Injection, transport and recombination in organic light-emitting diodes

Efficient conversion of electrical to optical energy in organic light-emitting diodes (OLEDs) depends on balancing the flux of holes injected at the anode with that of electrons at the cathode. In this paper, we discuss several concepts related to optimizing the power efficiency of OLEDs, and put them in the context of analytic and numerical models for OLED operation. A simple argument is used to relate the charge injection rate from each electrode to measurable properties of the organic layer, deriving the equivalent of the Richardson-Dushman equation for the metal-organic interface. We discuss the role of charge density in dictating the importance of both space charge effects and recombination. These ideas are illustrated with experimental data from device structures which exemplify the various types of behavior predicted.