Understanding the impact of polymorphism on the electronic structures and charge transport properties of contorted hexabenzocoronene

Abstract

Organic semiconductors with polymorphism characteristics have been attracted increasing attention for their great importance on disclosing the structure-property relationship of organic solids. The impact of polymorphism on the electronic structures and charge transport properties of contorted hexabenzocoronene (c-HBC) is explored based on density functional theory (DFT) method combined with Marcus electron transfer theory. The geometry structures, reorganization energies, frontier molecular orbitals, ionization energies, electronic affinities, crystal packing motif, transfer integrals as well as charge carrier mobilities of three polymorphs are investigated to establish the relationship between the structure and property. The results show that the polymorphism has little influence on the optimized geometry structures, reorganization energies, and the distribution of the frontier molecular orbitals. The reorganization energies of hole and electron for the three polymorphs are small, which are 0.11 and 0.15 eV, respectively. However, the crystal packing arrangements and the transfer integrals of the three polymorphs are significantly different, leading to different charge carrier mobility. All the three polymorphs show high hole mobilities, indicating that they could be used as p-type semiconductors. Specially, for polymorph II, the calculated hole mobility is as high as 0.90 cm2V−1s−1. Meanwhile, the electron mobilities of polymorphs II and III are in the same order of magnitude with the hole mobilities, which are 0.47 and 0.17 cm2V−1s−1, respectively. Due to the high hole and electron mobilities of polymorph II, it may be used as a bipolar transport semiconductor.