Tailoring the Back Contact Properties of Cu2ZnSn(S,Se)4 Thin Film with Mo-Foil by Introducing a Transparent CuCrO2 Buffer Layer

Chalcogenide Cu 2 ZnSn(S,Se) 4 (CZTSSe) is a promising absorber material for photovoltaic applications. When CZTSSe thin film is deposited on an Mo substrate, a Mo(S,Se) 2 layer easily forms between the CZTSSe and the Mo, which is detrimental to the back contact property of the CZTSSe. This work proposes a useful way to inhibit the formation of Mo(S,Se) 2 by sputtering a CuCrO 2 layer on a Mo-foil substrate before the deposition of the CZTSSe. The effects of CuCrO 2 thickness on the crystalline structures, morphologies, and electrical properties of the fabricated samples were studied. The results showed that the insertion of the CuCrO 2 layer prevented the formation of Mo(S,Se) 2 . As the thickness of the CuCrO 2 increased, the thickness of the Mo(S,Se) 2 layer decreased. The Mo(S,Se) 2 layer was absent from the cross-sectional scanning electron microscopy image when the CuCrO 2 thickness exceeded 85 nm. The back contact resistance of CZTSSe decreased monotonously as the CuCrO 2 layer thickened due to the reduction in the Mo(S,Se) 2 layer thickness. Therefore, by inserting a CuCrO 2 layer to separate the CZTSSe and the Mo-foil, the formation of the Mo(S,Se) 2 layer between them was effectively suppressed, and the back contact properties of the CZTSSe thin film were significantly enhanced.