Energy Band Alignment at p-n Heterojunction Interface in CZTSSe Solar Cells with Novel ZnMgO Buffer Layer

By substituting Zn1-xMgxO (ZMO) for the conventional CdS buffer layer, the CZTSSe solar cells with the efficiency of 11.2% are obtained herein, which can be attributed to the conduction band regulation in the heterojunction. An appropriate conduction band offset (CBO) value can effectively reduce nonradiative recombination loss of charge carriers at the interface, thereby improving the open-circuit voltage (V-oc). Herein, ZMO buffer layer with the optical bandgap ranging from 3.34 to 3.90 eV is applied to enhance the CBO in the heterojunction from 0.14 to 0.72 eV. The ZMO-buffered solar cells exhibit higher V-oc and short-current density (J(sc)) compared to CdS-buffered cells. The optimal efficiency of 11.2% is obtained in CZTSSe solar cell with the CBO of 0.27 eV, Jsc of 39.0 mA cm(-2), fill factor of 69.6%, and V-oc of 412 mV.