Interfacial dipole engineering by self-assembled molecules in n-i-p and p-i-n perovskite solar cells

Domain: neuroscience
Published: 2026-02-04
Editorial outcome: major_revision

Abstract
Self-assembled molecules are widely used as bottom interfacial layers in inverted perovskite solar cells, yet their application to perovskite top surfaces remains poorly understood. Here, we develop two self-assembled molecules for perovskite surface modification and interfacial optimization with the hole transport layer. Through solvent engineering, ordered and uniform molecular packing is achieved on the perovskite surface. These molecules optimize surface energetics and promote efficient hole transfer when coupled with a homologous hole transport layer. Their large molecular dipoles tune interfacial energy alignment and reduce energetic offsets, thereby accelerating charge extraction from the perovskite layer. This dipole-driven interfacial modulation is effective in both normal and inverted device architectures. As a result, a power conversion efficiency of 26.18% (certified 26.23%) is achieved in normal-structure devices, together with improved operational stability under maximum power point tracking. This work establishes a viable strategy for perovskite surface engineering using self-assembled molecules.

Introduction
Perovskite solar cells (PSCs) are widely recognized as a promising next-generation photovoltaic technology and have achieved certified power conversion efficiency (PCE) exceeding 27%1–5. As PSCs consist of a multilayer stacked structure, interfacial heterojunctions play an increasingly critical role, particularly given that current technologies have significantly improved the bulk quality of perovskite (PSK) films6–8. Among these interfaces, the heterojunction between the perovskite and the hole transport layer (HTL) is a key factor influencing device performance, as perovskite surface defects and energy-level misalignment contribute to non-radiative recombination. This results in losses in open-circuit voltage (V OC) and fill factor (FF), as well as long-term stability issue9,10. Introducing a rational passivation layer at this interface is an effective strategy to suppress non-radiative recombination and enhance device stability11,12. For example, the organic halide salt phenylethylamine iodide (PEAI) is widely used to passivate perovskite surface defects and suppress non-radiative recombination13. Beyond defect passivation, surface-modifying molecules can also function as interfacial dipole modifiers, improving energy-level alignment14,15. For example, Miyasaka et al. demonstrated that phenethylamine halides (PEAX) generate interfacial dipoles at the perovskite/HTL interface, leading to a downward shift in the HTL energy level and an increase in V OC16. Similarly, various interfacial molecules with combined passivation functions and tailored dipole moments have been successfully developed to optimize perovskite surface energetics and minimize interfacial charge accumulation17–21. Beyond passivation and dipole tuning, an ideal interfacial layer should also facilitate charge transfer by interacting with the HTL, for instance, by acting as a carrier channel to enhance charge selectivity and transport efficiency22,23.

Self-assembled molecules (SAMs, note that the term “self-assembled monolayer” is not used here due to the difficulty of verifying true monolayer formation), such as Me-4PACz and MeO-2PACz, which feature a phosphonic acid anchoring group and a carbazole terminal group, are widely employed in high-efficiency p-i-n perovskite solar cells (PSCs)24–31. In these architectures, SAMs function as interface dipole modulators and can even serve as a single HTL32. This is attributed to the molecular asymmetry of SAMs, which results in electronic asymmetry, spatially separating positively and negatively charged groups and generating strong dipole moments33–35. These dipole moments facilitate energy-level alignment, while the terminal groups of SAMs act as efficient hole collectors due to their hole-selective properties36–38. Additionally, studies have shown that SAMs can strongly interact with perovskite, effectively reducing surface defects39–42. These characteristics make SAMs promising candidates for perovskite/HTL interfacial modification, enabling both surface passivation and efficient hole extraction. However, the application of SAMs for perovskite/HTL interfacial modification in n-i-p PSCs remains largely unexplored43,44, and their functional roles in this configuration have yet to be thoroughly investigated. Furthermore, most reported SAMs exhibit relatively small dipole moments, and increasing the SAM layer thickness to enhance dipole accumulation often negatively impacts carrier transport. Therefore, developing suitable SAMs that can effectively modify the perovskite/HTL interface in n-i-p PSCs and elucidating their underlying mechanisms are critical yet challenging tasks.

Herein, we develop two SAMs, SFX-P1 and SFX-P2, with varying numbers of anchoring units to enhance the perovskite/HTL interface in n-i-p PSCs. Additionally, we employ a structurally similar material, SFX-DM, as HTL to establish layer-to-layer homogeneous hole transport (Fig. 1a). Our findings reveal that these SAM-modified perovskite surfaces effectively facilitate dipole tuning and enhanced hole extraction. The number of anchoring units plays a crucial role in determining key properties such as solubility, dipole moment, and adsorption behavior on the perovskite surface, leading to distinct surface energetics between SFX-P1 and SFX-P2. Specifically, SFX-P1, which contains a single phosphonic acid group and an ethyl chain, exhibits more uniform adsorption on the perovskite surface due to its greater molecular flexibility compared to SFX-P2. The larger dipole moment of the SFX-P1-modified layer optimizes energy-level alignment at the perovskite/HTL interface, yielding a PCE of 26.18% in n-i-p PSCs. The encapsulated devices also show improved long-term operational stability under ambient humidity. Notably, the interfacial dipole tuning effect of these SAMs is also effective in p-i-n PSCs, demonstrating the universality of this strategy across different device configurations.

Results
Molecule properties
The synthetic routes and detailed procedures for both SAMs are illustrated in Supplementary Fig. 1. The terminal group with a spiro[fluorene-9,9’-xanthene] (SFX) core is synthesized via Buchwald-Hartwig coupling and cyclization reactions. Precise control of reactant equivalents and reaction time enables the selective synthesis of SFX-P2 and SFX-P1, each with different numbers of phosphonic acid anchoring groups. The chemical structures are confirmed by nuclear magnetic resonance (NMR) spectroscopy (1H, 13C, and 31P) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (Supplementary Figs. 2-32). The electrostatic potential (ESP) distributions of both molecules are investigated using density functional theory (DFT) calculations (Fig. 1b). The results show that the negative ESP is primarily localized on the electron-rich phosphonic acid group, while the positive ESP is concentrated on the SFX core and donor units. Notably, SFX-P1 exhibits a larger dipole moment of 5.46 D, attributed to its greater electronegativity separation compared to SFX-P2 (3.43 D). This larger dipole moment enhances van der Waals interactions within the dipole array and the perovskite material, contributing to improved interfacial interactions4,19,45.

Both SAMs exhibit high thermal stability, with decomposition temperatures (T d) exceeding 210°C (Supplementary Fig. 33). Additionally, SFX-P1 shows a glass transition temperature (T g) of 133.8°C, whereas no significant T g is observed for SFX-P2, indicating their suitability for forming stable amorphous films46,47. The energy gap (E g) and energy levels of both SAMs in solution are determined by cyclic voltammetry (CV) in combination with UV-vis absorption spectroscopy (Supplementary Fig. 34 and Supplementary Table 1), showing consistency with the energy-level trend obtained from DFT calculations (Supplementary Fig. 35). Furthermore, photoelectron yield spectroscopy (PYS) measurements reveal ionization potentials of −5.25 eV, −5.20 eV, and −5.10 eV for SFX-P2, SFX-P1, and SFX-DM films, respectively (Supplementary Fig. 36). These results suggest that the electron-withdrawing nature of the phosphonic acid group lowers the ionization potential of the molecules, making them well-suited as interfacial layers between perovskite and SFX-DM for optimized energy-level alignment.

When SFX-P2 and SFX-P1 function as interfacial layers, they can interact with the HTL through C-H···π bonding or electron density delocalization, influencing the hole transport distance48–50. To investigate this effect, we examined the intermolecular interaction energy (E int) of SFX-P1 with Spiro-OMeTAD and SFX-DM using DFT calculations. As shown in Supplementary Fig. 37, the E int of SFX-P1 with SFX-DM is −684 meV, significantly stronger than the −432 meV interaction energy observed for SFX-P1 with Spiro-OMeTAD. Additionally, the distance between the central sp3-hybridized carbon atoms of SFX-P1 and SFX-DM is only 9.5 Å, which facilitates more efficient intermolecular hole transfer. These findings are consistent with the previous study49, which demonstrated that a homologous interface layer/HTL design can enhance hole transport from the perovskite to the HTL.

Beyond the computational studies, the packing properties of organic molecules, such as crystallinity and orientation, which are influenced by solution treatment methods, are also crucial for their performance51,52. To investigate these properties, we examined the solubility and stacking characteristics of the two SAMs in chlorobenzene (CB) and chloroform (CF) solvents. As shown in Supplementary Fig. 38, SFX-P1 exhibits high solubility in both CB and CF (>5 mg mL−1), whereas SFX-P2 shows lower solubility in both solvents. The enhanced solubility of SFX-P1 is likely due to its ethyl chain, which reduces molecular polarity and increases flexibility, thereby inhibiting molecular aggregation46,53. To further investigate the molecular stacking behavior, we performed grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements on SAM films. Since ultra-thin SAM layers deposited on perovskite films do not produce detectable GIWAXS signals, we coated the SAMs onto silicon wafers for characterization. When CB is used as the solvent (Fig. 1c), both SFX-P2 and SFX-P1 films exhibit no significant diffraction signals, indicating their amorphous nature. Interestingly, when CF is used as the solvent (Fig. 1c), lamellar structures are observed in both SFX-P1 and SFX-P2 films, suggesting a more ordered molecular arrangement. This is further confirmed by broad peaks in the 1D GIWAXS profiles, indicative of π-π stacking interactions (Supplementary Fig. 39). Furthermore, analysis of the 1D GIWAXS profile confirms the presence of π-π stacking interactions with slip-stacking54, as evidenced by a broad peak centered at approximately 1.35 Å−1, corresponding to an interplanar distance of 4.65 Å. These findings suggest that when deposited on the perovskite surface using CF as a solvent, SAM molecules may form a more ordered arrangement through their anchoring units, although the interaction is not as strong as that observed on hydroxyl-rich metal oxide substrates55. The differences in SAM packing behavior when using CF (with units facing downward) versus CB (random arrangement) and the hole transport behaviors are illustrated schematically in Fig. 1d.

Photovoltaic performance
The above discussion on the properties of SAMs and their interactions with perovskite and HTL strongly suggests that the SAM interlayer influences the photovoltaic performance of PSCs. To investigate this effect, we fabricated n-i-p PSCs with the configuration shown in Fig. 1a. The optimal concentration of doped HTLs in PSCs was used to avoid the influence of HTL concentration on the SAM modification effect (Supplementary Figs. 40, 41). The referenced device, based on SFX-DM as the HTL without SAM modification, is defined as the control. The J-V curve of the control device with champion performance is shown in Fig. 2a, exhibiting a PCE of 23.72%, a V OC of 1.15 V, a short-circuit current density (J SC) of 25.23 mA cm−2, and an FF of 81.56%. Subsequently, we introduced the SAM modification layer, optimizing its concentration to 1 mg mL−1 in CF (optimization data in Supplementary Fig. 42 and Supplementary Tables 2, 3). Notably, the SAM layer not only enhances efficiency but also reduces hysteresis in the J-V curves. The device incorporating SFX-P2 spin-coated from CF (SFX-P2@CF) achieves a PCE of 25.65%, with a V OC of 1.18 V, a J SC of 25.73 mA cm−2, and an FF of 84.51% (Fig. 2b). Meanwhile, the SFX-P1@CF-based device demonstrates an impressive PCE of 26.18% (certified 26.23%, Supplementary Fig. 43), with a V OC of 1.19 V, a J SC of 26.00 mA cm−2, and an FF of 84.81% (Fig. 2c). The J SC values are further confirmed by current density measurements from external quantum efficiency (EQE) spectra (Supplementary Fig. 44). Moreover, all three devices exhibit stable efficiency during stable power output tracking (Fig. 2d). We also achieve a high efficiency of 24.29% in a 1 cm2 SFX-P1@CF device (Fig. 2e and Supplementary Table 4), together with improved reproducibility (Supplementary Fig. 45), demonstrating the scalability of SAM modification for fabricating high-performance large-area PSCs.

Additionally, SAM@CB devices also show enhanced performance (Supplementary Fig. 46), achieving a PCE of 25.67% for SFX-P1@CB. The CF-processed samples outperform their CB-processed counterparts, likely due to the more ordered molecular packing of SAMs when deposited from CF. This improved packing promotes stronger interactions between the SAM, perovskite, and HTL, thereby enhancing carrier transport and boosting efficiency. Figure 2f clearly illustrates the difference in device performance under different solvent processing conditions. Furthermore, when Spiro-OMeTAD is used as the HTL, we observe performance improvements upon SAM treatment (Supplementary Fig. 47). However, the champion efficiency of 25.13% achieved with SFX-P1@CF remains lower than that of its counterpart based on SFX-DM HTL. These results are consistent with our computational predictions and strongly support the conclusion that our homologous SAM design, with SFX-DM as the HTL, effectively enhances device performance.

Interfacial interactions
To understand the mechanisms by which SAM modification enhances n-i-p device performance, we investigated the packing properties of SAMs on the perovskite surface. In the following discussion, CF is used as the processing solvent for SAM deposition. We simulated the adsorption morphology of SFX-P1, SFX-P2, and SFX-DM on the FAPbI3 perovskite surface and calculated the corresponding binding energy. As shown in Fig. 3a, the SFX-DM molecule adopts a parallel orientation on the perovskite surface, with a binding energy of only 33 meV due to the absence of anchoring groups (Supplementary Fig. 48), indicating negligible interaction between SFX-DM and the perovskite surface. In contrast, SAMs containing phosphonic acid anchoring groups exhibit strong charge redistribution upon adsorption onto the perovskite surface (Fig. 3b, c). The binding energy values for the SFX-P2 and SFX-P1 systems are −801 meV and −424 meV, respectively, suggesting that SAMs preferentially adsorb and interact with the perovskite surface via their anchoring groups. Furthermore, the adsorption morphology of SFX-P1 closely resembles that of SFX-DM, which may enhance the connectivity between the SAM layer and the HTL. We also conducted solvent rinse tests using CB (solvent for HTL). Energy-dispersive X-ray spectroscopy (EDS) elemental analysis reveals negligible reduction in phosphorus elemental mapping intensity (Supplementary Fig. 49), and photoluminescence (PL) intensity shows only a slight decrease after CB washing (Supplementary Fig. 50). This confirms that the SAM layer remains intact on the perovskite surface and is not affected by the HTL deposition process.

To further analyze the nanoscale molecular distribution on the perovskite surface, we employed atomic force microscopy coupled with infrared spectroscopy (AFM-IR), an ultra-high-resolution chemical analysis technique that detects molecular distributions by identifying IR responses at specific wavenumbers through AFM cantilever force signals39,48,56. The P-C stretching vibration located at 1,462 cm−1 was selected as the characteristic IR signal (Supplementary Fig. 51). As shown in Fig. 3d, the IR absorption intensity at grain boundaries in SFX-P2-coated perovskite films is lower than that at the surface, with numerous regions exhibiting weak IR absorption. This suggests poor and non-uniform adsorption of the SFX-P2 SAM on the perovskite surface. In contrast, SFX-P1-coated perovskite films exhibit a much more uniform IR absorption intensity (Fig. 3e), indicating uniform adsorption of SFX-P1 on the perovskite surface. The superior stacking uniformity of SFX-P1 can be attributed to the presence of ethyl chains, which reduce molecular self-aggregation and promote a more uniform molecular distribution.

