Highly Enhanced Efficiency of Planar Perovskite Solar Cells by an Electron Transport Layer Using Phytic Acid–Complexed SnO₂ Colloids

SnO₂ aqueous colloids as electron transport layers (ETLs) have been widely employed in planar perovskite solar cells (PSCs). However, the surface defects and energy level mismatch at the SnO₂ ETL/perovskite interface are still great challenges for the power conversion efficiency (PCE) improvement. Herein, a natural and nontoxic phytic acid (PA) compound is introduced into the SnO₂ aqueous colloids to prepare the ETL to depress its defects, and systematically study the influence of different PA complexation on the photovoltaic performance of PSCs. The results demonstrate that PA complexation can assemble unique coordination complexes between PA and SnO₂ nanocrystals (NCs) in a new bonding of Sn-O-P, which can passivate SnO₂ inherent surface defects and tune the electronic properties of SnO₂ ETLs. PA complexation can significantly disaggregate the SnO₂ oligomers and reduce the cluster size distribution from 98.37 to 15.87 nm. Meanwhile, the reduction of surface trap states inhibits the potential barriers, thus the electrical conductivity is about two times as high as compared with the pristine SnO₂ ETLs. Consequently, a high PCE of 21.43% in PA-SnO₂-based PSCs is obtained, which presents an improvement of 10.9% over that of the pristine SnO₂-based PSCs.