitrogen (oxygen and water contents are smaller than 10 ppm). Enli-tech class AAA Solar Simulator (model, SS-X180R-3A) with a 450 W xenon lamp was used as the light source. The EQE responses were measured by Solar Cell Spectral Response Measurement System QE-R3-011 (Enli Technology Co., Ltd., Taiwan). The light intensity at each wavelength was calibrated with a standard single-crystal Si photovoltaic cell. For the stability tests, all the devices were encapsulated, and measurement was performed under a LED that was adjusted to AM 1.5G (100 mW·cm−2) in ambient atmosphere.

Molecular simulations

Density functional theory (DFT) calculations were performed using the Vienna Ab initio Simulation Package (VASP). The projector augmented-wave (PAW) method was employed, and the Perdew–Burke–Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) was used to describe the exchange-correlation interactions. A Vacuum layer of 30 Å was used in the Z-direction to separate the slabs. The plane-wave cutoff energy was set to 600 eV. Structural relaxation was carried out using the conjugate gradient algorithm with an energy convergence criterion of 1 × 10-4 eV and a force convergence threshold of 0.05 eV/Å. The Brillouin zone was sampled using a Γ-centered 1 × 1 × 1 k-point mesh due to the large size of the supercell. Subsequently, total energies were calculated on the optimized geometries using a denser Γ-centered 3 × 3 × 1 mesh. VESTA was used for visualization.

The Molecular Dynamics simulation was performed using the Materials Studio (MS) 2020 software package (BIOVIA, USA). A model containing NiO, molecule MeOF-4PACz and molecule MeOF-4SHCz were built through Amorphous Cell (AC) modules with Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies II (COMPASS II) the force field. The Forcite module was used to optimize the molecular structure, during the geometric optimization process, the convergence threshold for maximum energy change, maximum force convergence threshold, and maximum displacement convergence threshold are 0.001 kcal/mol, 0.5 kcal/mol/Å, and 0.015 Å, respectively. To obtain a more optimized structure, a 100 ps dynamics simulation was conducted under the NVT ensemble with a step size of 1 fs. In the progress of MD, Electrostatic is calculated using Ewald, while van der Waals is calculated using atom based. The precise Nose-Hoover temperature control mode and Berendsen pressure control mode are used in the dynamic process.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors report a new SAM (MeOF-4SHCz), which is combined with MeOF-4PAC to modify NiO in an effort to enhance device efficiency and interface stability. Although the achieved efficiency is not particularly remarkable, the underlying working mechanism is quite interesting. However, the manuscript lacks in-depth discussion and raises several concerns. If the authors can address these issues, the work could provide valuable insights for the field. The specific points are as follows:\n1.Why is there only a single JV scan presented in the certification report (as shown in SI)? The efficiency value obtained from a single scan does not fully represent the final certified efficiency of the device, which is not sufficiently rigorous. It would be helpful if the authors could provide an explanation for this. Additionally, it is recommended to include the stabilized PCE.\n2.The authors mention that MeOF-4SHCz can reduce some of the high-valence states (Ni³⁺) in NiO. Given that the valence state of some Ni changes, what impact does this have on the final electrical properties of NiO, such as mobility and conductivity?\n3.Why do multiple valence states in nickel oxide affect the uniform distribution of the SAM on the surface? Alternatively, is this uneven distribution determined by the properties and quality of the SAM itself? It is suggested that the authors provide an explanation for this issue.\n4.It is widely reported that there are two main binding modes for phosphonic acid (anchoring group) on ITO, namely bidentate and tridentate modes [Nat. Energy 9, 308-315 (2024)]. Similarly, it is recommended that this work consider these possibilities and provide O 1s XPS data to confirm the binding modes. If these binding modes are indeed present, the DFT and molecular dynamics simulation results discussed in the manuscript (such as reaction energy and equilibrated molecular distribution) should be re-evaluated to ensure the reliability and rigor of the work.\n5.The authors stated that the redox-improved mixed SAM can improve the stability of the underlying NiO-based interface. However, the MPPT stability data presented in Figure 4g is somewhat limited. It is recommended that the authors provide NiO-based samples as a control, along with details of the testing conditions such as temperature, humidity, and encapsulation. Additionally, relevant thermal stability data should be included.\nMinor questions:\n1.When discussing PL and TRPL results, it is important to specify the direction of incidence, as charge transfer and film quality characterization can vary significantly depending on this factor.\n2.In the TA measurements, to which phase does the 540 nm signal correspond, and why is 780 nm, which corresponds to perovskite bleaching, not used? Additionally, it is recommended to indicate the direction of excitation light incidence in the figure captions.", "reviewer_2": "This study presents a redox-driven strategy for improving the quality and uniformity of self-assembled monolayers (SAM) on NiOx for inverted perovskite solar cells, realizing improved device efficiency and operational stability. Overall, the idea in utilizing MeOF-4SHCz to target Ni³⁺‐rich regions is interesting and the reported device performance are competitive. However, there are still some critical aspects require further in-depth studies. In particular, the underlying mechanisms by which the NiOx valence states affect SAM growth and the quantitative correlation between minor reduction in Ni³⁺ content and device stability need to be addressed. With thorough clarification of these points, the manuscript would be suitable for publication in Nature Communications.\nDetailed comments:\n1. The authors are encouraged to elaborate on the underlying mechanisms by which the different valence states of NiOx affect the formation and quality of the SAM. Also clearly clarify why the incorporation of MeOF-4SHCz significantly improves the overall coverage of the SAM on the NiOx substrate.\n2. Although XPS analysis shows that the Ni³⁺ content decreases from 78.2% to 75.3% (an absolute reduction of ~3%), this minor change appears to lead to an obvious enhancement in the device stability of the ROI-SAM based cells. The authors should provide a more detailed discussion on how such a subtle reduction in Ni³⁺ can contribute to such long-term stability improvements, or alternatively, provide additional supporting data to support this claim.\n3. Following comment #2, it is noted that MeOF-4SHCz reduces approximately 3% of Ni³⁺ to Ni²⁺, corresponding to only about 2% of the -SH groups being oxidized to –SO₃H. However, TOF-SIMS results indicate that the coverage of MeOF-4SACz over the examined area (200 x 200 μm) is much higher than 2%.\n4. Typically, MHP samples prepared on ITO/HTL or HSL, the carrier lifetime tends to be below 500 ns due to fast charge extraction at the interface. However, the carrier lifetime exceeds 1.5 μs for the NiOx/ROI-SAM based sample, which also contradict the authors’ claim of “fast decay time of TRPL measurement” in page 13.\n5. The authors claim that the decomposition of perovskite due to the oxidation of Ni³⁺ can be mitigated by this strategy. It is recommended that more direct experimental evidence be provided to support this conclusion. For example, detailed chemical or structural analysis demonstrating reduced degradation at the buried surface of perovskite layer would be valuable.\n6. SAM coverage is determined by both the terminal groups, linkers, anchoring groups, and the surface properties of the substrate. Besides, as Reference 11 does not explicitly address SAM coverage, further elaboration or additional references should be included in Introduction section.\n7. Please indicate which functional group corresponds to the vibration band observed at 1050 cm⁻¹ in Supplementary Fig. 9.