Stitching Perovskite Grains with Perhydropoly(Silazane) Anti‐Template‐Agent for High‐Efficiency and Stable Solar Cells Fabricated in Ambient Air

All inorganic CsPbI3 perovskite solar cells (PSCs) have emerged as disruptive photovoltaic technology owing to their admirable photoelectric properties and the non‐volatile active layer. However, the phase instability against moisture severely limits the fabrication environment for the high‐efficiency devices, breaking through the confinement region to achieve scalable manufacturing has been the primary issue for future commercialization. Here, we develop a curing‐anti‐solvent strategy for fabricating high‐quality and stable black‐phase CsPbI3 perovskite films in ambient air by introducing an inorganic polymer perhydropolysilazane (PHPS) into methyl acetate to form anti‐template agent. The cross‐linked PHPS reduces moisture erosions while the hydrolyzate silanol network (–Si(OH)4–) controls the perovskite crystal growth by forming Lewis adducts with PbI2 during the fabrication. The polycondensation adduct of Si–O–Si/Si–O–Pb strongly binds to CsPbI3 grains as a shield layer to hamper phase transition. Using the inorganic CsPbI3 perovskite thin‐film with PHPS‐modified anti‐solvent processing as the light absorber, the n–i–p planar solar cell achieved an efficiency of 19.17% under standard illumination test conditions. More importantly, the devices showed excellent moisture stability, retaining about 90% of the initial efficiency after 1000 h under 30% RH.


Introduction
All inorganic perovskite CsPbI 3 has become a research hotspot in perovskite solar cells (PSCs) due to its intrinsic chemical stability and prominent optoelectronic property. [1][2][3][4][5] In the past few years, CsPbI 3 -based PSCs have achieved tremendous progress in power-conversion efficiencies (PCEs) up to over 21%. [6][7][8] Most of these reported high-efficiency devices were fabricated in an inert gas-filled glove box with controlled water content since the CsPbI 3 films are notoriously sensitive to moisture. It is necessary to seek a more convenient production operation method for the fabrication of PSCs in air. [9][10][11][12] To stabilize the black phase of CsPbI 3 , a series of strategies have been proposed by worldwide researchers from the perspective of materials to tune tolerance factors, reduce grain size, and passivate perovskite surface. Along this line, though the phase stability of CsPbI 3 has been further boosted, there are certain hidden compromises for performance. For example, efforts devoted to addressing phase instability: tuning the tolerance factor by doping or alloying Br weaken the lightharvesting ability of CsPbI 3 , [13][14][15][16] forming 2D/3D heterojunctions by incorporating 2D perovskite capping layers hindered carrier transport, [17][18][19] and later developed organic ligand passivation layers with anchoring functional groups reduced the grain size of perovskites. [20,21] Furthermore, it is further necessary to realize the scalable fabrication techniques in pursuit of high-quality and pinhole-free perovskite films in a high-humidity environment for high-performance PSC. Recently, the use of organic molecule passivation engineering strategies combined with growth adjustment has been conducted to comprehensively study the phase stabilization of CsPbI 3 perovskite in air. [22,23] For example, Yoon et al. prepared a uniform and dense perovskite layer by facilitating the transition of the CsPbI 3 intermediate phase using sequential dripping of methylammonium chloride solution, combined with surface passivation using octyl ammonium iodides (OAI) in ambient air with strictly controlled relative humidity (below 30% RH). [24] To broaden the humidity operating window in a high-humidity environment, Fu et al. added maleic anhydride molecules into perovskite precursors which react with water molecules in air to reduce moisture erosions and regulate grains growth. [25] Liang et al. applied a synergetic All inorganic CsPbI 3 perovskite solar cells (PSCs) have emerged as disruptive photovoltaic technology owing to their admirable photoelectric properties and the non-volatile active layer. However, the phase instability against moisture severely limits the fabrication environment for the high-efficiency devices, breaking through the confinement region to achieve scalable manufacturing has