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White organic light-emitting diodes (WOLEDs) have drawn considerable attention for next-generation lighting and display applications owing to their remarkable advantages. Phosphorescent OLED technology is crucial to realize high-efficiency white OLEDs because phosphorescent emitters enable to achieve almost 100% internal quantum efficiency (IQE) by harvesting all the excitons of 75% of triplets and 25% of singlets. However, an efficiency roll-off at high-brightness and a shift in color under various operation biases remains challenges. With the goal towards commercial applications, it requires WOLEDs should simultaneously realize high efficiency at high-brightness region over 1000 cd/m2 and good color stability over a wide electroluminescent range. In this paper, we first investigated the energy transfer process between the blue-emitting Bis (3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium (III) (Firpic) and the orange emitting Iridium (III) bis(4-(4-tert-butylphenyl)thieno[3,2-c]pyridinato-N,C2')acetylacetonate (PO-01-TB), in addition to the behavior of the carrier trapping in the phosphorescent OLEDs with double emissive layers. Then we successfully fabricated phosphorescent WOLED with multiple emissive layers. The resulting phosphorescent WOLED achieves the maximum forward-viewing current efficiency (CE) of 34.6 cd/A and external quantum efficiency (EQE) of 13.5%, and the CE and the EQE remain 33.9 cd/A and 13.3% at 1000 cd/m2, respectively, indicating that the WOLED exhibits low efficiency roll-off. Furthermore, the WOLED shows very stable white emission with small Commission Internationale de L’Eclairage (CIE) coordinate varying range of (0.016, 0.011) from 1000 to 10000 cd/m2. The results provide a promising avenue to simultaneously achieve high efficiency, lower the efficiency roll-off at high brightness and color-stability for phosphorescent WOLEDs by carefully designing the device architecture to redistribute the charge carriers and excitons in the recombination zone.
1. 引 言
白色有机电致发光器件(WOLEDs)因其超薄、制造成本低、效率高、视角宽、响应速度快以及可柔性显示等优点, 成为最有应用前途的新一代平板显示和固态照明技术[1-6]. 由于磷光发光材料在常温下能同时利用电激发产生的单线态和三线态激子辐射发光, 理论上磷光OLEDs可实现接近100%的内量子效率[7-12]. 但是, 长寿命的三线态激子及其长距离的扩散引起的三线态-三线态湮灭(TTA)和三线态-极化子淬灭(TPQ) [13,14], 导致磷光WOLEDs在高亮度下发光效率的滚降(roll-off) [15]. 为了抑制TTA和TPQ效应, 人们通过选择合适的主客体材料、平衡载流子注入和传输及扩展载流子复合区域等方法, 使磷光WOLEDs在高亮度下获得了较高的发光效率[9,16-20]. 此外, 由于多发光层结构WOLEDs通常至少有两个发光层, 受载流子俘获、在电场诱导下有机材料迁移率的改变及载流子复合区移动等因素的影响, 易引起随器件内部电场变化的发光颜色漂移[21-23].
为了达到节能环保的商业化应用目标, 在发光亮度超过1000 cd/m2时, WOLEDs在具有高发光效率的同时还应具有高的发光颜色稳定性[9,22]. Liu等[24]报道的单发光层结构磷光WOLED在亮度为1000 cd/m2时电流效率为43.6 cd/A; 亮度从1000 cd/m2增至12000 cd/m2, 其CIE色度坐标变化量ΔCIE为(0.020, 0.005). Yang等[25]制备了以激基复合物为主体的多发光层结构磷光WOLED, 其亮度为1000 cd/m2时的电流效率为44.5 cd/A; 亮度从1000 cd/m2增至15000 cd/ m2, 其CIE色度坐标变化量ΔCIE为(0.006, 0.010), 上述两种磷光WOLED的发光层均采用三种材料掺杂的结构, 制备工艺复杂. 此外, 俞浩健等[26]制备了基于超薄发光层及双极性混合间隔层的四波段磷光WOLED, 在亮度为1000 cd/m2时器件的电流效率为14.8 cd/A; 亮度从465 cd/m2增至15950 cd/ m2, 其CIE色度坐标变化量ΔCIE为(0.023, 0.012).
