Development and analysis of wafer-bonded four-junction solar cells based on antimonides with 42% efficiency under concentration

The highest solar cell efficiencies today are reached with four-junction devices under concentrated illumination. The optimal bandgap combination for realistic four-junction cells is modelled to be 1.89/1.42/1.05/0.68 eV and indeed promises for efficiencies >50%. We present the development and analysis of a wafer-bonded four-junction solar cell based on GaInP/GaAs/GaInAs//GaInAsSb. This concept allows for the implementation of these ideal bandgaps and exhibits at present an efficiency of 42.0±2.5% at a concentration of 599x AM1.5d. The present loss mechanisms in this device are analyzed, which are dominated by current losses due to mismatched subcell currents and absorbing passive layers. Under the assumption of proper current matching, this device would achieve an efficiency above 44%.