Orbital gap predictions for rational design of organic photovoltaic materials

Ionization potentials (IP) and electron affinities (EA) of organic molecules with applications in photovoltaic devices are calculated using modern density functional theory (DFT). Calculated frontier orbital energies are compared to experimentally determined IPs and EAs at gas phase and thin film environments. Gas phase frontier orbital energies calculated with widely-used DFT functionals accidentally coincide with thin film measurements, reproducing condensed phase results for the wrong reasons. Recently developed range separated hybrid (RSH) functionals, on the other hand, provide gas phase frontier orbital energies that correspond properly to measured IPs and EAs. We also employ a polarizable continuum model to address the effects of the electrostatic environment in the solid state. We find that the environmentally-corrected RSH orbital energies compare well with thin film experimental measurements. (C) 2014 Elsevier B.V. All rights reserved.