To further understand how SAM modification influences perovskite morphology and crystallinity, we performed scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging. The results show that SAM treatment reduces the presence of secondary grains in pristine perovskite films, leading to smoother and more uniform surfaces (Supplementary Figs. 52, 53). Additionally, X-ray diffraction (XRD) patterns reveal a decrease in the full width at half maximum (FWHM) of SAM-modified perovskite films (Supplementary Fig. 54 and Supplementary Table 5), indicating improved crystallinity. This observation is further supported by the increased intensity of the (001) and (002) crystal planes in 2D GIWAXS images and their corresponding 1D profiles (Supplementary Figs. 55, 56, and Supplementary Table 6). Notably, all films exhibit identical absorption spectra (Supplementary Fig. 57), confirming that SAM modification primarily enhances interfacial quality rather than altering bulk optical properties. These results suggest that SAM treatment improves perovskite surface quality, thereby facilitating hole transport at the interface.

To investigate the chemical interactions between SAMs and the perovskite surface, we performed 31P NMR spectroscopy. The electron cloud density of phosphorus in the SAM increased, causing an up-field shift in the chemical signal after PbI2 addition (Fig. 3f and Supplementary Fig. 58), which can be attributed to P=O coordination with Pb2+57. FTIR furthers supports this interaction, as the P=O stretching vibrations of SFX-P1 and SFX-P2 shift from 1,178 cm−1 to 1,163 cm−1 and 1,173 cm−1, respectively, upon PbI2 addition (Fig. 3g and Supplementary Fig. 59), confirming coordination between P=O and Pb2+. X-ray photoelectron spectroscopy (XPS) analysis further verifies these interactions. The Pb 4f characteristic peaks in pristine perovskite films shift to lower binding energies after SAM modification (Fig. 3h), indicating an increase in the electron cloud density around Pb atoms58. Additionally, the P 2p peak in the SAMs shifts toward higher binding energy (Supplementary Fig. 60). In the perovskite/SFX-P2 film, stronger ionic Pb-O bonding signals arising from the interaction between Pb2+ and -P-O- ions are observed at 138.25 eV and 143.10 eV, which leads to the shift of the Pb peaks toward higher binding energies59,60. The difference in XPS curves between SFX-P1 and SFX-P2 can be attributed to the stronger anchoring effect of SFX-P2, enabled by its double phosphoric acid groups. This result is consistent with the calculated binding energy values. The I 3d peaks also shift (Supplementary Fig. 61), indicating a change in the [PbI6] electron cloud density. Kelvin probe force microscopy (KPFM) was performed to investigate the surface energetics of perovskite films by scanning surface potential fluctuations. As shown in Fig. 3i–k, the SFX-P1 SAM-modified perovskite surface exhibits the narrowest contact potential difference (CPD) distribution (~80 mV over a 4×4 μm2 area), compared to 160 mV for SFX-P2 SAM-modified films and 300 mV for pristine perovskite films. These CPD distributions are consistent with the AFM-IR results, indicating that the uniform molecular packing of SFX-P1 minimizes potential fluctuations. These findings confirm that SAM treatment effectively balances the surface energetics of perovskite films, thereby improving carrier extraction61,62. In summary, our results confirm that SAMs, particularly the SFX-P1 interfacial layer, form strong interactions with both the perovskite and HTL, enhancing hole transport and ultimately improving solar cell performance.

Carrier dynamics
To further investigate the impact of the SAM layer on carrier dynamics at the perovskite/HTL interface in n-i-p PSCs, we examined its influence on interfacial energy alignment. As discussed earlier, the large dipole moment of SAMs is expected to affect carrier transfer at the interface. Therefore, we analyzed the energy-level alignment properties using ultraviolet photoelectron spectroscopy (UPS) (Supplementary Fig. 62), and the detailed schematic of the energy-level arrangement is depicted in Fig. 4a. Specifically, the work function (WF) of bare perovskite decreases from 4.67 eV to 4.52 eV and 4.38 eV after surface treatment with SFX-P2 and SFX-P1, respectively. This reduction in WF is attributed to the negative dipole formed by the SAM at the perovskite/HTL interface17,44, which induces a downward shift in the local vacuum level. The valence band maxima (VBM) of bare perovskite, perovskite/SFX-P2, and perovskite/SFX-P1 films are determined to be −5.59 eV, −5.55 eV, and −5.48 eV, respectively, consistent with our PYS measurements (Supplementary Fig. 63). Given the constant band gap (E g) of 1.54 eV, the conduction band minima (CBM) are calculated as −4.05 eV, −4.01 eV, and −3.94 eV, respectively. Typically, the energy-level offset between the VBM of perovskite and the highest occupied molecular orbital (HOMO) of the HTL plays a crucial role in the efficient separation of photogenerated hole carriers. Since the exciton binding energy of perovskite materials is relatively low (20–73 meV), minimizing this energy offset is critical for reducing non-radiative exciton recombination in the active layer16. As shown in Fig. 4a, the SFX-P1-treated perovskite film exhibits a remarkably low energy-level offset of 90 meV, compared to 300 meV for SFX-P2 and 490 meV for the control sample. Additionally, SFX-P1 modification increases the energy gap between the CBM of perovskite and the HOMO of the HTL to 1.45 eV, which is expected to enhance the V OC by reducing carrier recombination63.

To evaluate the effect of SAMs on interfacial carrier transport, we developed a SCAPS-1D drift-diffusion (DD) model to simulate the band alignment and carrier diffusion behavior in different device configurations (Supplementary Fig. 64 and Supplementary Tables 7–9). The conduction band offset (CBO) and valence band offset (VBO) are calculated using the standard band alignment equations:

CBO = χ BaHfS3 − χ HTL (1)

VBO = χ HTL + E g HTL − (χ BaHfS3 + E g BaHfS3) (2)

In the control configuration, where SFX-DM is directly used as the HTL without any interfacial layer, the VBO at the perovskite/HTL interface is −0.338 eV, forming a small valence band cliff (Supplementary Fig. 65a and Supplementary Table 10). Such a small cliff can facilitate hole extraction by providing a gentle driving force. The large CBO of +1.7 eV at the HTL/perovskite interface helps suppress electron leakage into HTL, thereby reducing interfacial recombination. Introducing a buffer layer (SFX-P1) between the perovskite and SFX-DM further optimizes the interface. As shown in Supplementary Fig. 65b and Supplementary Table 10, the VBO at the perovskite/SFX-P1 interface remains −0.34 eV, while a slight positive VBO of +0.02 eV appears at the SFX-P1/SFX-DM junction. This small valence-band spike increases the built-in potential (V bi) across the interface, suppresses hole back-injection, and reduces interfacial recombination, while maintaining efficient hole extraction (spikes >0.3 eV would instead hinder transport). In addition, we exclude the influence of the SFX-P1 buffer-layer doping concentration on device performance (Supplementary Fig. 66 and Supplementary Tables 11, 12), indicating that interfacial band alignment is the key factor governing efficiency enhancement.

The recombination-generation profile (Supplementary Fig. 67) confirms that the SFX-P1-modified device exhibits a lower recombination rate compared with the control configuration. Solving the coupled semiconductor equations within the DD framework also predicts clear improvements in V OC and PCE for devices incorporating the SFX-P1 interfacial layer (Supplementary Table 13). These results confirm that the SFX-P1 layer not only optimizes energetical alignment but also suppresses recombination, enabling more efficient charge extraction and improved overall device performance.

Furthermore, improved band alignment enhances recombination resistance in SAM-modified actual PSCs (Supplementary Fig. 68), while suppressing interfacial charge accumulation and leading to a rise in V bi (Supplementary Fig. 69). Although Mott-Schottky analysis may not yield fully quantitative values under the present conditions, the observed trends are consistent with both the DD simulations and other experimental findings, supporting the proposed mechanism. Overall, as illustrated in Fig. 4b, SAMs induce energy-level realignment via dipole arrays, where the phosphonic acid unit anchors to the perovskite surface, generating interfacial polarization that enhances the V bi. These effects accelerate hole extraction and separation while suppressing carrier recombination at the interface, ultimately improving solar cell performance.

The PL and TRPL measurements (Supplementary Fig. 70) reveal that both the PL intensity and lifetime of SAM- and SAM/SFX-DM-coated samples are reduced, which may result from either increased non-radiative recombination or enhanced hole extraction at the interface. However, considering the improved device performance and structural characterizations, degradation of the perovskite film is unlikely. In the pristine perovskite samples, the τ 1 component associated with defect-assisted non-radiative recombination at interfaces or grain boundaries is relatively minor (Supplementary Table 14), while the τ 2 component from intrinsic luminescence dominates. After organic-layer deposition, τ 1 becomes shorter and its relative amplitude increases, supporting the occurrence of hole extraction. The τ 2 component also decreases due to efficient charge transfer. Transient photocurrent (TPC) and transient photovoltage (TPV) measurements (Supplementary Fig. 71) further confirm faster charge extraction (τ TPC = 0.60 µs vs. 0.87 µs) and longer recombination lifetimes (τ TPV = 4.56 µs vs. 3.60 µs) in SFX-P1-modified devices, evidencing improved interfacial charge transfer and suppressed trap-induced recombination. More importantly, the enhanced hole extraction exhibits a highly uniform distribution in PL mapping images (Fig. 4c–e), which is attributed to the uniform anchoring of SFX-P1 on the perovskite surface, as confirmed by AFM-IR.

The femtosecond transient absorption (fs-TA) spectroscopy was employed to further investigate carrier kinetics. The pseudo-color TA plots of the samples (Fig. 4f–h) display prominent ground-state bleaching at ≈ 769 nm, where bleaching intensity reflects the number of carriers in the conduction and valence bands of the perovskite64. The trend in bleaching intensity follows: perovskite/SFX-P1/SFX-DM < perovskite/SFX-P2/SFX-DM < perovskite/SFX-DM, indicating that the SFX-P1-modified perovskite/HTL interface is the most favorable for hole transport. This trend is consistent with the faster decay of the perovskite/SFX-P1/SFX-DM sample over time (Supplementary Fig. 72). The photo-bleaching decay curves are fitted to further analyze charge dynamics using a tri-exponential function (Supplementary Fig. 73), with the extracted decay parameters summarized in Supplementary Table 15. The shortest lifetime component (τ 1) corresponds to hole trapping at the perovskite/HTL interface65. Compared to perovskite/SFX-DM samples, the incorporation of SFX-P2 and SFX-P1 SAMs reduces τ 1 from 201.3 ps to 128.2 ps and 109.5 ps, respectively, indicating ultrafast trap filling and carrier injection, thereby enhancing V OC. Additionally, a significant reduction in the second lifetime component (τ 2), associated with hole extraction from perovskite to HTL, is observed for SAM-modified samples66. This effect is attributed to optimized energy-level alignment via the SAM-induced dipole effect, facilitating efficient exciton separation and resulting in higher FF. The longest lifetime component (τ 3), assigned to carrier lifetime, is longer in samples containing SAM, indicating suppressed carrier recombination. In summary, SAM modification, particularly with SFX-P1, not only passivates the perovskite surface but also accelerates hole extraction from the perovskite to the HTL through its dipole-induced energy-level tuning effect at the perovskite/HTL interface. The above results and discussion indicate that molecular adsorption behavior and interfacial energy-level modulation are the dominant factors affecting the performance of SFX-P2- and SFX-P1-based devices.

To validate our conclusions and assess the universality of our strategy, we also apply SAMs to modify the perovskite/NiOx HTL interface in p-i-n PSCs. We fabricated p-i-n devices with the structure ITO/NiOx/SAM/perovskite/C60/BCP/Ag and evaluated their photovoltaic performance (Supplementary Fig. 74). The corresponding EQE spectra (Supplementary Fig. 75) indicate that the SAM layer has a negligible effect on light absorption in the 300–450 nm range, which can be attributed to its minimal parasitic absorption. Compared with the control p-i-n PSCs, which exhibit a PCE of 22.71% (reverse scan) and 22.22% (forward scan), the device incorporating the SFX-P1 SAM achieves a higher performance of 24.10% (reverse scan) and 23.93% (forward scan), along with reduced hysteresis. The SFX-P2 SAM also enhances device performance, though less effectively than SFX-P1, consistent with previous discussions. These results confirm that SAMs can universally enhance photovoltaic performance in inverted PSCs, demonstrating their effectiveness across different device configurations. In the p-i-n architecture, SAMs anchor directly onto the NiOx surface, and the homologous interaction between the SAM and HTL, as discussed in the n-i-p structure, is absent. Consequently, dipole-moment modulation and enhanced hole extraction become the primary mechanisms driving performance improvement. To verify this, we employed UPS to investigate the band alignment at the buried interface. As shown in Supplementary Figs. 76–78, the SAM with negative dipole orientation at the buried interface reduces the work function of the NiOx layer and simultaneously induces a downward shift in the perovskite Fermi level. The resulting energy-level alignment, characterized by a reduced interfacial energy barrier, facilitates more efficient separation and transport of photo-generated holes at the perovskite bottom interface. Therefore, in p-i-n PSCs, our SAMs also effectively regulate interfacial energy alignment and enhance hole extraction.

Long-term durability
Finally, we evaluated the durability of n-i-p PSCs under various conditions. Compared to the bare perovskite film, SAM-treated perovskite films exhibit an increased water contact angle (Supplementary Fig. 79), indicating improved resistance to moisture ingress. XRD analysis further confirms this protective effect (Supplementary Fig. 80); after 240 hours of exposure to ambient air with 60% humidity, the pristine perovskite film fully degrades into the non-photoactive yellow phase, whereas the SAM-modified perovskite films retain their black-phase stability. Similarly, when unencapsulated devices are stored in humid air (30–40% humidity), PSCs incorporating SFX-P2 and SFX-P1 retain 83% and 90% of the initial PCE, respectively, after 2500 hours, whereas the control PSCs remained only 34% (Fig. 5a). Additionally, thermal stability tests were conducted at 85°C in an N2 atmosphere (Fig. 5b). After 500 hours of aging, the unencapsulated SFX-P1 device maintains 87% of its initial efficiency, outperforming the SFX-P2-based (80%) and the control ones (35%).

To elucidate the role of the SAM layer in enhancing the solar cell durability, we compared fresh devices with those aged for 100 hours under 30-40% humidity at 85°C. Cross-sectional SEM images of the devices before and after aging (Supplementary Fig. 81) reveal that perovskite degradation, specifically collapse at the perovskite/HTL interface, is observed only in the control sample, likely due to moisture infiltration. To further investigate the degradation mechanisms, we employed time-of-flight secondary ion mass spectrometry (TOF-SIMS) to analyze ion migration. As shown in Fig. 5c and 5e, during the aging process, Li+ ions from the HTL migrate toward the SnO2 ETL, consistent with previous reports67. This migration accelerates perovskite decomposition and phase transition in the presence of moisture68,69. Additionally, Li+ diffusion from the HTL into the perovskite reduces the conductivity of the HTL, leading to performance degradation under prolonged high-temperature conditions69. Encouragingly, Li+ ion migration is suppressed in devices incorporating the SFX-P1 layer, as indicated by the nearly unchanged Li+ ion distribution in fresh and aged samples (Fig. 5d and 5f). These findings confirm that SAMs not only mitigate moisture infiltration due to their hydrophobic properties but also effectively block Li+ ion migration across the device, thereby enhancing both moisture and thermal stability.

