Theoretical comparison of performance limits of single- and multiple-stage photovoltaic devices

Abstract

Theoretical projections of the power enhancement of photovoltaic (PV) devices offered by the multiple-stage interband cascade (IC) architecture are presented. This work focuses on the improvement this architecture offers for the case of single-bandgap PV devices with negligible series resistance and shunting effects. It is shown that the power efficiency enhancement offered by a multiple-stage device, compared to a simple single-absorber device, is roughly equal to the improvement in the particle conversion efficiency (PCE). In conventional single-absorber PV devices, the PCE is fundamentally limited by the parameters of the absorber material, i.e. the absorption coefficient and the minority carrier diffusion length. The IC architecture circumvents the diffusion length limitation and should be useful for narrow-bandgap semiconductors that are used for thermophotovoltaic applications. The ability to adjust both the absorber thickness in each stage and the number of cascade stages should enable IC PV devices to achieve optimized power conversion efficiency by achieving current matching in each stage.