Mechanism of Current Shunting in Flexible Cu_2Zn_(1-x)Cd_xSn(S,Se)_4 Solar Cells

摘要

Partial cation substitution is an effective way to inhibit defects and carrierrecombination, which can improve the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe)solar cells. Herein, flexible Cu_2Zn_(1-x)Cd_xSn(S,Se)_4 (x = 0–15%) solar cells arefabricated on Mo foils with partial Cd substitution for Zn via a green solutionprocess.The best device performance can be achieved when Cd/(Zn + Cd) = 8%,with an efficiency up to 6.49% and a significantly improved device repeatability.The EU decreases from 24 to 15 meV, indicating that antisite defects and bandtailings are effectively suppressed. C–V data reveal thatWd and Vbi are enhancedafter doping Cd, resulting in a stronger built-in electric field which facilitatesFermi-level splitting and hence increases band bending of the absorber towardthe junction interface. Furthermore, the mechanism of current shunting isstudied using an equivalent circuit model with three parallel current pathways tofit J–V curves. The key parameters for the solar cell diode such as A, J_0, and R_(sh) aresignificantly improved by partially substituting Zn with Cd, demonstrating thatcurrent shunting loss is suppressed and the junction quality is improved,resulting in a significant improvement in device repeatability.