Mechanism of Current Shunting in Flexible Cu2Zn1-xCdxSn(S,Se)4 Solar Cells

Partial cation substitution is an effective way to inhibit defects and carrier recombination, which can improve the efficiency of Cu2ZnSn(S,Se)(4) (CZTSSe) solar cells. Herein, flexible Cu2Zn1-xCdxSn(S,Se)(4) (x = 0-15%) solar cells are fabricated on Mo foils with partial Cd substitution for Zn via a green solution-process. 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 E-U decreases from 24 to 15 meV, indicating that antisite defects and band tailings are effectively suppressed. C-V data reveal that W-d and V-bi are enhanced after doping Cd, resulting in a stronger built-in electric field which facilitates Fermi-level splitting and hence increases band bending of the absorber toward the junction interface. Furthermore, the mechanism of current shunting is studied using an equivalent circuit model with three parallel current pathways to fit J-V curves. The key parameters for the solar cell diode such as A, J(0), and R-sh are significantly improved by partially substituting Zn with Cd, demonstrating that current shunting loss is suppressed and the junction quality is improved, resulting in a significant improvement in device repeatability.