Cu2ZnSnS4 thin film solar cells

Aiming to develop the solar cells free from the environmental contaminants, promising solar cell of a thin film type could be produced by using Cu2ZnSnS4 (CZTS) film as the absorber. The CZTS film possesses promising characteristic optical properties; band gap energy of about 1.5 eV and large absorption coefficient in the order of 104 cm−1, which means large possibility of commercial production of the most suitable absorber by using the CZTS film. In addition, as the CZTS film contains neither rare metals nor toxic materials, combining this film with Cd-free buffer layer, we can expect coming solar cells with nontoxic thin films in the near future.CZTS thin films were able to be produced successfully in our previous work by vapor phase sulfurization of the stacked precursors that were prepared by sequential vacuum evaporation of Cu, Sn, and ZnS. The best conversion efficiency with the heterojunction of ZnO:Al/CdS and CZTS was 5.45%, which showed the possibility of a very low cost solar cell. It has been, however, quite difficult to prepare CZTS film with high reproducibility.This paper showed the photovoltaic properties of CZTS-based thin film solar cells fabricated by using three types of precursors: (1) the conventional precursor with stacked layers of Cu/Sn/ZnS, (2) the modified precursor with the stacking order of Sn/Cu/ZnS, and (3) the precursor with five periods of Cu/SnS2/ZnS, which was produced to increase the amount of S and to enhance the interdiffusion in precursor.