Charge carrier mobilities in organic semiconductor crystals based on the spectral overlap

• Published in: Journal of computational chemistry 2016-09, Vol.37 (23), p.2146-2156
• Main Authors: Stehr, Vera, Fink, Reinhold F., Deibel, Carsten, Engels, Bernd
• Format: Article
• Language: English
• Subjects: Approximation; charge transport; hopping model; Molecules; organic crystals; Photovoltaic cells; Quantum physics
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.24441

The prediction of substance‐related charge‐transport properties is important for the tayloring of new materials for organic devices, such as organic solar cells. Assuming a hopping process, the Marcus theory is frequently used to model charge transport. Here another approach, which is already widely used for exciton transport, is adapted to charge transport. It is based on the spectral overlap of the vibrational donor and acceptor spectra. As the Marcus theory it is derived from Fermi's Golden rule, however, it contains less approximations, as the molecular vibrations are treated quantum mechanically. In contrast, the Marcus theory reduces all vibrational degrees of freedom to one and treats its influence classically. The approach is tested on different acenes and predicts most of the experimentally available hole mobilities in these materials within a factor of 2. This represents a significant improvement to values obtained from Marcus theory which is qualitatively correct but frequently overestimates the mobilities by factors up to 10. Furthermore, the charge‐transport properties of two derivatives of perylene bisimide are investigated. © 2016 Wiley Periodicals, Inc. The charge transport properties of organic semiconducting crystals are calculated via the spectral overlap of the vibrational donor and acceptor spectra, an approach which is so far used for exciton transport only. It contains less approximation than the Marcus theory, as the molecular vibrations are treated quantum mechanically. The approach is tested on different acenes and predicts most of the experimentally available hole mobilities in these materials within a factor of 2.