Recent advances in high-efficiency InGaAs concentrator cells

InGaAs concentrator cells with bandgaps of 1.15 and 1.35 eV have been developed. These cells are intended for eventual use in dual and triple-junction tandem solar cells, respectively. The InGaAs cell structures were grown by metal-organic chemical vapor deposition on GaAs substrates with grading layers to accommodate lattice mismatch. Efficiencies greater than 24% at 400 suns (AM1.5D, 100 mW/cm²) have been demonstrated for InGaAs cells with either bandgap. Since the 1.15 eV InGaAs has a bandgap close to that of silicon, comparison of the photovoltaic effect in materials with direct and indirect bandgaps is possible. InGaAs demonstrates open-circuit voltage up to 800 mW (130 mW higher than Si) under concentration. Conversely, Si demonstrates a one-sun short-circuit current of 42 mA/cm² compared to 31 mA/cm² for InGaAs. Possible reasons for the higher voltages are given, and implications regarding projected tandem cell performance are discussed.