\n8. The authors state that the control device retains 81% of its initial PCE. Kindly provide a detailed explanation of how this value was derived.\n9. In Fig. 3c, the VTFL for the ROI-SAM sample is reported as 0.19 V, which is higher than that for the pristine-SAM sample (0.17 V). The authors should explain this observation and discuss whether it might indicate any measurement or calculation discrepancies.\n10. The scale bar should be included in the PL mapping images (Figs. 3h–3i) for better clarity. Furthermore, please indicate the initial PCE values of both the control and target devices for the MPPT shown in Fig. 4g.\n11. Please specify the meaning of the unit “DA” used on the y-axis in Fig. 3g.", "reviewer_3": "In this manuscript, the authors improves the efficiency and stability of inverted perovskite solar cells by designing a self-assembled monolayer (MeOF-4SHCz) and mixing it with conventional MeOF-4PACz at a certain ratio as the SAM layer. The mechanism mainly involves the thiol groups in MeOF-4SHCz selectively reducing Ni³⁺ ions on the NiOₓ surface to form S–O–Ni bonds, while MeOF-4PACz acts on Ni²⁺ regions through P–O–Ni bonds, synergistically enhancing SAM uniformity and anchoring strength, while also reducing the impact of Ni³⁺ on halides in perovskite precursors. This method achieved a conversion efficiency of 26.5% (certified PCE of 26.2%) and maintained 90% of the initial efficiency after 1000 hours of MPPT. These results are promising and the work appears suitable for publication in Nature Communications after the following concerns are adequately addressed:\n1.The paper states that 20% MeOF-4SHCz was incorporated into ROI-SAM, which effectively reduces Ni³⁺, but XPS shows only a 2.9% decrease in Ni³⁺ content (from 78.2% to 75.3%). This raises questions: 1) Why is the reacted Ni³⁺ fraction so limited? Does MeOF-4SHCz fail to anchor most Ni³⁺ sites? Is there an optimal Ni³⁺ concentration? Has the MeOF-4SHCz dosage truly reached its optimization point?\n2.Please provide the original files for the reaction energy calculations.\n3.Some parts of the paper are unclear. For example, the description of Fig. 1e is incorrect; P 2p binding energies should be separately listed for both pristine-SAM and ROI-SAM samples in Table 5; In Fig.3g, the legend contradicts other panels in the same figure set and needs correction.", "reviewer_4": "This manuscript presents a well-executed study on improving the uniformity and effectiveness of self-assembled monolayer (SAM) hole transport layers in inverted perovskite solar cells (pero-SCs) by introducing a redox-interactive SAM molecule, MeOF-4SHCz, alongside the conventional MeOF-4PACz. The redox-driven interaction with Ni³⁺ on the NiOx surface results in improved SAM coverage, better interfacial contact, and enhanced device performance and stability. The authors support their conclusions with thorough materials characterization, device performance metrics, and mechanistic insights, including DFT calculations, XPS, TOF-SIMS, PL, TRPL, and transient absorption spectroscopy. The work is innovative and significant, and the manuscript is generally well-written and clearly organized. The results will be of strong interest to the photovoltaics and materials chemistry communities. This article meets the standard required for publication in Nature Communications. I recommend acceptance after minor revisions as outlined below.\n1. Quantify Improvement in SAM Uniformity:\nThe KPFM and c-AFM results in Fig. 2a–d clearly show improved homogeneity with ROI-SAM. However, the standard deviation values of the contact potential and current could be stated numerically in the figure caption or main text to better quantify this improvement.\n2. Improve Figure Quality and Captions:\nSeveral figures (especially Fig. 1b, 1c, and 2g) contain dense information. Enlarging some of the insects or separating subplots might help. Additionally, figure captions should state what each component shows more explicitly, especially for a multidisciplinary audience.\n3. Nomenclature Consistency:\nEnsure consistent abbreviation of ROI-SAM and pristine-SAM throughout the main text and figures. In a few instances, \"HTL with MeOF-4PACz:MeOF-4SHCz\" is used interchangeably with ROI-SAM—clarify this in the first usage.\n4. Literature Context (Introduction):\nWhile the background is comprehensive, a short paragraph contrasting this redox-improved SAM approach with other recent strategies targeting NiOx defects (e.g., hydrogen peroxide treatment, doping) would enhance the novelty of this paper.\n5. Minor Language Corrections:\nA careful proofreading is advised to correct small grammatical issues such as:\n\"a effective reduction agent\" → \"an effective reduction agent\".\n\"it hardly interact\" → \"it hardly interacts\".\n\"may cause issues to the growth\" → \"may hinder the growth\"."}, "author_response": "Response to Reviewer #1\nThe authors report a new SAM (MeOF-4SHCz), which is combined with MeOF-4PAC to modify NiO\nin an effort to enhance device efficiency and interface stability. Although the achieved efficiency is not\nparticularly remarkable, the underlying working mechanism is quite interesting. However, the\nmanuscript lacks in-depth discussion and raises several concerns. If the authors can address these\nissues, the work could provide valuable insights for the field. The specific points are as follows:\n1. Why is there only a single J-V scan presented in the certification report (as shown in SI)? The\nefficiency value obtained from a single scan does not fully represent the final certified efficiency of the\ndevice, which is not sufficiently rigorous. It would be helpful if the authors could provide an\nexplanation for this. Additionally, it is recommended to include the stabilized PCE.\nResponse: We fabricated devices and certificated again. The certification report was issued by the\nNational Institute of Metrology of China, which presents the forward and reverse J-V scans and the\nstabilized PCE. The mask changes from 0.08978 cm-2 to 0.10214 cm-2. The report has been added to\nthe Supplementary Fig. 23 (shown in Fig. R1).\nR1\nFig. R1 Photovoltaic performance of the pero-SC based on the ROI-SAM, certified by National\nInstitute of Metrology of China.\nR2\n2.The authors mention that MeOF-4SHCz can reduce some of the high-valence states (Ni3⁺) in NiO.\nGiven that the valence state of some Ni changes, what impact does this have on the final electrical\nproperties of NiO, such as mobility and conductivity?\nResponse: Thank the reviewer for raising this important point. Investigating the modification to\nelectronic properties of the entire HTL layer is important. We analyzed the hole mobility and the\nconductivity of the Pristine-SAM sample and the ROI-SAM sample.\n1)The hole mobility of the device could be estimated from space charge limited current method\nshown in Fig. 3c (updated as the other reviewer suggested), and for convenience, the corresponding\ngraphs are also provided in Fig. R2. based on the Mott–Gurney law {Trans. Faraday Soc. 1940, 35,\n1175.}, {Proc. R. Soc. Lond. A 1943, 182, 149.}:\n9𝜀 𝜀 𝜇𝑉2\n0 𝑟\n𝐽 =\n8𝐿3\nwhich can be rearranged as\n8𝐽𝐿3\n𝜇 =\n9𝜀 𝜀 𝑉2\n0 𝑟\nwhere V is the applied voltage, J is the current density. L is the thickness of the perovskite layer, and\nɛ and ɛ are the vacuum and relative permittivity, respectively.\n0 r\nFig. R2 Dark Current density-voltage curves using the SCLC model for hole-only devices:\nITO/NiO /SAM/Perovskite/Spiro-OMeTAD/Ag, with Pristine-SAM (a) or ROI-SAM (b).\nx\nR3\nThe relative permittivity ɛr is taken as 46.9 as reported in the literature {Adv. Mater. 2016, 28:\n2253-2258}. L is determined to be 740 nm by from the cross-sectional SEM image shown in Fig. 4a.\nThe devices were controlled by a mask with an area of 0.010214 cm2 during the measurement. Data\nfrom SCLC region was selected to calculate the hole mobility. The hole mobility for the ROI-SAM\nbased device was calculated to be 2.95×10-3 cm2·V-1·s-1, which is slightly higher than that in the\nPristine-SAM device (1.17×10-3 cm2·V-1·s-1).\nAs the devices based on the NiO /SAM combined HTL, we attribute this enhancement to the\nx\nimproved quality of the SAM layer, which facilitates more efficient hole extraction across the interface.