Limiting Efficiency of Erbium-Based Up-Conversion for Generalized Realistic c-Si Solar Cells

Up-conversion of sub-band-gap near-infrared light to absorbable wavelengths has been suggested as a means of greatly improving the efficiency of standard silicon solar cells. Most theoretical assessments of the potential of such designs have utilized a detailed-balance approach that invokes vastly idealized models of both the solar cell and the up-converting layers. In this study, we consider the limiting efficiency of an up-converting photovoltaic device based on more realistic models for the silicon solar cell and an up-conversion layer approximating the performance of an erbium-doped phosphor. While the generalized silicon cell has been previously shown to demonstrate good performance (a relative efficiency enhancement of 23%-26%) when coupled to an ideal up-converter, the modifications considered here result in drastically diminished device performance overall (a maximum relative enhancement of about 7%). This reduction may be compensated to some extent by the sensitization of erbium absorption by the addition of a suitable species to the up-converting layer; in this case, the relative limiting efficiency is pushed back up to 15%. Based on these results, we draw conclusions regarding device engineering that should guide future work in this area.