Multi-functional L-histidine self-assembled monolayers on SnO2 electron transport layer to boost photovoltaic performance of perovskite solar cells

• L-His modification induced better crystal quality of SnO 2 and perovskite films. • L-His layer enhanced interface interaction and modulated energy level structure. • The champion PCE of optimized MAPbI 3 -based PSCs has been enhanced to 21.04%. The photovoltaic performance of perovskite solar cells (PSCs) is sensitive to the interface properties between perovskite and electron transport layer (ETL). An appropriate interface engineering on SnO 2 ETL is highly desired for achieving efficient PSCs. Herein, we introduced L-histidine (L-His) self-assembly layer on SnO 2 ETL to realize three following functions. The crystal quality and conductivity of SnO 2 ETL have been improved since the carboxyl groups in L-His coordinate with the tin ion in SnO 2 and fill the oxygen vacancy. The improved wettability caused by L-His deposition induces the formation of perovskite films with larger grain size and better crystallization quality. The hydrogen bond formed between perovskite and L-His proved by proton nuclear magnetic resonance ( 1 H NMR) enhances the interface interaction, and the L-His also modulates the energy level structure of the ETL/perovskite interface, which not only enhances the charge transport properties but also leads to a higher open-circuit voltage. Based on these benign optimizations, the CH 3 NH 3 PbI 3 -based PSCs with the optimized SnO 2 /L-His ETL have achieved a power conversion efficiency of 21.04%. Such biological friendly modification technique is highly compatibility to the technique of large-scale production of PSCs.