Effect of an external electric field on the charge transport parameters in organic molecular semiconductors

Internal reorganization energies and interchain transfer integrals are two key parameters governing the charge-transport properties of organic semiconducting materials. Here, in order to model some aspects of device operation in field-effect transistors based on conjugated oligomers, we investigate via semiempirical quantum-chemical calculations the way these two parameters are modified when a static electric field in the range 106–108 V/cm is applied along the long axis of pentacene and sexithienyl molecules. For the highest fields, a pronounced redistribution of the charges along the oligomer chains occurs, which is accompanied by significant geometric distortions. However, these charge redistribution effects are found not to impact significantly the transport parameters.