Poly(3,4‐ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is widely used as a hole transport layer in inverted perovskite solar cells (PSCs). However, due to the serious interface defects, imperfect energy level arrangement, and low hole transfer rate between PEDOT:PSS and perovskite, the realization of efficient and stable inverted PSCs is hindered. Herein, ionic salt sodium borohydride is used as an interfacial modifier between PEDOT:PSS and MAPbI3−xClx. NaBH4 acts as an anchor to bond Pb2+ to the PEDOT:PSS surface and guides the growth of the perovskite. The champion power conversion efficiency (PCE) of the device based on NaBH4‐PEDOT:PSS reaches 20.21%, which is improved by 27.5% compared with the device based on PEDOT:PSS (15.84%). This PCE is one of the highest in inverted PSCs with PEDOT:PSS as the hole transport layer and MAPbI3−xClx as the active layer. The improved device performance is mainly attributed to the reduced valence band edge of PEDOT:PSS which matches better with the HOMO of MAPbI3−xClx, and the hole transfer rate is increased from 2.65 × 1010 to 3.69 × 1010 s−1. The long‐term stability of the optimized device exceeds 1000 h. This work provides a simple and effective strategy to improve the PCE and stability of inverted PSCs, which is a benefit for future popularization.

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used in inverted perovskite solar cells (PSCs) due to its simple preparation process and high stability. However, because of its low conductivity and charge transfer ability, the power conversion efficiency (PCE) of inverted device is poor. To solve this problem, AuCl3 is introduced to modify the interface between the hole transport layer (PEDOT:PSS) and electrode (ITO). The X‐ray photoelectron spectroscopy  (XPS) spectra of PEDOT:PSS confirms that the PSS chains are reduced and the conductivity are increased after AuCl3 doping. Moreover, AuCl3‐modified PEDOT:PSS is beneficial to guide crystal growth and to improve the grain size, crystallinity, and water contact angle of perovskite films. Meanwhile, the defects of PEDOT:PSS/perovskite interface are effectively passivated, which suppresses the nonradiative recombination. The hole extraction efficiency is improved from 8.88× to 1.31× s−1. As a result, the short‐current density (Jsc) and fill factor (FF) are improved, which leads to a champion device with PCE up to 18.08%, much higher than 16.03% of pristine one. The unencapsulated device remains 80% of the initial efficiency after 4 weeks under 45 ± 5% humidity. The results provide a new strategy for synergistically enhancing the efficiency and stability of PSCs by interfacial modification and doping.

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Air‐processed perovskite solar cells (PSCs) allay the need for costly fabrication in a controlled atmosphere but currently suffer from disadvantages in power conversion efficiency (PCE) and device stability. Herein, the systematic investigation into CH3NH3PbI3–xClx prepared with an antisolvent‐assisted process in a relative humidity of 40 ± 5% is reported, using cesium‐containing aqueous solutions of various strengths. Diffractometry and microscopy reveal how grain sizes vary among the samples, suggesting an optimum concentration for grain size. Those films are fabricated in air into solar cells, and their electrochemical impedance and current–voltage characteristics under light are measured. The films demonstrating optimum strength achieve PCEs of up to 16.6%, compared with the maximum of 14.4% achieved by untreated films. The air‐processed films also exhibit mitigated hysteresis, with indices decreasing to 0.021. Photoluminescence characterization reveals reduced defect densities in Cs‐doped materials and, together with photoelectron spectroscopy, suggests an upward shift in energy bands. Such changes explain the improvement in photovoltaic performance. Stability tests on unencapsulated cells over 14 days show that those made from the perovskite with optimum Cs‐doping degrade slowest, with their conversion efficiencies falling by <10% every 100 h. Our findings may contribute to the low‐cost commercialization of PSCs.

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