Theory Of Charge Transport Properties Of Organic Semiconductor Materials Research

In the application of field-effect transistors, light-emitting diodes, and photovoltaic cells, organic materials possess great potentials. The charge transport mechanism in organic materials has been studied for many years. Charge mobility is the most important issue for organic semiconductors. Basing on the first-principles calculations, the charge mobility were calculated within the Marcus electron transfer theory coupled with random walk simulation。(1) We calculate the hole mobilities for a,a-bis(dithieno[3,2-b:2,3-d]thiophene) (BDT) and trans-1,2-[dithieno(2,3-b:3'2'- d)thiophenes]ethane(TDT), The first-principles DFT calculations show that the hole mobility in BDT is nealy 15 times of that in TDT. The crystal packing effects on the frontier orbital coupling are found to be essential to understand such differences in transport behaviors.(2)We calculate the electron and hole mobilities for prototypical polycyclic hydrocarbon molecules, perylothiophene (pet) and benzo(g,h,i)-perylene (bnpery) The calculations show that the hole mobility is about an order of magnitude higher than the electron mobility in pet. However, we find that for bnpery, the electron and hole transports are balanced, namely, very close in mobility, indicating the possible application in light-emitting field-effect transistor.(3) We calculate the electron and hole mobilities for Phthalocyanines molecules. The calculations show that the hole mobility much larger than electron mobility in Phthalocyanines. As the substitute two hydrogen atoms by metal, the hole transport properties have been improved.