Effect Of Heteroatom Substitution / Doping On Carrier Transport Properties Of Benzene - Based Organic Semiconductor Materials

In this dissertation, we explored acenes-type molecules which is the typical organic semiconductors through theoretical methods. We hope this will provide theoretical supports in designing and synthsizing high-performance organic transport materials. The work mainly includes two parts as follows.1. Based on the experimental report about pentacene derivatives, we designed a series of chlorinated pentacene derivatives (nCl-PENT-n) and compared the effects of the chlorine number and position on their geometries and electronic properties based on the density functional theory (DFT) calculations at the B3LYP/6-31+G(d,p) level. Based on the crystal structures obtained with the molecular mechanics, we computed the charge transfer integrals at the PW91PW91/6-31G(d) level and predicted the hole and electron mobilities by using Marcus-Hush theory. Then we discussed the effects of chlorination on the packing motif, electronic coupling and carrier mobility. Finally, the anistropic electron mobilities in the a-b plane of the molecules were simulated by means of the steady-state master equation approach.The results indicate that the chlorination lower the frontier molecular energy levels which enhance their oxidation and reduction stability. Also the introduction of chlorine atoms exhibits lower LUMO energies to lower the electron injection barrier and large adiabatic electron affinities to enhance the stability of anions, which shows that the chlorination is benefit for electron transport. The predicted carrier mobilities indicate that DCP crystal may be a promising candidate as ambipolar OFET materials, and 4C1-PENT-1 should be good n-channel material (μe=2.74 cm2·V-1·s-1). In addition, the angular dependent simulation for electron mobility shows that the electron transport is remarkably anisotropic in the studied molecular crystals and the maximum μe appears along the crystal axis direction.2. The charge transport property of picene and its analogues (DNF-W, DNT-W and DNS-W) were investigated. The impact of substituting CH-CH with chalcogen atoms on the optimized structure, reorganization energy, frontier orbitals, transfer integrals, intermolecular interactions and charge mobility were explored based on B3LYP/6-31+G(d,p).The results reveal that the introduction of chalcogen atoms decreases the reorganization energy and lower the HOMO energy level. The doping of oxygen has no contribution to HOMO, while the C-H…O and C…O interactions and the enhanced C…C interactions change the molecular arrangement to one dimentional π-stacking and enhance the electronic coupling. The sulfur and selenium enhance the intermolecular electronic coupling through sulfur-sulfur and selenium-selenium interactions in the molecular crystals. So the doping of chalcogen atoms can change the charge transport properties and increase the carrier mobility by changing the molecular arrangement or enhancing chalcogen-chalcogen interactions.