Analysis of Carrier Transport at Zn1−xSnxOy/Absorber Interface in Sb2(S,Se)3 Solar Cells

Abstract

This work explores the effect of a Zn1−xSnxOy (ZTO) layer as a potential replacement for CdS in Sb2(S,Se)3 devices. Through the use of Afors-het software v2.5, it was determined that the ZTO/Sb2(S,Se)3 interface exhibits a lower conduction band offset (CBO) value of 0.34 eV compared to the CdS/Sb2(S,Se)3 interface. Lower photo-generated carrier recombination can be obtained at the interface of the ZTO/Sb2(S,Se)3 heterojunction. In addition, the valence band offset (VBO) value at the ZTO/Sb2(S,Se)3 interface increases to 1.55 eV. The ZTO layer increases the efficiency of the device from 7.56% to 11.45%. To further investigate the beneficial effect of the ZTO layer on the efficiency of the device, this goal has been achieved by five methods: changing the S content of the absorber, changing the thickness of the absorber, changing the carrier concentration of ZTO, using various Sn/(Zn+Sn) ratios in ZTO, and altering the thickness of the ZTO layer. When the S content in Sb2(S,Se)3 is around 60% and the carrier concentration is about 1018 cm−3, the efficiency is optimal. The optimal thickness of the Sb2(S,Se)3 absorber layer is 260 nm. A ZTO/Sb2(S,Se)3 interface with a Sn/(Zn+Sn) ratio of 0.18 exhibits a better CBO value. It is also found that a ZTO thickness of 20 nm is needed for the best efficiency.