Theoretical Simulation Of Carrier Mobility In Molecular Crystals Of Azaacenes

Carrier mobility is an important index to measure the conductivity of organic semiconductor materials and plays a crucial role in the performance of optoelectronic devices.Therefore,how to understand,predict and improve carrier mobility is one of the core issues in the development of organic electronics.Theoretical prediction and simulation can provide guidance for the realization of high mobility and the design of functional semiconductor materials,thus contributing to further discoveries in this field.Pentacene is one of the most common organic semiconductor materials,and many new organic semiconductor materials are derived from it.By introducing nitrogen atoms into pentacene,a large number of π-frameworks related to the structure of electrons,stability,solubility,and molecular stacking can be generated.This provides considerable freedom for the design of organic semiconductors and provides a good opportunity to study structure-attribute relationships.N-isopentacenes and its derivatives,which introduce nitrogen into the backbone,are a new type of organic semiconductors found in recent years,which have high performance in airport-effect transistors（OFETs）.This paper takes pentacene,N-isopentacenes and its chlorinated derivatives as the main research objects.QM computational methods are used to study the geometry,electronic properties of these compounds.The charge transport process in molecular crystals is studied explicitly by state-specific polarization force field（SS-PFF）,which aims to provide a theoretical reference for the design of semiconductor organic materials with high air stability and high carrier mobility.The main contents of the study are as follows:1.To investigate the effect of external reorganization energy on charge transport in a fully dominant way,this paper uses states to specified（both charged and neutral）polarizable force fields（SS-PFF）to describe intermolecular interactions.First,using the parameterized method proposed by our experimental group,combined with QM calculation,the SS-PFF,of neutral and charged states of pentacene（PEN）are obtained and the rationality of the SS-PFF is verified at the QM molecular level.Then at the SS-PFF potential energy surface,the hole and electron external reorganization energies of PEN were calculated using the two-point method.The calculated results show that using neutral SS-PFF、to ignore the external reorganization energy during charge transport,the calculated intrinsic mobility of holes and electrons is 7.84cm²V^-1s^-1 and 9.44cm²V^-1s^-1,which can be said to be basically the same;But when considering the external reorganization energy factor,the calculated hole and electron mobility are 4.03cm²V^-1s^-1 and 0.41cm²V^-1s^-1,respectively.The hole mobility is an order of magnitude larger than the electron mobility.Small hole external reorganization energy can lead to a tendency of PEN to hole transport materials,matching the widely experimentally obtained conclusions.2.The same method was used to calculate the hole mobility of the nitrogen derivatives-D AP and DHD AP of PEN under condensed phase.The structure of the three molecules is very similar,and the addition of nitrogen does not change the way of stacking molecules,the two molecules are still in herringbone.But experimentally measured hole mobility of DAP molecules is only 4-8×10^-5cm²V^-1s^-1,far lower than that of the other two molecules.The calculation shows that the hole mobility of DAP and DHDAP is basically the same when conducting charge transitions under the condensed phase,but both are one order of magnitude lower than that of PEN.So the hole mobility of the DAP is very low,independent of the eigenvalue,mainly because the HOMO of this molecule are too low compared with the other two molecules,resulting in the hole is difficult to inject,so the corresponding hole mobility is also very low.3.DAP and DHDAP chlorinated derivatives-TCDAP and TCDAHP under the condensed phase also calculated in this paper.The substitution of chlorine makes TCDAP and TCDAHP more inclined to π-π stacking,which makes it easier for charge transport to increase the electron transfer integral between adjacent molecules.The substitution of chlorine also reduced the HOMO and LUMO energy levels of the molecules to a certain extent.The calculation shows that the electron mobility of both TCDAP and TCDAHP is higher than that of holes,especially the electron mobility of TCDAP is one order of magnitude higher than that of holes.So we predict that both TCDAP and TCDAHP are electronic transport materials.The low LUMO level of the TCDAHP makes it difficult to inject electrons from the electrode,so TCDAHP was measured as a hole transport material.