An experimental and first-principles study on band alignments at interfaces of Cu₂ZnSnS₄/CdS/ZnO heterojunctions

We investigated band offsets at Cu2ZnSnS4(CZTS)/CdS and CdS/ZnO interfaces in a typical CZTS/CdS/ZnO heterojunction solar cell by combining x-ray photoelectron spectroscopy and optical absorption spectroscopy as well as first-principles calculations. X-ray photoelectron spectroscopy and optical absorption spectroscopy measurements indicate that the conduction-band offsets at both CZTS/CdS and CdS/ZnO interfaces show type-II alignment with values of 0.13 eV and 1.00 eV, respectively, which are well supported by first-principles calculations based on the hybrid functional method. Our results suggest that, although type-II alignment for CZTS/CdS heterojunction can form less of a barrier to electron transport across the interfaces, the narrowing of the 'interface bandgap' increases recombination of carriers.