Theoretical Investigations On Transport Properties Of Different Organic Semiconductor Molecular

We theoretically investigated the electronic and charge-transport properties of organic semiconductors molecules in this work.The charge carrier mobilities in organic semiconductor crystals were calculated by density functional theory?DFT?methods combined with the Marcus-Hush electron-transfer theory.Our thesis consists of the following three aspects:1.The applications of organic semiconductors and the theoretical method in the paper were introduced in detail.A great progress has been made in the organic semiconductors and their device applications.Organic semiconductors have been successfully employed as a new class of electronic materials for applications in electronic devices such as organic thin-film transistors?TFTs?,organic light-emitting diodes?OLEDs?and organic field-effect transistors?OFETs?.Organic semiconductors play a vital role in optoelectronic and electronic devices because of the remarkable advantages.The DFT methods,Marcus charge transfer theory,hopping model and the calculation software in our study.2.Four n-type Tatraazaperopyrenes?TAPPs?derivatives and three derivatives based on oligothiophenes were theoretically investigated.One significant finding is that the core substitution of TAPPs has a drastic influence on the charge-transport mobility.The maximum electron mobility value of the core-brominated tetraazaperopyrenes?TAPPs?is 0.521 cm²V^-1s^-1,which appears at the orientation angle in 95°and 275°.The electrochemical data demonstrate that 2,9-bis?perfluoroalkyl?-substituted tetraazaperopyrenes?TAPPs?with bromine substituents in ortho positions should exhibit the best charge-transfer efficiency of the four different TAPP derivatives.The calculated data demonstrated that the compound 1 should be a high-performance n-type organic material candidate and compound 3 may well be potential p-type materials with high mobility values.The predicted highest hole mobility is 0.218 cm²V^-1s^-1,and the highest electron mobility is 0.373 cm²V^-1s^-1 for oligothiophene derivatives at 300 K.Our work also indicates that the face-to-face ?-? interaction and S-S interactions is favorable for the molecular stacking and charge transport behaviors.3.The pyrene,NDT,TTF and TTP systems are remarkable candidates for good organic semiconductor materials.The theoretical investigation of electronic and transport properties of a series of Pyrene and NDT derivatives and four derivatives groups containing nineteen different the tetrathiafulvalene?TTF?derivative compounds have been carried out.Various structure modifications for different derivative molecules are investigated to reveal structure-mobility relationships of the organic materials,such as introducing different substitution groups in different positions,linking the backbone structure to changing the central core of the molecule.Theoretical calculation results are in good agreement with the experimental results,such as the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies.The reorganization energies and charge mobility are estimated based on molecule single-crystal structures and incoherent charge-hopping transfer model at 300 K.For designing high performance organic materials,the hole mobility are predicted to a high value as 2.945 cm²V^-1s^-1 of compound 2,7-diphenyl-substituted derivative,the largest electron mobility for 4,5-dithienypyrene as 6.24 cm²V^-1s^-1,and that the predicted highest hole and electron mobility values of TTF derivatives are 1.821 cm²V^-1s^-1 and 1.709 cm²V^-1s^-1 respectively at 300 K.The calculated data demonstrate that these derivatives should be high-performance organic material candidates with high mobility values and good stability.In the analysis,the charge transport properties are extremely dependent on the packing mode of organic semiconducting molecules and the structural change of the substituent group.These electron-withdrawing groups containing the methoxy groups and halogen groups are widely used to reduce the energies of frontier orbitals?HOMO and LUMO?and increase the stability of the TTF derivative.The comparative analysis of crystal structures reveals that the layer face-to-face structure and herringbone structure with slip-stacks of dimers exhibit higher charge transfer values compared with the disordered structures,and that the face-to-face ?-? interaction and S-S interactions are favorable for the molecular stacking and charge transport behavior.The interface charge conduction mechanism between two different molecule crystals are investigated,and we find there are high conducting interface and low resistances about 10-50 k?.The high mobility combined with the simple producing processing makes promising candidate materials for electronic devices where low-cost and flexibility are required.Our calculation results could provide detail enlightening information on possible methods to increase the charge mobility and design new molecular devices with high-performance.