n-Type charge transport and mobility of fluorinated perylene bisimide semiconductors

The intramolecular and intermolecular charge transport parameters are evaluated quantum chemically for three fluorinated derivatives of perylene bisimide (PBI) semiconductors, two of which feature a twisted PBI core. Charge transfer rates are computed within the Marcus-Levich-Jortner formalism including a single effective mode treated quantum mechanically and are injected in a kinetic Monte Carlo scheme to propagate the charge carrier in the crystal and to estimate charge mobilities at room temperature. The relative order of computed mobilities agrees with the observed trend, and the largest mobility is computed for the planar PBI derivative. It is suggested that thermally induced disorder effects should contribute considerably to the observed large mobility of the planar PBI derivative, while a retardation effect induced by the presence of alternating slow and fast jumps along pi-stacked PBI columns is responsible for the lower mobilities of the two twisted derivatives. The computed parameters reveal the subtle interplay between intramolecular and intermolecular contributions to the charge carrier propagation in these organic semiconductors and may guide the design of more efficient architectures.