We have studied efficient p-on-n homo- (InGaAsSb/GaSb) and hetero-junction (InGaAsSb/AlGaAsSb/GaSb) thermophotovoltaic (TPV) cells with respect to the recombination velocity at the cap-layer/emitter interface, S. In both cell types the open-circuit voltage, Voc, and the short-circuit current, Jsc, have about the same sensitivity to S. The dark current, J0, is the most sensitive of all. An examination of the essential factors in the one-dimensional minority-carrier diffusion model shows that under short-circuit conditions, photogenerated electrons diffuse rapidly away from the interface to the junction, whereas under open-circuit conditions, they remain in the emitter for a much longer bulk-recombination time, and therefore, they are more likely to recombine at the interface. A factor of 2.2 increase in S from 2.5 to 5.05×104cm/s produces a 25-mV decrease in Voc, a 12-percent decrease in Jsc or quantum efficiency, and a factor of two increase in J0. This work points out the critical importance of interfacial recombination even in efficient TPV cells.

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