Influence of some design parameters on the efficiency of solar cells with down-conversion and down shifting of high-energy photons

In this paper we analyze the system proposed by Trupke [J. Appl. Phys. 92, 1668 (2002)] to increase solar cell efficiency. The system consists of adding to the solar cell a so-called down-converter, which is a device able to convert the high-energy incident photons into photons of lower energy. The contribution consists of taking account (i) the nonradiative recombination in both solar cell and converter, (ii) the refractive index of solar cell and converter materials, and (iii) the solar radiation concentration. Two configurations are studied: the cell and rear converter (C-RC) and front converter and cell (FC-C). The main conclusions of this work are as follow. (1) For ideal down-converters, with radiative recombination only, the solar energy conversion efficiency may be, or may not be, increased by adding a front (or a rear) down-converter to the cell, depending on the value of the solar cell refractive index. (2) More realistic systems, where nonradiative recombinations exist inside the converter, are also considered. The efficiency of the FC-C system is generally less than the efficiency of a single cell. C-RC systems perform better than the cell operating alone for some values of the refractive indices. (3) C-RC systems perform generally better than FC-C systems whatever the values of the refractive indices and the concentration ratio.