Electricity generation of GeSn single-junction solar cell has been carefully examined in both its p-on-n and n-on-p configurations in its normal and inverted structures. The superior p + /n construction with a critical doping of the light-doped layer (N d = 7.5 Â 10 18 cm À3 ) has been observed. For the normal one, the active layer should be composed of 50-100 nm emitter and 3-5 μm base to less material costs. Moreover, dislocation density and 1 MeV electron fluence should be lower than 1 Â 10 5 cm À2 and 1 Â 10 10 cm À2 , respectively, which is helpful for obtaining a preferable conversion efficiency. To explore lower cost solar cell, the simulated results might be favorable to guide experimental fabrication of GeSn devices.

Based on the photovoltaic properties and tandem solar cells theory, Gallium Indium Arsenide/Germanium Stannide (GaInAs/GeSn)-based double-junction (DJ) solar cells have been numerically simulated for the first time. In this study, we explore the band gap combination under lattice matching and obtain the content of In/Sn at optimal efficiency, which is expressed as Ga0.84In0.16As/Ge0.93Sn0.07 DJ solar cell (1.20/0.58 eV). Afterward, it is optimized in terms of variation in the doping contents and active layer thickness. To take full advantage of the electron mobility of the material, the optimal 'inverted doping profile' concentration Na(d) is 1.5(5)/5(20)×1018 cm-3. In addition, the reasonable p(n) layer thickness could be comprised of 0.2-0.8(0.2-1)/0.5-3(1-4) μm of the DJ solar cells with less material consumption. When the p(n) layer thickness is 0.30(0.25)/0.9(1.35) μm, the tandem device can achieve an optimal efficiency of 31.00% with 28.98 mA/cm2 (JSC), 1.25 V (VOC) and 85% (FF). This study highlights that GeSn materials have the potential to combine with III-V materials to form low-cost and high-efficiency tandem devices.