Phosphate-Passivated\nSnO₂ Electron Transport Layer for High-Performance Perovskite\nSolar Cells

Abstract

Tin\noxide (SnO₂) is widely used in perovskite solar cells (PSCs)\nas an electron transport layer (ETL) material. However, its high surface\ntrap density has already become a strong factor limiting PSC development.\nIn this work, phosphoric acid is adopted to eliminate the SnO₂ surface dangling bonds to increase electron collection efficiency.\nThe phosphorus mainly exists at the boundaries in the form of chained\nphosphate groups, bonding with which more than 47.9% of Sn dangling\nbonds are eliminated. The reduction of surface trap states depresses\nthe electron transport barriers, thus the electron mobility increases\nabout 3 times when the concentration of phosphoric acid is optimized\nwith 7.4 atom % in the SnO₂ precursor. Furthermore, the\nstability of the perovskite layer deposited on the phosphate-passivated\nSnO₂ (P-SnO₂) ETL is gradually improved with\nan increase of the concentration. Due to the higher electron collection\nefficiency, the P-SnO₂ ETLs can dramatically promote the\npower conversion efficiency (PCE) of the PSCs. As a result, the champion\nPSC has a PCE of 21.02%. Therefore, it has been proved that this simple\nmethod is efficient to improve the quality of ETL for high-performance\nPSCs.