Methanol-Induced Surface Homogenization of ZnO for High-Performance Inverted Organic Solar Cells

The performance and stability of inverted organic solar cells (OSCs) are often limited by the inherent defects and photocatalytic activity of zinc oxide (ZnO) electron transport layers. A methanol-induced surface homogenization (MISH) strategy is proposed to simultaneously address these challenges. Through coordination and hydrogen bonding, methanol effectively passivates surface defects while suppressing the generation of hydroxyl radicals (-OH) under operational conditions. This dual-functional modification optimizes ZnO work function, enhances interfacial charge transport, and promotes a favorable vertical phase separation within the active layer. The optimized morphology effectively suppresses interfacial recombination while enhancing charge collection efficiency, leading to significant improvement in device performance. The inverted PM6:L8-BO-based OSCs achieve apower conversion efficiency (PCE) of 18.63% with exceptional thermal stability (T80 > 1000 h). Furthermore, the universality of the MISH strategy is demonstrated in PM6:L8-BO:BTP-eC9 ternary systems, yielding an impressive PCE of 18.85%. Comprehensive characterization, including atomic force microscopy, grazing-incidence wide-angle X-ray scattering, reveals that methanol treatment not only reduces trap states but also stabilizes molecular stacking during long-term operation. This work provides a simple and effective approach for ZnO modification, offering profound insights into interfacial engineering for high-performance and stable OSCs.