We then evaluated the operational stability of the devices. Under an N2 atmosphere without encapsulation, the control and SFX-P1 PSCs retain 71.5% and 95.2% of their initial efficiencies, respectively, after 1000 hours of MPP tracking (Supplementary Fig. 82). More importantly, under real environmental conditions (30–40% humidity) following the ISOS-L-2 protocol, encapsulated SFX-P1 PSC retains 89.6% of its initial efficiency after 1300 hours of MPP tracking (Fig. 5g), with a projected T 80 lifetime of 2800 hours based on linear extrapolation, far exceeding that of the control devices. Even under severe high-temperature conditions with continuous light illumination (Supplementary Fig. 83), the SFX-P1 PSCs maintain stable output due to enhanced interfacial quality and suppressed ion migration, in contrast to the control devices, which exhibit pronounced fluctuations during operation.

Discussion
We develop a strategy for modifying the perovskite/HTL interface using SAMs. The SAMs, particularly SFX-P1, exhibit strong and ordered molecular packing on the perovskite surface (achieved through solvent engineering), which effectively minimizes surface defects and enhances hole transfer to the homologous SFX-DM HTL. The dipole-induced energy-level modulation minimizes the interfacial energy offset to 90 meV, accelerating hole extraction and transfer. The uniform and densely packed SFX-P1 layer further improves carrier dynamics, resulting in a remarkable PCE of 26.18% (certified 26.23%) in n-i-p PSCs, along with enhanced long-term durability. Notably, encapsulated devices retain 89.6% of their initial efficiency after 1300 hours of MPP tracking under real-world conditions, with a projected T 80 lifetime of 2800 hours. Furthermore, this SAM interfacial modification is also effective in p-i-n PSCs, confirming its universality across different device architectures. This study introduces SAMs for perovskite surface modification and extends their applicability beyond specific device configurations, providing insights into the structural design of SAMs. In the future, tailoring SAM molecular structures and optimizing solvent processing are expected to play key roles in advancing perovskite photovoltaic technology.

Methods
Materials
Fluorine doped tin oxide (FTO) coated glass (TEC; 7 Ω sq−1, Advanced Election Technology Co., Ltd.), formamidinium iodide (FAI; 99.90%, Advanced Election Technology Co., Ltd.), lead (II) iodide (PbI 2; 99.999%, Advanced Election Technology Co., Ltd.), Spiro-OMeTAD (99.86%, Advanced Election Technology Co., Ltd.), Nickel oxide nanoparticles (NiOx, 99.999%, Advanced Election Technology Co., Ltd.), Fullerene (C60, 99.5%, Advanced Election Technology Co., Ltd.), Bathocuproine (BCP, 99.5%, Advanced Election Technology Co., Ltd.), Hellmanex (special cleaning concentrate for cuvettes, Sigma Aldrich), isopropyl alcohol (IPA; 99.9%, TCI), ethyl ether (Et 2O; Sinopharm Chemical Reagent), chloroform (CF; Sinopharm Chemical Reagent), titanium diisopropoxide bis(acetylacetonate) (75% in TPA, TCI), ethanol (≥99.5%, Aladdin), tin (IV) oxide (SnO 2) colloid precursor (15% in H 2O colloidal dispersion, Alfa Aesar), polyacrylic acid (PAA, avg. MW=450,000, Sigma Aldrich), 3-amino-1-propanesulfonic acid (SA; >98%, Sigma Aldrich), cesium iodide (CsI; >99%, TCI), methylammonium chloride (MACl; 99.5%, Xi’an Yuri Solar Co., Ltd.), li-bis(trifluoromethanesulfonyl)imide (Li-TFSI; 99%, Xi’an Yuri Solar Co., Ltd.), 4-tert-butylpyridine (tBP; 99%, Xi’an Yuri Solar Co., Ltd.), piperazine dihydriodide (PipDI, 99.5%, Xi’an Yuri Solar Co., Ltd.), N,N-dimethylformamide (DMF; 99.8%, Sigma-Aldrich), dimethyl sulfoxide (DMSO; 99.9%, Sigma-Aldrich), chlorobenzene (CB; 99.8%; Sigma-Aldrich), 2,7-dibromo-9H-fluoren-9-one (98%, Cat No. 1137728, Leyan, Shanghai, China), sodium tert-butoxide (NaOtBu; 99%, Cat No. 1253505, Leyan, Shanghai, China), tris(dibenzylideneacetone)dipalladium(0) (Pd 2(dba) 3; 98%, Cat No. 1034548, Leyan, Shanghai, China), p-Toluenesulfonic acid monohydrate (98%, Cat No. 1037939, Leyan, Shanghai, China), potassium carbonate (99%, Cat No. 1715105, Leyan, Shanghai, China), tri-tert-butylphosphonium tetrafluoroborate (P(tBu) 3HBF 4, 98%, Energy Chemicals), resorcinol (99%, Energy Chemicals), 1,2-dibromoethane (98%, Energy Chemicals), triethyl phosphite (98%, Energy Chemicals), bromoethane (99%, Energy Chemicals), bromotrimethylsilane (98%, Energy Chemicals). All chemical reagents were used as received without further purification unless otherwise specified.

Device fabrication
For fabricating n-i-p perovskite solar cells, the patterned FTO substrate was sequentially cleaned with Hellmanex (2%, deionized water), deionized water, acetone, and IPA in an ultrasonic bath, each for 20 min. The FTO substrate was then further cleaned using a UV-Ozone surface treatment for 15 minutes. A compact TiO 2 layer was deposited on top of the FTO glass using the spray pyrolysis method (O 2 as the carrier gas), and the substrate was preheated to 450°C. A compact TiO 2 precursor solution was prepared by diluting 0.6 mL titanium diisopropoxide bis(acetylacetonate) (75 wt% in isopropanol) in 5.4 mL absolute ethanol. Note that the spraying process must be even and dense. After spray pyrolysis, the FTO/c-TiO 2 substrate was heated at 450°C for 1 h and then cooled to ambient temperature. The thickness of c-TiO 2 is about 20 nm. The compact SnO 2 layer was fabricated by the PAA modification method. SnO 2 colloid precursor was diluted 25 times with deionized water and then mixed with PAA (1 mg mL−1) under stirring at 80°C for 2 h. The resulting solution was spin-coated onto the c-TiO 2 layer at 4000 rpm (2000 rpm s−1) for 30 s. The substrates were heated at 160°C for 30 min, followed by spin-coating 1 mg mL−1 SA solution at 3000 rpm (2000 rpm s−1) for 30 s and annealing at 100°C for 10 min. Before perovskite deposition, the FTO/TiO 2/SnO 2 substrate was treated with UV-Ozone for 15 min. The perovskite precursor solution comprising 20.2 mg MACl, 232.2 mg FAI, 39 mg CsI, 691.5 mg PbI 2, in 1 mL DMF-DMSO (4:1, v/v) was spin-coated in two steps, namely, 1000 rpm (500 rpm s−1) for 5 s and 6,000 rpm (2000 rpm s−1) for 45 s. With 20 s remaining, Et 2O (1 mL for FTO area of 15 mm × 15 mm) was quickly dispensed onto the middle of the substrate, and the films were annealed at 150°C for 10 min in ambient conditions (relative humidity of 30-40%). The 60 μL of SFX-P1 or SFX-P2 dissolved in CB or CF (0.5, 1, 1.5, or 2 mg mL−1) was dynamically spin-coated onto the perovskite film at 4000 rpm for 30 s, followed by annealing at 70°C for 5 min. The HTM was deposited on the perovskite film by depositing a doped HTMs solution at 4000 rpm for 25 s. The Spiro-OMeTAD solution (95 mg mL−1 in CB) doped with 39 μL tBP, 23 μL Li-TFSI (520 mg mL−1 in acetonitrile). The SFX-DM solutions (50 mg mL−1 in CB) were doped with 28 μL tBP, 17.5 μL Li-TFSI (520 mg mL−1 in acetonitrile). The Au electrode was thermally evaporated under high vacuum (<10−5 Pa) on top of the devices with the shadow mask. The thickness of the Au electrode was adjusted to 80 nm, and the evaporation speed was adjusted to 0.01 nm s−1 for the first 10 nm, 0.02 nm s−1 for the thickness between 10 nm and 20 nm, and 0.08 nm s−1 for the remaining 60 nm.

For fabricating p-i-n perovskite solar cells, the patterned ITO substrate was sequentially cleaned with Hellmanex (2%, deionized water), deionized water, acetone, and IPA in an ultrasonic bath, each for 20 min. The ITO substrate was then further cleaned by UV-Ozone surface treatment for 15 min. After that, NiOx (10 mg mL−1 in H 2O: IPA=3:1) solution was spin-coated onto the ITO substrate at 2000 rpm for 30 s and annealed in air at 120°C for 20 min. The 60 μL of SFX-P1 or SFX-P2 dissolved in CF (1 mg mL−1) was dynamically spin-coated onto the ITO/NiOx substrate at 5000 rpm for 30 s, followed by annealing at 70°C for 5 min. Afterwards, 100 μL of CF solution was dynamically spin-coated on ITO/NiOx/SAM substrate to wash away the disordered molecular arrangement. The perovskite precursor solution comprising 245.04 mg FAI, 19.5 mg CsI, 691.5 mg PbI 2, in 1 mL DMF-DMSO (4:1, v/v) was spin-coated in two steps, namely, 2000 rpm (1000 rpm s−1) for 10 s and 4000 rpm (2000 rpm s−1) for 45 s. With 8 s remaining, CB (200 μL for ITO area of 25 mm ⅹ 25 mm) was quickly dispensed onto the middle of the substrate, and the films were annealed at 110°C for 20 min in a N 2 glove box. Then, PipDI dissolved in IPA (0.3 mg mL−1 in IPA) solution was dynamically spin-coated on perovskite at 5000 rpm for 30 s and annealed at 110°C for 5 min. C60 (25 nm), BCP (7 nm), and Ag (100 nm) were thermally evaporated under high vacuum (<10−5 Pa) onto the perovskite films with the shadow mask.

Computational details
The theoretical calculations were performed as follows. ESP mapping profile and ground-state orbital distribution of the Spiro-OMeTAD and SFX-based molecules were studied by performing B3LYP calculations with 6-31G(d,p) basis set in Gaussian 09 software package. Then, the Vienna Ab Initio Simulation Package (VASP) program was used to investigate the binding energy, assembly structures, and charge redistributions between the SFX-based molecules and FAPbI 3 perovskite. The generalized gradient approximation in the form of Perdew-Burke-Ernzerhof (GGA-PBE) was used for the exchange correlation function. All the geometry optimizations were performed with a cut-off energy of 400 eV and 3 × 3 × 1 k-point sampling. The convergence criteria for forces and energies were 0.05 eV Å−1 and 10−6 eV, respectively. The optimized SFX-based molecules were added to the target surfaces to simulate their adsorption geometry and energy on the FAPbI 3 perovskite (001) surfaces.

Characterization and measurements
The material characterizations were performed as follows. NMR spectra were recorded on an Agilent VNMRS 400 (or 600) MHz, and the chemical shifts were referenced internally using the residual solvent resonances. Matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrum was acquired using an auto flex max Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry. UV-vis absorption spectra were recorded using a Shimadzu UV-2450 spectrophotometer. CV was carried out on a CHI 760E electrochemical workstation in dichloromethane containing tetrabutylammonium hexafluorophosphate (Bu 4NPF 6) (0.1 M) at a scan rate of 50 mV s−1 at room temperature under the protection of argon. The thermal decomposition temperatures of HTM were measured using TGA (Diamond TG/DTA) at a heating rate of 10°C min−1 under nitrogen protection with a heating range of 30-600°C. DSC (Discovery-DSC Q20) was performed under nitrogen flushing at a heating rate of 10°C min−1 from 30 to 250°C.

The film sample characterizations were performed as follows. The XPS and UPS were recorded by PHI 5000 VersaProbe III. PYS (AC-2, Riken keiki) was performed to measure the ionization potential of thin films in air. SEM images were taken on a JEOL JSM-7800. AFM, C-AFM, and KPFM were recorded using a Cypher ES, Oxford Instruments, UK. AFM-IR for measuring the mapping of IR response was conducted on the ICON IR AFM-IR system (tapping mode, BRUKER) using an antimony-doped Si tip with reflective Au coating (spring constant: 42 Nm−1), the scanning size was 2 × 2 μm2. GIWAXS images represented in the reciprocal lattice space were collected at the BL19B2 beamline at SPring-8 (Japan). The perovskite films were irradiated with an X-ray energy of 12.39 keV at a fixed-incident angle on the order of 0.12° and 2° through a Huber diffractometer. The 2D-GIWAXS images were recorded with a two-dimensional image detector (Pilatus 300K). The PL and TRPL spectra were measured on a fluorescent spectrometer (FLS920). Confocal PL intensity maps were recorded with a laser confocal Raman spectrometer (Princeton Instruments, Acton Standard Series SP-2558) equipped with a 485 nm laser (PicoQuant LDH-P-C-485, 0.4 mW with a 1% optical density filter) using a home-built confocal microscope. Fs-TAS studies were performed on a home-made pump-probe system including a CMOS detector (S12198-1024Q, Hamamatsu) and the InGaAs photodiode array (G9203-256DA, Hamamatsu). The light source is generated by a Yb:KGW laser (Light conversion, Pharos, 1030 nm, 1 kHz repetition rate, 150 fs, 2 mJ per pulse), and the output laser was split into the pump beam and probe beam. The pump beam was used to generate the 515 nm excitation, and the probe beam was focused on a YAG plate to generate continuous white light. Water contact angles were measured using a JC2000D1 (manufacturer) contact angle instrument.

