The band alignment at CdS/Cu 2 ZnSnSe 4 heterojunction interface

Band alignment at CdS/Cu 2 ZnSnSe 4 heterojunction interface is studied by X‐ray photoemission spectroscopy. The Cu 2 ZnSnSe 4 thin films are prepared by selenization of electrodeposited Cu‐Zn‐Sn precursors. CdS overlayers with different thickness are sequentially grown on the Cu 2 ZnSnSe 4 substrate by pulsed laser deposition process. Photoemission spectra are obtained before and after each growth to study the conduction and valence band offsets at the heterojunction interface. The determined conduction band offset of 0.34 eV indicates a spike‐like ‘type I’ band alignment at CdS/Cu 2 ZnSnSe 4 interface. The spike will avoid interface recombination, and it is low enough that electron could transfer from the Cu 2 ZnSnSe 4 layer to the buffer layer which is suitable for solar cell's fabrication.