been the primary issue for future commercialization. Here, we develop a curing-anti-solvent strategy for fabricating high-quality and stable black-phase CsPbI 3 perovskite films in ambient air by introducing an inorganic polymer perhydropolysilazane (PHPS) into methyl acetate to form anti-template agent. The cross-linked PHPS reduces moisture erosions while the hydrolyzate silanol network (-Si(OH) 4 -) controls the perovskite crystal growth by forming Lewis adducts with PbI 2 during the fabrication. The polycondensation adduct of Si-O-Si/Si-O-Pb strongly binds to CsPbI 3 grains as a shield layer to hamper phase transition. Using the inorganic CsPbI 3 perovskite thin-film with PHPS-modified anti-solvent processing as the light absorber, the n-i-p planar solar cell achieved an efficiency of 19.17% under standard illumination test conditions. More importantly, the devices showed excellent moisture stability, retaining about 90% of the initial efficiency after 1000 h under 30% RH. method of pre-heating the substrate and spraying the anti-solvent methyl acetate (MeOAc) treatment to accelerate precursor concentrations up to supersaturation and heterogeneous nucleation. [26] These reports proved that the attack of undesired moisture to perovskite films can be suppressed by reducing the time of the nucleation phase that exposure to high humidity and accelerating the growth of the intermediate phase during their air fabrication. Nevertheless, the rapid growth of crystals generally leads to low coverage with poor perovskite film morphology and associated high trap concentrations, consequently impairing PSC's efficiency and operational stability. Additionally, the volatility of organic molecule passivation agents remains a challenge to the thermal stability of PSCs. Therefore, to realize air fabricating of high-performance CsPbI 3 PSCs, it is urgently needed to solve the awkward situation of fast deposition and film quality. The perhydropolysilazane (PHPS) is an inorganic oligomer composed of alternating -(SiH 2 -NH)units, widely used as an environmental barrier or protective coatings in various applications. As depicted in Figure S1, during the air deposition, PHPS can react with water molecules to form crosslinking silanols (-Si(OH) 4 -), followed by condensing and transforming into a compact Si-O-Si network against external invasions (e.g., moisture and O 2 ) by the pyrolytic reaction. [27,28] Recently, PHPS has been used to spin-coat on the surface of the perovskite films to form a passivation layer, [29] inducing band bending to improve the opencircuit voltage (V oc ) for the solar cells, while it has so far not been used to affect the formation of the perovskite itself during the processing in air. Especially in a high-humidity environment, during hydrolysis and pyrolysis, it is worth looking forward to turning the harmful water erosions and playing an inorganic template for the nucleation and growth of the perovskite crystals by introducing PHPS.
Herein, we developed an effective curing-anti-solvent strategy combining green MeOAc anti-solvent and inorganic polymer perhydropolysilazane (PHPS) to prepare high-quality and stable black-phase CsPbI 3 films in high-humidity air. In this recipe, PHPS will quickly hydrolyze in reaction with moisture in the air, forming a strong Lewis acid-based interaction toward the CsPbI 3 precursor molecule (generated by hydrolyzed -Si(OH) 4and PbI 2 precursor molecule), which can robustly shield the intrusion of ambient moisture and control grains growth. After annealing, the pyrolysis-generated Si-O-Pb bonding to CsPbI 3 film further passivated surface defects, resulting in improved film quality and reduced energetic disorder. Meanwhile, ultrafast charge transfer at the interface could be realized due to the cascade energy level landscape within the PSCs induced by PHPS (i.e., the formation of energy gradients). Under the ultra-wide processing window offered by PHPS curing, an extremely uniform and dense perovskite film enables the fabrication of PSCs with a remarkably improved PCE up to 19.17% in RH 60%, exhibiting excellent operational stability with 90% of the initial PCE retained after exposed in RH 30% for 1000 h. Figure 1a shows a schematic illustration of the fabrication of perovskite layers by one-step spin-coating followed by the dripping green MeOAc anti-solvent solution in air. The inorganic PHPS moisture-curing agent was added to the anti-solvent solution at various volumes of addition (volume ratios with respect MeOAc) to fabricate high-quality perovskite films in a high-humidity window. Using this solvent-resistant deposition technique, we fabricated a series of perovskite films. The top-view scanning electron microscopy (SEM) images were performed to visualize the morphology of the CsPbI 3 films treated with PHPS/MeOAc mixed anti-solvent consisting of 0 to 3 vol.