Coordination-Induced Defects Elimination of SnO₂ Nanoparticles via a Small Electrolyte Molecule for High-Performance Inverted Organic Solar Cells

Tin oxide (SnO₂) is broadly used as an electron transport layer (ETL) in organic solar cells (OSCs). However, there are many hydroxyl groups and the defects of oxygen vacancy on the surface of SnO₂, resulting in charge recombination. Herein, an electrolyte 4-(dimethyl(pyridin-2-yl) ammonio)butane-1-sulfonate (PAS) is doped into SnO₂ films with an appropriate proportion to improve the performance of the inverted OSCs. The PAS can coordinate with the Sn atoms in SnO₂ films to reduce the surface defects, resulting adjustable work function and increased electron conductivity. Meanwhile, the PAS doping can decrease the surface energy of SnO₂ layer, forming vertical phase distribution of the active layer for better exciton dissociation and charge transport. The PM6:Y6 based inverted OSC with SnO₂ ETL shows a power conversion efficiency (PCE) of 14.72%, while the device with PAS-doped SnO₂ ETL demonstrates greatly enhanced PCE of 16.37%. The device performance can be further improved by using PM6:BTP-eC9 as active layer and a PCE of 17.12% can be achieved with PAS-doped SnO₂ ETL. Furthermore, PAS-doped SnO₂ can effectively enhance the device stability under continuous illumination. These findings demonstrate that exquisite regulation of SnO₂ layer via a small electrolyte molecule coordination is a promising approach to achieve efficient and stable inverted OSCs.