\nWe now added the hole mobility to the revised manuscript in the caption of the Fig. 3c: “Dark Current\ndensity-voltage curves using the SCLC model for hole-only devices:\nITO/NiO /SAM/Perovskite/Spiro-OMeTAD/Ag, with Pristine-SAM or ROI-SAM. The hole mobility\nx\nin the ROI-SAM based device is 2.95×10-3 cm2·V-1·s-1 while the Pristine-SAM device is 1.17×10-3\ncm2·V-1·s-1.” on p.12.\n2)The conductivity was measured using two different technologies. The conductive atomic force\nmicroscope measurements (Figs. 2c and 2d) show that the current of the two samples. The average\ncurrent is 0.181 nA for Pristine-SAM and 0.177 nA for ROI-SAM. The current for two samples are\nnot significantly changed. For clarity, now we have added the average current of two samples into the\ncaption of Fig. 2: “c-AFM current maps and corresponding current histograms of Pristine-SAM (c)\nand ROI-SAM (d) on NiO substrates. The average current is 0.181 nA for Pristine-SAM and 0.177\nx\nnA for ROI-SAM. The RMS of two samples are 0.197 and 0.134, respectively.” on p. 9. Additionally,\nwe also performed conductivity measurements on NiOₓ films before and after SAM modification with\na vertical device structure of ITO/NiO /SAM/Ag (Fig. R3).\nx\nR4\nFig. R3 The conductance of the ROI-SAM and Pristine-SAM sample-based devices .\nThe slope of the Pristine-SAM is 0.451 S and of the ROI-SAM is 0.439 S. These indicate that the\nconductivity of the bulk NiOₓ layer remains largely unchanged due to surface modification, while the\nhole mobility is higher likely attributing to the better quality of the SAM layer. These data have now\nbeen included and discussed in the revised manuscript: “Additionally, we performed conductivity\nmeasurements on both ROI-SAM and Pristine-SAM samples (Supplementary Fig. 14). The\nconductance showed a negligible change from 0.451 S to 0.439 S, indicating that the surface reaction\nhad little impact on the bulk conductivity.” on p. 9.\nR5\n3. Why do multiple valence states in nickel oxide affect the uniform distribution of the SAM on the\nsurface? Alternatively, is this uneven distribution determined by the properties and quality of the SAM\nitself?\nResponse: Thank the reviewer for the insightful comment. The distribution of the SAM layer is\ninfluenced by both the properties of the substrate {Langmuir 2019, 35, 15834–15848}, {Science 2023,\n382,1399-1404} and the intrinsic characteristics of the SAM molecules {Nature 2024, 632, 301–306.}.\nSpecifically, we thought that the blend of the Ni3+ and Ni2+ species introduces surface heterogeneity\nsuch as coordination environment (Fig. R4) and redox activity (Fig. 1e), which may disrupt the\nuniform adsorption of SAM molecules. However, probing the spatial distribution of Ni valence states\nremains challenging. It is challenging to directly correlate Ni valence state distribution with SAM\nuniformity. The measurements conducted in Figs. 2a-d show the combined effects of the substrate and\nthe SAM. After the introduction of the MeOF-4SHCz, the SAM layer becomes more uniform. The\nstandard deviation of KPFM measurements is 22.6 mV for Pristine-SAM and 14.5 mV for ROI-SAM\nsample. While the c-AFM also shows a decreased RMS value, from 0.197 to 0.134. We clarified the\nhomogeneity measurements in the revised manuscript: “a, b, KPFM surface potential maps and\ncorresponding potential histograms of the Pristine-SAM (a) and ROI-SAM (b) on NiOx substrates.\nScale bar: 1 μm. The mean surface potential is 339.2 mV for Pristine-SAM and 274.2 mV for ROI-\nSAM. The corresponding standard deviations are 22.6 mV and 14.5 mV, respectively. c, d, c-AFM\ncurrent maps and corresponding current histograms of Pristine-SAM (c) and ROI-SAM (d) on NiOx\nsubstrates. The average current is 0.181 nA for Pristine-SAM and 0.177 nA for ROI-SAM. The RMS\nvalues of two samples are 0.197 and 0.134, respectively.” on p. 9.\nR6\n4.It is widely reported that there are two main binding modes for phosphonic acid (anchoring group)\non ITO, namely bidentate and tridentate modes [Nat. Energy 9, 308–315 (2024)]. Similarly, it is\nrecommended that this work consider these possibilities and provide O 1s XPS data to confirm the\nbinding modes. If these binding modes are indeed present, the DFT and molecular dynamics\nsimulation results discussed in the manuscript (such as reaction energy and equilibrated molecular\ndistribution) should be re-evaluated to ensure the reliability and rigor of the work.\nResponse: We conducted XPS measurements and analyzed the O 1s XPS data of NiO and\nx\nNiO /MeOF-4PACz sample, respectively (Fig. R4 a and b). To our surprise, there is a peak at around\nx\n532.8 eV in the bare NiO sample, which may be ascribed to O species in a double-bonded\nx\nconfiguration. We then checked the C 1s of the NiO sample and found the existence of the C=O group\nx\n(Fig. R4 c). As the high sensitivity of XPS measurements, to eliminate the possibility of the\ncontamination, we performed the Fourier-transformed infrared spectroscopy with the NiO powder\nx\n(Fig. R4 d). A peak appeared at around 1400 nm-1, confirming the carbonate group in NiO .\nWe\nx\nattribute it to the dispersants of the nanoparticles or the residues of nickel ligand. After the bonding\nwith MeOF-4PACz, the intensity of the peak at 532.8 eV increases, which may be attributed to the\ndeposition of the P=O group. Then we analyzed the results. In the DFT calculations, geometry\noptimization was first performed. Then the energy of the isolated surface, isolated molecule and the\nabsorbed system was calculated without predefining the bond mode of the final state. The calculation\nresults show that there is tridentate bond mode at NiO surface (Fig. R4 e) because it exhibits the\nlowest energy. However, the atom distances in Ni O are much larger, hindering the interaction\n2 3\nbetween P=O and Ni atoms (Fig. R4 f and j), so calculation shows a bidentate mode. The discussion\nis added to the revised manuscript: “The results show that there is a tridentate bond mode at NiO\nsurface because of the thermodynamically favorable configuration with the lowest total energy, while\na bidentate mode at Ni O surface due to the larger lattice spacing, and this larger lattice spacing limits\n2 3\nthe interaction between the anchor group and the substrate (Supplementary Fig. 10).” on p. 5, and the\nsource data is uploaded with the filename of Supplementary Data.\nR7\nFig. R4 a,b, O 1s XPS spectrum and fitted peaks of the NiO and NiO /MeOF-4SHCz samples,\nx x\nrespectively. The fitted components include O2- (green), OH 2p (brown) and C=O (blue). c, C 1s\n1/2\nXPS spectrum and fitted peaks of the NiO sample. The fitted components include C-H (grey), C-O\nx\n(grey), C=O (brown) and O=C-O (blue). d, Fourier transform infrared spectroscopy of the NiO\nx\nsample. e, The bond mode of the NiO-MeOF-4PACz at final state. f, The crystal structure of NiO and\nNi O . g, The bond mode of the Ni O -MeOF-4PACz at final state.\n2 3 2 3\nR8\n5.The authors stated that the redox-improved mixed SAM can improve the stability of the underlying\nNiO-based interface. However, the MPPT stability data presented in Fig. 4g is somewhat limited.\nIt is recommended that the authors provide NiO-based samples as a control, along with details of the\ntesting conditions such as temperature, humidity, and encapsulation. Additionally, relevant thermal\nstability data should be included.\nResponse: We conducted measurements of NiO-based samples and now have added MPPT data for\ncontrol devices (Fig. R5) in the revised manuscript with the discussion: “The ROI-SAM based devices\nretained 90% of their initial efficiency after about 1000 hours. In contrast, the Pristine-SAM based\ncontrol devices maintained 81% of their initial PCE under the same conditions, while the unmodified\nNiOx-based devices exhibited the T around 600 hours, which showed the enhanced stability of the\nmeasurements, we now explicitly describe the conditions in both updated graph and the main text:\n“Besides the increased efficiency, we evaluated the long-term operational stability of the encapsulated\ndevice by tracking the maximum power point (MPP) under 1 sun illumination at 25 °C and 30%\nrelative humidity (Fig. 4g).” on p. 14 and in the captions of the Fig. 4g: “MPP tracking of the\nencapsulated pero-SCs using Pristine-SAM or ROI-SAM as HTLs (LED lamp, 100 mW cm−2, 25℃,\n30% RH).” on p.16.