% of PHPS to evaluate their crystallization in 60 RH% operating windows. Pristine CsPbI 3 films treated without PHPS show a non-dense morphology with pinholes or cracks, which is not unexpected due to the rampant erosion of water molecules and similar to the previous reports ( Figure 1b). [24,30] After incorporating small amounts of PHPS (0.3 and 0.5 vol.%) into the anti-solvent process, we found that the morphologies of the PHPS-CsPbI 3 films gradually densified with an increase in grain size to approximately 768 AE 0.19 nm ( Figure S2), indicating PHPS-derived controlled growth. Besides, the surface roughness of the optimized films is flattened from 24.1 nm (pristine film) to 16.9 nm, offering better interface contact ( Figure S3). With PHPS increasing in antisolvent MeOAc, at 0.7 vol.%, for example, the film began to present some thin burrs layer on the crystal surface of perovskite that can be observed by AFM, which should be related to the coating of Si-O-Pb or Si-O-Si linkage deriving from cured PHPS and this will be discussed below. At the same time, the emergence of the thin burr layer is accompanied by larger grains and a reduction in the surface area of grain boundary (GBs). This could be expected as PHPS polymer converts the harmful water erosions into -Si(OH) 4which may interact with the PbI 2 of perovskite precursor film to control crystal growth, followed by thermally-triggered PbI 2 ÁSi(OH) 4 adduct to transform into cross-linked Si-O-Pb bonding to the surface of CsPbI 3 . This strong interaction anchors the [PbI 6 ] 4− octahedron to form a bridge to connect crystalline grains through the Si-O-Pb bond loading, thereby forming large perovskite crystals with Si-O-Pb/Si-O-Si coverage during nucleation and growth. A cross-linked Si-O-Pb network possesses a high hydrophobicity to prevent moisture invasion, which effectively passivates the surface traps and enhances the long-term stability of perovskite films. [31] However, for V PHPS > 0.7 vol.%, the burrs grow up to form the flocculent structure (1 vol.%) followed by transformation into a compact capping layer on the surface of perovskite films (3 vol.%, Figure S4), which could be unfriendly to the photoelectric properties of the devices but favor the encapsulation layer. In addition, I-V characteristics of the CsPbI 3 films treated with various volumes of PHPS further indicated moderate PHPS does not affect the conductivity of the CsPbI 3 film ( Figure S5). To further analyze the elemental distribution of CsPbI 3 film treated by 0.5 vol.% PHPS, X-ray energy-dispersive spectroscopy mapping was carried out. Figure S6 presents a uniform distribution of Cs, Pb, I, Si, N, and O elements, indicating that the PHPS-derived products uniformly cover the surface of the perovskite crystals without segregation or aggregation. Since the PHPS used in this work was stored in an N-butyl ether solvent, to exclude the effect of N-butyl ether solvent from PHPS on the growth of perovskite film, an equal volume of Nbutyl ether was added to the anti-solvent for fabricating perovskite films under the same conditions. The results showed that the effect of Nbutyl ether additive plays an ignorable role in the growth of perovskite film (details see Figure S7). Figure S8 shows that the PHPS treatment has a slightly enhanced light absorption on the UV-visible spectra of the CsPbI 3 perovskite thin films, particularly in the wavelength region from 400 to 600 nm, which was attributed to the compact and large grains sizes after PHPS treatment. We further calculated Urbach energies (E u ) for the corresponding films by fitting the absorption spectra near the band edge. [32][33][34] In contrast, after treatment with the 0.5 vol.% PHPS, the film showed a significantly lower E u (Figure 1h), and the decreased E u usually reflected the lower density of shallow traps. [35,36] This shows that the electronic quality of the perovskite layers was enhanced by 0.5 vol.