Prospects of potential ZnMgO front layer in CZTS solar cells

In the CZTS structure, ZnMgO alloy can be a promising alternative buffer layer candidate to toxic cadmium sulphide (CdS) material. The effects of conduction band offset (CBO) at ZnMgO/CZTS interface are investigated by numerical approach. The main factor examined is the Mg concentration of ZnMgO and at high values of this parameter, a significantly higher barrier is observed, leading to a distortion in the current-voltage curve (S-shape). This phenomenon caused by degraded open circuit voltage (Voc) and fill factor (FF) parameters leads to overall poor performance. Zn1-xMgxO with 20% Mg concentration decreases maximally the CBO and eliminates the S-shape while increasing the conversion efficiency. The suggested design by ultimately replacing both CdS buffer and ZnO window layers by a single layer of ZnMgO leads to an optimised CZTS based solar cell exhibiting a conversion efficiency of 11.50% with Voc = 0.78 V, Jsc = 22.37 mA/cm² and FF = 66.11%.