\nFig. R5 MPP tracking of the encapsulated pero-SCs using Pristine-SAM or ROI-SAM as HTLs (LED\nlamp, 100 mW cm−2, 25℃, 30% RH).\nR9\nTo further support the improved stability, we conducted thermal aging tests at 85 °C in N\n2\natmosphere for 600 h (Fig. R6). The ROI-SAM devices showed improved thermal tolerance (T ＞\n90\n576 h) compared to the control (T ~ 72 h) and Pristine-SAM (T ~ 312 h) devices.\n90 90\nThese new results\nand testing conditions have been included and referenced in the revised manuscript: “We then conduct\nthermal test at 85 ℃ under N atmosphere. The ROI-SAM devices showed improved thermal\n2\ntolerance (T ＞576 h) compared to the control (T ~ 72 h) and Pristine-SAM (T ~ 312 h) devices\n90 90 90\n(Supplementary Figure 25).” on p.15.\nFig. R6 Thermal stability of encapsulated pero-SCs with NiO , Pristine-SAM, and ROI-SAM HTLs\nx\nunder 85 ℃ in N glove box for 600 h.\nMinor Comments\n1.When discussing PL and TRPL results, it is important to specify the direction of incidence, as charge\ntransfer and film quality characterization can vary significantly depending on this factor.\nResponse: We have now specified that PL and TRPL measurements were performed with excitation\nlight from the ITO side. This detail has been added to the captions of Fig. 3: “a,b, PL and TRPL spectra\nof perovskite films deposited on NiO /Pristine-SAM and NiO /ROI-SAM substrates, respectively.\nx x\nThe excitation light was incident from the ITO side.” on p. 12.\n2. In the TA measurements, to which phase does the 540 nm signal correspond, and why is 780 nm,\nwhich corresponds to perovskite bleaching, not used? Additionally, it is recommended to indicate the\ndirection of excitation light incidence in the figure captions.\nResponse: The broad excited-state absorption with a peak at 540 nm mainly attributes to the free\ncarriers in the perovskite layer upon photoexcitation{J. Phys. Chem. Lett. 2021, 12, 6907}, {Phys.\nRev. Lett. 2015, 114, 116601}. Its dynamics reflect the carrier extraction to the adjacent layers as well\nas recombination of the carriers. The ground state bleaching signal at ~780 nm, the 540 nm excited-\nstate absorption offers a more sensitive probe of hole transfer dynamics in our system. The negative\nsignal at 780 nm is the ground state bleaching and has overlapped with the stimulated emission of the\nperovskite, making it less suitable for distinguishing the hole extraction processes under investigation.\nThis detail has been added to the relevant figure captions: “g, Kinetic traces probing at 540 nm for the\nESA of carriers in Pristine-SAM and ROI-SAM based perovskite films. The pump light was incident\nfrom the ITO side.” on p.12.\nR11\nResponse to Reviewer #2\nThis study presents a redox-driven strategy for improving the quality and uniformity of self-assembled\nmonolayers (SAM) on NiO for inverted perovskite solar cells, realizing improved device efficiency\nx\nand operational stability. Overall, the idea in utilizing MeOF-4SHCz to target Ni³⁺‐rich regions is\ninteresting and the reported device performance are competitive. However, there are still some critical\naspects require further in-depth studies. In particular, the underlying mechanisms by which the NiO\nx\nvalence states affect SAM growth and the quantitative correlation between minor reduction in Ni³⁺\ncontent and device stability need to be addressed. With thorough clarification of these points, the\nmanuscript would be suitable for publication in Nature Communications.\n1. The authors are encouraged to elaborate on the underlying mechanisms by which the different\nvalence states of NiO affect the formation and quality of the SAM. Also clearly clarify why the\nx\nincorporation of MeOF-4SHCz significantly improves the overall coverage of the SAM on the NiO\nx\nsubstrate.\nResponse: Thank the reviewer for the reasonable comment. We performed the calculation of the\nadsorption process about the MeOF-4PACz and MeOF-4SHCz with NiO and Ni O respectively to\n2 3\nclarify the mechanism of the SAM with different valence states of Ni species. And the adsorbed energy\nshows the MeOF-4SHCz selectively interacts with Ni3+ species through a redox reaction, while\nMeOF-4PACz preferentially coordinates with Ni2+ species. Additionally, the calculation results show\nthat there is a tridentate bond mode at NiO surface because its favorable atomic distance and exhibits\nthe lowest energy (Fig. R7 a). However, the atom distances in Ni O are much larger, hindering the\n2 3\ninteraction between the anchoring group of SAMs (P=O group) and Ni atoms so calculation shows a\nbidentate mode (Fig. R7 b). The crystal structure of NiO and Ni O are shown in the Fig. R7 c and d.\n2 3\nThe discussion is added to the revised manuscript: “The results show that there is a tridentate bond\nmode at NiO surface because of the thermodynamically favorable configuration with the lowest total\nenergy, while a bidentate mode at Ni O surface due to the larger lattice spacing, and this larger lattice\n2 3\nR12\nspacing limits the interaction between the anchor group and the substrate (Supplementary Fig. 10).”\non p. 5. And the source data is uploaded with the filename of Supplementary Data.\nFig. R7 a,b, The bond mode of the NiO-MeOF-4PACz and the Ni O -MeOF-4PACz at final state,\n2 3\nrespectively. c,d, respectively.\nThe molecular dynamics simulation (Fig. 2e) shows the incomplete SAM coverage during the\nphosphonic acid adsorption {Nature 2023, 624, 289–294.}. And the increase in SAM coverage can be\nexplained by the SAM formation process. During the self-assemble process after the introduction of\nthe MeOF-4SHCz, the −SH group of which could interact with the −PO(OH) group and function as\n2\na dispersant, reducing the clusters formed in the self-assemble process. When annealing, the −SH\ngroup is oxidized to −SO H group and bonds to the substrate, which makes the dispersant itself also\n3\nfunction as an HTL, improving the homogeneity and the coverage of SAM on NiO (Fig. 2f). To\nx\nclarify why the incorporation of MeOF-4SHCz significantly improves the overall coverage of the\nSAM on the NiO substrate. We added the annealing process to the main text to explain this\nx\nmechanism: “When annealing, MeOF-4SHCz undergoes oxidation to form –SO H groups, which\n3\nanchor onto the NiO substrate and function as part of the HTL, improving the overall quality of the\nx\nSAM layer.” on p.11.\nR13\n2. Although XPS analysis shows that the Ni3+ content decreases from 78.2% to 75.3% (an absolute\nreduction of ~3%), this minor change appears to lead to an obvious enhancement in the device\nstability of the ROI-SAM based cells. The authors should provide a more detailed discussion on how\nsuch a subtle reduction in Ni3+ can contribute to such long-term stability improvements, or\nalternatively, provide additional supporting data to support this claim.\nResponse: In the XPS measurement, the signal of elements In and Sn at the bottom ITO layer was\ndetected (Fig. R 8a). So this proportion may detect reflects the change of bulk NiO , and the valence\nx\nchanges mainly on the surface. To further clarify the oxidation of Ni3+, we mixed the powder of Ni O\n2 3\n(insoluble in water) and MeOF-4SHCz and performed XPS measurement. The powder XPS shows\ndifferent properties of film (Fig. R 8b). However, we can still conduct peak fittings to explore its\nproperty. The peak fitted curves show there is ~47% of MeOF-4SHCz molecule oxidized to the −SO H\n3\nbased MeOF-4SACz, indicating the high oxidation properties of the Ni3+. The thiol group of MeOF-\n4SHCz could efficiently reduce the proportion of Ni3+ at the surface. Meanwhile, it then binds to the\nNiOx substrate and functions as HTL, enhancing the overall quality of the SAM layer, and this\ndiscussion has been added to the main text: “Considering that the reaction mainly occurs at the surface,\nto further investigate the oxidation of Ni3+ species, Ni O powder was mixed with the MeOF-4SHCz\n2 3\npowder, resulting in the oxidation of approximately 47% of MeOF-4SHCz to MeOF-4SACz, which\nconfirms the surface oxidative role of the Ni3+ (Supplementary Fig. 12). And this process can be\nillustrated as Fig. 1g.” on p. 7.\nR14\nFig. R8 a, The full spectrum of MeOF-4SHCz deposited on NiO substrate. b, S 2p XPS spectra and\nx\nfitted peaks of the Ni O /MeOF-4SHCz powder sample after thermal annealing. The fitted\n2 3\ncomponents include S2- 2p (green), S2- 2p (brown), and SO 2- (blue).