Analysis of the performance of In_xGa_1−xN based solar cells

We have modeled In_xGa_1−xN single homo-junction solar cells considering realistic carrier transport parameters. It is shown that the maximum efficiency will be less than 19% for an Indium content around 60%. This practical efficiency limit is due to technological issues such as the residual high electron background making it difficult to have p-type doping, causing a low open circuit-voltage and the reduction of the absorber depletion region, and as a result a drop in the photo-current generation. Besides, the difficulty for incorporating In concentrations higher than 40% without phase separation in addition to highly defective material should also be considered. The model does not take in account the carrier lifetime variation as a function of the In content because there are no experimental studies about this yet. To overcome this lack of knowledge, the solar cell with the highest possible In content was modeled by varying the carrier lifetimes from picoseconds to nanoseconds giving calculated efficiencies in the range from 3.9 to 18.9%, respectively. These results explain the poor experimental efficiencies already reported for In_xGa_1−xN single homo-junction solar cells and suggest that, even in the best case, the expected efficiency will be below that obtained for more conventional Si and GaAs solar cells. Hence, our analysis indicates that alternative ways, such as using nanoparticles or nanowires engineered for making competitive solar cells using this kind of materials, should be looked for in the near future.