Quaternary InGaAsSb Thermophotovoltaic Diodes

In _x Ga _1-x As _y Sb _1-y thermophotovoltaic (TPV) diodes were grown lattice matched to GaSb substrates by metal-organic vapor phase epitaxy in the bandgap range of EG = 0.5 to 0.6 eV. InGaAsSb TPV diodes, utilizing front-surface spectral control filters, are measured with thermal-to-electric conversion efficiency and power density (PD) of n _TPV = 19.7% and PD = 0.58 W/cm ² , respectively, for a radiator temperature of T _radiator = 950 degC, diode temperature of T _diode = 27 degC, and diode bandgap of EG = 0.53 eV. Practical limits to TPV energy conversion efficiency are established using measured recombination coefficients and optical properties of front surface spectral control filters which for 0.53-eV InGaAsSb TPV energy conversion are n _TPV = 28% and PD = 0.85 W/cm ² at the above operating temperatures. The most severe performance limits are imposed by 1) diode open-circuit voltage (V _OC ) limits due to intrinsic Auger recombination and 2) parasitic photon absorption in the inactive regions of the module. Experimentally, the diode V _OC is 15% below the practical limit imposed by intrinsic Auger recombination processes. Analysis of InGaAsSb diode electrical performance versus diode architecture indicates that V _OC and thus efficiency are limited by extrinsic recombination processes such as through bulk defects