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

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 multilayer crystallization is revealed, that is, the 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 cm(2)) and 10.69% (mask area: 0.17586 cm(2)) certified power-conversion-efficiency have been achieved with significant increase in the open-circuit voltage and fill factor.