% PHPS treatment, which can be attributed to the passivating charged defects at GBs and surface in perovskite. Figure 1i presents the X-ray diffraction (XRD) pattern of corresponding perovskite films with various volumes of PHPS addition in the MeOAc anti-solvent. All the films exhibit clear XRD peaks at 14.2°and 28.7°that are indexed to the (110) and (220) planes of the β-phase perovskite CsPbI 3 materials, respectively. Meanwhile, no impurity phases such as silicon oxide were observed, indicating that the perovskite lattice structure has not been disrupted by introducing PHPS, and PHPS-derived silicon oxide was in an amorphous state. [29] Compared with the control sample, the diffraction peaks of the sample prepared by 0.5 vol.% PHPS were the strongest and sharpest, indicating better lattice order and crystal quality for CsPbI 3 films, which was consistent with the SEM observation. With the PHPS increasing in anti-solvent MeOAc, the position of main diffraction peaks for (110) and (220) planes of perovskite kept constant but became smaller and smaller in intensity, signifying that introduced PHPS had little effect on the lattice structure of the CsPbI 3 phase, which better ensured the role of PHPS in the formation of CsPbI 3 films. While the reduction of perovskite characteristic XRD peaks is due to the coverage of more amorphous silica originating from PHPS on the perovskite film. Grazing incident wide-angle X-ray scattering (GIWAXS) was conducted to further analyze the crystalline orientation of the perovskite with and without 0.5 vol.% PHPS treatment. As shown in Figure 2, the 0.5 vol.% PHPS treated perovskite displays stronger scattered spots and rings at q = 1Å −1 (110) and q = 2Å −1 (220) planes of perovskite than the ref. Furthermore, by normalizing the half-widths of the corresponding diffraction peaks (Δq, Δq being the full width at half maximum values), uniform equal breadth was observed in PHPS-CsPbI 3 perovskite film ( Figure 2d). As reported, uniform equal breadth represents a diffraction profile from a finite-size-dominated sample, while the different broadening of the diffraction peaks shows the cumulative disorder caused by an accumulation of distortions and defects. [37,38] These results indicate that 0.5 vol.% PHPS treatment could promote the lattice order and crystallite uniformity, which is consistent with the Urbach energies result. Ultraviolet photoelectron spectroscopy (UPS) was used to evaluate the effect of PHPS treatment on energy bands of perovskite ( Figure S9a). Compared with pure perovskite film, the Fermi-level of perovskite surface treated with 0.5 vol.% PHPS downshifted by 0.25 eV, maximizing the gap between the valence band edge of the perovskite and the highest occupied molecular orbital energy level of HTL ( Figure S9b), which would cause band-bending and promote hole-extraction for HTL. This is beneficial for enhancing V oc , which was further confirmed by increasing the build-in potential (V bi ) below. The band-bending is due to the passivation of perovskite surface defects by PHPS during the oxidation process, which is consistent with previous reports. [39] From the mechanism of moisture-cure of PHPS and the above experimental results ( Figure S1), we expect the intermediary-formed silanol groups can form an intermediate adduct with PbI 2 to control crystal growth, and hamper [PbI 6 ] 4− distortion and passivate the shallow traps at the GBs of perovskite though the final formation strong interaction of Pb/SiO x (Figure 3a). To test the hypothesis and investigate the interaction between PHPS and perovskite, we performed Fourier transform infrared (FTIR) spectra analysis of the cured and uncured PHPS, and Energy Environ. Mater. 