[Effect of temperature and applied voltage on the recombination efficiency in double layer organic light emitting diodes].

In this paper, the theoretical model of recombination was presented and the effect of temperature and applied voltage on the recombination efficiency was investigated in double layer organic light-emitting diodes: ITO/PPV/PBD/Ca. At lower applied voltage, two peaks have been observed in the curve of recombination efficiency vs. temperature. With increasing voltage, the two peaks shifted toward each other, and at voltage around 9 V the two peaks converged. These phenomena were attributed to the excited deep and shallow trap levels and the change of recombination zone. In the Frenkel exciton model, the temperature dependence of the quantum efficiency depended on the carriers mobilities and carriers densities. The carriers mobilities increased with decreasing temperature, while the carriers densities decreased with decreasing temperature. Therefore, a peak in the curve of quantum efficiency vs. temperature was expected in the model. The high-temperature peak originated due to radiative recombination of the deep trap levels, but the low-temperature peak due to shallow ones. On the other hand, as the voltage increased, the recombination zone would be changed, which had some effects on the recombination efficiency. Some experiments proved our theoretical prediction.