Heterovalent Samarium Cation-Doped SnO2 Electron Transport Layer for High-Efficiency Planar Perovskite Solar Cells

Tin oxide (SnO₂) has demonstrated significant potential as an electron transport layer (ETL) owing to its low-temperature processing in perovskite solar cells (PSCs). However, the poor energy-level alignment and the presence of interface defects between the SnO₂ and perovskite layer aggravate the power conversion efficiency (PCE) of the PSCs. Herein, heterovalent samarium cation (Sm³⁺) is deliberately doped into SnO₂, optimizing the energy-level alignment between SnO₂ and the perovskite layer, and effectively passivating the oxygen vacancy defects on the surface of SnO₂. Experimental and theoretical conclusions reveal that Sm-doping successfully passivates the defects in the ETL and improves the perovskite crystal quality, thereby reducing interface charge recombination, and enhancing electron extraction from perovskite to the SnO₂ layer. Consequently, the optimized Sm-doped SnO₂-based PSCs achieve a PCE of 24.10% with a V_OC of 1.174 V, negligible hysteresis, and improved durability under ambient conditions.