Excitonic effects in photovoltaic materials with large exciton binding energies

We investigate the effect of excitons on charge transport in photovoltaic materials with large exciton binding energies using Cu_2O as a model system. We develop a thermodynamic model to estimate the fraction of excitons in Cu_2O at quasi-equilibrium and find that over 20% of the generated population of carriers during photovoltaic operation could be excitons. Experiments show the presence of excitons at room temperature under visible light excitation and current collection due to excitons during device operation. This work demonstrates that excitons can play a fundamental role in photovoltaic materials with large exciton binding energies and lays the foundation for further studies.