Resolving spectral overlap issue of intermediate band solar cells using non-uniform sub-bandgap state filling

Abstract

Intermediate band solar cell provides novel alternative to multi-junction solar cell, but its efficiency is significantly degraded when spectral overlap exists between different absorption bands. Here, a scheme using non-uniform sub-bandgap state filling together with intermediate band transport is proposed to resolve the spectral overlap issue. On the basis of detailed balance calculation, spectrally decoupled devices using low-high state filling is shown to achieve 52.8% conversion efficiency when 4 eV spectral overlap is present between absorption coefficients of different bands, compared with baseline efficiency equal to 35.1% for conventional half-filled intermediate band devices. If a base material without intermediate band is added to the two section low-high state filling devices, the efficiency is further increased to 61.5%, which approaches efficiency of 63.2% for intermediate band devices with no spectral overlap and 63.8% for unconstrained triple-junction tandem cells. The junction thermalization loss associated with proposed new structures is shown to be equal to conventional half-filled intermediate band devices.