Spatial bandgap tailoring via a novel injection chemical bath deposition enables highly efficient carbon-based Sb2(S,Se)3 thin film solar cells

In recent years, significant progress has been made in the fabrication of sulfoselenide Sb2(S,Se)3 solar cells using a widely adopted hydrothermal method. However, the record efficiency is still far behind the theoretical values partly due to an unfavorable spatial bandgap distribution, which is induced by the complicated chalcogenide growth kinetics of the hydrothermal synthesis. Herein, a novel solution growth method, called Injection Chemical Bath Deposition (ICBD), is developed to prepare Sb2(S,Se)3 alloys for the first time. With this open CBD process, the selenium (Se) source is facilely incorporated during intermediate stages of reaction, and then successfully constructing a V-shaped bandgap via carefully tailoring the vertical gradients in chemical constituents, which synergistically enhances light absorption and carrier separation in the Sb2(S,Se)3 absorber. As a result, the solar cell with a full-inorganic FTO/CdS/Sb2(S,Se)3/Carbon structure achieves an impressive conversion efficiency of 7.63 %, which is among the highest efficiency of carbon-based Sb2(S,Se)3 solar cells based on CBD method. This study demonstrates a flexible strategy for manipulating the gradient band gap for highly efficient Sb2(S,Se)3 solar cells.