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 MAPbI 3 , CsFAPbI 3 , and Cs 2 AgBiBr 6 . Severe hysteresis is observed in devices employing planar TiO 2 or SnO 2 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 TiO 2 thickness and incorporating mesoscopic TiO 2 architecture with controlled thicknesses. An optimized configuration featuring an approximately 140 nm mesoporous layer substantially reduces hysteresis, lowering the hysteresis index (HI) in MAPbI 3 PSCs from 0.52 for planar TiO 2 to 0.19, enhancing stability while maintaining high PCE. Similar improvements are demonstrated for CsFAPbI 3 , where the HI decreases from 0.56 for planar TiO 2 and 0.47 for planar SnO 2 to 0.38, and for Cs 2 AgBiBr 6 , 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.