Investigation of InGaAsP-based solar cells for double-junction photovoltaic devices

This paper deals with the design, implementation and assessment of single-junction solar cells using the quaternary semiconductor material InGaAsP. Two bandgaps of 1.0 and 1.2eV were considered in n/p and p/n structure configurations lattice-matched to InP. These solar cells are being investigated for their subsequent integration, together with single-junction 0.74eV bandgap InGaAs thermophotovoltaic (TPV) cells, as double-junction three-terminal photovoltaic (PV) devices. The devices were grown using MOVPE on InP substrates, with layer thicknesses and doping concentrations optimised through prior modelling. The assessment of the cells was undertaken using current–voltage measurements with a calibrated TPV simulator on mesa diodes of different sizes. Open-circuit voltages of up to 695 and 655mV, and fill factors of 0.48 and 0.6 were measured for 1.2 and 1.0eV solar cells, respectively. The best energy conversion efficiency recorded was 7% on a 1.0eV bandgap n/p device. These cells were further investigated using spectral response measurements and the results are presented, compared and discussed.