Multistage Interband Cascade Thermophotovoltaic Devices with ∼0.2 eV Bandgap

Five narrow-gap interband-cascade (IC) thermophotovoltaic (TPV) devices were examined, which differed from each other in the number of cascade stages (1-, 3-, 5-, 6- or 7-stages) and the thickness of the InAs/GaSb superlattice absorber. The bandgap of the absorber embedded in the five devices is slightly larger than 0.2 eV at 300 K, which should be the narrowest bandgap ever reported in TPV cells. The largest open-circuit voltage of 691 meV was obtained from the 7-stage device. A comparison between the measured J-V curves and 100%-collected ideal J-V curves clearly showed that the photocurrent of these TPV devices is a function of the applied voltage. These findings further support the advantages of the multi-stage narrow-gap IC structure over the single absorber configuration used in the conventional TPV cells.