A Comparative Study of Front and Back Illuminated Strain Balanced InGaAs MQW Thermophotovoltaic Cells on n-InP Substrate For High Power Applications

Abstract

We have processed and characterised front (P-Grid) and back (N-Grid) illuminated strain balanced multi-quantum well InGaAs/InP thermophotovoltaic cells with a bandedge at 1980nm. We find that the inverted cells (N-Grid) dark currents are comparable to the conventional (P-Grid) MQW cells and have power conversion efficiencies of 10% under AM0 incident radiation. Inverted cells are shown to have better performance at high power densities, with improved fill factors of 74% compared to 62-67% for conventional illumination. Inverted cell external quantum efficiencies were measured to be lower than that of the conventional cell due to different reflectance losses, while the internal quantum efficiencies were found to be similar. The percentage absorption per well in the inverted cell is 1% at the bandedge. These results suggest that quantum efficiency can be improved with optimised reflective back metallisation and with increased number of wells to absorb above bandgap incident light in two passes.