Development of High-Quantum-Efficiency, Lattice-Mismatched, 1.0-eV GaInAs Solar Cells

High-quantum-efficiency, lattice-mismatched, 1.0-eV GaInAs solar cells grown by organometallic vapor phase epitaxy have been developed for ultimate integration into AlGaAs/GaAs/GaInAs 3-junction, 2-terminal monolithic devices. The more standard n/p junction was replaced with an n-i-p structure in the GaInAs cell in order to increase the short-circuit current by overcoming the material deficiencies which arise as a result of accommodating the lattice mismatch. This led to single junction 1.0-eV GaInAs cells with internal quantum efficiencies >90% and short-circuit-current densities that match or closely approach those needed to current match the upper AlGaAs and GaAs cells. A 4.1% (1-sun, air mass 0,25°C) power conversion efficiency was achieved with a developmental structure, indicating the potential of the lattice-mismatched n-i-p 1.0-eV GaInAs cell. An analogous device designed to allow direct monolithic integration with the upper AlGaAs and GaAs cells, with a modified grading layer of AlGaInAs in place of the usual GaInAs, achieved an efficiency of 2.2%, primarily due to a lower open-circuit voltage. The open-circuit voltage is perhaps limited by structural defects revealed in transmission electron micrographs.