Strong exciton bandwidth reduction in pentacene as a function of temperature

The motion of excitons in organic semiconductors represents a key contribution to the performance of organic solar cells. It is determined by intermolecular exciton coupling. In momentum space, exciton coupling results in the exciton dispersion and defines the exciton bandwidth. We demonstrate that the exciton bandwidth in pentacene as measured using electron energy-loss spectroscopy is substantially temperature dependent, and it is drastically reduced going from 20 to 380 K. Following recent theoretical developments, we rationalize this reduction by a huge reduction of the (effective) charge carrier transfer integrals by about 60%. Our results indicate a strongly temperature-dependent energy transport in pentacene and related organic semiconductors.