| Charge carrier transport is a dynamic progress that the holes and electrons injected movetoward the cathode and anode under the influence of external electric field. The transportprocess across organic semiconductors has been the subject of intense investigations since itis one of the most important factors in determining the performance of （opto）electronicdevices such as organic light-emitting diodes （OLEDs） and organic field effect transistors（OFETs）. In the past decade, most investigations in this field have been devoted to the p-typeOSC. However, the developments of the n-type and ambipolar OSCs are hindered because ofthe high injection barrier of electrons and the instability of radical anions in the air.In this paper, we combined quantum chemistry with Marcus charge transfer theory toinvestigate the complicated relations among molecular structure, crystal structure （crystalpacking manner）, intermolecular interaction and charge transport in depth. We hope that ourstudies will be helpful for the design of high-performance materials with largecharge-transport mobility prior to chemical synthesis. Our work mainly includes four aspectsas follows.1. The bridging effect on the charge transport properties of cyclooctatetrathiophene and itsderivatives was investigated in detail. Increasing charge mobilities both for hole and electronwere predicted in cyclooctatetrathiophene derivatives as the number of bridging sulfur atomsincreased. The improved charge transport from cyclooctatetrathiophene to “sulflower” systemcan be interpreted from two contributions associated to be:（i） decreased reorganizationenergy with improved molecular planarity under the consideration of intermolecularinteractions; and （ii） enhanced transfer integral derived from π-stacking arrangement, andmultidimensional S···S interactions are found to contribute to charge transport in “sulflower”system besides π···π interactions. The potential ambipolar transport property of “sulflower”system was reconfirmed by its largest charge mobility both for hole (6.777×10-1cm2V-1s-1)and for electron (1.716cm2V-1s-1), and the large HOMO-LUMO gap also rendered“sulflower” system to make a trade-off between the high mobility and the stability.2. The fascinating effect of dehydrogenation on the charge transport properties ofN-heteropentacene （N-PEN） derivatives was systematically investigated. For the design ofelectron transfer materials, low LUMO level （high electron affinity）, small molecularreorganization energy and large intermolecular charge transfer integrals are necessary. In thiswork, we demonstrate that the dehydrogenation of N-PEN derivatives presents an integrated three-in-one advantage for transforming p-type semiconductor to n-type. First,dehydrogenation of N-PENs lowers the LUMO levels by at least1eV, which can facilitateelectron injection. Second, the dehydrogenated systems have smaller charge reorganizationenergies than its hydrogenated congeners. Last, from the hydrogenated to the dehydrogenatedspecies, the electron transfer integrals of π-dimers increase dramatically.3. The fascinating effect of dehydrogenation on the charge transport properties ofP-heteropentacene （P-PEN） derivatives was deeply investigated. For the design of ambipolarOSCs, reasonable FMO levels （band gap <1.8eV）, large and balanced mobility for hole andelectron are necessary. In this work, we demonstrate that introducing dehydrogenatedphosphorus atoms to PEN scaffold is an efficient strategy to transform p-type semiconductorto ambipolar one. First, dehydrogenation of P-PENs keeps the planarity of PEN core,increases the HOMO level and lowers the LUMO levels, which can facilitate both hole andelectron injection. Second, the dehydrogenated systems have smaller charge reorganizationenergies than its hydrogenated congeners, which are attributed to the different bonding natureof phosphorus atoms. Last, the crystal structure of TIPS-4P-2p was constructed and fullyoptimized for the coupling integral estimation. The hole and electron V values were similar. |
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