Coexistence of band-like and thermally activated charge transport through nuclear tunneling effect in organic semiconductors

In this study, the coexistence of band-like and thermally activated charge transport in organic semiconductors is demonstrated through the first-principles calculation of the electric field dependent charge mobilities of TIPS-pentacene, which strongly deviates from the semi-classical Marcus theory. The nuclear tunneling hopping rates simultaneously exhibit band-like and thermally activated conduction for the downward and upward hoppings, respectively, which explains the puzzling observation of the transition from thermally activated transport to band-like transport with increasing field strength. As the hopping rates are very sensitive to the site-energy fluctuations induced by defect configurations, the transition from band-like transport to thermally activated transport with increasing energetic disorder is found. The results suggest that the interplay of the quantum-mechanical effect and disorder is of particular importance in the understanding of the temperature and field dependence of mobility in organic materials.