The device characterizations were performed as follows. TOF-SIMS (IONTOF system, PS02B11) was applied to detect the elemental depth profiles in the PSC in a negative-ion mode. A Bi+ primary beam (30 keV and 3 pA) and a Cs+ sputter beam (1 keV and 75 nA) were used for ToF-SIMS measurement. The sputter size was 500 μm × 500 μm, and the analysis size was 100 μm × 100 μm for depth profiling. The light source for the J-V measurements comprises an AM 1.5G solar simulator. The incident light intensity was 100 mW cm−2, calibrated with a standard Si solar cell. The J-V curves were obtained by the linear sweep voltammetry (LSV) method using a Keithley 2400 source-measure unit. The measurement of the EQE was performed with a Newport QEPVSI-B photoelectric chemical quantum efficiency testing and analysis system. The active areas of the laboratory-test solar cells are 0.0625 cm2 and 1 cm2, and the aperture area for certification is 0.0434 cm2.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Dear Editor:\nA manuscript entitled “Self-Assembled Molecules for Perovskite Surface Modification” reported enhanced efficiency and\nstability by SAM modification on the perovskite top surface in n-i-p PSCs. In contrast to buried SAM interfaces in p-i-n PSCs,\nthe authors innovatively designed SAM molecules that can be strongly associated with HTL and systematically analyzed the\nbeneficial role of SAM for top interfaces in n-i-p PSCs. In addition, the authors investigated the effect of solvent on SAM\norientation and the importance of SAM interfacial dipoles, which is crucial for research in the field. These SAM not only\ncontribute to the superior performance of n-i-p devices but also apply equally well to p-i-n devices. This manuscript’s\nfindings could provide a guide for designing novel high-performance SAM; thus, I recommend acceptance of this manuscript\nafter the following minor comments are properly considered or addressed.\n1. Does the schematic in Figure 1g imply that carriers pass through the gap between the SAM?\n2. The Pb peaks of PSK/SFX-P1 and PSK/SFX-P2 seem to exhibit different behavior in XPS characterization. The authors\nshould discuss the reasons for this.\n3. Theoretical calculations show that the binding energy of SFX-P2 is much higher than that of SFX-P1. However, the defect\nstate density and performance show that the SFX-P1-based device is better. Can the authors analyze the reasons for this?\nOr what is the dominant factor for the performance improvement?\n4. The difference in peak strength between the GIWAXS 2D pattern and the 1D profile line diagram for perovskite is barely\ndiscernible. I think the authors can present the data more clearly in table form.\n5. Unnecessary text is present in Figure S12.\n6. Could the SFX-P1 modification layer improve reproducibility in large-area fabrications?\n7. The authors mentioned that SFX-SAM can enhance the performance of p-i-n PSCs through dipole interaction. However,\nno data on the energy levels of the SAM/perovskite interface in p-i-n PSCs have been provided in the manuscript.\n8. What is the purpose of using PEACl in the p-i-n PSCs? Is PEACl also used in NiOx-only devices? I think evaluating the\nrole of the SAM layer in the p-i-n device should not include an additional PEACl layer.\n9. Please provide the IPCE data in the p-i-n device to evaluate the effect of SAM on light absorption in the range of 300 nm\nto 450 nm.\n10. The manuscript mentioned the solvent effect on SAM orientation. I suggest that the authors appeal to researchers in the\nconclusion to focus on this issue to better optimize SAMs and thus advance the development of PSCs.", "reviewer_2": "Perovskite solar cells has attracted great attention for its rapidly enhanced power conversion efficiency and facile device\nfabrication process. The interface between perovskite layer and hole transporting layer determines the device efficiency and\nstability. Recently, interface engineering has been proved as efficient way the enhance device performance. In this work,\nauthors have introduced a self-assembled molecule into the interface. Though the device efficiency and stability were\nenhanced, which can not be accepted in this journal for the following questions.\n1. High device performances would be one of the key issues in PSC research. Therefore, authors must certify the\nphotovoltaic parameters which would further strengthen the superiorities of the new HTMs in this work and make the results\nare more convincing.\n2. Did the authors study the effects of the concentration of doped-HTMs on the device performance?\n3. The fully UPS figure should be provided.\n4. How about the light-soaking stability of the device at high temperature.\n5. In previous reports, though spiro-OMeTAD or SFX-DM own high Tg, which would decrease after doping with TBP and Li-\nTFSI. Therefore, the device can not show high stability. [https://doi.org/10.1038/s41560-018-0200-6]\n6. The monolayer should be further confirmed using different method.", "reviewer_3": "The paper by Zhai et al. introduced new SAMs as interlayers primarily for nip-type perovskite cells. 2 SAMs, namely SFX-P1\nand SFX-P2, improve the performance of nip-type cells from about 23% to 26%. The working mechanism is attributed to\nvarious factors: perovskite surface defect passivation, improved energy alignment, enhanced hole extraction, and partially\nenhanced built-in voltage. The stability improves as well, although not quite to the state-of-the-art values achieved for\nperovskite cells. The manuscript is solid, contains a lot of data, and the results are valuable. However, unfortunately, the\ninterpretation of some results falls into various traps that are present in the literature, especially related to the passivation.\nTherefore, I would suggest a major revision of the manuscript before a renewed review.\nFirstly, with regard to the device performance, I think a certification should be provided for an NC-level publication. The\nEQE-integrated current seems to be somewhat off as well.\nWith regard to the passivation of the perovskite surface through the SAMs, I am not quite convinced about that. On the\nhand, this is due to the reduction of the PL emission (S45), which is not consistent with defect passivation. The shifts in the\nPb4f core levels do not prove defect passivation either.\nAlso, other measurements provide no further evidence for passivation, such as SCLC and the intensity-dependence of the\nVoc. Please note that it has been shown several times (https://dx.doi.org/10.1021/acsenergylett.0c02599,\nhttps://doi.org/10.1021/acsenergylett.1c01449), that SCLC on such thin films cannot be used to determine the trap density.\nThere are at least 5 factors that make the trap density estimation unreliable.\nRegarding the ideality factor, a value closer to 1 rather than 2 indicates by no means a radiative recombination-dominated\nprocess. It's clear from the PL that non-radiative recombination dominates by far. Also, it does not mean that radiative\nrecombination becomes more dominant if the values go to 1. In fact, it can be the opposite, that a value close to 1 indicates\nsevere interfacial or surface recombination (e.g. DOI: 10.1039/c7ee02415k, DOI: 10.1021/acsenergylett.6b00719). The\nintensity range used is also very small. Please try to improve the argument here, or remove it since it does not add much\nvalue in my opinion.\nJudging from the strong dipole effects and better energy alignment, I think the energy alignment will very likely be able to\nexplain the gain in Voc and partially FF, while better charge extraction is also likely due to the dipole effect.\nIn general, I would strongly suggest including drift-diffusion simulations to back up the interpretation of these results.\nSimilar to above, with regard to the reduction of the PL emission in the presence of the transport layer, this cannot be taken\nas proof of better charge extraction (although it might be related to extraction). At the end, given that the PL is the ratio of\nradiative to total recombination, it means that the non-radiative recombination increases in the presence of the transport\nlayer with the SAMs (Figure S61), limiting the QFLS and Voc-potential. It's hard to explain a better device performance with\nsuch a reduction of the radiative efficiency in the presence of the SAM and transport layer. Maybe this has something to do\nwith lateral diffusion if an extremely small laser spot was used for the measurement (I am not sure; details such as intensity\nand laser spot should be provided in the caption). I would strongly suggest avoiding correlating quenching in PL with\nimproved charge extraction. Perhaps, the TRPL decay and TAS are better ways to analyse the enhanced charge extraction,\nif their influence can be clearly disentangled from interfacial recombination.\nAnother point with regard to TRPL is the averaging of the 2 decay times to obtain an average lifetime. Considering that the\ndifferent decay components include charge transfer and interfacial recombination, it does not make sense to me to specify\nan average lifetime. Please try to disentangle extraction and recombination and specify the characteristic time constants for\nboth processes. Furthermore, the laser fluence should be specified to correctly interpret the results.\nAs for the Vbi, its determination from the Mott-Schottky analysis is also not straightforward (DOI: 10.1021/acsaem.8b01119). There might be some correlation between the apparent Vbi and the real Vbi, but often, the extrapolation just follows the Voc.\nI would suggest adding at least a comment that the interpretation is still up for debate for thin film perovskite, or providing DD\nsimulations for further justification.\nOverall, I would suggest identifying the dominant mechanism governing the improvement, rather than proposing a large\nrange of mechanisms, potentially putting more emphasis on the improved energy alignment, removing questionable\ninterpretation and corresponding data (considering that the manuscript certainly has sufficient data), and corroborating the\ninterpretation with DD simulations.", "reviewer_4": "The manuscript entitled: \"Self-assembled molecules for perovskite surface modifications' presents an original approach to\nusing self-assembled molecules as selective contacts in perovskite solar cells\". However, the results pertain only to a single\ntype of molecular structure, despite the authors' aim to extend their findings to a broader perspective, with which I disagree\nentirely. The hype in the title, which I believe aims to generalise the findings, would be more appropriate for an extensive\nreview rather than a communication. Moreover, in the abstract, the authors assume that the observed large dipole on their\nparticular molecules is the sole reason for the improvement in their device performance. They claim that the underlying\nmodification mechanisms and molecular design principles for the SAMS action remain unclear, yet it is evident that a myriad\nof manuscripts already explain the different actions observed for SAMS on perovskite solar cells depending on their\nmolecular structure. Several reviews compile these various actions, and the authors have neglected to cite them in this\nmanuscript.\nRegarding the science in the manuscript, I believe that the authors have assembled a comprehensive collection of\ncharacterisation techniques to support their hypothesis, which includes both experimental and computational work. Indeed, the\nresults bolster their specific hypothesis. Moreover, the achieved efficiency in n-i-p devices is remarkable, as well as the\nstability. However, to the best of my knowledge, there is nothing new that justifies an urgent communication instead of a\nmore structured manuscript. Neither the approach nor the hypothesis is novel, and the efficiency and stability of perovskite\nsolar cells are well documented in the bibliography.\nLast but not least, the references used by the authors fall short in providing perspective for Sams-based solar cells. They\nhave cited important work on dipole moments, perovskite composition, and others, but have missed or neglected important\nreferences on SAMS from pioneering groups and significant work that describes the use of SAMS as dipoles ( for instance,\nAbate et al.)."}, "author_response": "Response to reviewers:\nReviewer 1 comments:\nA manuscript entitled “Self-Assembled Molecules for Perovskite Surface Modification”\nreported enhanced efficiency and stability by SAM modification on the perovskite top\nsurface in n-i-p PSCs. In contrast to buried SAM interfaces in p-i-n PSCs, the authors\ninnovatively designed SAM molecules that can be strongly associated with HTL and\nsystematically analyzed the beneficial role of SAM for top interfaces in n-i-p PSCs. In\naddition, the authors investigated the effect of solvent on SAM orientation and the\nimportance of SAM interfacial dipoles, which is crucial for research in the field. These\nSAM not only contribute to the superior performance of n-i-p devices but also apply\nequally well to p-i-n devices. This manuscript’s findings could provide a guide for\ndesigning novel high-performance SAM; thus, I recommend acceptance of this\nmanuscript after the following minor comments are properly considered or addressed.\n1.Does the schematic in Figure 1g imply that carriers pass through the gap between the\nSAM?\nResponse:\nWe appreciate the reviewer’s careful observation. The schematic in Figures 1g-h\nis intended to illustrate the potential differences in hole transfer at the interface, rather\nthan implying that carriers physically pass through the gaps between the SAM\nmolecules. To avoid any confusion, we have revised the schematic accordingly in\nFigures 1g-h of the revised manuscript.\nRevision:\nhole transport characteristics of SAM layers fabricated with (g) CB and (h) CF solvents.\n2. The Pb peaks of PSK/SFX-P1 and PSK/SFX-P2 seem to exhibit different behavior\nin XPS characterization. The authors should discuss the reasons for this.\nResponse:\nWe appreciate the reviewer’s helpful comment. We have added the following\ndiscussion to clarify this point on Page 13 of the revised manuscript.\nRevision:\n“In the perovskite/SFX-P2 film, stronger ionic Pb-O bonding signals arising from\nthe interaction between Pb2+ and -P-O- ions were observed at 138.25 eV and 143.10 eV,\nwhich led to the shift of the Pb peaks toward higher binding energies. The difference in\nXPS curves between SFX-P1 and SFX-P2 can be attributed to the stronger anchoring\neffect of SFX-P2, enabled by its double phosphoric acid groups. This result is consistent\nwith the calculated binding energy values.”\n3.Theoretical calculations show that the binding energy of SFX-P2 is much higher than\nthat of SFX-P1. However, the defect state density and performance show that the SFX-\nP1-based device is better. Can the authors analyze the reasons for this? Or what is the\ndominant factor for the performance improvement?\nResponse:\nWe appreciate the reviewer’s insightful suggestion. The defect state density and\ndevice performance are influenced by several interrelated factors. Although SFX-P2\n2\nexhibits stronger interaction with the perovskite surface due to its double phosphoric\nacid anchoring groups, this also results in less favorable molecular adsorption, as\nrevealed by AFM-IR and PL mapping. Poorer and non-uniform adsorption behavior\ncan hinder effective interfacial defect passivation.\nIn addition, the interfacial dipole effect differs significantly between the two\nSAMs. In practical devices, the larger dipole moment of SFX-P1 reduces the interfacial\nenergy-level offset, thereby enhancing hole extraction and overall optoelectronic\nperformance. Therefore, the dominant factors governing device performance are\nmolecular adsorption behavior and interfacial energy-level modulation.