Limiting factors and efficiencies of narrow bandgap single-absorber and multi-stage interband cascade thermophotovoltaic cells under monochromatic light illumination

Abstract

In this work, the factors that limit the conversion efficiency of narrow bandgap thermophotovoltaic (TPV) cells are identified and their impact on device performance is explored through studying their effects on key aspects such as quantum efficiency (QE), fill factor, open-circuit voltage, and voltage efficiency. These factors are closely associated with short carrier lifetime, high dark saturation current density, small absorption coefficient, and the limiting effects of diffusion length on the collection of photogenerated carriers. Calculations are carried out for narrow bandgap InAs/GaSb superlattice materials to illustrate how the conversion efficiency is limited by these factors for specific material parameters such as the product of absorption coefficient α and diffusion length L. We show that the multistage interband cascade (IC) architecture is capable of circumventing the diffusion length limitation to overcome the problem of a low QE in conventional single-absorber TPV cells, thereby enhancing the conversion efficiency by about 10% in wide ranges of αL and bandgaps with the particle conversion efficiency approaching 100%. The enhancement of conversion efficiency with the multistage IC architecture is especially significant with small αL, which is more than double of that in the single-absorber TPV cell. Also, the device performance dependence on the illumination source is investigated, which demonstrates flexibilities and advantage of the multistage IC architecture to achieve its maximum conversion efficiency with the energy of incident photons near the bandgap of absorbers. Finally, the future directions are discussed in terms of what can be further improved or need to be addressed with the remaining issue for the development of narrow bandgap TPV cells.In this work, the factors that limit the conversion efficiency of narrow bandgap thermophotovoltaic (TPV) cells are identified and their impact on device performance is explored through studying their effects on key aspects such as quantum efficiency (QE), fill factor, open-circuit voltage, and voltage efficiency. These factors are closely associated with short carrier lifetime, high dark saturation current density, small absorption coefficient, and the limiting effects of diffusion length on the collection of photogenerated carriers. Calculations are carried out for narrow bandgap InAs/GaSb superlattice materials to illustrate how the conversion efficiency is limited by these factors for specific material parameters such as the product of absorption coefficient α and diffusion length L. We show that the multistage interband cascade (IC) architecture is capable of circumventing the diffusion length limitation to overcome the problem of a low QE in conventional single-absorber TPV cells, thereby enhancing ...