Harvesting Excitons Via Two Parallel Channels for Efficient White Organic LEDs with Nearly 100% Internal Quantum Efficiency: Fabrication and Emission-Mechanism Analysis
Harvesting Excitons Via Two Parallel Channels for Efficient White Organic LEDs with Nearly 100% Internal Quantum Efficiency: Fabrication and Emission-Mechanism Analysis
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DOI：
10.1002/adfm.200800918
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发表时间：
2009-01-09
影响因子：
19
通讯作者：
Wang, Fosong
中科院分区：
文献类型：
--
作者：
Wang, Qi;Ding, Junqiao;Wang, Fosong
通过引入两种磷光染料，即铱（III）[双（4，6-二氟苯基）-吡啶并-N，C-2 ']吡啶甲酸酯（Flrpic）用于蓝色发射和双（2-（9，9-二乙基-9H-芴-2-基）-1-苯基-1H-苯并咪唑-N，C-3）铱（乙酰丙酮化物）（（fbi）（2）Ir（acac）），用于橙子发射，进入单能阱状发射层，展示了具有优异颜色稳定性的极高效率的白色有机发光二极管（WOLED）。该器件的前视峰值功率效率为42.5lmW-1，对应的外量子效率为19.3%，电流效率为52.8cdA（-1）。系统研究了掺杂剂、基质和掺杂基质薄膜的物理化学性质（包括吸收光谱、光致发光光谱和激发光谱）、瞬态光致发光光谱、电流密度-电压特性和温度依赖的电致发光光谱，由此得出结论：Flrpic和（fbi）（2）Ir（acac）的发射性质分别为：主-客体能量转移和直接激子形成过程。这两个平行的路径用于将全部激子引导到两种掺杂剂，大大减少了不利的能量损失。值得注意的是，多功能橙子掺杂剂（fbi）（2）Ir（acac）（用作空穴捕获位点或电子传输通道）的引入对于这一概念是必不可少的，因为它可以改善电荷平衡并加宽复合区。基于这一独特的工作模型，详细研究了这种WOLED的轻微色移。定量证明，橙色掺杂位点上的空穴捕获与发射层上不受干扰的空穴传输之间的竞争是真正的原因。此外，计算了（fbi）（2）Ir（acac）位置上的空穴捕获分数随电压的变化，结果表明，随着驱动电压的增加，橙子掺杂的空穴捕获效应降低，导致橙子发射的降低.
By incorporating two phosphorescent dyes, namely, iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C-2']picolinate (Flrpic) for blue emission and bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1 H-benzoimidazol-N,C-3) iridium(acetylacetonate) ((fbi)(2)Ir(acac)) for orange emission, into a single-energy well-like emissive layer, an extremely high-efficiency white organic light-emitting diode (WOLED) with excellent color stability is demonstrated. This device can achieve a peak forward-viewing power efficiency of 42.5 lm W-1, corresponding to an external quantum efficiency (EQE) of 19.3% and a current efficiency of 52.8 cd A(-1). Systematic studies of the dopants, host and dopant-doped host films in terms of photophysical properties (including absorption, photoluminescence, and excitation spectra), transient photoluminescence, current density-voltage characteristics, and temperature-dependent electroluminescence spectra are subsequently performed, from which it is concluded that the emission natures of Flrpic and (fbi)(2)Ir(acac) are, respectively, host-guest energy transfer and a direct exciton formation process. These two parallel pathways serve to channel the overall excitons to both dopants, greatly reducing unfavorable energy losses. It is noteworthy that the introduction of the multifunctional orange dopant (fbi)(2)Ir(acac) (serving as either hole-trapping site or electron-transporting channel) is essential to this concept as it can make an improved charge balance and broaden the recombination zone. Based on this unique working model, detailed studies of the slight color-shift in this WOLED are performed. It is quantitatively proven that the competition between hole trapping on orange-dopant sites and undisturbed hole transport across the emissive layer is the actual reason. Furthermore, a calculation of the fraction of trapped holes on (fbi)(2)Ir(acac) sites with voltage shows that the hole-trapping effect of the orange dopant is decreased with increasing drive voltage, leading to a reduction of orange emission.