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

Cu ₂BaSn(S,Se) ₄ is gaining tremendous attention as a potential absorber due to its non-toxicity, earth abundance, and low antisite defects opposing Cu ₂ZnSn(S,Se) ₄. However, the highest experimental efficiency of 6.17 % is achieved with the device structure Al:ZnO/Mg:ZnO/Zn _1-xCd _xS/Cu ₂BaSn(S,Se) ₄/Mo where the drawback is large open circuit voltage (V _OC) 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, Cu ₂BaSn(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/TiO ₂/Cu ₂BaSn(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 Cu ₂BaSn(S,Se) ₄ solar cells to enhance their efficiency.