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采用瞬态EL和延迟EL测试方法研究磷光掺杂体系的内部发光过程
Research on the emission pro cess of dop ed PhOLED by transient EL and delay luminescence measurement
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摘要: 有机磷光发光二极管(OLED)因为理论内量子效率能达到100%而成为研究热点，但是至今有机磷光OLED器件发光机理及过程仍然不完全清楚，需进一步研究。本文中搭建了一套瞬态电致发光和延迟电致发光的测量系统，并首次综合运用瞬态电致发光和延迟电致发光测量来探测有机磷光OLED 器件发光层内部电荷载流子的运动，从而分析研究其内部发光过程及机理。研究中首先制备了一种高效红色磷光材料(pbt)2Ir(acac)衍生物(Irf)掺杂荧光材料作为发光层的器件，对其进行了瞬态EL测量，发现当驱动脉冲信号撤销时瞬态发光强度会突然出现一个瞬时过冲现象(transient overshoot)，通过实验分析证实这个发光的瞬时过冲是由于发光层内部电子和空穴累积造成的，还证实了在发光层与空穴传输层界面存在空穴的累积。通过延迟电致发光的研究发现在这种掺杂体系中发光主要来自于客体材料Irf的直接俘获电子空穴复合发光，而不是来自于主客体之间的能量传递，器件中的空穴传输发生在客体材料Irf上，而电子传递则主要在主体材料TAZ上。同时还发现空穴注入是整个掺杂体系中重要的影响因素。Abstract: The organic phosphorescent OLED (PhOLED) has been widely studied because its inner quantum efficiency can reach 100%, but there has been much debate about the internal luminescence mechanism and process, mainly because they are explained using the luminescence theory of inorganic LED. In this paper, we set up a transient electroluminescence (EL) and delay EL measurement system, and for the first time as far as we know use this measurement system to study the internal luminescence mechanism and process of PhOLED. In these studies we first fabricate a PhOLED which uses a kind of new efficient red-emitting iridium(III) complexes (Bis[2-(9, 9-dimethyl-9H-flouren-2-yl) benzothiazolato-N, C2’] iridium(III) (acetylacetonate)) doped with TAZ as the emitting layer. From the results, we find that there exists an overshoot at the end edge of the driving pulse; through the research we find that this is reasonable for the holes and electrons to accumulate in the object materials Irf and host TAZ, respectively. We also find that at the interface between host transfer layer and emission layer there exist a large number of holes. Through the delay luminescence measurement, we have proved that the emission of this doped system mainly comes from the directly trapped holes and electrons in Irf, and then excitons are formed.
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