Improvement of the structural and electronic properties of CZTSSe solar cells from spray pyrolysis by a CuGe seed layer

Abstract

We have produced CZTSSe solar cells by a sequential growth process. First, CZTS precursors were deposited on Mo-coated soda lime glass substrates by chemical spray pyrolysis from an aqueous solution containing Cu, Zn and Sn metal salts and thiourea. In a second step the precursor was selenized at 530 °C for 8 min, resulting in fair solar cell properties. Further, we have investigated the influence of a 20 nm CuGe seed layer, which was sputtered on the Mo-surface prior to CZTS precursor deposition, on the morphology of the resulting absorber and on the performance of CZTSSe solar cells. We observe that the formation of MoSe₂ and the consequent decomposition reactions at the back contact region of the CZTSSe layers during the annealing process were suppressed by introducing the CuGe seed layer, and that grain growth at the Mo/CZTSSe interface region was enhanced. The performance of CZTSSe solar cells prepared with a 20 nm CuGe seed layer shows considerable improvement compared to the processing without CuGe introduction.