Non-Lambertian Reflective Back Scattering and Its Impact on Device Performance of Ultrathin GaAs Single-Junction Solar Cells

This paper studies non-Lambertian scattering and its impacts on the optical properties and device performance of the ultrathin GaAs single-junction solar cell with a reflective back scattering layer. The Phong distribution is used to quantify the scattering effectiveness of the textured back surface, as well as its impacts on device absorptance, emittance, photon extraction and recycling factor, short-circuit current density (J_sc), external quantum efficiency (EQE), and power conversion efficiency. Both a general GaAs cell design and the ultrathin cell design are carefully investigated. A Phong exponent m of ~12 is determined by fitting both simulated Jsc and EQE to their experimental values, with a more accurate averaged reflectivity of the textured Al_0.52In_0.48P/Au interface taken into account. Additionally, the measured open-circuit voltage (V_oc) is lower than the best achievable value due to the nonradiative recombination in the device, and a limited lifetime of ~130 ns is determined by fitting the simulated and measured V_oc; a specific series resistivity of 1.2 Ω·cm² is determined to account for the 77.8% fill factor.