\nWe have added the following discussion on this point on Page 17 of the revised\nmanuscript.\nRevision:\n“The above results and discussion indicate that molecular adsorption behavior and\ninterfacial energy-level modulation are the dominant factors affecting the performance\nof SFX-P2- and SFX-P1-based devices.”\n4.The difference in peak strength between the GIWAXS 2D pattern and the 1D profile\nline diagram for perovskite is barely discernible. I think the authors can present the data\nmore clearly in table form.\nResponse:\nWe appreciate the reviewer’s helpful suggestion. To present the data more clearly,\nwe have added a table in the revised Supporting Information summarizing the\ncrystalline intensities derived from the 2D GIWAXS patterns.\nRevision:\nTable S6. The values of crystalline intensity derived from the 2D GIWAXS patterns.\nSamples hkl Intensity\n001 38095\nPSK\n002 17318\n001 40006\nPSK/SFX-P2\n002 18566\n001 40153\nPSK/SFX-P1\n002 17726\n3\n5.Unnecessary text is present in Figure S12.\nResponse:\nWe appreciate the reviewer’s careful observation. We have updated Figure S12 in\nthe revised Supporting Information to remove the unnecessary text.\nRevision:\nFigure S12. 31P-NMR spectrum of compound 4 recorded in THF-d .\n8\n6. Could the SFX-P1 modification layer improve reproducibility in large-area\nfabrications?\nResponse:\nWe appreciate the reviewer’s constructive comment. To evaluate the\nreproducibility in large-area fabrication, we fabricated 12 individual 1 cm2 PSCs for\nboth the control and SFX-P1@CF-based devices. As shown in Figure S44, the SFX-P1\nmodification significantly improved the reproducibility of performance. The\ncorresponding data have been added to the revised Supporting Information, and the\ndiscussion on Page 9 of the manuscript has been updated accordingly.\nRevision:\n“We also achieved a high efficiency of 24.29% in a 1 cm2 SFX-P1@CF device\n(Figure 2f and Table S4), together with improved reproducibility (Figure S44),\ndemonstrating the scalability of SAM modification for fabricating high-performance\nlarge-area PSCs.”\nOC SC\n12 individual 1 cm2 PSCs using SFX-DM as HTL without and with SFX-P1 SAM\nmodification. The processing solvent for SAM is CF.\n7.The authors mentioned that SFX-SAM can enhance the performance of p-i-n PSCs\nthrough dipole interaction. However, no data on the energy levels of the\nSAM/perovskite interface in p-i-n PSCs have been provided in the manuscript.\nResponse:\nWe appreciate the reviewer’s helpful comment. To clarify this point, we conducted\nUPS measurements to investigate the energy alignment at the buried perovskite\ninterface in p-i-n devices (Figures S74-S76). The corresponding discussion has been\nadded to Page 17 of the revised manuscript.\nRevision:\n“In the p-i-n architecture, SAMs anchor directly onto the NiOx surface, and the\nhomologous interaction between the SAM and HTL, discussed in the n-i-p structure, is\nabsent. Consequently, dipole-moment modulation and enhanced hole extraction\nbecome the primary mechanisms driving performance improvement. To verify this, we\nemployed UPS to investigate the band alignment at the buried interface. As shown in\nFigures S74-S76, the SAM with negative dipole orientation at the buried interface\nreduces the work function of the NiOx layer and simultaneously induces a downward\nshift in the perovskite Fermi level.The resulting energy-level alignment, characterized\n5\nby a reduced interfacial energy barrier, facilitates more efficient separation and\ntransport of photo-generated holes at the perovskite bottom interface. Therefore, in p-\ni-n PSCs, our SAMs also effectively regulate interfacial energy alignment and enhance\nhole extraction.”\nFigure S74. UPS spectra of NiOx, NiOx/SFX-P2 and NiOx/SFX-P1 at the buried\ninterface, respectively.\nP1 substrates, respectively.\nFigure S76. Energy level diagram of the NiOx, NiOx/SFX-P2 and NiOx/SFX-P1-\ntreated perovskite film at the buried interface.\n7\n8.What is the purpose of using PEACl in the p-i-n PSCs? Is PEACl also used in NiOx-\nonly devices? I think evaluating the role of the SAM layer in the p-i-n device should\nnot include an additional PEACl layer.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. In the initial manuscript,\nthe PEACl layer was employed to improve the wettability of the NiOx film during\nperovskite deposition. As suggested by the reviewer, to exclude the influence of PEACl,\nwe fabricated p-i-n devices without this additional layer. The corresponding results and\ndiscussion have been added on Page 17 of the revised manuscript.\nRevision:\n“We fabricated p-i-n devices with the structure\nITO/NiOx/SAM/perovskite/C60/BCP/Ag and evaluated their photovoltaic\nperformance (Figure S72). The corresponding EQE spectra (Figure S73) indicates that\nthe SAM layer has a negligible effect on light absorption in the 300-450 nm range,\nwhich can be attributed to its minimal parasitic absorption. Compared with the control\np-i-n PSCs, which exhibited a PCE of 22.71% (reverse scan) and 22.22% (forward\nscan), the device incorporating the SFX-P1 SAM achieved higher performance of 24.10%\n(reverse scan) and 23.93% (forward scan), along with reduced hysteresis.”\nFigure S72. (a) Device architecture of the p-i-n PSCs. (b) J-V curves of champion p-i-\nn PSCs without SAM modification. (c) J-V curves of champion p-i-n PSCs with SFX-\nP2 SAM modification. (d) J-V curves of champion p-i-n PSCs with SFX-P1 SAM\nmodification.\n9. Please provide the IPCE data in the p-i-n device to evaluate the effect of SAM on\nlight absorption in the range of 300 nm to 450 nm.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. The corresponding EQE\nspectra for the p-i-n-type PSCs have been added to the revised Supporting Information\n(Figure S73). The results show that the SAM layer has a negligible influence on light\nabsorption in the 300-450 nm range, which can be attributed to its minimal parasitic\nabsorption. The related discussion has been incorporated on Page 17 of the revised\nmanuscript.\nRevision:\n“The corresponding EQE spectra (Figure S73) indicates that the SAM layer has a\nnegligible effect on light absorption in the 300-450 nm range, which can be attributed\nto its minimal parasitic absorption.”\nFigure S73. EQE plots (left) and integrated J (right) of p-i-n type PSCs without and\nSC\nwith SFX-P2 or SFX-P1 SAM modification.\n10.The manuscript mentioned the solvent effect on SAM orientation. I suggest that the\nauthors appeal to researchers in the conclusion to focus on this issue to better optimize\nSAMs and thus advance the development of PSCs.\nResponse:\nhave updated the conclusion on Page 20 of the revised manuscript to emphasize the\nimportance of solvent effects in guiding future SAM optimization.\nRevision:\n“The SAMs, particularly SFX-P1, exhibited strong and ordered molecular packing\non the perovskite surface (achieved through solvent engineering), which effectively\nminimized surface defects and enhanced hole transfer to the homologous SFX-DM\nHTL.”\n“This study introduces novel SAMs for perovskite surface modification and\nextends their applicability beyond specific device configurations, providing new\ninsights into the structural design of SAMs. In the future, tailoring SAM molecular\nstructures and optimizing solvent processing are expected to play key roles in\nadvancing perovskite photovoltaic technology.”\nPerovskite solar cells has attracted great attention for its rapidly enhanced power\nconversion efficiency and facile device fabrication process. The interface between\nperovskite layer and hole transporting layer determines the device efficiency and\nstability. Recently, interface engineering has been proved as efficient way the enhance\ndevice performance. In this work, authors have introduced a self-assembled molecule\ninto the interface. Though the device efficiency and stability were enhanced, which\ncannot be accepted in this journal for the following questions.\n1.High device performances would be one of the key issues in PSC research. Therefore,\nauthors must certify the photovoltaic parameters which would further strengthen the\nsuperiorities of the new HTMs in this work and make the results are more convincing.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. We fully agree that certified\nefficiency data are essential to validate the reliability of high-performance PSCs.\nTherefore, we conducted third-party certification for our best-performing devices, and\nthe certified results are presented in Figure S42. The certified values of 26.23% for\nreverse PCE and 25.55% for forward PCE are in excellent agreement with the values\nmeasured in our laboratory, confirming the reliability of our results. The corresponding\ndiscussion has been added on Page 9 of the revised manuscript.\nRevision:\n“Meanwhile, the SFX-P1@CF-based device demonstrated an impressive PCE of\n26.18% (certified 26.23%, Figure S42), with a V of 1.19 V, a J of 26.00 mA cm-2,\nOC SC\nand an FF of 84.81%.”\n“(certified 26.23%)” was included in the Abstract and Conclusions.\n2.Did the authors study the effects of the concentration of doped-HTMs on the device\nperformance?\nResponse:\nWe appreciate the reviewer’s constructive comment. Yes, we evaluated the device\nperformance using various concentrations of doped HTMs. As shown in Figures S39-\nbe 50 mg/mL and 95 mg/mL, respectively. All subsequent studies on SAM\nmodification were performed using these optimized HTM concentrations to ensure that\nHTM loading did not influence the observed effects. The following discussion has been\nadded on Page 8 of the revised manuscript.\nRevision:\n“The optimal concentration of doped HTLs in PSCs was used to avoid the\ninfluence of HTL concentration on the SAM modification effect (Figures S39-S40).”\nFigure S39. Statistical diagrams of (a) V , (b) J , (c) FF, and (d) PCE parameters for\nOC SC\n12 individual PSCs using different concentrations of doped SFX-DM as HTL without\nany modifications.\nOC SC\n12 individual PSCs using different concentrations of doped Spiro-OMeTAD as HTL\nwithout any modifications.\n3.The fully UPS figure should be provided.\nResponse:\nWe appreciate the reviewer’s helpful comment. The complete and separated UPS\nspectra have been added to the revised Supporting Information (Figure S61) and are\nmentioned on Page 13 of the revised manuscript.\nRevision:\nSFX-P1 SAM modification.\n4.How about the light-soaking stability of the device at high temperature.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. To address this point, we\nevaluated the operational stability of the encapsulated devices under continuous light\nillumination at 85 °C and 30-40 % relative humidity, as shown in Figure S81. The\nresults show that the SFX-P1 PSCs maintain stable output even under such harsh\nconditions, owing to enhanced interfacial quality and suppressed ion migration,\nwhereas the control devices exhibit significant performance fluctuations during\noperation. The corresponding discussion has been added to Page 20 of the revised\nmanuscript.\nRevision:\n“Even under severe high-temperature conditions with continuous light\nillumination (Figure S81), the SFX-P1 PSCs maintained stable output due to enhanced\n14\ninterfacial quality and suppressed ion migration, in contrast to the control devices,\nwhich exhibited pronounced fluctuations during operation.”\nFigure S81. Operational stability measurements of encapsulated PSCs without and with\nSFX-P1 SAM modification under one-sun illumination in ambient air (30-40%\nhumidity) at 85 °C with MPP tracking.\n5.In previous reports, though spiro-OMeTAD or SFX-DM own high Tg, which would\ndecrease after doping with TBP and Li-TFSI. Therefore, the device cannot show high\nstability. [https://doi.org/10.1038/s41560-018-0200-6]\nResponse:\nWe appreciate the reviewer’s insightful comment. As correctly noted, Jangwon\nSeo et al. (https://doi.org/10.1038/s41560-018-0200-6) reported that the T of DM and\ng\nspiro-OMeTAD were 161 °C and 121 °C, respectively, but decreased to 90 °C and\n50 °C after the addition of dopants such as TBP and Li-TFSI. In their study, the PSCs\nbased on doped DM exhibited better thermal stability owing to the intrinsically higher\nT of DM, and they concluded that employing an HTM with a high T is beneficial for\ng g\nimproving device stability.\nSubsequent studies (Nat Photonics 2022, 16, 119-125; Energy Environ Sci 2023,\n16, 3534-3542; Angew Chem Int Ed 2023, 62, e202304350; ACS Energy Lett 2025,\n10, 915-924) have also demonstrated that structural modification of spiro-OMeTAD to\nraise T enhances the thermal stability of PSCs.\ng\nIn this work, we evaluated the T of the HTM SFX-DM used in our devices. As\ng\nshown in Figure R1, SFX-DM exhibits a T of 152.2 °C, higher than that of spiro-\ng\nelevated temperatures than the latter. However, as commented by the reviewer, T is\ng\nreduced after doping, making our control device employ SFX-DM retain only 50 % of\nits initial efficiency after 300 hours of MPP tracking at 85 °C. On the other hand, the\nSFX-P1-modified device showed markedly enhanced durability, which we attribute to\nthe improved interfacial quality and suppressed ion migration induced by the SAM\nmodification.\nFigure R1. DSC analysis curves of SFX-DM.\n6.The monolayer should be further confirmed using different method.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. In most reports, the term\nself-assembled monolayer (SAM) is used to describe single-molecule hole-transporting\nlayers in inverted PSCs, although their true monolayer nature on metal oxide or\nperovskite surfaces has not been conclusively verified. As highlighted in a recent report\n(ACS Energy Lett 2025, 10, 5192-5198), researchers have begun reconsidering whether\n“self-assembled monolayer” is an appropriate term in this context.\nIn this work, we intentionally use the term self-assembled molecules (SAMs)\ninstead of self-assembled monolayers, where “self-assembled” refers to the chemical\nanchoring behavior on the perovskite surface rather than the formation of an ideal\nmonolayer. Given the rougher morphology of perovskite films compared with ITO or\nNiOx substrates, forming a true monolayer is unlikely. Our AFM-IR results reveal a\nuniform molecular distributionthat could not be achieved by a perfect monolayer. This\n16\ninterpretation aligns with previous findings showing that in some monolayer systems\non metal oxides, the actual coverage is often below 40% (J Am Chem Soc 2023, 145,\n13, 7528-7539; J Am Chem Soc 2025, 147, 3, 2797-2808), which would not produce\nthe AFM-IR features observed in our study.\nWe acknowledge that confirming monolayer formation would require atomic-\nresolution techniques such as scanning tunneling microscopy (STM) or low-energy\nelectron diffraction (LEED). As these methods are not applicable to our spin-coated\nperovskite surfaces, we believe that “self-assembled molecules” to be a more accurate\nand broadly acceptable term. To clarify this point, we have added the following\nexplanation on Page 4 of the revised manuscript.\nRevision:\n“Self-assembled molecules (SAMs, note that the term “self-assembled monolayer”\nis not used here due to the difficulty of verifying true monolayer formation), such as\nMe-4PACz and MeO-2PACz, which feature a phosphonic acid anchoring group and a\ncarbazole terminal group, are widely employed in high-efficiency p-i-n perovskite solar\ncells (PSCs).”\nThe paper by Zhai et al. introduced new SAMs as interlayers primarily for nip-type\nperovskite cells. 