\n3/2 1/2 3\nAdditionally, to further support the stability improvement, the thermal stability measurements\nwere conducted at 85℃ under N atmosphere. The ROI-SAM devices showed improved thermal\n2\ntolerance (T ＞576 h) compared to the control (T ~ 72 h) and Pristine-SAM (T ~ 312 h) devices\n90 90 90\n(Fig. R9, confirming the improvement of this strategy. This discussion has been added to the revised\nmanuscript: “We then conduct thermal test at 85 ℃ under N atmosphere. The ROI-SAM devices\n2\nshowed improved thermal tolerance (T ＞576 h) compared to the control (T ~ 72 h) and Pristine-\n90 90\nSAM (T ~ 312 h) devices (Supplementary Figure 22).” on p. 15.\nx\nunder 85 ℃ in N glove box for 600 h.\n3. MeOF-4SHCz reduces approximately 3% of Ni³⁺ to Ni²⁺, corresponding to only about 2% of the –\nSH groups being oxidized to –SO H. However, TOF-SIMS results indicate that the coverage of MeOF-\n3\n4SHCz over the examined area (200 × 200 μm) is much higher than 2%.\nResponse: Thank the reviewer for very insightful observation. As partly addressed in our response to\nComment 2, we talked about the content of Ni species. This proportion detected reflects the change\nof bulk NiO , and the valence changes mainly on the surface, so we conducted measurements with\nx\nNi3+ and MeOF-4SHCz. From the perspective of the charge transfer, if around 3% reduction of the\nNi3+ species to Ni2+ species, it indeed indicates a smaller amount of MeOF-4SHCz undergoing\noxidation. However, the absolute amount of NiO and MeOF-4SHCz are different. The concentration\nx\nof NiO is 15 mg·mL-1 while the MeOF-4SHCz is 0.25 mg·mL-1. Therefore, although the relative\nx\nchange of Ni is around 3%, this does not directly correspond to the same percentage change of MeOF-\n4SHCz. Therefore, we thought that the results of XPS and TOF-SIMS measurements are not\ncontradictory.\nR16\n4. Carrier lifetime exceeds 1.5 μs for the NiO /ROI-SAM based sample, which also contradicts the\nx\nauthors’ claim of “fast decay time of TRPL measurement” in page 13.\nResponse: We appreciate the reviewer’s careful reading. The reason for this contradicts is the\nincomplete modification during preparing the manuscript. In most cases, articles that explain the\nTRPL data are fitted by the biexponential model:\n𝐼(𝑡) = 𝐴 ⋅𝑒−𝑡/𝜏1 +𝐴 ⋅𝑒−𝑡/𝜏2\n1 2\nMany researchers called the shorter τ the fast decay time, which is associated with the carrier\n1\nextraction. While the longer one τ is called the slow decay time, which reflects the recombination.\nexplain that a shorter τ is coordinated with the effective carrier extraction. Then we want to use the\n1\ncarrier extraction to link the TRPL and TPC measurements. The TRPL measurement reflects carrier\nextraction focusing on the optical properties while the TPC focuses on the electrical properties.\nHowever, we read an article talking about the mathematics meaning of the TRPL fitting { Adv. Energy\nMater. 2025, 15, 2403279}. And we deleted the statements about the fast/slow decay time and kept\nthe mean average of the τ to present the recombination of the perovskite layer (Supplementary Table\navg\n7, last list).\nThe calculation of the τ :\navg\n𝐴 𝜏2 +𝐴 𝜏2\n1 1 2 2\n𝜏 =\n𝑎𝑣𝑔 𝐴 𝜏 +𝐴 𝜏\n1 1 2 2\nThe ROI-SAM sample has a longer decay time, corresponding to less non-radiative recombination.\nHowever, in the following text, we forget to delete this sentence, which still contains fast decay time,\nso this statement is ambiguous. We now delete this sentence and thank the reviewer for pointing out.\nR17\n5.The authors claim that the decomposition of perovskite due to the oxidation of Ni3+ can be mitigated\nby this strategy.\nResponse: Following the reviewer’s suggestion, we performed additional analyses to directly\ninvestigate the interfacial degradation. Specifically, we deposited FAI onto the NiO layer and the\nx\nNiO /MeOF-4SHCz layer, and annealed to compare chemical changes using XPS measurements (Fig.\nx\nR10 a). After annealing, a shoulder peak appeared at 398.5 eV in N 1s of NiO /FAI sample,\nx\ncorresponding to the species of sp3-N. As the FA+ only has sp2-N species, the formation of the natural\nFA molecule can be confirmed. However, the NiO /MeOF-4SHCz sample shows a single sp2-N,\nx\nindicating no FA molecule generated.\nFig. R10 a, N 1s XPS spectra and fitted peaks of the NiO (top), the annealed NiO /FAI (middle), and\nx x\nthe NiO /MeOF-4SHCz/FAI (bottom) samples. The fitted components include FA+ (brown),\nFA\nx\n(green), and chemisorbed N (blue). b, UV-vis absorption spectra of toluene solution extracted from\nthe NiO /FAI after soaking and a reference I solution.\nx 2\nR18\nTo figure out the chemical transformation, we immersed the NiO /FAI sample into anhydrous\nx\ntoluene, and performed UV measurements to analysis the component of the solution (Fig. R10 b).\nThe UV-vis absorption spectrum shows a peak at ~500 nm, characteristic of molecular iodine,\nconfirming the oxidation of I- during the process. The reaction can be summarized as\nNiO𝑥\n2FAI → 2FA + I\nstability of the device. And this decomposition of perovskite due to the oxidation of Ni3+ can be\nmitigated by redox-improved strategy. These results are added in the revised manuscript:\n“Measurements were conducted to characterize the oxidation influence of HTL on the perovskite layer\n(Supplementary Fig. 13).” on p. 7. And the discussion is added in the caption of Supplementary Fig.\n13.\n6. SAM coverage is determined by both the terminal groups, linkers, anchoring groups, and the\nsurface properties of the substrate. Besides, as Reference 11 does not explicitly address SAM coverage,\nfurther elaboration or additional references should be included in Introduction section.\nResponse: Our statement the terminal group usually determines the energy level and surface\nwettability of the HTL, while the anchoring group influences the resulting SAM coverage on substrate,\nis not rigorous enough. The SAM coverage is determined by both the molecule properties and the\nsurface properties of the substrate. We have now revised the statement that “the anchoring group\nshows great influence on the resulting SAM coverage on substrate” in the introduction section on p.\n2 as we want to introduce the anchoring group. Additionally, to explicitly address the SAM coverage,\nfour more relevant literatures were cited on the role of SAM coverage to the influence of SAM\ncoverage. {Langmuir 2006, 22, 6249–6255.},{ Langmuir 2006 22, 11113–11125.},{ Langmuir, 2002,\n18, 5205–5212.} ,{ J. Am. Chem. Soc. 2006, 128, 15874–15881.}\nR19\n7.Please indicate which functional group corresponds to the vibration band observed at 1050 cm⁻¹ in\nSupplementary Fig. 9.\nResponse: The vibration band observed at 1050 cm-1 is the stretch of the S=O bond, and the functional\ngroup is −SO H. Comparing the Fourier-transform Infrared spectroscopy of three compounds (MeOF-\n3\n4PACz, MeOF-4SACz and MeOF-4SHCz), the increase of the intensity at 1050 cm-1 is attributed to\nthe formation of the S=O bond (Fig. R11). This assignment has been clarified in the caption of\nSupplementary Fig. 9: “a,b, PiFM images of NiO /Pristine-SAM (a) and NiO /ROI-SAM (b) at 1050\nx x\ncm-1 on ITO substrates, where the S=O stretches. The intensity at 1050 cm-1 increases after\nintroduction MeOF-4SHCz to SAM layer, which is attributed to the formation of the S=O bond. c,\nThe Fourier-transform Infrared spectroscopy of MeOF-4PACz, MeOF-4SACz and MeOF-4SHCz.”\nFig. R11 The Fourier-transform Infrared spectroscopy of MeOF-4PACz, MeOF-4SACz and MeOF-\n4SHCz.\nR20\n8. The authors state that the control device retains 81% of its initial PCE. Kindly provide a detailed\nexplanation of how this value was derived.\nResponse: The PCE was calculated based on the linear fitting of the MPPT data for the Pristine-SAM\nsample. The fitted function is y = 1.0197-0.000192 * x with an R2 value of 0.99 (Fig. R12), where y\nrepresents the normalized PCE and x represents the time. We set the x to 0 and 1000, respectively, and\nget a fitted normalized PCE value, and then divide by the initial PCE value and get a ratio around\n81.2%. And finally the PCE retains 81% of its initial PCE.