Interband Cascade Photovoltaic Devices for Conversion of Mid-IR Radiation

Interband cascade structures are investigated for applications in the photovoltaic conversion of mid-infrared radiation. We present detailed studies of the performance characteristics and the temperature dependence of seven-stage, single-bandgap devices. These cascade structure devices were able to achieve open-circuit voltages as high as 1.68 V with a cutoff wavelength of 4.0 μm at 80 K. The total power efficiency was broken down into a product of individual efficiencies in order to determine the power loss from each of the physical mechanisms that are involved in the conversion process. We find that at low temperature, the power conversion is limited by incomplete absorption of the incident light and a fill factor below 50%. At higher temperature, the drop in open-circuit voltage limits the efficiency. We comment on how the results of this efficiency analysis will steer the direction of our future efforts toward device improvement.