本文采用蓝色磷光材料Bis (3, 5-difluoro-2-(2-pyridyl) phenyl- (2-carboxypyridyl) iridium (III) (Firpic)和橙色磷光材料Iridium (III) bis (4-(4-tert- butylphenyl) thieno[3,2-c]pyridinato-N, C2') acetylacetonate (PO-01-TB)分别作为发光客体, 分别以空穴传输材料1, 3-Bis (carbazol-9-yl) benzene (mCP)和电子传输材料1, 3, 5-Tri[(3-pyridyl)-phen-3-yl] benzene (TmPyPB)作为发光层主体, 研究了双发光层结构磷光OLEDs的发光机制和载流子传输过程. 在此基础上制备了蓝色/橙色互补色发光的多发光层结构磷光WOLED. 该器件同时实现了高亮度下的高发光效率和较宽亮度范围内稳定的白光发射, 并且制备工艺相对简单. 器件的最大电流效率和外量子效率分别为34.6 cd/A和13.5%; 亮度为1000 cd/m2时, 其电流效率和外量子效率分别为33.9和13.3%, 外量子效率滚降仅为1.5%; 亮度从1000 cd/m2增至10000 cd/m2, 其CIE色度坐标变化量ΔCIE为(0.016, 0.011).
2. 实验部分
图1为器件中所使用材料的能级图及Firpic和PO-01-TB的化学结构. PO-01-TB和Liq购自西安宝莱特光电科技公司, 其余有机材料及涂覆有ITO的玻璃基底从台湾激光科技公司购买. 有机材料的最低未占有分子轨道(lowest unoccupied molecular orbital, LUMO)和最高占有分子轨道(highest occupied molecular orbital, HOMO)能级以及三线态能量(ET)均从已发表的文献中获得. 所有OLEDs均采用方块电阻约为15 Ω/sq的ITO作为阳极, 4, 4', 4"-Tris (N- 3-methylphenyl-N-phenyl-amino) triphenylamine (m-MTDATA)和N, N'-Bis (naphthalen-1-yl)-N, N'-bis(phenyl)-benzidine (NPB)分别作为空穴注入层和空穴传输层, 非掺杂的mCP作为激子阻挡层, TmPyPB兼作电子传输层和空穴阻挡层, 8-Hydroxyquinolinolato-lithium (Liq)/Al为复合阴极.
图 1 器件中所使用材料的能级示意图及Firpic和PO-01-TB的化学结构Fig. 1. Energy level diagram of materials used in the devices, and the chemical structures of Firpic and PO-01-TB.所有已刻蚀的ITO玻璃基底经由丙酮、乙醇和去离子水依次循环清洗、超声三次, 每次超声时间为10 min, 然后用高速N2吹干基底表面, 最后在温度120 oC恒温真空干燥箱中干燥30 min. 将预处理后的基底移入多源有机分子气相沉积系统的腔室内. 样品室内的真空度优于4 × 10–4 Pa. 各有机功能层依次蒸镀在ITO基底之上, 蒸镀速率为0.1—0.2 nm/s (Liq的蒸镀速率为0.02 nm/s), 之后覆盖掩膜版并蒸镀阴极Al (~0.5 nm/s). 样品制备过程中, 采用FTM-V型石英晶体膜厚监测仪对薄膜厚度进行在线监测. ITO层与阴极Al交叉覆盖形成的发光单元面积为4 mm2. 器件的光电性能采用由电压电流源(Keithley 2400)和光谱扫描光度计(PR655)所构成的测试系统进行测量. 外量子效率(EQE)采用Tanaka等[27]提出的方法由电流密度、发光亮度和电致发光光谱计算得出. 有机薄膜的吸收光谱和光致发光光谱(PL)分别采用紫外-可见光分光光度计(UV 1700, Shimadzu)和荧光光谱仪(Horiba JY Fluorolog-3)进行测量. 器件均未封装且未加光输出耦合装置, 所有测量均在室温条件下大气环境中进行.
