Mechanism of enhanced power conversion efficiency of Cu2ZnSn(S, Se)4 solar cell by cadmium surface diffusion doping

Abstract

In the present work, Cd-doped Cu2ZnSn(S,Se)4 (CZTSSe) films (CZCTSSe) were prepared by selenizing precursor films, which consist of thin Cd-doped Cu2ZnSnS4 (CZTS) at top layer and a thick CZTS layer at bottom. Using the CZTSSe and CZCTSSe as absorbers, solar cells with conventional structure were fabricated. It is found that Cd diffusion doping can improve the crystal quality of CZTSSe film, decrease the charge density of depletion layer and suppress the formation of secondary phases at surface of CZTSSe. The CZCTSSe solar cells have larger short-circuit current density (Jsc), open-circuit voltage (Voc) and filling factor (FF) than the CZTSSe solar cell, and so have superior power conversion efficiency (PCE) than CZTSSe solar cells. The increased Jsc is mainly due to the enhancement in photocurrent density (JL) of CZCTSS. The increased Voc is dominantly attributed to the decrease in reverse saturation current density (J0), followed by increase in JL and lastly increase in shunt resistance. The increased FF comes mainly from the contribution of Rsh. By optimizing the Cd doping content, the PCE is improved from 3.04% of CZTSSe solar cell to 7.30% of CZCTSSe solar cell. The influence mechanism of Cd-doping on PCE was suggested by analysis of effect of Cd doping on JL, Rsh and J0.