Theoretical Study On Molecular Structure,Aggregation Behavior,and Semiconductor Properties Of Bithienyl-diketopyrrolopyrrole-based Oligomers

Organic semiconductors are widely used in organic optoelectronic devices such as field-effect transistors（OFETs）,organic photovoltaic cells（OPVs）,light-emitting diodes（OLEDs）and other advantages due to light weight,good flexibility,easy preparation,and low price.Its performance can be comparable to inorganic semiconductors,so it has become a research focus of new materials.The performance of organic semiconductors is closely related to the size of carrier mobility.To obtain high-performance organic semiconductor materials,the value of carrier mobility needs to be high.Therefore,it is important challenge to investigate molecules with high mobility.This mainly combines the classical Marcus theory and dynamics simulation from a microscopic perspective to theoretically investigate the relationship between molecular structure-properties,and further lays the foundation for experimentally designing new organic semiconductor molecules.The chapter 1 mainly introduces development background of the organic semiconductor,classification,basic structure and working principle.Common organic semiconductor types,research progress on diketopyrrolopyrrole（DPP）oligomers,and the significance of this article.In chapter 2 the theoretical part mainly introduces the theoretical knowledge used in this article including density functional theory,the prediction of crystal structure,provides theoretical knowledge for the calculation of mobility.The available force fields commonly used in dynamics simulation,the theoretical knowledge of the lineage and the software used in the research process.In Chapter 3,based on the current research on donor-acceptor conjugated oligomers,diketopyrrolopyrrole（DPP）oligomers were selected as the research object.Explored the relationship of different structures and properties using DPP as the acceptor,connecting different donors（BDT,TT,TVT,BT）,the length of the oligomer conjugated main chain,different donor-acceptor connection modes,etc.Finally,it is obtained that the recombination energy gradually decreases with the increase of the length of the conjugated main chain,and the obtained mobility value gradually increases,and the high hole/electron transfer mobilities of 4DTDPPTT,4DTDPPBT,and 4DTDPPTVT are 9.62/7.54 cm²V^-1s^-1and 10.73/8.06 cm²V^-1s^-1,12.60/15.56cm²V^-1s^-1respectively.The mobility values of these are greater than other semiconductor values,therefore,it can provide theoretical guidance for a good ambipolar semiconductor.In Chapter 4 in order to further study how the molecular structure affects the performance of the semiconductor,first,different force fields were used to explore the stacking method between the molecules in the BDTDPPBT crystal structure,the differences in the crystal structure under different force fields were discussed,and finally Dreiding was selected to calculated the BDTDPPBT molecules.After cooling,the energy of the crystal structure decreases after thermal annealing,and the distance between the molecules gradually decreases.The stacking methods between the molecules are mainly parallel stacking and herringbone stacking,both of which are beneficial to carrier transport,which is the main reason for BDTDPPBT to obtain ambipolar transport.