Crossover from static to dynamic Non-Condon effecton charge Transport in Organic Semiconductors

Abstract

The computed charge transport key parameters like, charge transfer integral, site energy and reorganization energy are used to study the hole and electron transport in dialkyl substituted thienothiophene caped benzobisthiazole (BDHTT-BBT) and methyl-substituted dicyanovinyl-capped quinquethiophene (DCV5T-Me) molecular crystals. The effect of structural fluctuation on charge transport in these molecules is analysed by Monte-Carlo simulations. To estimate the equilibrium speed during the charge transport process in these molecular solids, we have introduced the parameters such as, potential equilibrium rate and density flux rate. Here, the density flux rate is directly related with the drift force which facilitates the charge transfer along the consequential hopping sites. Our theoretical study reveals that the charge transfer up to the crossover point (or disorder drift time) is exponential, non-dispersive and it follows the static non-Condon effect. Beyond the disorder drift time, the charge transfer is partially exponential, dispersive and it follows the dynamic non-Condon principle. The expressions of density flux and diffusion shows their dependency on dynamic disorder and is in agreement with the Troisi’s model on diffusion limited by thermal disorder.