3. 结果与讨论
3.1 双发光层结构OLEDs
选用磷光材料Firpic和PO-01-TB分别作为器件蓝光层和橙光层的发光客体, 制备了双发光层结构的磷光OLEDs. 图2为器件A—D的结构示意图. 由于Firpic具有较高的三线态能量(2.62 eV), 为了防止Firpic至其主体的反向能量传递而导致的非辐射能量损失, 选用高三线态能量(2.9 eV)的空穴传输材料mCP作为其主体. 器件A橙光层与蓝光层的主体相同, 而器件B则选用电子传输材料TmPyPB作为橙光层的主体. 此外, mCP具有较高空穴迁移率(~3.2 × 10-4 m2/Vs), 大约是其电子迁移率的1.6倍[28], TmPyPB具有较深的HOMO能级(6.7 eV)和高的电子迁移率(~1.0 × 10–3 m2/Vs) [29], 可以使空穴和电子积累在mCP/TmPyPB界面处. 同时, 由位于发光层两侧高三线态能量的非掺杂mCP和TmPyPB(2.78 eV)层形成的激子限制结构, 能够将激子有效限制在发光层中. 为了研究Firpic与PO-01-TB之间的能量传递问题, 在器件A和B的蓝光层与橙光层之间分别插入3 nm厚的非掺杂mCP和TmPyPB间隙层, 对应器件分别为C和D. 一般Dexter和Förster能量传递的半径均不超过3 nm [30], 3 nm厚的间隙层可阻挡从Firpic到PO-01-TB的能量传递.
通常OLEDs中有两种主要的激子形成机制, 即能量传递和载流子俘获[31,32]. Förster能量传递的效率与发光层主体和客体之间的分子轨道重叠程度密切相关. 为了研究器件A—D的电致发光过程, 我们在石英基底上分别制备了mCP(20 nm), Firpic(20 nm)和PO-01-TB(20 nm)薄膜, 测量了常温下薄膜的吸收光谱和PL谱. 如图3所示, Firpic和PO-01-TB的主发光峰分别位于470 nm和558 nm. 在350 nm到450 nm范围内Firpic有较宽的吸收谱, 与mCP的PL谱有较大范围的重叠区域, 表明从mCP至Firpic可实现有效的能量传递. 另外, PO-01-TB的吸收光谱在430—550 nm范围内与Firpic的PL谱也有重叠, 说明Firpic的能量还可以进一步传递给PO-01-TB.
图 3 薄膜的紫外-可见光吸收光谱和光致发光光谱Fig. 3. UV-vis absorption and PL spectra of the deposited films.图4给出了器件A—D的电致发光光谱. 四种器件的光谱均呈现出位于468 nm处较强的Firpic蓝光发射, 而位于556 nm处PO-01-TB的相对发光强度则存在一定差别. 器件B橙光最强, 并且间隙层对器件B橙光相对强度减弱的影响明显大于器件A, 可见器件B中经由Firpic能量传递产生的PO-01-TB激子比例较大, 这是该器件橙光较强的主要因素. 该实验结果表明, 器件A—D中载流子复合区位于mCP/TmPyPB的界面处. 器件B中的橙光层紧邻载流子复合区, 蓝光层中Firpic激子能量可以有效传递给相邻橙光层中的PO-01-TB, 呈现出较强的橙光发射; 而器件A中橙光层与载流子复合区的距离较远, 在mCP:PO-01-TB/mCP:Firpic界面附近Fipic激子的密度较低, 使传递给PO-01-TB能量的Firpic激子数量较少, 导致PO-01-TB发光强度较弱. 另外, 值得注意的是含间隙层器件B和D的光谱中仍存在PO-01-TB的辐射发光.
图 4 器件A−D的归一化电致发光光谱(电流密度为20 mA/cm2)Fig. 4. Normalized EL spectra of devices A−D at 20 mA/cm2为了研究器件A和B发光层中客体发光材料的电学特性, 制备四种单空穴(hole-only)器件H1—H4和四种单电子(electron-only)器件E1—E4, 其结构如图5(a)所示. 分别对比图5(b)和图5(c)中单空穴和单电子器件电流密度-电压曲线可以发现, mCP:Firpic中客体Firpic既未俘获空穴, 也未见明显俘获电子的现象, 表明器件A—D的mCP:Firpic层中Firpic激子应来自其主体mCP的能量传递, 而非Firpic的载流子俘获. 此外, 对于PO-01-TB作为客体的掺杂结构, PO-01-TB在mCP:PO-01-TB中对空穴和电子均具有俘获作用, 而TmPypB:PO-01-TB中PO-01-TB仅对空穴具有较强俘获作用. 上述实验结果主要是由于在mCP:PO-01-TB中PO-01-TB的HOMO和LUMO能级均陷在mCP的对应能级之中, 使其易于成为空穴或电子的陷阱; 在TmPypB:PO-01-TB中PO-01-TB与TmPypB高达1.7 eV的HOMO能级也使其成为较深的空穴陷阱点, 表现出较强的空穴俘获作用. 因此, 含间隙层器件B和D中仍然存在的橙光发射应主要来自客体PO-01-TB俘获载流子形成的激子辐射发光.
