Multi-functional\nStrategy: Ammonium Citrate-Modified\nSnO₂ ETL for Efficient and Stable Perovskite Solar Cells

Abstract

The tin oxide (SnO₂) electron transport layer\n(ETL)\nplays a crucial role in perovskite solar cells (PSCs). However, the\nheterogeneous dispersion of commercial SnO₂ colloidal precursors\nis far from optimized, resulting in dissatisfied device performance\nwith SnO₂ ETL. Herein, a multifunctional modification material,\nammonium citrate (TAC), is used to modify the SnO₂ ETL,\nbringing four benefits: (1) due to the electrostatic interaction between\nTAC molecules and SnO₂ colloidal particles, more uniformly\ndispersed colloidal particles are obtained; (2) the TAC molecules\ndistributed on the surface of SnO₂ provide nucleation sites\nfor the perovskite film growth, promoting the vertical growth of the\nperovskite crystal; (3) TAC-doped SnO₂ shows higher electron\nconductivity and better film quality than pristine SnO₂ while offering better energy-level alignment with the perovskite\nlayer; and (4) TAC has functional groups of CO and N–H\ncontaining lone pair electrons, which can passivate the defects on\nthe surface of SnO₂ and perovskite films through chemical\nbonding and inhibit the device hysteresis. In the end, the device\nbased on TAC-doped ETL achieved an increased power conversion efficiency\n(PCE) of 21.58 from 19.75% of the reference without such treatment.\nMeanwhile, the PSCs using the TAC-doped SnO₂ as the ETL\nmaintained 88% of their initial PCE after being stored for about 1000\nh under dark conditions and controlled RH of 10–25%.