The Limits to Organic Photovoltaic Cell Efficiency

We consider the fundamental limits to organic solar cell efficiency, and the schemes that have been used to overcome many of these limitations. In particular, the use of double and bulk heterojunctions, as well as tandem cells employing materials with high exciton diffusion lengths, is discussed. We show that in the last few years, a combination of strategies has led to a power conversion efficiency of νP = 5.7% (under AM 1.5 G. simulated solar radiation at 1 sun intensity) for tandem cells based on small-molecular-weight materials, suggesting that even higher efficiencies are possible. We conclude by considering the ultimate power conversion efficiency that is expected from organic thin-film solar cells.