Back Surface Reflectors for Thin III-V Multi-junction Space Photovoltaics

In this work, textured back surface reflectors (BSR) produced by inverse progression metal-assisted chemical etching (I-MacEtch) is used to render wavelength-specific (WS) light trapping structures for thin GaAs solar cells. The HAZE reflectance measured on the MacEtch BSR shows 80% HAZE in the GaAs absorbing region indicative of high diffused photon scattering. The MacEtch BSR was implemented in a 500 nm thick GaAs solar cell, and the external quantum efficiency shows a 17% enhancement in the photogenerated carrier collection from the base of the solar cell when compared to the flat BSR device. The Fabry-Pérot EQE fringes show a photon lifetime enhancement factor of 5.7 in the MacEtch BSR device, especially evident near the GaAs band edge. The recovered photoabsorption provides evidence that the WS BSR can be implemented into a dual-junction InGaP/GaAs solar cell to provide high current output in a radiation-tolerant thinned GaAs subcell.