CuAgBeGeSe4/c-Si monolithic tandem solar cell with high open-circuit voltage (>1.9 eV) and efficiency (>32 %): A numerical study

The photoelectric conversion efficiency (PCE) of unijunction solar cells cannot break through its own theoretical efficiency because of the limitation of the band gap. Relative to unijunction solar cells, multijunction solar cells have a wide sunlight absorption range and exhibit high PCE. This work proposes a novel two-terminal chalcogenide-base tandem solar cell. To achieve the optimal efficiency from this new tandem design, we selected CuAgBeGeSe₄ (CABGSe) with a band gap of 1.58 eV and the traditional crystalline silicon (c-Si) with a band gap of 1.12 eV as the absorber materials for the top cell and the bottom cell respectively, and utilized the SCAPS-1D software to conduct structural simulation and optimization on this CABGSe/c-Si tandem solar cell (TSC). Under an independent illumination condition, the CABGSe top cell and the c-Si bottom cell are upgraded to achieve an efficiency of 20.17 % and 25.79 %, respectively. Based on the optimal parameters obtained from unijunction solar cells, the matching condition of electric currents of the CABGSe/c-Si TSC is further analyzed. The results show that the best matched current, 18.54 mA/cm², can be obtained when the thicknesses of the absorbing layers of the CABGSe top cell and the c-Si bottom cell are 2.5 μm and 335 μm, respectively. At this point, the open-circuit voltage, fill factor, and efficiency of CABGSe/c-Si TSC are 1.98 V, 87.94 %, and 32.12 %, respectively. The research results provide a useful reference for the research and development of high-performance solar cells and are expected to further improve the energy conversion efficiency in the future solar photovoltaic field.