Modelling temperature dependent current-voltage characteristics of an MEH-PPV organic light emitting device

We present results from a device model in which the current-voltage (I-V) characteristics of an ITO/MEH-PPV/Al organic light emitting device have been simulated over a range of temperatures by fitting the mobilities and barrier heights. Good agreement with experimental data has been achieved at temperatures of 200-300 K at bias voltages exceeding 2 V, but there are some shortcomings of the model at lower temperatures. We have found that a discrete trap level in the simulated device improved the fit,of the simulated I-V data in the low field regime at high temperatures. It has also been noted in the experimental data that cooling the device led to improved efficiency, with the ratio of light output to device current increasing by a factor of approximately 50 times. when the device was cooled from 300 to 10 K. The model exhibited increased efficiency upon cooling, provided the electron barrier height, phi(bn), was decreased at a greater rate than the hole barrier height, phi(bp).