Multistage Interband Cascade Thermophotovoltaic Devices with ~0.2 eV Bandgap    
Wenxiang Huang, Lu Li, Jeremy Massengale, Rui Yang, Tetsuya Mishima, Michael Santos
University of Oklahoma, Norman, OK, United States

We studied five narrow-gap interband-cascade (IC) thermophotovoltaic (TPV) devices that differ in the number of cascade stages (one, three, five, six or seven stages) and the thickness of the InAs/GaSb superlattice (SL) absorbers. 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. Our TPV devices are evaluated at 300 K under illumination of a mid-infrared IC laser with multiple different output powers. The largest open-circuit voltage (Voc) of 691 meV was obtained from the seven-stage device. The comparison between the measured J-V curves and the corresponding100%-collected ideal J-V curves clearly showed that the photocurrent of these TPV devices is a function of the applied voltage. Our comparative studies have further illustrated the advantages of the multi-stage discrete absorbers of our narrow-gap IC TPV devices.