Functional ZnO/TiO₂ Bilayer as Electron Transport Material for Solution‐Processed Sb₂S₃ Solar Cells

Electron transport materials (ETMs) are considered a keystone component of third‐generation solar cells. Among the alternative ETM, metal oxide bilayers have attracted increasing attention due to their easy processing and tunability of cascade energy alignment. Herein, a metal oxide bilayer that combines ZnO and TiO₂ compact films (ZnO/TiO₂) is implemented as ETM for solution‐processed Sb₂S₃ planar solar cells. The bilayer ETM achieves the highest photovoltaic performance when compared with devices based on single ETM. Thus, the optimized device based on ZnO/TiO₂ ETM yields a champion efficiency of 5.08% with an open‐circuit voltage of 0.58 V and a current density of 16.17 mA cm⁻². Using surface photovoltage, electrochemical impedance spectroscopy, and current density–voltage analyses, it is demonstrated that the use of ZnO/TiO₂ promotes charge injection, decreases series resistance and shutting paths, and leads to the reduction of charge recombination at the ETM/Sb₂S₃ interface.