\nThe intercept (1.0197) of the function stands for the initial PCE. This value exceeds 1 due to\nthere is a slight increase in the normalized PCE during the initial time of MPPT, which is commonly\nobserved in stabilized tests, and this shows an influence on linear fitting. If we use the normalized 1\nas the initial PCE, the value is around 82.7%. We thought both results are reasonable, and the\nconclusion that the ROI-SAM based devices show a better stability is not changed.\nTo increase readability, we added auxiliary lines in the Fig. 4g.\nFig. R12 The fitted line of the MPPT of the Pristine-SAM device.\nR21\n9.In Fig. 3c, the V for the ROI-SAM sample is reported as 0.19 V, which is higher than that for the\nTFL\nPristine-SAM sample (0.17 V). The authors should explain this observation and discuss whether it\nmight indicate any measurement or calculation discrepancies.\nResponse: We thank the reviewer for the careful observation. The original SCLC measurements\nshown in Fig. 3c are not convincing enough, particularly due to the unclear transition between Ohmic\nregion and the tarp-filled region. This unclear transition introduced uncertainty to identify of the V .\nTFL\nTo address this issue and obtain a more reliable data, we fabricated fresh devices and performed\nSCLC measurements again. The updated V value forthe Pristine-SAM sample is 0.33 V while for\nTFL\nthe ROI-SAM sample is 0.29 V (Fig. R13). Compared to the original graph, the new graphs show\nmore obvious transition for line fitting, allowing for a more accurate V value, and the figure is\nTFL\nupdated in Fig. 3c. The reduced V of the ROI-SAM sample attributes to the higher quality of the\nTFL\nburied SAM layer, significantly influences the crystallization and growth of the perovskite layer, and\nthis explanation is also added to the main text: “This reduction is likely due to the higher quality of\nthe buried SAM layer, which facilitates better crystallization and growth of the perovskite film,\nthereby reducing interfacial defects, consistent with the observations from the slow decay time of\nTRPL spectrum.” on p.11.\nFigure R13 a, b, Dark Current density-voltage curves using the SCLC model for hole-only devices:\nITO/NiO /SAM/Perovskite/Spiro-OMeTAD/Ag, with Pristine-SAM (a) or ROI-SAM (b).\nx\nR22\n10. The scale bar should be included in the PL mapping images (Figs. 3h–3i) for better clarity.\nFurthermore, please indicate the initial PCE values of both the control and target devices for the\nMPPT shown in Fig. 4g.\nResponse: We have added the scale bars to the caption of Fig. 3 to provide clearer spatial information.\nAdditionally, color bars are also added in the Figs. 3h-3i. The initial PCE values for control and target\ndevices are also shown in Fig. 4g.\n11.Please specify the meaning of the unit “DA” used on the y-axis in Fig. 3g.\nResponse: “DA” refers to “ΔA”, the change in absorbance in transient absorption (TA) measurements.\nThis has now been changed in the y-axis title of Fig. 3g.\nR23\nResponse to Reviewer #3\nIn this manuscript, the authors improve the efficiency and stability of inverted perovskite solar cells\nby designing a self-assembled monolayer (MeOF-4SHCz) and mixing it with conventional MeOF-\n4PACz at a certain ratio as the SAM layer. The mechanism mainly involves the thiol groups in MeOF-\n4SHCz selectively reducing Ni3+ ions on the NiOₓ surface to form S–O–Ni bonds, while MeOF-4PACz\nacts on Ni2+ regions through P–O–Ni bonds, synergistically enhancing SAM uniformity and anchoring\nstrength, while also reducing the impact of Ni3+ on halides in perovskite precursors. This method\nachieved a conversion efficiency of 26.5% (certified PCE of 26.2%) and maintained 90% of the initial\nefficiency after 1000 hours of MPPT. These results are promising and the work appears suitable for\npublication in Nature Communications after the following concerns are adequately addressed:\n1. The paper states that 20% MeOF-4SHCz was incorporated into ROI-SAM, which effectively\nreduces Ni3+, but XPS shows only a 2.9% decrease in Ni3+ content (from 78.2% to 75.3%). This raises\nquestions: 1) Why is the reacted Ni3+ fraction so limited? Does MeOF-4SHCz fail to anchor most Ni3+\nsites? Is there an optimal Ni3+ concentration? Has the MeOF-4SHCz dosage truly reached its\noptimization point?\nResponse: Thank the reviewer for the insightful comment. The proportion of the MeOF-4SHCz is\nmuch higher than the proportion of Ni3+ reduced, we thought there are several reasons. Firstly, the\nabsolute amount of NiO and MeOF-4SHCz are different. Therefore, although the relative change of\nx\nNi is ~3%, this does not directly correspond to the same percentage change of MeOF-4SHCz.\nMoreover, we thought the redox reaction between MeOF-4SHCz and Ni3⁺ is mainly on the surface of\nthe NiOₓ layer, where the self-assembled monolayer forms. However, the XPS measurement may\ndetect the signal of elements In and Sn in the ITO layer (Fig. R14 a), so the proportion reflects the\nchange of the bulk NiO . To further investigate the oxidation proportion of MeOF-4SHCz. We mixed\nx\nthe powder of Ni O (insoluble in water) and MeOF-4SHCz and annealed, and performed the XPS\n2 3\nmeasurements. The powder XPS shows different properties of film (Fig. R14 b). However, we can\nstill conduct peak fittings to explore its property. The results showed that around 47% of MeOF-\nR24\n4SHCz is oxidized by Ni3+, and this discussion has been added to the revised manuscript:\n“Considering that the reaction mainly occurs at the surface, to further investigate the oxidation of Ni3+\nspecies, Ni O powder was mixed with the MeOF-4SHCz powder and performed XPS measurement.\n2 3\nThe results show about 47% of MeOF-4SHCz oxidized to MeOF-4SACz, which confirms the surface\noxidative role of the Ni3+ (Supplementary Fig. 12). And this process can be illustrated as Fig. 1g.” on\np.7.\nFig. R14 a, The full spectrum of MeOF-4SHCz deposited on NiO substrate. b, S 2p XPS spectra and\nx\nfitted peaks of the Ni O /MeOF-4SHCz powder sample after thermal annealing. The fitted\n2 3\ncomponents include S2- 2p (green), S2- 2p (brown), and SO 2- (blue).\n3/2 1/2 3\nThere is currently no universal optimal Ni3+ concentration that has been established for NiO -SAM\nx\nhole transfer layers. However, our findings suggest that excessive Ni3+ may affect the performance of\nthe devices, possibly due to the interaction of the NiO with the perovskite active layer. We added the\nx\nexperiments exploring the oxidation influence of HTLs on perovskite layer (Supplementary 13). The\nredox improved strategy reduces the reactivity of the NiO layer and increases the stability of the\nx\ndevices. The oxidized product also functions as the HTL enhances the overall quality of the SAM.\nThe device results indicate that the 20% of MeOF-4SHCz lead to best performance.\nR25\n2.Please provide the original files for the reaction energy calculations.\nResponse: We thank the reviewer for this helpful comment. Upon reviewing the reviewer’s comment,\nwe realized that certain computational details were omitted from the Methods and References sections.\nA description of the computational setup and convergence criteria has been added to the Methods\nsection, and the appropriate reference has been included in the References section:\n“Density functional theory (DFT) calculations were performed using the Vienna Ab initio Simulation\nPackage (VASP) . {Phys. Rev. B 1996, 54, 11169.} The projector augmented-wave (PAW) method\nwas employed, and the Perdew–Burke–Ernzerhof (PBE) functional within the generalized gradient\napproximation (GGA) was used to describe the exchange-correlation interactions. {Phys. Rev. B 1994,\n50, 17953.},{Phys. Rev. Lett. 1996, 77, 3865.} A Vacuum layer of 30 Å was used in the Z-direction to\nseparate the slabs. The plane-wave cutoff energy was set to 600 eV. Structural relaxation was carried\nout using the conjugate gradient algorithm with an energy convergence criterion of 1×10-4 eV and a\nforce convergence threshold of 0.05 eV/Å. The Brillouin zone was sampled using a Γ-centered 1×1×1\nk-point mesh due to the large size of the supercell. Subsequently, total energies were calculated on the\noptimized geometries using a denser Γ-centered 3 × 3 × 1 mesh. VESTA was used for visualization.\n{J. Appl. Cryst. 2008, 41, 653-658.