2023, 6, e12554 3 of 9 PHPS treated CsPbI 3 film (Figure 3b). The FTIR spectra of uncured PHPS (blue line) show absorption bands in the 3324, 1217, 862, and 2108 cm −1 regions, attributing to typically functional groups of N-H stretching, N-H bending, Si-N stretching, and Si-H bending modes in PHPS, respectively. [40,41] Moreover, a new absorption peak at 955 cm −1 corresponding to the Si-OH group of PHPS hydrolysis was observed, marking the hydrolysis reaction. [42] For the FTIR spectra of the CsPbI 3 as-quenched in the presence of PHPS (green line), these characteristic vibrations still persisted, but only red-shifting to 984 cm −1 for the Si-OH, and 908 cm −1 for the Si-N stretching (Figure 3c), respectively, indicating an interaction effect between -Si (OH) 4groups and PbI 2 ÁDMSO adduct to form a Si(OH) 4 ÁPbI 2 ÁDMSO adduct. Meanwhile, the CsIÁMeOAc adduct was observed at 1732 cm −1 . [43] After moisture-cured PHPS-treated CsPbI 3 film in the open air (60 RH% at 180°C) (tiffany blue line), the above characteristic vibrations significantly weakened or disappeared. Furthermore, new absorption peaks at 1080 cm −1 and was identified as Si-O-Si vibration formed by condensation of cross-linked silanol under pyrolysis. [44] Notably, compared with the cured pure PHPS (60 RH% at 180°C), Si-O-Si and smaller N-Si-O peaks in PHPS-treated CsPbI 3 film showed a clear blue-shifting, as illustrated in Figure 3d. This shift indicates an interaction effect between PHPS-derived products and CsPbI 3 , resulting from the pyrolysis of Si(OH) 4 ÁPbI 2 ÁDMSO adducts forming Si-O-Pb at the interface with CsPbI 3 film, thereby providing effective trap states passivation during the process of film formation. For the decreased Si-N in the cured film, it is mainly due to the incomplete substitution of N atoms near bulk PHPS by O atoms, as the dense top surface of the Si-O-Si network impedes the further diffusion of O atoms, leading to a compositional gradient of cured product in the thickness direction (i.e., Si-O-Si on the top and O-Si-N on the bottom) after curing. [45] Based on the above FTIR information, it is indicated that the PHPS plays a dominant role in the growth and passivation of orthorhombic CsPbI 3 crystal during air fabrication. X-ray photoelectron spectroscopy (XPS) measurement was conducted to further confirm the existence of PHPS-derived passivation products on perovskite films. The survey spectrum of PHPS-CsPbI 3 ( Figure S10) shows the presence of Si 2p, N 1s, and O 1s (Figure 3e) peaks besides Cs 3d, Pb 4f, and I 3d peak from the CsPbI 3 perovskite materials, which further confirmed the presence of PHPS-derived products from the reaction of PHPS with oxygen or water in open air. It is found that the Si 2p spectrum in Figure S9b showed two peaks at 103.5 eV and 102.3 eV attributed to Si 4+ and O-Si-N in PHPS-CsPbI 3 , which marks the PHPS oxidation in ambient air. [25] Meanwhile, two feature peaks of the O1s signal were found at 531.95 eV and 530.4 eV, which were identified as Si-O bonds and Pb-O bonds, respectively (Figure 3e). [46] This indicates that the SiO 2 was linked onto the CsPbI 3 surface by ionic O-Pb bonds, which were formed by the condensation reaction of PbI 2 ÁDMSOÁSi(OH) 4 adduct, thus inhibiting [PbI 6 ] 4− distortion and passivating defect, conducive to stabilize orthorhombic CsPbI 3 . The intensity of the signal peak of the PHPS-derived silicon oxide and silicon oxynitride increased with increasing PHPS concentration. Remarkably, after introducing PHPS, the characteristic peaks of the Pb 4f and the I 3d shift toward higher binding energy as displayed in Figure S10e,f. This situation becomes even more significant for CsPbI 3 films treated with a high concentration of PHPS (ie, where strong Si-O and O-Si-N signals are present). This suggests a strong change in the electronic state around the perovskite surface atoms, which is attributed to the interaction of Pb/SiOx or O-Si-N, respectively.

Results and Discussion
These experimental findings are supported by density functional theory (DFT) calculations ( Figure S11). Our calculations show that the PHPS molecule attaching to CsPbI 3 exhibited good stability (adhesive energy being approximately −1.491 eV in Figure S11c), and the water molecules exhibit higher adsorption energy (E ads = −1.197 eV) on the PHPS molecules than CsPbI 3 surface (E ads = −1.153 eV). This indicates that PHPS molecules deposited on the CsPbI 3 film would form a robust shield to insulate the perovskite from external moisture erosion during air fabrication. Furthermore, the electron localization function was used to detect and visualize the localized electron density distribution between the Si-O-Si/CsPbI 3 configuration ( Figure S12). As depicted in Figure S12b, the localized states (light red cloud) between the bridge oxygen atom on SiO 2 and the lead atom on CsPbI 3 demonstrated a newly formed Pb-O bond characteristic, which is consistent with the experimental results from XPS.
