Boost efficiency with buffer and bottom stack optimization in Cu2BaSn(S, Se)4 solar cells by simulation

Cu2BaSn(S,Se)4 is gaining tremendous attention as a potential absorber due to its non-toxicity, earth abundance, and low antisite defects opposing Cu2ZnSn(S,Se)4. However, the highest experimental efficiency of 6.17 % is achieved with the device structure Al:ZnO/Mg:ZnO/Zn1-xCdxS/Cu2BaSn(S,Se)4/Mo where the drawback is large open circuit voltage (VOC) loss stemming from the large cliff at the absorber/buffer interface and back contact recombination. Therefore, finding a suitable non-toxic buffer with modification of the bottom stack is crucial. In this regard, Cu2BaSn(S,Se)4 solar cells based on diverse buffers are numerically simulated using SCAPS-1D with Ni as back contact and introducing back surface field (BSF) at the absorber/Ni interface. At first, a baseline model validating the experimental efficiency is designed. The application of Ni enhanced efficiency to 7.92 % due to the formation of ohmic contact. Further, it is improved to 9.91 % with anti-reflection coating. Afterward, a total of 780 solar cells were designed with six buffer and eight BSF combinations by optimizing the absorber, buffer, and interface properties where the highest efficiency of 28.11 % with incredible fill factor (90 %) and less V OC loss (0.24 V) is accomplished for the Al:ZnO/Mg:ZnO/TiO2/Cu2BaSn(S,Se)4/CuI/Ni solar cell. Further, the importance of BSF is analyzed via energy band diagrams, Mott-Schottky and Nyquist plots. The outcomes disclosed that the BSF greatly influences the energy band alignment, built-in potential, depletion width, and recombination resistance of solar cells, underscoring its significance in improving performance. Overall, the present work proposes an efficient strategy to modify the device configuration of Cu2BaSn(S,Se)4 solar cells to enhance their efficiency.