Theoretical design and temperature-dependent analysis of high-efficiency quadruple-junction solar cells based on GaSb and Ge

III-V multijunction solar cells, holding the record for the highest photovoltaic conversion efficiencies exceeding 47 %, currently serve as the dominant technology for space power systems and terrestrial concentrator photovoltaics. Based on the Shockley-Queisser (SQ) theory, this study proposes two four-junction solar cell designs that combine high photovoltaic conversion efficiency with manufacturing feasibility. These designs utilize a graphical analysis method and a MATLAB numerical traversal algorithm. The proposed structures are Ga 0.664 In 0.336 P / Al 0.061 Ga 0.939 As / Ga 0.778 In 0.222 As / GaSb (2.01 eV / 1.50 eV / 1.12 eV / 0.73 eV) and Ga 0.657 In 0.343 P / Al 0.053 Ga 0.947 As / Ga 0.786 In 0.214 As / Ge (2.00 eV / 1.49 eV / 1.11 eV / 0.67 eV). Under the Air Mass 1.5 Global (AM1.5 G) spectrum at 300 K, the two structures achieved conversion efficiencies of 55.0 % and 54.8 %, respectively. These efficiencies are close to the theoretical limit, demonstrating their superior photovoltaic performance. Further analysis reveals that fluctuations in the bandgaps of key subcells within a certain range have a controllable impact on the overall efficiency. This indicates that the proposed structures possess favorable fabrication tolerance. Furthermore, we systematically evaluated the performance variation across an operating temperature range from −20 °C to 60 °C. The results show that the GaSb-based structure exhibits superior thermal stability, maintaining an efficiency of 52.28 % even at 60 °C. This work provides a theoretical basis and design guidelines for the material selection, bandgap engineering, and practical application of GaSb- and Ge-based high-efficiency four-junction solar cells.