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 C 70 and the superior charge transport characteristics of C 60, the bilayer ETL employs a functional stratification approach to regulate interfacial charge kinetics. An ultrathin C 70 is positioned in direct contact with the perovskite active layer, significantly accelerates electron extraction and effectively passivates interfacial defects. The upper C 60 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 C 60 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.