Theoretical Study On Charge Transport Of Organic Semiconductor Materials

Organic semiconductors are the focus of current research, since organic semiconductor materials have many typical properties, such as:flexible, diversity of synthesis, easy for processing, low cost. Organic materials are also emerging as promising candidates for the fabrication of transistors, photo-diodes and solar cells, and (bio)chemical sensors. Charge transport is the most fundamental process in organic semiconductor transistors, and theoretical research of charge transport proved basic understanding to the performance of organic semiconductor devices.We investigated the charge transport properties of various organic semiconductors using semicalssical Marcus theory and full quantum theory Fermi Golden Rule (FGR) based on the first-principle, and simulated charge mobilities with the randomwalk model. The main contents of the thesis are as following:1. A full quantum theory combining with molecular dynamics was adopted to evaluate the ambipolar charge transport property of cocrystals. Using Marcus theory as a reference, our results suggested that the full quantum theory FGR was more favorable to assess the mobilities of the cocrystals, because the quantum nuclear tunneling effect in the charge transfer could be involved. The excellent ambipolar transport characteristics of the cocrystals are mainly attributed to the high and balanced hole and electron transfer integrals on the main transport channels. Furthermore, we demonstrated that the thermal fluctuation plays an important role on the mobilities of the cocrystals as the superexchange of the D-A-D or A-D-A clusters is very sensitive to the thermal motions.2. We have investigated the charge transport property of single structures of DPh-NDXn (X= O, S, Se, n=1,2,3,4). Single structures of DPh-NDXn were predicted in a simple method. In addition, based on obtained single structures, we simulated hole mobilities of DPh-NDXn, which indicates these molecules are promising p-type organic semiconductors. Furthermore, calculated results indicated that the type of heteroatioms and the shape of molecules play a key role on electronic properties of molecules.3. We have simulated single crystal mobilities of pyrazine N-heteropentacenes and its derivatives synthesized in our lab. We analyzed the difference between the thin film model and single crystal model, and the single crystal model was adopted to calculate the crystal mobility. Calculated results indicate that the introduction of N and halogen atoms into molecules can cause obvious effects on the charge transport properties.4. We have investigated the electronic property of tetrathiafulvalene (TTF) derivatives decorated by fluorinated phenyls. HOMO, LUMO energy orbitals and electrostatic potential maps of the molecules were calculated in this paper. The calculated results suggest that the number and space position of F atoms on fluorinated phenyls can adjust HOMO and LUMO energy orbitals of the molecules.