Based on the above material characterization, we proposed a plausible mechanism of CsPbI 3 crystal modulation and defect passivation by the anti-template agent PHPS method in ambient moisture. The function of the anti-template agent PHPS can be described by the following reactions: The effect of the Si-O-Si/Si-O-Pb cross-linking on the surface of CsPbI 3 as a protection layer to stabilize CsPbI 3 has been studied. We systematically explored the moisture resistance and phase stability of CsPbI 3 with PHPS treatment. First, the contact angle tests in Figure 4a showed that the PHPS-treated film was more hydrophobic in comparison with the control perovskite film ( Figure S13). When the pure and PHPS-treated perovskite films were exposed to ambient air at room temperature (RT) with 80%-90% RH for 0.5 h, an obvious degradation was observed for the pure film, as revealed by the UV-vis spectra which exhibits a signal of δ-phase peak at 420 nm (Figure 4b). The XRD patterns (Figure 4c) also show a characteristic δ-phase peak at around 11°in the aged pure film. In contrast, the PHPS-treated film did not show significant degradation under the same condition, and the perovskite black phase was maintained. The evolution of the color of the film photographs further visualizes the longer stability of PHPS-CsPbI 3 for over 1 month in a dry box with <30% RH at RT. The PHPS-CsPbI 3 with Si-O-Si/Si-O-Pb network protection would start to slightly degrade at the edges of the film after aging for 30 days, while the whole pure CsPbI 3 film had completely decomposed. The enhanced moisture resistance and phase stability should be ascribed to the largesize crystal and hydrophobic Si-O-Si network, which would significantly prevent the attack of the H 2 O and O 2 , thereby improving the stability of CsPbI 3 films. In addition, the thermogravimetric analysis in Figure S14 indicated that PHPS-CsPbI 3 showed enhanced thermal stability versus pure CsPbI 3 , which might attribute to the intrinsic thermal stability of cured-PHPS and its strong interaction with perovskites.
Photovoltaic experiments were conducted to evaluate the performance of PHPS-CsPbI 3 devices fabricated in ambient conditions. Figure 5a presents the forward scan and reverse scan photocurrent density-voltage (J-V) characteristics of various devices. The detailed photovoltaic parameters are summarized in Table 1. Specifically, for the perovskite layer without PHPS treatment, the devices showed poor performance, with open-circuit voltage (V oc ) of 1.09 V, short-circuit current density (J sc ) of 19.70 mA cm −2 , fill factor (FF) of 76.56%, and PCE of only 16.22%. The lower performance might be attributed to the severe leakage and recombination induced by pinhole perovskite films formed by anti-solvent treatment without PHPS protection. While PHPS was introduced into anti-solvent, the device performance-enhanced significantly (Figure 5b). A champion PCE of 19.17% was obtained when the perovskite layer was treated with 0.5 vol.% PHPS, with the V oc of 1.18 V, J sc of 20.17 mA cm −2 , and FF of 80.55% under reverse scan ( Figure S15, Table S2). Compared with the previous reports on CsPbI 3based PSCs prepared under high humidity conditions, the efficiency of our devices represents a great improvement, as listed in Table S1. Simultaneously, the good reproducibility in PCE (Figure 5b) and the negligible hysteresis phenomenon from the J-V curves in both reverse and forward scans (Figure 5a) also substantiate the promise to fabricate CsPbI 3 PSC devices with the assistance of PHPS in the open air. The external quantum efficiency (EQE) of PHPS-CsPbI 3 -based devices can reach up to 90% with the integrated current of 20.10 mA cm −2 ( Figure S16), which is almost consistent with the J-V result. Besides the higher efficiency, the PHPS-CsPbI 3 -based devices also exhibit better . The PHPS-CsPbI 3 -based device without any encapsulation still maintained approximately 90% of its initial PCE after 1000 h, while the PCE of the pristine device without PHPS treatment was only approximately 60% of its initial PCE after 400 h. These results indicate that applying an inorganic PHPS passivation strategy can achieve high stability during ambient storage. The improved stability can be ascribed to the effective defect passivation of PHPS and the "self-encapsulation" effect of the PHPS-derived Si-O-Si network (i.e., preventing the penetration of ambient moisture), as discussed earlier. Moreover, the longterm operational stability of the PHPS-CsPbI 3 -based devices using a 400 nm thick PHPS encapsulation layer was further tested under ambient conditions ( Figure S17b). The PSC featuring the encapsulation layer presented a fine waterproof effect and stability, and maintained over 95% of its initial PCE over 1000 h aging.