2 SAMs, namely SFX-P1 and SFX-P2, improve the performance of\nnip-type cells from about 23% to 26%. The working mechanism is attributed to various\nfactors: perovskite surface defect passivation, improved energy alignment, enhanced\nhole extraction, and partially enhanced built-in voltage. The stability improves as well,\nalthough not quite to the state-of-the-art values achieved for perovskite cells. The\nmanuscript is solid, contains a lot of data, and the results are valuable. However,\nunfortunately, the interpretation of some results falls into various traps that are present\nin the literature, especially related to the passivation. Therefore, I would suggest a major\nrevision of the manuscript before a renewed review.\n1. Firstly, with regard to the device performance, I think a certification should be\nprovided for an NC-level publication. The EQE-integrated current seems to be\nsomewhat off as well.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. We conducted third-party\ncertification for our best-performing devices, as shown in Figure S42 in the revised\nmanuscript. The certified values of 26.23% for reverse PCE and 25.55% for forward\nPCE are in excellent agreement with the values measured in our laboratory, confirming\nthe reliability of our results.\nRegarding the EQE-integrated current, it is common for J to be slightly\nSC, EQE\nlower than the J in PSCs. This difference arises because the J-V measurement is\nSC, JV\nperformed under strong AM1.5G illumination (100 mW/cm2), whereas the EQE\nmeasurement uses monochromated light source (typically tungsten bromine or xenon)\nwith a power density below 1 mW/cm2, approximately two orders of magnitude lower.\nFor devices exhibiting mild nonlinear response, such as PSCs, a deviation of less than\n5% between J and J is well within the acceptable range. In this work, the\nSC, EQE SC, JV\nEQE-integrated currents of the control, SFX-P2@CF, and SFX-P1@CF devices are\n24.75 mA cm-2, 25.17 mA cm-2, and 25.36 mA cm-2, respectively. The corresponding\nSC, EQE SC, JV\nmeasurements.\nThe corresponding discussion has been added on Page 9 of the revised manuscript.\nRevision:\n“Meanwhile, the SFX-P1@CF-based device demonstrated an impressive PCE of\n26.18% (certified 26.23%, Figure S42), with a V of 1.19 V, a J of 26.00 mA cm-2,\nOC SC\nand an FF of 84.81%.”\n“(certified 26.23%)” was included in the Abstract and Conclusions.\n2.With regard to the passivation of the perovskite surface through the SAMs, I am not\nquite convinced about that. On the one hand, this is due to the reduction of the PL\nemission (S45), which is not consistent with defect passivation. The shifts in the\nPb4f core levels do not prove defect passivation either. Also, other measurements provide no\nfurther evidence for passivation, such as SCLC and the intensity-dependence of the\nVoc. Please note that it has been shown several times\n(https://dx.doi.org/10.1021/acsenergylett.0c02599, https://doi.org/10.1021/acsenergyl\nett.1c01449), that SCLC on such thin films cannot be used to determine the trap density.\nThere are at least 5 factors that make the trap density estimation unreliable.\nResponse:\nWe appreciate the reviewer’s constructive and well-founded comments. After\nreviewing the cited literature, we fully agree that the SCLC method is unreliable for\ndetermining trap densities in thin perovskite films. Accordingly, we have removed the\nSCLC data and the associated discussion on defect-density reduction from the revised\nmanuscript.\nWe also attempted to operate our PSCs as LED devices to evaluate\nelectroluminescence (EL) intensity as an indirect indicator of defect passivation, but\nthe signal was too weak to extract reliable data. At present, we lack a technical approach\nthat can conclusively confirm the defect-passivation function of SAMs on the\nperovskite surface. Therefore, in the revised manuscript, we now use the term\n19\n“interaction” instead of “defect passivation” to describe the interfacial modifications\ninduced by SAMs, in order to avoid potentially misleading interpretations.\nThe following revisions have been made.\nRevision:\nAbstract:\nOriginal: “We demonstrate that SAMs effectively reduce perovskite defects\nthrough strong molecular interactions and facilitate hole transfer when paired with the\nhomologous SFX-DM HTL.”\nRevised: “We demonstrate that SAMs effectively optimize the surface energetics\nof perovskites and facilitate hole transfer when paired with the homologous SFX-DM\nHTL.”\nPage 5:\nOriginal: “Our findings reveal that these SAMs effectively facilitate dipole tuning,\nperovskite surface defect passivation, and enhanced hole extraction.”\nRevised: “Our findings reveal that these SAMs-modified perovskite surfaces\neffectively facilitate dipole tuning and enhanced hole extraction.”.\nPage 13:\nDeleted: “Collectively, these results demonstrate that SAMs effectively passivate\nsurface defects, particularly undercoordinated Pb2+ sites.”\nOriginal: “Kelvin probe force microscopy (KPFM) was performed to examine\nsurface potential fluctuations, which are associated with surface defects.”\nRevised: “Kelvin probe force microscopy (KPFM) was performed to investigate\nthe surface energetics of perovskite films by scanning surface potential fluctuations.”\nOriginal: “These findings confirm that SAM treatment effectively reduces\nperovskite surface defect density, thereby enhancing carrier extraction and reducing\nV losses.”\nOC\nRevised: “These findings confirm that SAM treatment effectively balances the\nsurface energetics of perovskite films, thereby improving carrier extraction.”\ninterfacial layer form strong interactions with both the perovskite and HTL, efficiently\npassivating perovskite defects, enhancing hole transport, and ultimately improving\nsolar cell performance.”\nRevised: “In summary, our results confirm that SAMs, particularly the SFX-P1\ninterfacial layer, form strong interactions with both the perovskite and HTL, enhancing\nhole transport and ultimately improving solar cell performance.”\nConclusion:\nOriginal: “The strong and ordered anchoring of SAMs, particularly SFX-P1,\non the perovskite surface effectively reduced surface defects and enhanced hole transfer to\nthe homologous SFX-DM HTL.”\nRevised: “The SAMs, particularly SFX-P1, exhibited strong and ordered\nmolecular packing on the perovskite surface (achieved through solvent engineering),\nwhich effectively minimized surface defects and enhanced hole transfer to the\nhomologous SFX-DM HTL.”\n3.Regarding the ideality factor, a value closer to 1 rather than 2 indicates by no means\na radiative recombination-dominated process. It's clear from the PL that non-radiative\nrecombination dominates by far. Also, it does not mean that radiative recombination\nbecomes more dominant if the values go to 1. In fact, it can be the opposite, that a value\nclose to 1 indicates severe interfacial or surface recombination (e.g. DOI:\n10.1039/c7ee02415k, DOI: 10.1021/acsenergylett.6b00719). The intensity range used\nis also very small. Please try to improve the argument here or remove it since it does\nnot add much value in my opinion.\nResponse:\nWe appreciate the reviewer’s constructive comment and fully agree with this point.\nConsidering the reviewer’s remarks and those raised in Comment 2, we have removed\nthe light-intensity-dependent V data and the associated discussion from the revised\nOC\nmanuscript to avoid potential misinterpretation of recombination mechanisms.\nRevision:\nOC\n4.Judging from the strong dipole effects and better energy alignment, I think the energy\nalignment will very likely be able to explain the gain in Voc and partially FF, while\nbetter charge extraction is also likely due to the dipole effect. In general, I would\nstrongly suggest including drift-diffusion simulations to back up the interpretation of\nthese results.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. To further support our\nconclusions, we performed drift-diffusion (DD) simulations using the SCAPS-1D\nmodel, as presented in Figures S63-S65 and Tables S7-S11 of the revised Supporting\nInformation. The simulation results are consistent with our experimental observations\nand reinforce the proposed mechanism that SAMs improve energy-level alignment and\ninterfacial charge transport. The relevant discussion has been added on Page 15 of the\nrevised manuscript. Dr. Abdul Haseeb Hassan Khan, Prof. Ying-Chiao Wang, and Prof.\nShuai Zhao assisted with the DD simulations and have been added to the author list in\nrecognition of their contributions.\nRevision:\n“To evaluate the effect of SAMs on interfacial carrier transport, we developed a\nSCAPS-1D drift-diffusion (DD) model to simulate the band alignment and carrier\ndiffusion behavior in different device configurations (Figure S63 and Tables S7-S9).\nThe conduction band offset (CBO) and valence band offset (VBO) were calculated\nusing the standard band alignment equations:\n(1)\n𝐶𝐵𝑂 = 𝜒𝐵𝑎𝐻𝑓𝑆3 −𝜒𝐻𝑇𝐿 (2)\nIn the con𝑉tr𝐵o𝑂l c=onf𝜒ig 𝐻 u 𝑇 r 𝐿 a+tio𝐸n 𝑔 , 𝐻 w 𝑇𝐿 he−re( S𝜒F 𝐵𝑎 X 𝐻 - 𝑓 D 𝑆3 M+ is𝐸 𝑔 d𝐵ir𝑎e𝐻c𝑓tl𝑆y3 )used as the HTL without\nany interfacial layer, the VBO at the perovskite/HTL interface is -0.338 eV, forming a\nsmall valence band cliff (Figure S64a and Table S10). Such a small cliff can facilitate\nhole extraction by providing a gentle driving force. The large CBO of +1.7 eV at the\nHTL/perovskite interface helps suppress electron leakage into HTL, thereby reducing\n22\ninterfacial recombination. Introducing a buffer layer (SFX-P1) between the perovskite\nand SFX-DM further optimizes the interface. As shown in Figure S64b and Table S10,\nthe VBO at the perovskite/SFX-P1 interface remains -0.34 eV, while a slight positive\nVBO of +0.02 eV appears at the SFX-P1/SFX-DM junction. This small valence-band\nspike increases the built-in potential (V ) across the interface, suppresses hole back-\nbi\ninjection, and reduces interfacial recombination, while maintaining efficient hole\nextraction (spikes > 0.3 eV would instead hinder transport).”\n“The recombination-generation profile (Figure S65) confirms that the SFX-P1-\nmodified device exhibits a significantly lower recombination rate compared with the\ncontrol configuration. Solving the coupled semiconductor equations within the DD\nframework also predicts clear improvements in V and PCE for devices incorporating\nOC\nthe SFX-P1 interfacial layer (Table S11). These results confirm that the SFX-P1 layer\nnot only optimizes energetic alignment but also suppresses recombination, enabling\nmore efficient charge extraction and improved overall device performance.”\nFigure S63. Representation of (a) control device and (b) SFX-P1 device architectures\nsimulated by the SCAPS-1D drift-diffusion model.\nand (b) SFX-P1 device.\nFigure S65. The variation in the (a) generation and (b) recombination rates of devices\nwith and without SFX-P1 interface layers.\nTable S7. Model parameters for PSCs device simulations.\nParameters SnO Perovskite SPX-DM SPX-P1 FTO\nBand Gap (eV) 3.5 1.54 2.92 2.9 3.5\nElectron Affinity 3.9 3.9 2.2 2.2 4\nDielectric Permittivity ( r) 9.0 22 3.0 3 9\n(χ)\nCB Effective Density of states (cm-3) 2.2 x 1017 3.0 x 1018 2.2 x 1018 2.2 x 1018 2.2 x 1018\nε\nVB Effective Density of states (cm-3) 2.2 x 1017 3.0 x 1018 2.2 x 1018 2.2 x 1018 1.8 x 1019\nHole Thermal Velocity (cm/s) 1 x 107 1 x 107 1 x 107 1 x 107 1 x 107\nElectron Thermal Velocity (cm/s) 1 x 107 1 x 107 1 x 107 1 x 107 1 x 107\nElectron Mobility (cm2/Vs) 2.0 x 101 1.0 x 101 4.0 x 10-2 2.0 x 10-2 2.0 x 101\nHole Mobility (cm2/Vs) 1.0 x 10-1 1.0 x 101 4.0 x 10-1 2.0 x 10-1 1.0 x 101\nNA Doping Concentration (cm-3) - 1.3 x 1012 1.0 x 1018 1.0 x 1021 -\nDefect Density (1/cm3) 1.0 x 1017 2.0 x 1013 1.0 x 1014 1.0 x 1010 1.0 x 1014\nTable S8. Characteristics of interfacial defects.\nPerovskite/SFX- SFX-P1/SFX-\nCharacteristics FTO/SnO SnO /perovskite\n2 2\nP1 or SFX-DM DM\nDefect Type Neutral Neutral Neutral Neutral\nCapture Cross Section\n1.0 x 10-19 1.0 x 10-19 1.0 x 10-19 1.0 x 10-19\nfor Electron (cm2)\nCapture Cross Section\n1.0 x 10-19 1.0 x 10-19 1.0 x 10-19 1.0 x 10-19\nfor Holes (cm2)\nEnergetic Distribution Single Single Single Single\nReference for Defect Above the Above the Above the Above the\nEnergy Level highest Ev highest Ev highest Ev highest Ev\nEnergy Level with\n0.60 0.60 0.60 0.60\nRespect to Ev\nCharacteristic Energy\n0.1 0.1 0.1 0.1\n(eV)\nTotal Density (cm-3) 1.0 x 1010 1.0 x 1010 1.0 x 108 1.0 x 108\nTable S9. Characteristics of bulk defect.\nCharacteristics FTO SnO Perovskite SPX-P1 SPX-DM\nCapture Cross Section\n1.0 x 10-15 1.0 x 10-15 1.0 x 10-19 1.0 x 10-19 1.0 x 10-19\nfor Electron (cm2)\nCapture Cross Section\n1.0 x 10-15 1.0 x 10-15 1.0 x 10-19 1.0 x 10-19 1.0 x 10-19\nfor Holes (cm2)\nEnergetic Distribution Single Single Single Single Single\nReference for Defect\nAbove Ev Above Ev Above Ev - -\nEnergy Level\nEnergy Level with\n0.60 0.60 0.60 0.60 0.60\nRespect to Ev\nCharacteristic Energy\n0.1 0.1 0.1 0.1 0.1\n(eV)\nTotal Density (cm-3) 1.0 x 1014 1.0 x 1017 2.0 x 1013 1.0 x 1010 1.0 x 1014\nTable S10. Valance band offset and conduction band offset between different interfaces.\nInterfaces Valance band offset Conduction band offset\nPerovskite/SFX-DM -0.338 1.7\nPerovskite/SnO 1.96 0\n2\nSFX-P1/SFX-DM 0.02 0\nTable S11. Drift-diffusion simulation results under AM1.5G solar illumination at an\nintensity of 1000 W/m2.\nJ V FF PCE\nSC OC\nDevice structure\n(mA/cm2) (V) (%) (%)\nFTO/SnO /perovskite/SFX-DM/Au 24.68 1.22 85.84 25.87\n2\n5.Similar to above, with regard to the reduction of the PL emission in the presence of\nthe transport layer, this cannot be taken as proof of better charge extraction (although\nit might be related to extraction). At the end, given that the PL is the ratio of\nradiative to total recombination, it means that the non-radiative recombination increases\nin the presence of the transport layer with the SAMs (Figure S61), limiting the QFLS and\nVoc-potential. It's hard to explain a better device performance with such a reduction of\nthe radiative efficiency in the presence of the SAM and transport layer. Maybe this has\nsomething to do with lateral diffusion if an extremely small laser spot was used for the\nmeasurement (I am not sure; details such as intensity and laser spot should be provided\nin the caption). I would strongly suggest avoiding correlating quenching in PL with\nimproved charge extraction. Perhaps, the TRPL decay and TAS are better ways to\nanalyse the enhanced charge extraction, if their influence can be clearly disentangled\nfrom interfacial recombination.\nResponse:\nWe appreciate the reviewer’s constructive and detailed suggestions. In accordance\nwith the reviewer’s advice, we have provided the parameters for the excitation spot size\nand power density in the captions of Figures S49 and S68 in the revised Supporting\nInformation.\nWe agree that interpreting the PL data of perovskite/HTL samples with SAMs\n(Figure S68a) is complex because both non-radiative recombination and hole transfer\nprocesses are involved. Therefore, to isolate the SAM effect, we first analyzed\nperovskite/SAM samples without the HTL. As shown in Figure S49, the PL intensity\n26\nof perovskite films decreases after SAM deposition. Re-measured TRPL spectra of\nperovskite/SAM samples (Figure S68b) also show a reduction in lifetime. This\nreduction could, in principle, arise from either (i) enhanced non-radiative\nrecombination due to film degradation or (ii) more efficient hole extraction at the\ninterface. However, given that the overall device performance, XRD, and GIWAXS\nresults all indicate unchanged or improved perovskite crystallinity, we exclude the\npossibility of film deterioration. Furthermore, DFT calculations and XPS, FTIR, and\n31P-NMR results demonstrate that the SAM molecules chemically interact with the\nperovskite surface, potentially reducing trap-mediated non-radiative recombination.\nThus, we attribute the observed decrease in PL intensity and lifetime mainly to\nimproved interfacial charge extraction.