Theoretical characterization of hole mobility in N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine

Density-functional theory (DFT) and Marcus charge transport theory were employed to investigate the hole transport property of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) which is a prototype of good hole-transporting materials. Using an incoherent transport model we calculated its hole mobility (μ). Both reorganization energy and electronic coupling, especially the electronic couplings are considered and calculated in detail. The factors influencing its electronic coupling are revealed. It has high hole transport efficiency (μ = 1.26 × 10⁻² cm²/(V s)) and the reason was explained in terms of the spatial extent of the frontier orbitals.