Enhanced light absorption in GaAs solar cells with internal Bragg reflectors

The use of epitaxial multilayer dielectric mirrors (Bragg reflectors) as back-surface reflectors in thin-film GaAs solar cells on GaAs and silicon substrates is investigated. Al/sub 0.3/Ga/sub 0.9/As/Al/sub 0.85/Ga/sub 0.15/As Bragg reflectors were grown by low-pressure MOCVD on GaAs substrates and shown to exhibit near-ideal optical reflectance and excellent structural perfection. Thin GaAs solar cells grown on Bragg reflectors showed increases in short-circuit current (0.5 to 1.0 mA/cm/sup 2/) and efficiency (0.7 percentage points) relative to cells without back reflectors. Efficiencies of 24.7% at one sun AM 1.5 were measured for GaAs cells only 2 mu m thick on Bragg reflectors. In addition to the optical enhancements, Bragg reflectors also appear to improve the defect structure of GaAs-on-Si solar cells. This approach should lead to improved efficiency for GaAs-on-Si solar cells and improved radiation resistance on GaAs cells.<
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