Hole transport and electrical properties in polyspirobifluorene with copolymerized hole transport units

摘要

The hole transport and electrical properties in blue light-emitting polyspirobifluorene (PSF) with copolymerized N, N, N, N tetraaryldiamino biphenyl (TAD) hole transport units are investigated. It is shown that the temperature dependent and TAD concentration dependent current density versus voltage characteristics of PSF hole-only devices can be accurately described by using our recently introduced improved mobility model based on both the Arrhenius temperature dependence and non-Arrhenius temperature dependence. For the light-emitting diodes based on PSF with 0% and 5% TAD units, it is found that the boundary carrier density has an important effect on the current density versus voltage characteristics. Too large or too small values of the boundary carrier density lead to incorrect current density versus voltage characteristics. In order to reach the same current density at the same boundary carrier density, the stronger electric field and corresponding larger voltage are needed at 5% TAD concentration than that of 0% TAD concentration. In addition, it is found that the numerically calculated carrier density is a decreasing function of the distance from the interface, and the numerically calculated electric field is an increasing function of the distance from the interface. Both the maximum of carrier density and the minimum of electric field appear near the interface.