![]() Through simulations with realistic material parameters based on InAs/GaSb superlattice heterostructures, RCE ICPV cells are capable of achieving a conversion efficiency that exceeds 60%, which is much higher than what can be achieved with any other approach, especially with materials of a bandgap smaller than 0.3 eV. The proposed resonant cavity enhanced (RCE) ICPV cells can significantly alleviate the challenging issues in narrow bandgap semiconductor materials, which include a small absorption coefficient, a short diffusion length, and a high dark current density. ![]() 21 Our theoretical modeling results 25,26 have also shown clearly that the multistage IC architecture is capable of circumventing the diffusion length limitation to increase the conversion efficiency by about 10% and the device performance of an ICPV cell is determined mainly by the particle conversion efficiency instead of quantum efficiency in a conventional single-stage PV cell, which can approach 100% with the multistage discrete absorber configuration.īy combining an interband cascade (IC) configuration with an optical cavity, a novel approach to achieve efficient narrow bandgap photovoltaic (PV) cells is proposed. For example, a very high open-circuit voltage (e.g., >0.5 V) was achieved even with a bandgap as low as 0.2 eV at 300 K, and a conversion efficiency of 9.6% was measured at 300 K for a three-stage device with a 0.4 eV bandgap. These advantages of ICPV cells were demonstrated experimentally based on InAs/GaSb type-II superlattice (SL) absorbers (that can be tailored to cover a wide range of bandgap without changing constituent materials), although they were not optimized. 21 Our theoretical modeling results 25,26 have also shown clearly that the multistage IC architecture is capable of circumventing the diffusion length limitation to increase the conversion efficiency by about 10% and the device performance of an ICPV cell is determined mainly by the particle conversion efficiency instead of quantum efficiency in a conventional single-stage PV cell, which can approach 100% with the multistage discrete absorber configuration. ![]() These results have further validated the potential and advantages of narrow bandgap IC structures for TPV cells. Additionally, the open-circuit voltage, the fill factor, the output power, and the power conversion efficiency can be significantly increased in IC TPV devices compared to the conventional single-absorber TPV structure. Furthermore, this study revealed that multi-stage interband cascade (IC) TPV structures with thin individual absorbers can circumvent the diffusion length limitation and are capable of achieving a collection efficiency approaching 100% for photo-generated carriers. By comparing the characteristics of three narrow bandgap TPV structures with a single absorber or multiple discrete absorbers, it is clearly demonstrated that the device performance of a conventional single-absorber TPV cell is limited mainly by the small collection efficiency associated with a relatively short diffusion length (1.5 μm at 300 K). We report on a comparative study of narrow-bandgap (∼0.2 eV at 300 K) thermophotovoltaic (TPV) devices with InAs/GaSb type-II superlattice absorbers.
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