C 70 /C 60 : Efficient Electron Transport Layer for High-Performance Perovskite Solar Cells

Electron transport layers (ETLs) are paramount important to enhance the performance in inverted perovskite solar cells (PSCs); however, modulation of the interfacial charge transfer (electron extraction) process at the perovskite/ETL interface is rarely achieved. In this study, a bilayer ETL was strategically designed to simultaneously improve electron extraction and optimize charge transport dynamics in inverted PSCs. Capitalizing on the strong electron extraction ability of C70 and the superior charge transport characteristics of C60, the bilayer ETL employs a functional stratification approach to regulate interfacial charge kinetics. An ultrathin C70 is positioned in direct contact with the perovskite active layer, significantly accelerates electron extraction and effectively passivates interfacial defects. The upper C60 layer, benefiting from its high electron mobility, establishes an efficient charge transport pathway while also suppressing hole back-injection. Comprehensive device characterization revealed that the PSCs incorporating this bilayer ETL exhibit enhanced device performance which achieved a PCE of 24.51%, being much larger than that of the control one (23.34% for C60 based device). Furthermore, the use of vacuum thermal evaporation ensures excellent film uniformity and reproducibility, providing a viable strategy for the industrialization of high-performance perovskite photovoltaic technologies.