\nTo further validate this interpretation, we performed transient photovoltage (TPV)\nand transient photocurrent (TPC) measurements for control and SFX-P1-modified\nPSCs (Figure S69). The photocurrent decay time decreased from 0.87 to 0.60 µs after\nSAM modification, indicating faster charge extraction. Meanwhile, the TPV decay\nlifetime increased from 3.60 to 4.56 µs, suggesting suppressed trap-assisted\nrecombination.\nBased on these analyses, we conclude that SFX-P1 and SFX-P2 SAMs, which\npossess intrinsic hole-transporting capability, enhance hole extraction from the\nperovskite layer to the HTL and mitigate non-radiative recombination losses, thereby\ncontributing to improved device performance. The revised discussion has been added\nto Page 16 of the manuscript.\nRevision:\n“The PL and TRPL measurements (Figure S68) reveal that both the PL intensity\nand lifetime of SAM- and SAM/SFX-DM-coated samples are reduced, which may\nresult from either increased non-radiative recombination or enhanced hole extraction at\nthe interface. However, considering the improved device performance and structural\ncharacterizations, degradation of the perovskite film is unlikely. In the pristine\nperovskite samples, the τ component associated with defect-assisted non-radiative\n1\n27\nrecombination at interfaces or grain boundaries is relatively minor (Table S12), while\nthe τ component from intrinsic luminescence dominates. After organic-layer\n2\ndeposition, τ becomes shorter and its relative amplitude increases, supporting the\n1\noccurrence of hole extraction. The τ component also decreases due to efficient charge\n2\ntransfer. Transient photocurrent (TPC) and transient photovoltage (TPV) measurements\n(Figure S69) further confirm faster charge extraction (τ = 0.60 µs vs. 0.87 µs) and\nTPC\nlonger recombination lifetimes (τ = 4.56 µs vs. 3.60 µs) in SFX-P1-modified devices,\nTPV\nevidencing improved interfacial charge transfer and suppressed trap-induced\nrecombination.”\nFigure S49. Steady-state PL spectra of perovskite film and different perovskite/SAM\nfilms before and after CB wash. The photoexcitation spot is roughly 3 x 8 mm2. The\nphotoexcitation power is 1.6 mW/cm2.\nFigure S68. (a) Steady-state PL spectra of perovskite film, perovskite/SFX-DM film,\nperovskite/SFX-P2/SFX-DM film and perovskite/SFX-P1/SFX-DM film. The\nphotoexcitation spot is roughly 3 x 8 mm2. The photoexcitation power is 1.6 mW/cm2.\n28\n(b) TRPL spectra of perovskite film, perovskite/SFX-P1 film, perovskite/SFX-P2 film,\nperovskite/SFX-P1/SFX-DM film and perovskite/SFX-P2/SFX-DM film. The laser\nfluence used is 150 nJ/cm2.\nFigure S69. (a) Transient photocurrent spectra and (b) transient photovoltage curves of\nthe control PSCs and SFX-P1 PSCs.\n6.Another point with regard to TRPL is the averaging of the 2 decay times to obtain an\naverage lifetime. Considering that the different decay components include charge\ntransfer and interfacial recombination, it does not make sense to me to specify an\naverage lifetime. Please try to disentangle extraction and recombination and specify the\ncharacteristic time constants for both processes. Furthermore, the laser fluence should\nbe specified to correctly interpret the results.\nResponse:\nWe appreciate the reviewer’s constructive suggestion. In response, we remeasured\nthe TRPL spectra for samples containing SAM-modified layers, as shown in Figure\nS69b and Table S12. The laser fluence used was 150 nJ/cm2. Following the reviewer’s\nrecommendation, we no longer report an averaged lifetime but instead discuss the two\ncharacteristic decay components separately to distinguish between charge extraction\nand interfacial recombination. The corresponding discussion has been updated on Page\n16 of the revised manuscript.\nRevision:\n“In the pristine perovskite samples, the τ component associated with defect-\n1\nassisted non-radiative recombination at interfaces or grain boundaries is relatively\nminor (Table S12), while the τ component from intrinsic luminescence dominates.\n2\n1\nsupporting the occurrence of hole extraction. The τ component also decreases due to\n2\nefficient charge transfer.”\nFigure S69b. TRPL spectra of perovskite film, perovskite/SFX-P1 film,\nperovskite/SFX-P2 film, perovskite/SFX-P1/SFX-DM film and perovskite/SFX-\nP2/SFX-DM film. The laser fluence used is 150 nJ/cm2.\nTable S12. TRPL kinetics parameters for PSK, PSK/SFX-P2, PSK/SFX-P1, PSK/SFX-\nP2/SFX-DM and PSK/SFX-P1/SFX-DM samples. The laser fluence is 150 nJ/cm2.\nRelative Relative\nSample (μs) amplitude of (μs) amplitude of\n(%) (%)\n𝜏1 𝜏2\nPSK 0.39 33.1 9.13 66.9\n𝜏1 𝜏2\nPSK/SFX-P2 0.08 61.4 1.48 38.6\nPSK/SFX-P1 0.08 63.6 1.5 36.4\nPSK/SFX-P2/SFX-DM 0.05 61.7 1.07 38.3\nPSK/SFX-P1/SFX-DM 0.02 70.7 0.62 29.3\n7. As for the Vbi, its determination from the Mott-Schottky analysis is also not\nstraightforward (DOI: 10.1021/acsaem.8b01119). There might be some correlation\nbetween the apparent Vbi and the real Vbi, but often, the extrapolation just follows the\nVoc. I would suggest adding at least a comment that the interpretation is still up for\ndebate for thin film perovskite or providing DD simulations for further justification.\nWe appreciate the reviewer’s constructive suggestion. To obtain a deeper\nunderstanding of the V enhancement and V behavior, we performed DD simulations.\nOC bi\nThe results indicate that the introduction of SAMs modulates the interfacial band\nalignment, suppresses charge-carrier back injection, reduces recombination, and\npromotes more efficient charge separation, collectively leading to higher V . The\nOC\ndetails of the DD simulations and discussion are provided in the revised manuscript, as\ndescribed in our response to Comment 4.\nWe also acknowledge the ongoing debate regarding the quantitative accuracy of\nMS analysis in thin-film perovskite systems. Accordingly, we have revised the related\ndiscussion to note this limitation while emphasizing that the observed V trends remain\nbi\nconsistent with other experimental and simulated results. The updated discussion\nappears on Page 16 of the revised manuscript.\nRevision:\n“Furthermore, improved band alignment enhances recombination resistance in\nSAM-modified actual PSCs (Figure S66), while suppressing interfacial charge\naccumulation and leading to a rise in V (Figure S67). Although Mott-Schottky\nbi\nanalysis may not yield fully quantitative values under the present conditions, the\nobserved trends are consistent with both the DD simulations and other experimental\nfindings, supporting the proposed mechanism.”\n8. Overall, I would suggest identifying the dominant mechanism governing the\nimprovement, rather than proposing a large range of mechanisms, potentially putting\nmore emphasis on the improved energy alignment, removing questionable\ninterpretation and corresponding data (considering that the manuscript certainly has\nsufficient data), and corroborating the interpretation with DD simulations.\nResponse:\nWe sincerely appreciate the reviewer’s insightful and constructive suggestions.\nFollowing this advice, we have revised the manuscript to focus on the dominant\nmechanism—namely, the improved interfacial energy alignment and enhanced carrier\n31\ntransfer induced by the SAMs. To strengthen this interpretation, we added DD\nsimulations that corroborate our experimental findings, while removing less conclusive\ndata and discussions (such as the SCLC and light-intensity-dependent V analyses).\nOC\nThese revisions have significantly improved the clarity and coherence of the manuscript.\nThe manuscript entitled: \"Self-assembled molecules for perovskite surface\nmodifications' presents an original approach to using self-assembled molecules as\nselective contacts in perovskite solar cells\". However, the results pertain only to a single\ntype of molecular structure, despite the authors' aim to extend their findings to a broader\nperspective, with which I disagree entirely. The hype in the title, which I believe aims\nto generalise the findings, would be more appropriate for an extensive review rather\nthan a communication. Moreover, in the abstract, the authors assume that the observed\nlarge dipole on their particular molecules is the sole reason for the improvement in their\ndevice performance. They claim that the underlying modification mechanisms and\nmolecular design principles for the SAMS action remain unclear, yet it is evident that\na myriad of manuscripts already explain the different actions observed for SAMS on\nperovskite solar cells depending on their molecular structure. Several reviews compile\nthese various actions, and the authors have neglected to cite them in this manuscript.\nRegarding the science in the manuscript, I believe that the authors have assembled a\ncomprehensive collection of characterisation techniques to support their hypothesis,\nwhich includes both experimental and computational work. Indeed, the results bolster\ntheir specific hypothesis. Moreover, the achieved efficiency in n-i-p devices is\nremarkable, as well as the stability. However, to the best of my knowledge, there is\nnothing new that justifies an urgent communication instead of a more structured\nmanuscript. Neither the approach nor the hypothesis is novel, and the efficiency and\nstability of perovskite solar cells are well documented in the bibliography.\nLast but not least, the references used by the authors fall short in providing perspective\nfor Sams-based solar cells. They have cited important work on dipole moments,\nperovskite composition, and others, but have missed or neglected important references\non SAMS from pioneering groups and significant work that describes the use of SAMS\nas dipoles (for instance, Abate et al.).\nResponse:\nwhich have encouraged us to clarify the originality, scope, and positioning of our work.\nTitle and scope overgeneralization:\nOur initial intention was to emphasize the originality and universality of this study\nthrough the title. Following the reviewer’s valuable feedback, we have revised the title\nto a more specific and accurate one:\n“Interfacial Dipole Engineering by Self-Assembled Molecules in n-i-p and p-i-n\nPerovskite Solar Cells”\nThis new title better reflects the focus of the manuscript and avoids any\novergeneralization.\nWe fully agree with the reviewer that various SAMs have been developed and\ntheir functions in PSCs have been extensively investigated. To provide a more balanced\nand up-to-date perspective, we have added several key references to recent pioneering\nworks and comprehensive reviews on SAMs (including those by Abate et al. and others).\nThese citations clarify the current understanding of SAM-induced dipole effects,\nanchoring chemistries, and interfacial modification strategies.\nNovelty and significance:\nWhile SAMs have been widely applied in p-i-n PSCs, their utilization in n-i-p\ndevices remains largely unexplored. Possible reasons include (i) the lack of suitable\nSAM materials compatible with the top perovskite surface and (ii) insufficient\nunderstanding of how to construct robust SAM layers directly on perovskite rather than\non conventional metal oxide substrates. In this work, we designed and synthesized our\nown SAMs and successfully applied them to n-i-p devices as top interfacial modifiers—\nan approach that has rarely been reported and whose mechanisms had not yet been\nclarified. This study thus represents an early and systematic exploration of SAMs in n-\ni-p PSCs, demonstrating their potential to regulate energy alignment and improve\nperformance.\nImportantly, unlike previously reported SAMs that primarily interact with metal\noxide substrates, our SAMs interact directly with the perovskite surface, forming a\n34\nchemically anchored and energetically favorable interface. Furthermore, the molecular\ndesign of our SAMs induces a homologous effect with the corresponding HTL (SFX-\nDM), which is difficult to achieve with conventional SAMs in p-i-n architectures. We\nalso confirmed that these SAMs can function effectively in p-i-n PSCs, suggesting a\ndegree of universality that expands the applicability of SAMs beyond specific device\nconfigurations.\nMechanism clarification:\nTo clarify the dominant mechanism responsible for the observed improvements,\nwe performed comprehensive characterizations. Initially, we proposed that the SAMs\nmight reduce surface defects, tune interfacial energy levels, and enhance carrier\ntransport. Following Reviewer 3’s insightful suggestions, we conducted additional\nstudies, including transient photovoltage (TPV), transient photocurrent (TPC), and\ndrift–diffusion (DD) simulations to pinpoint the primary mechanism. The results\nconsistently indicate that the interfacial energy-level tuning and enhanced carrier\nextraction play the dominant roles in performance enhancement. The uncertain\ndata/discussion on the perovskite defect passivation effect has been removed from the\nmanuscript.\nPerformance certification:\nAdditionally, as suggested by the reviewers, we have certified the photovoltaic\nperformance of our devices at an independent third-party agency. The certified\nefficiency (26.23% for reverse PCE and 25.55% for forward PCE) closely matches our\nlaboratory-measured values (26.18% for reverse PCE and 25.69% for forward PCE),\nconfirming the reliability of our results. This certified PCE represents one of the highest\nefficiencies reported so far for n-i-p PSCs. During the revision, we also included new\ndevice and material characterization data to strengthen the mechanism discussion and\noverall scientific rigor of the manuscript.\nFinally, we are deeply grateful to the reviewer for the valuable comments, which\nprompted us to re-examine the originality and novelty of our study, refine its\npresentation, and further improve the quality and impact of the manuscript.\nWe have substantially revised the manuscript, including the title, data\ninterpretation, and the logic of manuscript writing, according to the reviewers’\ncomments. All modifications are highlighted in yellow in the revised manuscript for\nclarity.\nRegarding the reviewer’s comment on missing key references:\nThe important work by Abate et al. on SAM-induced dipole effects in PSCs\n(Energy Environ Sci 2021, 14, 1429-1438) and the earlier foundational studies by\nAlbrecht et al. (Energy Environ Sci 2019, 12, 3356-3369) were already cited in our\noriginal submission, as they directly inspired aspects of our molecular design strategy.\nIn the revised manuscript, we have further expanded the contextual background by\nadding several key contributions from pioneering groups that have advanced the\nunderstanding of SAM chemistry, dipole formation, and interfacial engineering in PSCs.\nAdditional references added in the revision include:\nACS Nano 2014, 8, 12701-12709;\nJ Am Chem Soc 2015, 137, 2674-2679;\nAdv Energy Mater 2018 8, 1701683;\nAdv Energy Mater 2018, 8, 1801892;\nNanoscale 2019, 11, 2401-2411;\nScience 2020, 370, 1300-1309;\nJoule 2021 5, 2915-2933;\nAdv Energy Mater 2025, 15, 2400205.\nThese additional citations help position our work more accurately within the\ncurrent state of the field and address the reviewer’s concern regarding the completeness\nof the literature discussion.\nReviewer 3 comments:\nThe paper by Zhai et al. has improved during the revision. I also appreciate that the\nauthors refined their conclusions by removing ambiguous measurements and tried to\nsimulate their devices using SCAPS. However, I think the simulations need to be\nconsiderably improved.\n1.First, regarding the statement: \"Small valence band cliff (Figure S64a and Table S10).\nSuch a small cliff can facilitate hole extraction by providing a gentle driving force.\"\nSuch a cliff (energy misalignment) should not provide more driving force for extraction\nin perovskite cells but lowers the selectivity, increases interface recombination, and\nreduces the extraction efficiency (e.g. ref.10.1039/c9ee02020a).