图 5 (a) 单空穴器件H1−H4和单电子器件E1−E4的结构示意图; (b) 单空穴器件H1−H4和(c) 单电子器件E1−E4的电流密度-电压关系特性曲线Fig. 5. (a) Structure schematic of hole-only devices H1−H4 and electron-only devices E1-E4; current density-voltage characteristics of (b) hole-only devices H1−H4 and (c) electron-only devices E1−E4.图6为器件A和B在不同工作电压下的归一化电致发光光谱. 随工作电压升高, 器件A的橙光先减弱后增强; 而器件B则相反, 且橙光相对强度变化幅度较大. 该实验结果反映了发光层中激子分布随器件内部电场的变化情况. 对于器件A, 电压从6 V增至9 V的过程中, mCP/TmPyPB界面处的空穴密度增加幅度较大, 使mCP:Firpic层中Firpic激子的相对数量有所增加, 导致橙光强度有所减弱; 随电压进一步升高, 器件内部电场增强, mCP的电子迁移率增大, 使向阳极一侧传输的电子密度增加幅度变大, 较多的电子传输至mCP:PO-01-TB层, 使PO-01-TB激子的相对数量有所增加, 导致橙光强度有所增强. 与器件A相似, 器件B橙光相对强度随电压变化也遵循低电场下受mCP/TmPyPB界面处空穴密度变化影响, 高电场下受电子密度变化影响的规律, 其相对强度变化幅度较大主要归因于橙光层TmPyPB:PO-01-TB紧邻载流子复合区, PO-01-TB激子数量受mCP/TmPyPB界面处空穴密度的影响较大.
图 6 (a)器件A和(b)器件B在不同电压下的归一化电致发光光谱; 插图为波长在540−570 nm之间的光谱放大图Fig. 6. Normalized EL spectra of devices A(a) and B(b) with different voltage. Inset is the corresponding enlarged spectra at 540−570 nm.图7为器件A和B的亮度-电压及外量子效率-亮度关系特性曲线. 在工作电压为10 V时, 器件A和B的亮度分别为442 cd/m2和1823 cd/m2, 对应的CIE色度坐标分别为(0.209, 0.352)和(0.302, 0.412), 前者为蓝绿光, 后者发光颜色接近白光区. 另外, 当亮度为1000 cd/m2时, 器件A和B的外量子效率分别为6.1%和11.7%, 分别滚降了16.4%和1.7%.
图 7 器件A和B的亮度-电压关系特性曲线; 插图为器件A和B的外量子效率-亮度关系特性曲线Fig. 7. Luminance-voltage characteristics of devices A and B. Inset is EQE-luminance characteristic of devices A and B3.2 多发光层结构WOLEDs
为了充分利用电激发产生的激子, 同时提高器件发光颜色稳定性, 将mCP:Firpic置于mCP:PO-01-TB和TmPyPB:PO-01-TB之间, 形成三明治结构的发光层, 并通过改变Firpic的掺杂浓度, 制备了多发光层结构的WOLEDs. 图8(a)给出了器件W1和W2的能级结构和发光层中激子的复合过程. 器件W1和W2中Firpic的掺杂浓度分别为6%和4%. 如图8(b)所示, 在工作电压为10 V时, 器件W1和W2的亮度分别为2252 cd/m2和3496 cd/m2, 对应的CIE色度坐标分别为(0.315, 0.386)和(0.333, 0.397), 均位于白光区. 由图8(c)可知, 器件W1和W2的最大电流效率、外量子效率分别为29.4 cd/A, 11.8%和34.6 cd/A, 13.5%. 可见, 器件W2表现出更优的光电性能. 如表1所列, 当亮度为1000 cd/m2时, 器件W2的外量子效率为13.3%, 仅滚降了1.5%; 即使在5000 cd/m2时, 其外量子效率仍为11.7%, 滚降为13.4%.
