Kesterites—a challenging material for solar cells

ABSTRACT Kesterite materials (Cu 2 ZnSn(S,Se) 4 ) are made from non‐toxic, earth‐abundant and low‐cost raw materials. We summarise here the structural and electronic material data relevant for the solar cells. The equilibrium structure of both Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 is the kesterite structure. However, the stannite structure has only a slightly lower binding energy. Because the band gap of the stannite is predicted to be about 100 meV lower than the kesterite band gap, any admixture of stannite will hurt the solar cells. The band gaps of Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 are 1.5 and 1.0 eV, respectively. Hardly any experiments on defects are available. Theoretically, the Cu Zn antisite acceptor is predicted as the most probable defect. The existence region of the kesterite phase is smaller compared with that of chalcopyrites. This makes secondary phases a serious challenge in the development of solar cells. Copyright © 2012 John Wiley & Sons, Ltd.