Theoretical Studies On The Charge Transport Performances Of Indolo[3,2-b]carbazole And Oligothiophene-diketopyrrolopyrrole Derivatives

Comparing with the traditional inorganic materials, organic optoelectronicmaterials have the advantages such as low costs, easy production and high flexibility,so many excellent organic materials have been employed in organic field effecttransistors (OFET), organic light-emitting diodes (OLED), and organic photovoltaiccells (OPV). Based on the transport type, it could be divided into hole transport(p-type) materials、electronic transport (n-type) materials and bipolar transportmaterials. In addition, changing the functional group will lead to varieties ofmolecular packings, which can sensitively influence its transport efficiency. In thispaper, we used quantum chemistry method, employing hopping model and bandmodel to investigate the traditional organic transport materials. We hope that this willprovide theoretical supports for designing and synthesizing high efficient materials.1. Comparative theoretical investigation on the influence of introduction of chlorineand long alkyl side chains on the hole transport properties of indolo3,2-b carbazolederivatives. The results show that the introduction of chlorine atoms induces moredelocalized HOMO of compounds2(2,8-dichloro-indolo[3,2-b]carbazole) and3thancompound1(indolo[3,2-b]carbazole), while the LUMO is just the opposite. Besides,both the HOMO/LUMO energy levels and the reorganization energies of compounds2and3(2,8-dichloro-5,11-dihexyl-indole[3,2-b]carbazole) are lower thancompound1, and the former is ascribed to chlorine exerting conjugate effect toHOMO but electron-withdrawing effect to LUMO. With the introduction of bothchlorine and long alkyl side chains on indolo3,2-b carbazole derivatives, compound3has higher mobility than compounds2and1, which is the result of denserintermolecular packing of dimer A in compound3than those in compounds1and2,thus larger electronic coupling and higher the mobility is measured for compound3.The results obtained from the band model are consistent with those calculated byhopping regime. Finally, our calculation clarify again in theory that rational chemicalmodification can improve the carrier transport property of indolo3,2-b carbazolederivatives.2. Investigating the transport mechanism of threeoligothiophene-diketopyrrolopyrrole (T-DPP) derivatives. The results show thatquinoidal molecule1which has dicyanovinyl has lower the lowest unoccupiedmolecular orbital (LUMO) energy level and larger adiabatic electron affinity (EAa)comparing with quinoidal2which has monocyanovinyl as terminal groups, signifying that to increase the extent of quinoid could improve the stability of the molecules inthe air. Moreover, quinoidal molecules1and2have lower LUMO energy level, largerEAaand electron transfer integral (Ve) comparing than aromatic molecule3, whichindicates that quinoidal T-DPP derivatives are more in favor of electron than holetransport compared with their aromatic ones. Thus, constructing quinoidalarchitecture was also an effective way to design n-type transport materials besides theconventional idea that introducing electron-withdrawing groups.