Minimum material quality threshold for intermediate band solar cells using a multi-band device simulator with fully coupled optics
Matthew M. Wilkins1,2, Eduard C. Dumitrescu1, Jacob J. Krich1,2
1Department of Physics, University of Ottawa, Ottawa, ON, Canada
/2School of Electrical Engineering and Computer Science, Ottawa, ON, Canada

Intermediate band (IB) solar cells hold the promise of efficiency as high as triple-junction solar cells with much simpler cell design, containing only two semiconductor material interfaces. Though several intermediate band materials have been demonstrated, no cells have shown promising efficiencies. Many of the fundamental required properties of IB materials are well known: they should have strong subgap absorption, long carrier lifetimes, and good carrier mobilities. The tradeoffs between these properties, however, are not well understood. We present the first results using a new coupled Poisson/drift-diffusion model designed for IB materials, called Simudo. We perform a systematic study of a figure of merit for IB materials. We consider the standard p-IB-n architecture with a high density IB, in which two depletion junctions are formed. Considering fictitious materials with identical electron and hole properties (i.e., mobilities, capture cross sections), we show that this simple figure of merit provides a necessary condition for making efficient devices. Further, we show for the first time a threshold behavior, where the efficiency of the IB device exceeds that of the standard pn-junction only for sufficiently high quality material. These results both give guidance for experiments about required IB material properties and demonstrate how detailed device modeling can aid in the design of IB devices, for example by choosing layer thicknesses optimally.