Interface engineering for efficient ETL-free perovskite solar cells via self-assembled bifunctional monolayer

Simplified structure perovskite solar cells (PSCs) without typical charge transport layer (CTL) have attracted much attention because of their simple manufacturing, low production costs, great stability, and high power conversion efficiency. However, it still has lots of challenges, such as poor interface contact and mismatched energy level, which limits the electron transfer and extraction as well as the photovoltaic performance of the device. In this work, a bifunctional monolayer 3-Chloropropyltriethoxysilane is self-assembled on FTO and applied in electron transport layer (ETL)-free PSCs. A dipole layer was developed, which could bend the band at the FTO/perovskite interface, improve interface contact, enhance the carrier transfer, and inhibit the charges recombination. The chloridion of silane forms halogen bonds with the uncoordinated Pb 2+ ions of the perovskite, thereby passivating the defects of the perovskite films and improving the quality of perovskite films. Eventually, the ETL-free with 3-CPTES SAM PSCs achieves a 21 % efficiency, which has increased by 40 % compared to 14.93 % of the pristine device. Concurrently, the perovskite solar cell (PSC) based on the modified FTO demonstrates notable stability improvements under various environmental and extreme conditions. Specifically, the PSC maintains 79.7 % PCE under high temperature conditions, 77.8 % under high humidity conditions, and an impressive 62.6 % under illumination.