Hydrazine Hydrate‐Induced Surface Modification of CdS Electron Transport Layer Enables 10.30%‐Efficient Sb(2)(S,Se)(3) Planar Solar Cells

Antimony selenosulfide (Sb(2)(S,Se)(3)), a simple alloyed compound containing earth‐abundant constituents, with a tunable bandgap and high absorption coefficient has attracted significant attention in high‐efficiency photovoltaic applications. Optimizing interfacial defects and absorber layers to a high standard is essential in improving the efficiency of Sb(2)(S,Se)(3) solar cells. In particular, the electron transport layer (ETL) greatly affects the final device performance of the superstrate structure. In this study, a simple and effective hydrazine hydrate (N(2)H(4)) solution post‐treatment is proposed to modify CdS ETL in order to enhance Sb(2)(S,Se)(3) solar cell efficiency. By this process, oxides and residual chlorides, caused by CdCl(2) treated CdS under a high temperature over 400 °C in air, are appropriately removed, rendering smoother and flatter CdS ETL as well as high‐quality Sb(2)(S,Se)(3) thin films. Furthermore, the interfacial energy band alignment and recombination loss are both improved, resulting in an as‐fabricated FTO/CdS‐N(2)H(4)/Sb(2)(S,Se)(3)/spiro‐OMeTAD/Au solar cell with a high PCE of 10.30%, placing it in the top tier of Sb‐based solar devices. This study provides a fresh perspective on interfacial optimization and promotes the future development of antimony chalcogenide‐based planar solar cells.