Functional ZnO/TiO_2 Bilayer as Electron Transport Material for Solution-Processed Sb_2S_3 Solar Cells

摘要

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 TiO_2 compact films (ZnO/TiO_2) is implemented as ETM for solution-processed Sb_2S_3 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/TiO_2 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/TiO_2 promotes charge injection, decreases series resistance and shutting paths, and leads to the reduction of charge recombination at the ETM/Sb_2S_3 interface.