Diffusion-controlled charge injection model for organic light-emitting diodes

We present an compact model to describe the charge injection for organic light- emitting diodes. By identifying a critical distance where the concentration of carriers in the extended states equals that of the trapped carriers, we obtain a model for the injection current, which links the drift- diffusion and the multiple- trapping theories. This model yields the injection current as a function of electric field, temperature, and barrier height between metal and organic semiconductor. Good agreement with recent experimental data is observed. The effect of the field- dependent mobility on the injection current is also discussed. (C) 2007 American Institute of Physics.