Sn doped ZnO thin films as high resistivity window layer for Cu(In,Ga)Se2 solar cells

Abstract

For high efficiency Cu(In,Ga)Se2 (CIGS) solar cell, the high-resistivity layer with high optical transmittance has to be adopted between the buffer layer and the high-conductivity window layer. In this paper, we propose Sn doped ZnO (ZTO) film, instead of the traditional intrinsic ZnO (i-ZnO) film, as an alternative n-type high-resistivity window layer for CIGS solar cell. In this experiment, both ZTO and i-ZnO films are strong (002) oriented, and the surface morphologies of the two films are almost the same. The statistical roughnesses of i-ZnO film and ZTO film are 0.58 nm and 0.63 nm, respectively. However, the optical transmittance of ZTO film is higher than that of i-ZnO film with the same thickness. The efficiency of ZTO based CIGS cell was 14.24%, which is almost the same as the efficiency of i-ZnO based CIGS cell. These results fully suggest that it is very feasible to replace i-ZnO with ZTO as the high resistant window layer.