A Water Solution Processed Hybrid Electron Transport Layer Simultaneously Enhances Efficiency and Stability in Inverted Structure Organic Solar Cells

Abstract Achieving both high efficiency and stability in organic solar cells (OSCs) remains a significant challenge. Inverted structure OSCs, compared to those with a normal structure, show great potential for combining high efficiency with enhanced stability. However, despite their improved stability, the efficiencies of inverted OSCs still lag behind those of conventional structure OSCs, largely due to the performance of electron transport layers (ETLs). Herein, a water‐soluble hybrid ETL is developed by modifying SnO 2 nanoparticles with an aqueous potassium carboxylate salt, PMA. This modification effectively passivates the oxygen vacancy defects in the SnO 2 nanoparticles and eliminates the light soaking issue observed in the control device. As a result, the PM6:Y6‐based device shows an improvement in efficiency from 16.68% to 17.85% with PMA modification. Notably, an exceptional efficiency of 19.07% is achieved for the PM6:BTP‐eC9‐based device using this hybrid ETL, marking the highest efficiency reported to date for single‐junction inverted OSCs. In addition, all tested OSCs with the hybrid ETL demonstrate superior stability under both thermal and light illumination at the maximum power point compared to the control devices. Furthermore, utilizing this water‐processed hybrid ETL, a large‐area module based on PM6:BO‐4Cl is fabricated and shows an outstanding efficiency of 15.02%.