Xu Xue-mei, Peng Jing-cui, Li Hong-jian, Qu Shu, Zhao Chu-jun
Department of Applied Physics, Hunan University, Changsha 410082, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2004 Jan;24(1):12-4.
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.
本文提出了复合的理论模型，并在双层有机发光二极管ITO/PPV/PBD/Ca中研究了温度和外加电压对复合效率的影响。在较低的外加电压下，复合效率与温度的曲线中观察到两个峰值。随着电压升高，两个峰值相互靠近，在约9V的电压下两个峰值会合。这些现象归因于激发的深陷阱能级和浅陷阱能级以及复合区域的变化。在弗伦克尔激子模型中，量子效率的温度依赖性取决于载流子迁移率和载流子密度。载流子迁移率随温度降低而增加，而载流子密度随温度降低而减小。因此，在该模型中，量子效率与温度的曲线中预期会出现一个峰值。高温峰值源于深陷阱能级的辐射复合，而低温峰值源于浅陷阱能级的辐射复合。另一方面，随着电压升高，复合区域会发生变化，这对复合效率有一定影响。一些实验证明了我们的理论预测。
