Synergistic Benefits of Cesium‐Doped Aqueous Precursor in Air‐Processed Inverted Perovskite Solar Cells

Abstract

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.