C60 Self-Assembled Monolayer-Modified SnO2 Electron Transport Layer for Efficient and Stable Inverted Organic Solar Cells

Compared to conventional configurations, inverted organic solar cells (IOSCs) demonstrate superior stability, holding greater potential for commercial application. However, their performance is constrained by inherent limitations of the commonly used zinc oxide (ZnO) electron transport layer (ETL). Herein, we introduce tin oxide (SnO2) as a replacement ETL, leveraging its higher electron mobility and enhanced environmental stability. To further address interfacial issues, the SnO2 surface is modified with a C60 self-assembled monolayer (C60-SAM), which can passivate surface defects, optimize the energy-level alignment, and improve interfacial contact. Systematic studies comparing ZnO, pristine SnO2, and SnO2/C60-SAM as ETLs validate this approach. In devices based on the PM6:L8-BO system, the SnO2/C60-SAM ETL delivers a champion power conversion efficiency (PCE) of 18.39%, outperforming those with pristine SnO2 (17.92%) and ZnO (16.91%). These devices also exhibit improved operational and shelf-life stability. Moreover, applying this strategy to a ternary PM6:BTP-eC9:L8-BO system elevates the PCE to 19.05%. This work not only confirms the superiority of SnO2 over ZnO as an ETL but also provides a facile and effective interface-modification strategy, paving the way for developing high-performance and stable organic photovoltaics.