Eliminating multi-layer crystallization of Cu2ZnSn(S,Se)4 absorber by controlling back interface reaction

Abstract For Cu2ZnSn(S,Se)4 (CZTSSe) solar cells, eliminating multi-layer crystallization is a key issue of achieving high quality CZTSSe absorber layers and high cell performance. In this work, the formation mechanism of the multi-layer crystallization is revealed, that is, the well-known reaction between CZTS and Mo may give the secondary phase, which subsequently acts as crystal nucleus to facilitate the CZTSSe crystal growth at back interface (Mo/CZTSSe), leading to multi-layer crystallization. By introducing MoO3 isolating layer, this undesired reaction can be well prevented, and high quality single-layer crystals are obtained. This absorber film with fewer defects and secondary phases exhibits better semiconductor properties. Based on this regulated CZTSSe absorber layer, 11.68% (active area: 0.16092 cm2) and 10.69% (mask area: 0.17586 cm2) certified power-conversion-efficiency have been achieved with significant increase in the open-circuit voltage and fill factor.