Phys. Rev. A 84, 053818 (2011)

Quantum coherence between competing energy-level pathways is known to help optimize photosynthesis and enable phenomena such as lasing without inversion. Researchers from Texas A&M University and Princeton University in the USA have now suggested that quantum coherence could also be used to enhance the performance of solar cells. One idea is to split degenerate excited energy levels by exploiting tunnelling between two adjacent quantum dots. The two split energy levels (known as an energy level doublet) both couple to the conduction state. Fano interference between the two pathways minimizes unwanted radiative transitions and helps to maximize the generated photocurrent. An alternative approach is to create an energy level doublet from two lower-energy levels and use Fano interference to enhance the absorption of solar energy. Theoretical analysis of this scheme suggests that the photocurrent and peak power of a photovoltaic cell employing fully coherent Fano interference could be improved by up to 50%. The researchers also suggest the possibility to engineer the cell such that the Fano interference is robust against environmental decoherence. The challenge now is for the research community to realize such a cell in practice.