Quantification of effective thermal conductivity in the annealing process of Cu2ZnSn(S,Se)4 solar cells with 9.7% efficiency fabricated by magnetron sputtering

Abstract

Cu₂ZnSn(S,Se)₄ (CZTSSe) has attracted much attention as the absorption layer of photovoltaic devices because of its appropriate bandgap energy and low cost. However, CZTSSe solar cells have so far shown low power conversion efficiency compared to other solar cells and studies are being conducted to improve it. In this study, we achieved an improvement in the shunt resistance and power conversion efficiency (PCE) of CZTSSe solar cells with quantification of the effective thermal conductivity. A CZTSSe solar cell fabricated using a graphite box designed with high thermal conductivity exhibited a high shunt resistance of 413 Ω cm² and a fill factor of 63.8%, and additionally, secondary phases such as Cu₂S/Se and CuS/Se were not detected. On the other hand, a CZTSSe solar cell fabricated using a graphite box with low thermal conductivity showed a rougher surface and low shunt resistance mainly related to secondary phase formation. As a result, a PCE of 9.72% was achieved using a graphite box designed with high thermal conductivity.