Enhancing performance of Cu2ZnSn(S, Se)4 solar cells via non-uniform gradient and flat bands induced by Cd substitution.

The PCE of CZTSSe solar cells doped with non-uniform Cd doped in the middle of the absorber layer increased from 8.88% to 10.89%. The "V"-shaped gradient band gap structure in the absorption layer provides a favorable back electric field and reduces the carrier recombination at the Mo/CZTSSe interface for the collection of photogenerated carriers. In addition, the optimal position of non-uniform Cd doped absorber film is simulated theoretically and investigated experimentally. It is worth noting that when studying the stability of the cell PCE, we found that the efficiency of the non-uniform Cd-doped cell was further improved from 10.28% to 10.94% after being exposed to air for 30 days. Compared with undoped cells, Cd-doped cells decay significantly slower and show better stability. [Display omitted] • "V"-shaped gradient band gap prepared via Cd doped in the middle of the absorber layer of CZTSSe. • The "V"-shaped gradient band gap structure in the absorption layer provides a favorable back electric field. • Cell performance of non-uniform Cd doping is superior to that of uniform Cd doping. • The optimal position of non-uniform Cd doped absorber film is simulated theoretically and investigated experimentally. • Cd doping can enhance the stability of the CZTSSe solar cells. Severe carrier recombination at the back (Mo/CZTSSe) and front (CZTSSe/CdS) interfaces is one of the most important reasons hindering the development of open-circuit voltage (V OC) and fill factor (FF) in Cu 2 ZnSn(S, Se) 4 (CZTSSe) solar cells. In this study, we intentionally introduced a non-uniform distribution of Cd impurities into the middle of the absorber layer, designing and fabricating a CZTSSe solar cell with a non-uniform "V"-shaped graded bandgap structure. This structure is aimed at providing a favorable back electric field, reducing carrier recombination at the Mo/CZTSSe interface. The PCE of the CZTSSe solar cell improved from 8.88 % to 10.89 %, significantly enhancing FF and V OC. Additionally, we utilized the solar cell simulation software SCAPS-1D to simulate the position of the minimum point in the V-shaped graded bandgap and combined this with experimental results to explore the effect of Cd doping location on the performance of CZTSSe solar cells. It's worth noting that the non-uniform Cd-doped solar cell displayed exceptional stability, demonstrating an efficiency enhancement from 10.28 % to 10.94 % after being exposed to air for 30 days. [ABSTRACT FROM AUTHOR]