Improved model for solar cells with down-conversion and down-shifting of high-energy photons

A system for converting high-energy incident photons into photons of lower energy was proposed by Trupke et al (2002 J. Appl. Phys. 92 1668). In the present paper we re-analyse this system by using a more elaborate model. The main conclusions of this work are as follows. (1) When non-radiative recombination is neglected, our results confirm the findings of Trupke et al. Both the front and rear down-converter systems improve the performance of a single mono-facial solar cell. However, the present model shows that the conversion efficiency is smaller than estimated before. (2) When both the cell and the front (or rear) converter have the same low radiative recombination efficiency, their combination does not increase the cell conversion efficiency. (3) Adding a converter with a high (near unity) value of the radiative recombination efficiency to a solar cell shows beneficial effects. (4) In this case (i) for high-quality solar cells, the combination cell-rear converter provides a higher efficiency than the combination front converter-solar cell whereas (ii) for low quality solar cells, the front converter system performs better than the rear converter system. Conclusions (3) and (4) may be dependent on the details of the model adopted here.