Impact of Electron Transport Layers on Hysteresis and Performance of Ambient-Processed Perovskite Solar Cells

Ambient processing of perovskite solar cells (PSCs) offers a promising route to scalable and low-cost manufacturing. While substantial progress has been achieved in improving power conversion efficiency (PCE), the hysteresis behavior of ambient-processed devices remains insufficiently understood. This study examines hysteresis in PSCs fabricated in ambient air at 40-65% Relative humidity (RH) using multiple absorber compositions, including MAPbI₃, CsFAPbI₃, and Cs₂AgBiBr₆. Severe hysteresis is observed in devices employing planar TiO₂ or SnO₂ electron transport layers (ETLs), attributed to amplified moisture- and oxygen-induced defect formation in ambient air. To overcome this challenge, ETL architecture is systematically engineered by adjusting planar TiO₂ thickness and incorporating mesoscopic TiO₂ architecture with controlled thicknesses. An optimized configuration featuring an approximately 140 nm mesoporous layer substantially reduces hysteresis, lowering the hysteresis index (HI) in MAPbI₃ PSCs from 0.52 for planar TiO₂ to 0.19, enhancing stability while maintaining high PCE. Similar improvements are demonstrated for CsFAPbI₃, where the HI decreases from 0.56 for planar TiO₂ and 0.47 for planar SnO₂ to 0.38, and for Cs₂AgBiBr₆, where the HI decreases from 0.32 to 0.08. These findings highlight ETL structural engineering as an effective strategy for mitigating hysteresis and enabling reliable ambient-processed PSCs for scalable manufacturing.