Improvement of Performance of Cu ₂ ZnSn(S,Se) ₄ Solar Cells by Adding SiN _<i>x</i> Buffer Layer and Optimizing its Position and Thickness

Many results have demonstrated that high interfacial recombination is one of the main leading to low power conversion efficiency (PCE) of Cu 2 ZnSn(S,Se) 4 (CZTSSe). Herein, interfacial recombination of CZTSSe solar cell by addition of silicon nitride (SiN x ) buffer layer in front interface of CdS/CZTSSe and back interface of CZTSSe/Mo is reduced. It is found that the PCE decreases sharply when the SiN x layer is deposited at the front interface. Quantitative analysis indicates that the decreased PCE is mainly attributed to the decrease in photogeneration density ( J L ), followed by increase in reverse saturation current density ( J 0 ). However, when the SiN x layer is deposited at the back interface, the PCE increases from 9.11 to 9.78% as the thickness of the SiN x increases from 0 to 5 nm. Quantitative analysis indicates that the increased PCE is mainly attributed to the increase in J L , followed by the decrease in J 0 and series resistance ( R s ). This work provides a reference for the study of using SiN x passivation to improve the efficiency of CZTSSe or other solar cells.