The above results suggest that the introduction of PHPS not only increases grain size but also may passivate the shallow-or deep-level defects in inorganic CsPbI 3 perovskite. Steady-state photoluminescence (PL) and time-resolved PL (TRPL) characterization of these perovskite films were performed to evaluate the effect of PHPS on charge-carrier and trap-state passivation. The PL peak shows twice increasement in the intensity for CsPbI 3 film with 0.5 vol.% PHPS treatment compared to the pristine film (Figure 5c), which indicates a significantly reduced density of trap states and associated charge recombination. Furthermore, the PL decay lifetimes were fitted with a bi-exponential decay function (Figure 5d), I (t) = I 0 + A 1 exp(−t/τ 1 ) + A 2 exp(−t/τ 2 ), where τ 1 and τ 2 represent nonradiative recombination of surface traps near the external interface (grain boundaries) and the internal radiative recombination in perovskite, respectively. [47] For 0.5 vol.% PHPS treated film, τ 1 was estimated to be 39.595 ns and τ 2 to 206.187 ns, while τ 1 was 12.307 ns and τ 2 to 69.336 ns for the pristine film. Apparently, the 0.5 vol.% PHPS treated perovskite film possesses a longer τ 2 and also a higher ratio of τ 2 /τ 1 , further demonstrating that the introduction of PHPS can effectively passivate trap states, which is consistent with the PL results.
Trap-state density (N t ) of perovskite film was evaluated from admittance spectroscopy, obtained from frequency-dependent capacitance test of devices. The frequency-dependent capacitance spectrum of CsPbI 3 and 0.5 vol.% PHPS-CsPbI 3 perovskite devices were shown in Figure 5e. According to the following equation: [48]   where C is the capacitance, ω is the angular frequency, k is the Boltzmann constant, and T is the temperature. E ω (E ω = E T -E V ) represents the energy level difference between trap energy and valence band maximum. V bi and W represent the built-in potential and depletion width of the heterojunction in perovskite devices, respectively, which were measured with the Mott-Schottky plot (inset in Figure 5e). The measured V bi values of CsPbI 3 and PHPS-CsPbI 3 perovskite were 1.05 and 1.17 V, respectively, correlating with enhanced V oc with PHPS treatment. Then, the distributions of N T could be calculated for the two perovskite systems, as demonstrated in Figure 5f. It has been found that the device with PHPS treatment has overall the lowest N T over the whole trap depth region, and the trap state energy level is also slightly pushed down to shallower levels. This indicates that PHPS-derived products may diffuse into grain boundaries and inner surfaces of perovskite to coordinate the under-coordinated metal cations (Si-O-Pb) on the crystal surface and passivate them, as discussed above.

Conclusion
In summary, we have successfully demonstrated a bifunctional PHPS as anti-template agent for enhancing grain growth and passivating defects during air fabrication, achieving the high-quality CsPbI 3 film in RH 60% ambient condition. During the process of film formation, PHPS can consume the water erosions and convert them into the Lewis base silanol to regulate the crystallization and preferred orientation of the CsPbI 3 film, followed by condensing into a compact Si-O-Si/Si-O-Pb network to suppress phase transition and resist moisture and O 2 invasion externals. As a result, the PCE of the CsPbI 3 -based solar cell was enhanced from 16.22% to 19.17% upon an optimized addition of PHPS in an anti-solvent solution. Besides, the unencapsulated target devices exhibit greatly enhanced long-term stability, and PCE remains at approximately 90% of its initial PCE after 1000 h under below 30% RH. This work presents an effective strategy for addressing the moisture erosion of air-fabricated PSCs and provides new approaches to further enhance the photovoltaic performance of PSCs for air fabrication.

Experimental Section
Detailed information related to the synthesis of active electrodes, physicochemical characterization, and electrochemical evaluation of bifunctional electrodes towards UOR and supercapacitor application is provided in Supporting Information.