Kesterite Cu2ZnSnS4 thin film solar cells by a facile DMF-based solution coating process

Kesterite Cu2ZnSnS4 (CZTS) thin films were fabricated using a low-cost and environmentally friendly route from a dimethylformamide (DMF) solution of a metal-thiourea complex. Thermal gravimetric analysis (TGA) has been performed to reveal the thermal decomposition behavior of the CZTS precursors for drying and sulfurization process design. A facile solution method of in situ introducing sodium dopant by adding NaOH into the precursor solution is presented. The sodium dopant improves the open circuit voltage (V-oc) and fill factor (FF) and thereby enhances the power conversion efficiency from 4.47% to 5.68%. The enhanced performance is related to the increased grain size and increased minority carrier lifetime. A large number of large voids observed in the bulk absorber and at the absorber/back contact interface are considered to be the main reason for the low short circuit current density (J(sc)).