Inverted metamorphic photovoltaics for space applications utilizing a distributed Bragg reflector compatible with epitaxial lift-off

Abstract

Abstract MicroLink Devices manufactures triple-junction inverted metamorphic solar cells on GaAs wafers with a selectively etched release layer in an epitaxial lift-off (ELO) process to create ultra-thin foils of semiconductor with a metal backing. To improve radiation tolerance, each absorber layer is thinned and doping levels are reduced. The bottom subcell employs a mirror structure to maintain current, while the middle subcell requires a distributed Bragg reflector (DBR) to increase the absorption path length and maintain current. MicroLink utilizes a non-conventional In x (Al y Ga1−y )1−x P/GaAs DBR that is compatible with ELO. The DBR has a bandwidth of ∼110 nm and a peak reflectance in air near 95%. Average cell efficiencies of 28% (1-Sun AM0) are achieved with a power retention of 84% after 1E15 cm−2 electron dosing (1 MeV energy). Large-area cells and coupons underwent internal thermal stress testing and showed no degradation. Clear pathways to achieve >29% efficient cells with >85% power retention are discussed.