\nResponse:\nWe appreciate the reviewer’s constructive comments. Also, we agree that, in line\nwith Stolterfoht et al. A large valence-band cliff at the perovskite/hole transport layer\n(HTL) interface generally reduces contact selectivity, enhances interfacial\nrecombination, and can lower the extraction efficiency and open-circuit voltage (V ).\nOC\nHowever, the impact of a small cliff is more nuanced and depends on the full set of\ninterfacial parameters (band offsets, trap density, capture cross sections) and on whether\ntransport is drift- or diffusion-dominated, rather than on the sign of the offset alone.\nThe cliff is simply one manifestation of the energy-level alignment between the\nperovskite and the charge transport layer (CTL). A negative valence band offset (VBO)\ncorresponds to a cliff (downward step for the valence band), i.e. no barrier for hole\nextraction but a reduced hole-blocking ability for HTL. Whether this configuration is\nbeneficial or harmful depends on how strongly it couples to recombination. Interfacial\nrecombination in drift-diffusion models is usually described by Shockley-Read-Hall\n(SRH) statistics, where the lifetimes ( ) are directly controlled by the trap density ,\nthe thermal velocity , and the captu 𝜏 re cross sections . 𝑁𝑡\n𝑣th 𝜎𝑛,𝜎𝑝\n1 1\nThese lifetimes determ𝜏in 𝑛 e= the SRH re c,𝜏o 𝑝 m=bination rate:\n𝜎𝑛𝑣𝑡ℎ𝑁𝑡 𝜎𝑛𝑣𝑡ℎ𝑁𝑡\n1\n2\n𝑛𝑝−𝑛𝑖\n𝑈𝑅𝑆𝐻 =\nso that a given valence-band cliff 𝜏w𝑝i(ll𝑛 b+e 𝑛m1u)c+h 𝜏m𝑛o(r𝑝e +de𝑝tr1i)mental when and\nare large (short , strong SRH recombination), but can be relatively b\n𝑁\ne𝑡nign w\n𝜎\nh𝑛e,n𝑝\nthe interface is w\n𝜏\ne𝑛ll\n, 𝜏\np𝑝assivated (small , moderate ). In that sense, the same VBO\ncan either severely increase recombin𝑁a𝑡tion or rema𝜎i𝑛n, 𝑝acceptable, depending on the\ninterfacial defect of physics. In our description, the “driving force” for extraction does\nnot mean that the cliff itself increases the Quasi-Fermi-level Splitting. Rather, a small\nnegative VBO ensures a monotonically downhill valence-band profile from the\nperovskite towards the HTL, so that holes do not experience an energetic barrier at the\ninterface. Within the drift-diffusion framework, the hole current density is given by:\n𝑑𝑝\nwhich shows that hole extractio𝐽n𝑝 i=s g𝑞o𝑝v𝜇e𝑝rn𝐸ed− b𝑞y𝐷 t𝑝he local electric field E and the hole\n𝑑𝑥\nconcentration gradient , while the band offset mainly sets whether there is a barrier\n𝑑𝑝\nor a smooth pathway fo𝑑r 𝑥holes across the interface. Other than that, several numerical\nstudies explicitly show that small spikes or cliffs can be close to optimal when\ncombined with low interfacial recombination:\n1. Minemoto and Murata et al. performed a systematic SCAPS study of\nCH NH PbI Cl PSCs and found that the optimum valence band position of the hole\n3 3 3-x x\ntransport material (HTM) is lower than that of the perovskite absorber, i.e., a small\nvalence-band cliff. Under these conditions, J remains essentially constant, and the\nSC\ndevice performance is not limited by extraction, but by recombination.\n(https://doi.org/10.1016/j.solmat.2014.10.036)\n2. Benatallah et al. used drift-diffusion simulations for flexible perovskite solar\ncells (PSCs) and showed that, for their perovskite/SeTeCu O interface, a tailored VBO\n2\nwith a small cliff can still allow efficient hole transfer from the perovskite to the HTL.\n(https://doi.org/10.1002/adts.202401161)\n2\n3. Liu et al reported negative VBO for CsSnI , CsSn Ge I , and CsGeI ,\n3 0.5 0.5 3 3\nand\nshowed that such cliff-like alignments can still facilitate hole extraction when the\ninterface is appropriately engineered. (https://doi.org/10.1088/1674-1056/ae156b)\n4. Chabri et al. and other SCAPS-based works on Cs-based perovskites show\nthat a negative CBO cliff at the electron transport layer/perovskite interface enables\nelectrons to flow freely towards the front contact, J remains almost unchanged as long\nSC\nas the cliff is moderate, whereas very large negative offsets enhance recombination and\nreduce V (https://doi.org/10.1016/j.solmat.2023.112426)\nOC\n5. Ahmad et al. compared different CTLs for Cs Bi I and CsSnI and explicitly\n3 2 9 3\nshowed that a large VBO cliff of about -0.65 eV at Cs Bi I /GO leads to poor\n3 2 9\nperformance, whereas a much smaller cliff (-0.12 eV) at CsSnI /GO gives significantly\n3\nbetter efficiency, demonstrating that “too much” cliff is detrimental, but a small one\ncan be acceptable. (https://doi.org/10.1016/j.nexus.2025.100400)\nTaken together, these studies support the view that both spikes and cliffs have\noptimal windows in which they balance selectivity and extraction, a very large spike\nblocks the majority carrier, a very large cliff indeed enhances non-selective\nrecombination but a small spike or cliff, combined with low interface trap density and\nsuitable capture cross sections, can still yield high performance and in some cases\nmaximize power conversion efficiency (PCE). In our specific case, the valence-band\ncliff at the perovskite/SFX-P1 interface is small, and our drift-diffusion simulations\ninclude explicit bulk and interfacial SRH recombination with material-specific ,\n, and . Within this parameter set, the small negative VBO does not create\n𝑁\na𝑡n\n𝜎ad𝑛d,𝑝itional 𝐸b𝑡arrier for hole extraction; instead, it maintains a barrier-free path for holes\nwhile the overall recombination losses are controlled by the assumed defect\ndistributions.\n2. More importantly, however, in the following, the authors then explain that:\n\"Introducing a buffer layer (SFX-P1) between the perovskite and SFX-DM further\noptimizes the interface. As shown in Figure S64b and Table S10, the VBO at the\nperovskite/SFX-P1 interface remains -0.34 eV, while a slight positive VBO of +0.02\n3\neV appears at the SFX-P1/SFX-DM junction. This small valence-band spike increases\nthe built-in potential (Vbi) across the interface, suppresses hole back-injection, and\nreduces interfacial recombination, while maintaining efficient hole extraction (spikes >\n0.3 eV would instead hinder transport).” I quickly checked this claim, and it appears to\nme that the main effect in the simulation is that the SFX-P1 interlayer is highly doped\n(NA=1e21 cm3, which is much higher than the SPX-DM, 1e18 cm3). Indeed, such a\nhighly doped interlayer can improve the voltage drop over the perovskite (rather than\nthe total Vbi) and thereby suppress interface recombination (10.1002/solr.202100219).\nHowever, it seems to be totally unrelated to the main effects claimed in the paper. In\nFigure 4a the authors discuss the improved energy level alignment through the SFX-P1\nmolecule. Therefore, they could simply simulate a better-aligned transport layer as an\napproximation.\nResponse:\nWe appreciate the reviewer’s constructive comments. In our drift-diffusion\nmodeling, the SFX-P1 layer is treated as an ultrathin interfacial layer with a thickness\nnm, much smaller than the 130 nm thickness of the SFX-DM HTL.\nSFX-P1\nConsequently, its bulk contribution to the electrostatics is limited: the electrostatic\n𝑡 ≈ 5\npotential and electric field are obtained from Poisson’s\nequation\n𝜙(𝑥) 𝐸(𝑥) = −𝑑𝜙/𝑑𝑥\n2\n𝜕 𝜑 𝜕𝐸 𝜌 𝑞 + −\nwhere the acc2ept=or −de nsity= − = is −non- z[e 𝑝ro− on𝑛l𝑁y 𝐷ov(𝑥er) a− v e𝑁ry𝐴 n±ar𝑁ro𝑑w𝑒𝑓 r(e𝑥g)io]n for SFX-\nP1. To explicitly quantify th\n𝑁\ne𝐴 r\n(\n𝑜\n𝑥\n𝑙\n)\ne of this doping, we performed a systematic sweep of\nthe SFX-P1 acceptor concentration from 1010 to 1021 cm-3 while keeping all\nP1\nother parameters fixed. Over the ent\n𝑁\nir𝐴e, 𝑆r𝐹a𝑋n−ge of\nP1\n, the resulting variations in\nV\nOC\n, J\nSC\n, FF and PCE are extremely small, as sum 𝑁𝐴m,𝑆a𝐹r𝑋iz−ed in Table S11 and the PCE\ntrend in Figure S65a.\nThis indicates that, for such a thin interfacial layer, changes in mainly\nP1\nadjust the local screening but do not significantly modify the global\n𝑁\nf𝐴ie,SlFdX d−istribution\nor overall device performance. In contrast, when we vary the valence-band alignment\n4\nat the SFX-P1/SFX-DM from a negative VBO cliff to a small positive spike, the drift-\ndiffusion results in Table S12 and the PCE evolution in Figure S65b show a clear,\nmonotonic improvement in device efficiency.\nTo further support this, we added contour plots (Figure S65c) of the potential and\nrecombination profile, which clearly illustrate that the main changes in performance\ncorrelate with the band alignment at the SFX-P1/SFX-DM interface, while the impact\nof SFX-P1 doping remains marginal. Based on the drift-diffusion, we note that the SFX-\nP1 interlayer is extremely thin of 5 nm, so changes in its bulk doping have only a\nmarginal influence on the overall electrostatics and PCE. In contrast, the valence-band\nalignment at the SFX-P1/SFX-DM interfaces exert a much more dominant effect on\ncarrier extraction and recombination, and therefore we focus our analysis primarily on\noptimizing the band alignment as the key lever to improve device performance.\nRevision: The corresponding data have been added to the revised Supporting\nInformation, and the discussion on Page 15 of the manuscript has been updated\naccordingly.\n“Besides, we also excluded the doping concentration of the SFX-P1 buffer layer from\naffecting device performance (Figure S65 and Tables S11-S12), with results indicating\nthat interface band alignment is the key lever for enhancing device efficiency.”\nFigure S65. (a) The dependence of the doping concentration on the PCE of the SFX-\nP1 device. (b) The effect of band alignment on the PCE of SFX-P1 device. (c) Contour\nmaps illustrate the combined influence of doping concentration and band alignment on\ninternal potential and recombination distribution.\nphotovoltaic parameters.\nSFX-P1 doping concentration (N ) J V FF PCE\nA SC OC\n(cm-3) (mA/cm2) (V) (%) (%)\n1.0 x 1010 24.6 1.30 85.0 27.3\n1.0 x 1011 24.6 1.30 85.0 27.3\n1.0 x 1012 24.6 1.30 85.0 27.3\n1.0 x 1013 24.6 1.30 85.0 27.3\n1.0 x 1014 24.6 1.30 85.0 27.3\n1.0 x 1015 24.6 1.30 85.0 27.3\n1.0 x 1016 24.6 1.30 85.0 27.3\n1.0 x 1017 24.6 1.30 85.0 27.3\n1.0 x 1018 24.6 1.30 85.0 27.3\n1.0 x 1019 24.6 1.30 85.0 27.3\n1.0 x 1020 24.6 1.30 84.6 27.1\n1.0 x 1021 24.6 1.30 84.6 27.0\nTable S12. Band alignment of SFX-P1/SFX-DM and corresponding device-simulated\nphotovoltaic parameters.\nSFX-P1/SFX-DM band alignment J V FF PCE\nSC OC\n(eV) (mA/cm2) (V) (%) (%)\n0.02 24.6 1.30 85.0 27.3\n-0.08 24.6 1.30 84.8 27.2\n-0.18 24.6 1.29 84.4 27.0\n-0.28 24.6 1.29 84.4 27.0\n-0.38 24.6 1.29 82.7 26.5\n-0.48 24.6 1.29 75.8 24.3\n-0.58 24.6 1.27 64.8 20.8\n-0.68 24.6 1.24 32.6 11.4\n-0.78 2.2 1.0 9.6 0.4\n1. In addition, I note that Table S7 includes several errors, e.g., in the first line of the\nthicknesses.\nResponse: We appreciate the reviewer’s careful observation. Previously, some values\nwere expressed in micrometers (μm). All values are now uniformly expressed in\nnanometers (nm).\nRevision:\nTable S7. Model parameters for PSCs device simulations.\nParameters SnO Perovskite SPX-DM SPX-P1 FTO\nBand Gap (eV) 3.5 1.54 2.92 2.9 3.5\nElectron Affinity 3.9 3.9 2.2 2.2 4.0\nDielectric Permittivity ( r) 9.0 22 3.0 3.0 9.0\n(χ)\nCB Effective Density of states (cm-3) 2.2 x 1017 3.0 x 1018 2.2 x 1018 2.2 x 1018 2.2 x 1018\nε\nVB Effective Density of states (cm-3) 2.2 x 1017 3.0 x 1018 2.2 x 1018 2.2 x 1018 1.8 x 1019\nHole Thermal Velocity (cm/s) 1.0 x 107 1.0 x 107 1.0 x 107 1.0 x 107 1.0 x 107\nElectron Thermal Velocity (cm/s) 1.0 x 107 1.0 x 107 1.0 x 107 1.0 x 107 1.0 x 107\nElectron Mobility (cm2/Vs) 2.0 x 101 1.0 x 101 4.0 x 10-2 2.0 x 10-2 2.0 x 101\nHole Mobility (cm2/Vs) 1.0 x 10-1 1.0 x 101 4.0 x 10-1 2.0 x 10-1 1.0 x 101\nND Doping Concertation (cm-3) 1.8 x 1017 1.3 x 1012 - - 1.0 x 1019\nNA Doping Concentration (cm-3) - 1.3 x 1012 1.0 x 1018 1.0 x 1021 -\nDefect Density (cm-3) 1.0 x 1017 2.0 x 1013 1.0 x 1014 1.0 x 1010 1.0 x 1014\n2. Regarding the explanation of non-linearity in EQE. Indeed, the EQE is often lower,\nbut I am not sure if this explanation makes sense, since a lower light intensity should\nnot lead to a lower EQE. Anyway, the authors have now provided certification, and the\nvalues are close.\nResponse:\nWe thank the reviewer for the valuable comment, and we agree that EQE values do not\nnecessarily decrease due to lower illumination intensity alone. The difference between\nJ–V-derived and EQE-integrated J in perovskite solar cells can originate from several\nSC\nexperimental factors, including ion migration and material degradation during the\nlonger acquisition time required for EQE measurements, the frequency dependence of\n7\nthe EQE response, and differences in measurement conditions and illumination profiles,\nas discussed previously (10.1021/acsenergylett.0c01642).\nConsistent with reports in the field, a small deviation (typically 2–5%) between J\nSC,J-V\nand J is commonly observed and is considered acceptable. In our measurements,\nSC,EQE\nthe integrated EQE values fall within this expected range and remain consistent with\nthe J–V results. In addition, the certified efficiency obtained from an accredited third-\nparty laboratory further confirms the accuracy and reliability of the reported\nperformance.\n8"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed all the comments from reviewers, I thus suggest that the current version can be accepted for\npublication.", "reviewer_2": "In my opinion, the work can be accepted now.", "reviewer_3": "The paper by Zhai et al. has improved during the revision. I also appreciate that the authors refined their conclusions by\nremoving ambiguous measurements and tried to simulate their devices using SCAPS. However, I think the simulations need to be\nconsiderably improved.\nFirst, regarding the statement: \"Small valence band cliff (Figure S64a and Table S10). Such a small cliff can facilitate hole\nextraction by providing a gentle driving force.\" Such a cliff (energy misalignment) should not provide more driving force for\nextraction in perovskite cells but lowers the selectivity, increases interface recombination, and reduces the extraction\nefficiency (e.g. ref.10.1039/c9ee02020a).\nMore importantly, however, in the following, the authors then explain that: \"Introducing a buffer layer (SFX-P1) between the\nperovskite and SFX-DM further optimizes the interface. As shown in Figure S64b and Table S10, the VBO at the\nperovskite/SFX-P1 interface remains -0.34 eV, while a slight positive VBO of +0.02 eV appears at the SFX-P1/SFX-DM\njunction. This small valence-band spike increases the built-in potential (Vbi) across the interface, suppresses hole back-\ninjection, and reduces interfacial recombination, while maintaining efficient hole extraction (spikes > 0.3 eV would instead\nhinder transport).” I quickly checked this claim, and it appears to me that the main effect in the simulation is that the SFX-P1\ninterlayer is highly doped (NA=1e21 cm3, which is much higher than the SPX-DM, 1e18 cm3). Indeed, such a highly doped\ninterlayer can improve the voltage drop over the perovskite (rather than the total Vbi) and thereby suppress interface\nrecombination (10.1002/solr.202100219). However, it seems to be totally unrelated to the main effects claimed in the paper.\nIn Figure 4a the authors discuss the improved energy level alignment through the SFX-P1 molecule. Therefore, they could\nsimply simulate a better-aligned transport layer as an approximation.\nMinor points:\nIn addition, I note that Table S7 includes several errors, e.g., in the first line of the thicknesses.\nRegarding the explanation of non-linearity in EQE. Indeed, the EQE is often lower, but I am not sure if this explanation\nmakes sense, since a lower light intensity should not lead to a lower EQE. Anyway, the authors have now provided\ncertification, and the values are close."}, "author_response": ""}, {"round": 3, "reviewer_comments": {"reviewer_3": "The authors have now clarified the remaining points and therefore, I can recommend the paper for publication as well."}, "author_response": ""}]

Decision letter