Development of a self-supporting, transparent AlGaAs top solar cell for mechanical attachment to an existing solar cell

A technique for fabricating AlGaAs solar cells on transparent AlGaAs substrates has been developed which utilizes the most advanced wide-bandgap material on a transparent substrate. The rugged, self-supporting, transparent AlGaAs top solar cell can be mechanically stacked on any well-developed existing solar cell. The key to this success is the growth technique, liquid-phase epitaxy (LPE). Fabrication of tandem or triple stacks is impossible with this transparent, self-supporting AlGaAs device. To obtain high stack efficiencies, the top solar cell must be state-of-the-art. A 1.93 eV AlGaAs top cell results in two-stack solar cells with efficiencies over 30% AM0 and triple stacks approaching 35% AM0. Transmission of 91% of the photons less energetic than the top solar cell bandgap has been demonstrated for the self-supporting AlGaAs substrate. The design rules for the tandem structure and progress in the development of the transparent AlGaAs top solar cell are discussed.