Effect of Ge Thin Layer Position on Formation and Property of CZTSSe Thin Films and Solar Cells Prepared by Sputtering Method

Abstract

In this work we deposited a Ge thin layer under or upon Cu-Zn-Sn-S precursor by sputtering, followed by selenization process to obtain Ge doped CZTSSe thin films. A comparison of structural, morphology and optoelectrical property on Ge doped CZTSSe thin films with different Ge layer position was studied. It was found that even a little amount of Ge doping could affect the crystallization of CZTSSe grains. The solar cells based on two kinds of precursors both had VOC improvement compared with undoped CZTSSe solar cell. However, due to the inner stress in CZTSSe thin film, cracks appeared between the interface of buffer layer and window layer in CZTSSe solar cell with Ge bottom layer, leading to the decrease of conversion efficiency. With the help of Ge in reducing bulk recombination, CZTSSe solar cell based on Cu-Zn-Sn-S precursor with Ge top layer had a conversion efficiency of 5.38%, in contrast to 3.01% and 4.30% of CZTSSe solar cell with Ge bottom layer and undoped CZTSSe solar cell, respectively.