Yang Shao-Peng, Zhang Xue-Feng, Zhao Su-Ling, Xu Zheng, Zhang Fu-Jun, Yang Ya-Ru, Li Qing, Pang Xue-Xia
College of Physics Science and Technology, Hebei University, Baoding 071002, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2008 Mar;28(3):512-6.
With the increasing development of organic light emitting devices (OLED), interest in the mechanisms of charge carrier photogeneration, separation, transport and recombination continues to grow. Electromodulation of photoluminescence has been used as an efficient probe to investigate the evolution of primary excitation in all electric field. This method can provide useful information on carrier photogeneration, the formation and dissociation of excitons, energy transfer, and exciton recombination in the presence of electric field. The operation of OLED brings electrons and holes from opposite electrodes and generates singlet and triplet excitons. However, triplet excitons are wasted because a radiative transition from triplets is spin-forbidden. Spin statistics predicts that singlet-to-triplet ratio is 1 : 3 in organic semiconductors. One way to harvest light from triplet excitons is to use phosphorescent materials. These materials incorporate a heavy metal atom to mix singlet and triplet states by the strong spin-orbit coupling. As a result, a spin forbidden transition may occur allowing an enhanced triplet emission. Among phosphorescent materials, Ir(ppy)3 has attracted much attention because of its short triplet lifetime to minimize the triplet-triplet annihilation. High quantum efficiencies have been obtained by doping organic molecules and in polymers with Ir(ppy)3. In the present paper, the photoluminescence and electroluminescence spectra of Ir(ppy)3 doped PVK film are measured at room temperature. The device structure is ITO/PEDOT : PSS/PVK Ir(ppy)3/BCP/Alq3/Al. The results show that the luminescence capabilities of devices are different when the concentration of Ir(ppy)3 is different. When the concentration of Ir(ppy)3 is suitable, the luminescence of PVK is lower but that of Ir(ppy)3 is stronger relatively, indicating that the energy transfer from the host materials to the guest materials is sufficient. It is concluded that the device with 5% of Ir(ppy)3 has the best luminescence properties according to its light power-current-voltage curve, meaning that the best concentration of Ir(ppy)3 in such kind of device is 5%.
随着有机发光器件（OLED）的不断发展，人们对电荷载流子的光生、分离、传输和复合机制的兴趣持续增长。光致发光的电调制已被用作一种有效的探针，以研究全电场中初级激发的演变。该方法可以提供有关电场存在下的载流子光生、激子的形成和解离、能量转移以及激子复合的有用信息。OLED的工作从相反电极注入电子和空穴，并产生单重态和三重态激子。然而，三重态激子被浪费了，因为从三重态的辐射跃迁是自旋禁阻的。自旋统计预测，在有机半导体中，单重态与三重态的比例为1:3。从三重态激子中获取光的一种方法是使用磷光材料。这些材料包含一个重金属原子，通过强自旋轨道耦合混合单重态和三重态。结果，可能会发生自旋禁阻跃迁，从而增强三重态发射。在磷光材料中，Ir(ppy)3因其短的三重态寿命可使三重态-三重态湮灭最小化而备受关注。通过用Ir(ppy)3掺杂有机分子和聚合物，已获得了高量子效率。在本文中，在室温下测量了Ir(ppy)3掺杂PVK薄膜的光致发光和电致发光光谱。器件结构为ITO/PEDOT:PSS/PVK Ir(ppy)3/BCP/Alq3/Al。结果表明，当Ir(ppy)3的浓度不同时，器件的发光能力也不同。当Ir(ppy)3的浓度适当时，PVK的发光较低，但Ir(ppy)3的发光相对较强，这表明从主体材料到客体材料的能量转移是充分的。根据其光功率-电流-电压曲线得出，含有5% Ir(ppy)3的器件具有最佳的发光性能，这意味着在这种器件中Ir(ppy)3的最佳浓度为5%。