}”\nOur DFT calculations consist of two main steps: geometry optimization and static energy\ncalculations. The PAW-PBE pseudopotentials from the VASP library were employed, with Ni, O, H,\nS, C, N, F, and P species. To compute the reaction energies, we calculated the total energies of the\nadsorbed systems, isolated surfaces, and isolated molecules. As suggested, we have now provided the\nfull set of input files used in all DFT reaction energy calculations as a compressed dataset in the\nSupplementary Data.\nR26\n3. Some parts of the paper are unclear. For example, the description of Fig. 1e is incorrect; P 2p\nbinding energies should be separately listed for both Pristine-SAM and ROI-SAM samples in Table 5;\nIn Fig. 3g, the legend contradicts other panels in the same figure set and needs correction.\nResponse: We have made the following corrections:\n1) The description of Fig. 1e has been corrected.\n2) Table 5 now includes individual P 2p binding energies for both the Pristine-SAM and ROI-SAM\nsamples to avoid ambiguity (Table R1).\nTable R1. Binding Energy of phosphorus species derived from peak fitting of the P 2p core level of\nXPS spectra in Supplementary Fig. 11.\nBinding Energy (eV) Binding Energy (eV)\nP 2p P 2p\n3/2 1/2\nPristine-\n132.4 133.4\nSAM\nROI-SAM 132.4 133.4\n3) The legend of Fig. 3g has been corrected to match the color scheme and labels in the other subpanels.\nR27\nResponse to Reviewer #4\nThis manuscript presents a well-executed study on improving the uniformity and effectiveness of self-\nassembled monolayer (SAM) hole transport layers in inverted perovskite solar cells (pero-SCs) by\nintroducing a redox-interactive SAM molecule, MeOF-4SHCz, alongside the conventional MeOF-\n4PACz. The redox-driven interaction with Ni³⁺ on the NiOx surface results in improved SAM coverage,\nbetter interfacial contact, and enhanced device performance and stability. The authors support their\nconclusions with thorough materials characterization, device performance metrics, and mechanistic\ninsights, including DFT calculations, XPS, TOF-SIMS, PL, TRPL, and transient absorption\nspectroscopy. The work is innovative and significant, and the manuscript is generally well-written and\nclearly organized. The results will be of strong interest to the photovoltaics and materials chemistry\ncommunities. This article meets the standard required for publication in Nature Communications. I\nrecommend acceptance after minor revisions as outlined below.\n1. Quantify Improvement in SAM Uniformity:\nThe KPFM and c-AFM results in Fig. 2a–d clearly show improved homogeneity with ROI-SAM.\nHowever, the standard deviation values of the contact potential and current could be stated\nnumerically in the figure caption or main text to better quantify this improvement.\nResponse: The standard deviation of the contact potential difference decreased from 22.6 mV\n(Pristine-SAM) to 14.5 mV (ROI-SAM). And the root mean roughness (RMS) of c-AFM dropped\nfrom the Pristine-SAM sample RMS=0.197 nA to ROI-SAM sample RMS =0.134 nA. We have now\nquantified the improvement in SAM homogeneity by reporting the standard deviation of contact\npotential from the KPFM histograms and RMS from c-AFM maps in the main text, and these values\nhave been also included in the figure captions of Fig. 2:\n“The mean surface potential is 339.2 mV for Pristine-SAM and 274.2 mV for ROI-SAM. The\ncorresponding standard deviations are 22.6 mV and 14.5 mV, respectively. c,d, c-AFM current maps\nand corresponding current histograms of Pristine-SAM (c) and ROI-SAM (d) on NiO substrates. The\nx\nR28\naverage current is 0.181 nA for Pristine-SAM and 0.177 nA for ROI-SAM. The RMS of two samples\nare 0.197 nA and 0.134 nA, respectively.” on p. 9.\n2.Improve Figure Quality and Captions:\nSeveral figures (especially Fig. 1b, 1c, and 2g) contain dense information. Enlarging some of the\ninsets or separating subplots might help. Additionally, figure captions should state what each\ncomponent shows more explicitly, especially for a multidisciplinary audience.\nResponse: We agree with the reviewer’s observation. Fig. 1b, 1c and 2g contain dense information,\nwhich reduces the readability for readers. As the reviewer suggest, we have enlarged the selected\ninsets, increased font size and line thickness, and adjusted the spacing of the graphs in Fig. 1 and Fig.\n2. In addition, we also have revised the figure captions to explicitly describe each graph’s content in\nFigs. 1b-1c, Fig. 1f, Fig. 1i and Supplementary Fig.10-13. We hope these changes will help\nmultidisciplinary audience better interpret the data. To further enhance readability, we have revised\nthe figures and illustrations to improve clarity and help readers to understand.\n3.Nomenclature Consistency:\nEnsure consistent abbreviation of ROI-SAM and Pristine-SAM throughout the main text and figures.\nIn a few instances, “HTL with MeOF-4PACz:MeOF-4SHCz” is used interchangeably with ROI-\nSAM—clarify this in the first usage.\nResponse: We appreciate the reviewer’s careful reading. We have revised the manuscript to ensure\nconsistent use of the abbreviations “Pristine-SAM” and “ROI-SAM” throughout the text, figures, and\nfigure captions. In the first mention in the Abstract section, we give a short definition to readers\n“redox-improved(ROI)-SAM HTL of MeOF-4SHCz/MeOF-4PACz = 4:1 (w/w)”. In the first mention\nin the main text (paragraph 3), we defined redox-improved (ROI)-SAM again. And in the following\ntext, all the related descriptions change to ROI-SAM. At the beginning of the mechanism part, we use\nMeOF-4SHCz to stress the molecule structure instead of the condition, and in the comparison\nmeasurements at paragraph 7 and below, we define and use the concept of the “Pristine-SAM”. We\nR29\nthought these modifications increase the consistency of the nomenclature.\n4.Literature Context (Introduction):\nWhile the background is comprehensive, a short paragraph contrasting this redox-improved SAM\napproach with other recent strategies targeting NiO defects (e.g., hydrogen peroxide treatment,\nx\ndoping) would enhance the novelty of this paper.\nResponse: Comparing with these strategies above, we would like to develop a strategy to improve the\nquality of the SAM as well as reduce the reactivity of the NiO layer. As the oxidation properties of\nx\nthe high valence species in NiO , we want to utilize the oxidation of the NiO to increase the\nx x\nhomogeneity of the SAM layer. So we would like NiO to react with a reduced agent, and the agent\nx\nitself could increase the quality of the SAM layer. We have added a paragraph in the Introduction\ncomparing our redox-driven SAM strategy with previously reported methods: “To simultaneously\nenhance the quality of the SAM and reduce the intrinsic reactivity of the NiO surface, comparing\nx\nwith these strategies above, we aimed to develop a dual-functional interfacial strategy. Given the\nstrong oxidative nature of high-valence nickel species in NiO , we sought to exploit this oxidative\nx\nproperty to promote the formation of a more homogeneous SAM layer. Specifically, we envisioned\nintroducing a reducing agent that could react with NiO to passivate its surface while concurrently\nx\nfunctioning as an HTL and facilitating the formation of a high-quality SAM layer.” on p.3.\n5.Minor Language Corrections:\nA careful proofreading is advised to correct small grammatical issues such as:\n“a effective reduction agent” → “an effective reduction agent”;\n“it hardly interact” → “it hardly interacts”;\n“may cause issues to the growth” → “may hinder the growth”.\nResponse: We have carefully corrected the grammatical errors the reviewer has mentioned.\nR30"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed most of my concerns well. However, I still have a minor question regarding the surface modified NiO. Typically, mobility and conductivity are proportional; yet in the authors’ experiments (Q2), the mobility of the surface modified NiO increased while the conductivity (pristine sample) remained unchanged or even decreased slightly. This is a bit confusing to me.", "reviewer_2": "The authors have addressed the most of my previous comments. I only have a few minor issues that should be resolved before the manuscript can be considered for publication in Nature Communications.