Langevin and Trap-Assisted Recombination in Phosphorescent Organic Light Emitting Diodes
Langevin and Trap-Assisted Recombination in Phosphorescent Organic Light Emitting Diodes
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DOI：
10.1002/adfm.201303453
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发表时间：
2014-08-06
影响因子：
19
通讯作者：
Kim, Jang-Joo
中科院分区：
文献类型：
--
作者：
Lee, Jeong-Hwan;Lee, Sunghun;Kim, Jang-Joo
利用扩散电流区的电流-电压-亮度特性，沿着测量了小分子磷光有机电致发光器件（PhOLED）的瞬态电致发光和电容，研究了双分子和陷阱辅助复合机理.研究了两种不同的PhOLED，一种具有单一主体，4，4-双（咔唑-9-基）联苯，另一种具有激基复合物形成共主体。陷阱辅助复合与大量的陷阱电荷是占主导地位的PhOLED与单一的主机，因为主机和掺杂状态之间的大的能隙。相比之下，双分子朗之万复合在PhOLED中占主导地位，其中激基复合物形成共主体，其中磷光染料掺杂在共主体中。结果，共主体系统中的累积电荷密度低于单一主体发射层中的累积电荷密度，导致接近理论极限的高效率，具有极低的效率滚降。
Bimolecular and trap-assisted recombination mechanisms are investigated in small molecule-based phosphorescent organic light emitting diodes (PhOLEDs) using the current-voltage-luminance characteristics in the diffusion current region, along with transient electroluminescence and capacitance measurements. Two different PhOLEDs, one with a single host, 4,4-Bis(carbazol-9-yl)biphenyl, and the other with an exciplex-forming co-host, are studied. Trap-assisted recombination with a large number of trapped charges is dominant in the PhOLED with the single host because of the large energy gap between the host and the dopant state. In contrast, bimolecular Langevin recombination is dominant in the PhOLED with the exciplex forming co-host, where a phosphorescent dye is doped in the co-host. As a result, the accumulated charge density is lower in the co-host system than in the single host emission layer, leading to high efficiency that approaches the theoretical limit, with an extremely low efficiency roll-off.