Mechanism of improvement of efficiency of Cu2ZnSn(S,Se)4 solar cells by optimization of deposition temperature of CdS buffer layer

The physical properties of CdS buffer layers and the interface quality between CdS layer and Cu2ZnSn(S,Se)4 (CZTSSe) absorber have a significant impact on the performance of CZTSSe solar cells. In the present work, five types of CZTSSe solar cells with conventional structure (denoted as CdS-x-cells, x = 55, 60, 65, 70 and 75) were fabricated by using CdS prepared at deposition temperatures of 55, 60, 65, 70 and 75 & DEG;C, respectively, as buffer layer, and influence mechanism of the deposition temperature of CdS layers on power conversion efficiency (PCE) of the CdS-x-cells was investigated. It is found that the PCE of the CdS-x-cells increases from 8.52% to 10.36% as the deposition temperature rises from 55 to 60 & DEG;C but falls from 10.36% to 7.14% from 60 to 75 & DEG;C. The analysis on the photovoltaic and electrical parameters indicates that the increase in PCE is predominantly derived from the decreased reverse saturated current density (J0), followed by the decreased series resistance (RS) and increased shunt resistance (RSh). The decreased PCE with the further increasing deposition temperature is mainly contributed from the increased J0, followed by the decreased RSh and photogenerated current density (JL). The influence mechanism of deposition temperature of the CdS layer on PCE is suggested via quantitatively analysis of influence of electrical, optical properties and crystal quality of CdS prepared at various deposition temperatures on JL and electrical parameters of CdS-x-cells. This work is helpful for improvement of PCE of CZTSSe solar cells by modification of properties of buffer layer.