\n1. For TRPL, the average carrier lifetimes of the perovskite films deposited on quartz, ITO/NiOx, and ITO/NiOx/ROI-SAM substrates are reported as approximately 12 µs, 11 µs, and 1.7 µs, respectively. These values are significantly higher than those reported in the literature (e.g., Science 2023, 382, 284–289). The authors should explain this discrepancy and provide the TRPL curves for the perovskite films prepared on quartz and NiOx.\n2. It appears that the PbI₂ ratio in the NiOx-based perovskite is lower than that in other samples (see Fig. 1h). The authors are suggested to accurately calculate this ratio by integrating the peak areas of PbI₂ and the (100) lattice plane of the perovskite, and to include the details of the fitting and calculation in the Supplementary Information.\n3. Although TOF-SIMS cannot precisely quantify the thickness of each functional layer in PSCs, the current range for the SAM relative to the perovskite layer appears unreasonable. The authors should carefully check Fig. 2g.", "reviewer_3": "The authors have provided satisfactory responses to the points I raised. I have also reviewed the other reviewers' comments and the authors' replies to them, and found the responses to be generally appropriate and constructive. I recommend its acceptance for publication in Nature Communications.", "reviewer_4": "The authors have made sufficient revision for this manuscript and answered my questions properly, I therefore recommend to publish this paper as is."}, "author_response": "Response to Reviewers\nResponse to Reviewer #1\nThe authors have addressed most of my concerns well. However, I still have a minor question\nregarding the surface modified NiO. Typically, mobility and conductivity are proportional; yet in the\nauthors’ experiments (Q2), the mobility of the surface modified NiO increased while the conductivity\n(pristine sample) remained unchanged or even decreased slightly. This is a bit confusing to me.\nResponse:\nWe appreciate the reviewer’s observation. The mobility and conductivity are generally correlated\nthrough 𝜎 = 𝑛𝑞𝜇. In our measurement, the conductivity measurements performed with the device\nstructure ITO/NiO /SAM/Ag. The bulk carrier concentration of NiO remains nearly unchanged after\nx x\nSAM modification, so the conductance of the pristine and modified films is almost the same. In\ncontrast, the SCLC measurements performed with the device structure\nITO/NiO /SAM/perovskite/Sprio-OMeTAD/Ag, where the modification reduces interfacial traps\nx\n{Adv. Mater. 2024, 36, 2311970.} and improves SAM ordering, leading to an increase in mobility.\nThus, the seemingly contradictory results arise because bulk conductivity is dominated by the carrier\ndensity of HTL without considering the active layer, whereas SCLC mobility is sensitive to the trap\ndensity of perovskite layer and interfacial quality.\nResponse to Reviewer #2\n1. For TRPL, the average carrier lifetimes of the perovskite films deposited on quartz, ITO/NiOx, and\nITO/NiOx/ROI-SAM substrates are reported as approximately 12 µs, 11 µs, and 1.7 µs, respectively.\nThese values are significantly higher than those reported in the literature (e.g., Science 2023, 382,\n284–289). The authors should explain this discrepancy and provide the TRPL curves for the perovskite\nfilms prepared on quartz and NiOx.\nResponse:\nWe thank the reviewer for this pointing this out. The carrier lifetimes could be influenced by both the\nperovskite films and the measurement conditions. Perovskite layer with low trap density can exhibit\nhigh carrier lifetime, while a low excitation fluence could suppress the recombination, which also lead\nto high carrier lifetime. To address the reviewer’s concern, we performed the TRPL measurements\nagain without changing the default measurement settings.\nThe TRPL decay curves of perovskite films on the quartz and NiO substrates are shown in Figure\nx\nR1 a and Supplementary Fig. 19, and the films on the NiO /ROI-SAM and NiO /Pristine-SAM\nx x\nsubstrates are provided in Figure R1 b and Figure 3b (updated). The curve of quartz-based sample\ndoes not fully return to the baseline even after several repeated measurements, likely due to the\npresence of long-lived trap-assisted recombination components. Since the decay cannot be fully\ncaptured within the measurement window, this curve was omitted from the main figure. For\ncomparison, the perovskite film on bare NiO shows an average lifetime of about 333 ns, on\nx\nNiO /ROI-SAM is 73.1 ns and on NiO /Pristine-SAM is 37.0 ns, which is attributed to efficient hole\nx x\nextraction through the SAM layers. Meanwhile, the longer lifetime of ROI-SAM compared with\nPristine-SAM indicates reduced nonradiative recombination due to better interfacial passivation.\nAlthough the trend of these samples doesn’t change, the average carrier changes significantly. We\nattribute this to the slight aging of the perovskite/SAM interface. In the first measurements, the\nsamples were stored overnight and the PL measurements was conducted first, which induces the mild\ninterface degradation, reducing hole-extraction efficiency at the NiOₓ/SAM/perovskite interface.\nSimilar TRPL lifetimes are also reported in the literatures {Nature 2025, 646, 95–101.}. In this\nmeasurement, we prepared fresh samples and conducted TRPL measurements immediately after\nfabrication. The quartz-based perovskite sample still exhibited a very long lifetime, while the HTL-\nbased samples showed much shorter lifetimes, consistent with efficient carrier extraction. All data are\nupdated in Supplementary Table 10.\nFigure R1. a) TRPL decay curves of perovskite deposited on quartz and NiO substrate, respectively.\nx\nb)TRPL decay curves of perovskite deposited on NiO /ROI-SAM and NiO /Pristine-SAM substrate,\nx x\nrespectively.\n2. The PbI₂ ratio in the NiOx-based perovskite is lower than that in other samples (see Fig. 1h). The\nauthors are suggested to accurately calculate this ratio by integrating the peak areas of PbI₂ and the\n(100) lattice plane of the perovskite, and to include the details of the fitting and calculation in the\nSupplementary Information.\nResponse:\nFollowing the reviewer’s suggestion, we have calculated the PbI /FAPbI (100) ratio by integrating the\n2 3\npeak areas at 2θ = 12.6° for PbI and 14.1° for FAPbI (100). For NiO sample, the value changes\n2 3 x\nfrom 0.136 to 0.128, for Pristine-SAM sample, the value changes from 0.105 to 0.103, and for ROI-\nSAM sample, the value is still 0.091. The data updated the relative ratios in revised Fig. 1h and\nmanuscript on p.7. The detailed integrating data have been added to Supplementary Table 7.\n3.Although TOF-SIMS cannot precisely quantify the thickness of each functional layer in PSCs, the\ncurrent range for the SAM relative to the perovskite layer appears unreasonable. The authors should\ncarefully check Fig. 2g.\nResponse:\nAs the thickness of the perovskite layer is much larger than that of the SAM, when sputtering is\nperformed at a constant rate, the SAM signal appears only briefly and then rapidly disappears in the\nTOF-SIMS depth profile. To make the SAM signal more distinguishable, which is the focus of the\nstudy, we prepared thinner perovskite films. We have now clarified these details in the Methods section.\n“TOF-SIMS analysis was performed on a TOF-SIMS-M6 spectrometer (ION-TOF GmbH,\nMünster, Germany) equipped with a 30 keV Bi + primary ion gun pulsed at 10 kHz (mass range: 0 –\n3\nion spectra were calibrated by O-, OH-, C -, C H-, and Cl-, etc. An electron flood gun for charge\n2 2\nneutralization was applied throughout the experiments. The scan sputter area was 400 × 400 μm2 and\nthe analysis area was 200 × 200 μm2. Data were processed by ION-TOF SurfaceLab software (Version\n7.4, ION-TOF GmbH) by signal of corresponding ions or fragment ions. To better resolve the SAM\nsignal in TOF-SIMS, perovskite films with reduced thickness were prepared by diluting the perovskite\nprecursor solution. To visualize the SAM layer more clearly, the perovskite precursor solution was\ndiluted to form a thinner perovskite film.” on p.24."}, {"round": 3, "reviewer_comments": {"reviewer_1": "I have no further comments and recommend acceptance for publication in Nature Communications.", "reviewer_2": "The authors have adequately addressed my previous concerns in their revision. I am satisfied with the changes made and therefore recommend the manuscript for publication in its current form"}, "author_response": ""}]

Decision letter