Theoretical Studies On The Charge Transport Properties Of Thiophene And Tetrathiafulvalene Based Materials

Organic semiconductors have been dramatically developed in the past two decades.Owing to their potential merits, such asflexibility,large-area coverage, low-costand ease ofprocessing, the material can be applied into many inexpensive and paintable electronicdevices. Applications like electronic paper, organic complementary circuits (CMOS), radiofrequency identification (RIFD), electronic ink and smart card etc.. According to the differenttypes of carriers the materials can be classified into p-type, n-type, and ambipolar transportingmaterials. Among them the development of n-type is relative lagging behind development ofefficient n-type semiconductors is far behind the p-type’s, meanwhile it will keep the boom ofambipolar transporting material.The paper set oligothiophene and tetrathiafulvalene and their derivatives as the object ofthe study. The density functional theory (DFT) and carrier transporting theories (includinghopping theory and band model) are combined, probing to give an explanation to the carriertransport mechanism. Based on the experimental results we designed and calculated potentialn-type transporting materials with good electron transporting performance. We hope our studywill give a hand to scientists in developing and designing high-performance n-type organictransport materials. And the works have two main parts as follows:Six planar polycyclic aromatic hydrocarbon fusedtetrathiafulvalene derivatives werecalculated in this part and the effects of halogen and cyan substitutions and nitrogen weredetailed investigated. The molecular geometry, frontier molecular orbital, molecularreorganization energy, the transfer integral, carrier transporting mobility, weak contact effectand band structure were thereby studied. It was confirmed that introducing N-atoms wouldlower molecular reorganization energy and the effects of substituting cyan group was strongerthan introducing halogen substitutions. The calculated electron drift mobility of cyan groupsubstituted DPBCN-TTF was1.15cm2V-1s-1, more than that the system also maintain thelowest LUMO energy level and the smallest electron reorganization energy implying thesystem may have good electron transporting property. The S S, S N and N Nweak-contact effects between molecules in crystal were inspected, and we concluded thatwhen S or N atom has contribution on HOMO (or LUMO) the corresponding hole (orelectron) transporting property would increase.The effects of the fluorination and carbonylation on electron transport properties of threetypes of quarterthiophene-based systems were systematically compared and discussed at DFTlevel. Insights into their geometry optimization, FMO, VEA, λele, tele, μeleand band structureswere provided in detail. Both fluorination and carbonylation, especially for the latter, improve the electron transport properties of the systems studied here, with higher VEA and lowerLUMO energy levels and λelethan the precursors. It was confirmed that the ESP can to someextent explain the packing manners. The μeleresults with different molecular geometryoptimization methods based on2-D and3-D transport behaviors were compared.