Highly Efficient Amorphous Zn₂SnO₄ Electron-Selective Layers Yielding over 20% Efficiency in FAMAPbI₃-Based Planar Solar Cells

Amorphous Zn2SnO4 (am-ZTO) films with extreme surface uniformity, high electron mobility, and fewer charge traps were successfully developed by controlling the concentrations of 2-methoxyethanol solutions containing the 2:1 stoichiometric ratio of Zn to Sn. For the first time, we demonstrate that solution-processed am-ZTO thin films are highly efficient as an electron-selective layer (ESL) for mixed perovskite solar cells (PSCs). When am-ZTO ESLs were combined with bandgap-tuned FAMAPbI3 perovskites, a champion efficiency of 20.02% was achieved. In addition, devices based on am-ZTO showed a statistical reproducibility of 18.38 ± 0.61% compared to 15.85 ± 1.02% of the TiO2-based counterparts. This high efficiency is achieved by the significant increase in both the short-circuit current and open-circuit voltage owing to improved charge transport/extraction and recombination. Moreover, am-ZTO ESL-based devices show improved stability and reduced hysteresis, which is a promising result for future PSC research.