Novel insights in the electron and hole mobility in organic semiconductors used in OLEDs for lighting applications.

摘要

The development of organic light-emitting diodes (OLEDs) for lighting applications is hampered by a lack of understanding of the carrier mobility which determines the electric conduction in organic materials. In order to rationally design state-of-the-art OLEDs, which consist of multiple organic layers with different functions, a proper understanding of the carrier mobility is of crucial importance. In earlier work, only a field and temperature dependence of the mobility was assumed. Recent developments show that the effect of carrier concentration on the mobility is very important [1,2]. Furthermore, distinguishing between hopping transport in between molecules with a random Gaussian distributions of energy levels and hopping in between molecules with positionally correlated energy levels is of crucial importance for understanding transport in multilayer devices. We find that current (J) versus voltage (V) characteristics in polymer OLED materials can be described best by a model based on random Gaussian disorder whereas the small-molecule materials studied (hole transport in a-NPD and electron transport in BAlq and Alq3) are characterized more convincingly by the correlated disorder model.