Performance analysis of narrow-bandgap interband cascade thermophotovoltaic cells

We present the detailed characterization and performance analysis of two sets of four interband cascade thermophotovoltaic devices with InAs/GaSb type-II superlattice (SL) absorbers. The bandgaps of the SL absorbers in the four devices were between 0.22 and 0.25 eV at 300K. With different numbers of cascade stages and individual absorber thicknesses, we are able to show how possible material quality variations and current mismatch between stages can affect the device performance. Based on the calculated effective quantum efficiency in each stage and experimental results, it is shown that the current mismatch between stages due to the deviation of absorption coefficient from the designed value can be substantial with more stages. On the other hand, the collection efficiency can be much improved with more stages and thin individual absorbers. Also, the carrier lifetime is extracted through measured dark current density to evaluate the material quality. The effects of material quality, current mismatch and collection efficiency on device performance are quantified and a comparison shows that material quality plays the most important role.