Highly Efficient Nondoped Green Organic Light-Emitting Diodes with Combination of High Photoluminescence and High Exciton Utilization

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• 作者：Chu Wang ; Xianglong Li ; Yuyu Pan ; Shitong Zhang ; Liang Yao ; Qing Bai ; Weijun Li ; Ping Lu ; Bing Yang ; Shijian Su ; Yuguang Ma
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：February 10, 2016
• 年：2016
• 卷：8
• 期：5
• 页码：3041-3049
• 全文大小：529K
• ISSN：1944-8252

文摘

Photoluminescence (PL) efficiency and exciton utilization efficiency are two key parameters to harvest high-efficiency electroluminescence (EL) in organic light-emitting diodes (OLEDs). But it is not easy to simultaneously combine these two characteristics (high PL efficiency and high exciton utilization) into a fluorescent material. In this work, an efficient combination was achieved through two concepts of hybridized local and charge-transfer (CT) state (HLCT) and “hot exciton”, in which the former is responsible for high PL efficiency while the latter contributes to high exciton utilization. On the basis of a tiny chemical modification in TPA-BZP, a green-light donor–acceptor molecule, we designed and synthesized CzP-BZP with this efficeient combination of high PL efficiency of η_PL = 75% in the solid state and maximal exciton utilization efficiency up to 48% (especially, the internal quantum efficiency of η_IQE = 35% substantially exceed 25% of spin statistics limit) in OLED. The nondoped OLED of CzP-BZP exhibited an excellent performance: a green emission with a CIE coordinate of (0.34, 0.60), a maximum current efficiency of 23.99 cd A^–1, and a maximum external quantum efficiency (EQE, η_EQE) of 6.95%. This combined HLCT state and “hot exciton” strategy should be a practical way to design next-generation, low-cost, high-efficiency fluorescent OLED materials.