表 1 器件A, B和器件W1, W2的电致发光性能参数Table 1. EL performance parameters of the OLEDs in our studies.Device Max EQE/CE/Luminance/(%/[cd/A]/[cd/m2]) At 1000 cd/m2 At 5000 cd/m2 EQE/CE/(%/[cd/A]) CIE/(x, y) CRI EQE/CE/(%/[cd/A]) CIE/(x, y) CRI A 7.3/16.5/8589 6.1/13.8 0.209, 0.351 44 4.2/9.6 0.215, 0.354 46 B 11.9/31.2/13890 11.7/30.8 0.303, 0.413 56 9.0/23.4 0.294, 0.408 56 W1 11.7/29.4/17260 11.4/28.3 0.320, 0.390 64 9.8/23.7 0.309, 0.383 65 W2 13.5/34.6/18340 13.3/33.9 0.342, 0.403 64 11.7/29.3 0.331, 0.395 65 
图 8 白光器件W1和W2的 (a) 能级结构和发光层中激子复合过程示意图, 蓝色虚线框为载流子复合区, S1和S0分别代表单线态能级和基态(○), T1代表三线态能级(△); (b) 亮度-电压和关系特性曲线和归一化电致发光光谱(插图); (c) 电流效率-亮度-外量子效率关系特性曲线; (d) 器件B和W2的外量子效率-电流密度关系特性曲线, 图中红线和蓝线分别为的器件B和W2拟合曲线(TTA模型)Fig. 8. (a) Energy diagram and exciton dynamics of the WOLEDs W1 and W2. S1 and T1 are respectively the singlet (○) and triplet (△) energy levels, and S0 is the ground state (○). The blue dashed box depicts the main region of carrier recombination. Luminance-voltage characteristics and the normalized EL spectra (b), and current efficiency-Luminance-external quantum efficiency characteristics (c) of the WOLEDs W1 and W2; (d) EQE-current density of the OLEDs B and W2. The red and blue lines are corresponding fitting curves based on the TTA model, respectively.通常磷光OLEDs在高亮度下的效率滚降现象与TTA, TPQ以及电场诱导的激子淬灭密切相关. 由于三线态激子的寿命较长, 且磷光OLEDs中载流子复合区的激子密度很大, TTA是导致器件效率滚降的重要因素. Baldo等[13]报道的TTA模型中外量子效率
ηTText 与电流密度J的关系为ηTTextη0=J04J(√1+8JJ0−1), (1) 式中η0为低电流密度下近似无三线态激子淬灭时的初始外量子效率, J0为ηext = η0/2时的临界电流密度. 临界电流密度J0越大, TTA的程度越低. 为了对比双发光层和多发光层结构器件随电流变化的激子淬灭程度, 分别选择器件B和W2作为研究对象, 采用TTA模型对实验数据进行了拟合, 如图8(d)所示, 该模型的拟合结果与实验数据匹配度较好, 表明TTA是引起器件B和W2激子淬灭的主导因素. 器件W2的临界电流密度(J0 ≈ 106 mA/cm2)约为器件B (J0 ≈ 72 mA/cm2)的1.5倍, 进一步表明多发光层结构降低了TTA的程度. 从图8(a)中可以看出, Firpic三线态激子能量可以传递给两侧相邻的PO-01-TB, 降低了载流子复合区中Firpic三线态激子的密度并扩展了发光区的宽度, 从而降低了TTA的程度, 减缓了器件在高亮度下发光效率的滚降. 此外, 两个橙光层中PO-01-TB的载流子俘获及Firpic能量传递的共同作用, 平衡了不同电场下WOLEDs的蓝光和橙光发射, 减弱了因器件内部电场变化而引起的发光层中激子分布变化所带来的发光颜色漂移的影响. 如图9所示, 器件W2在较宽发光亮度范围内呈现出发光颜色稳定的白光发射. 当亮度从1000 cd/m2增至10000 cd/m2过程中, CIE色度坐标从(0.342, 0.403)变化至(0.326, 0.392), 变化量仅为(0.016, 0.011), 显色指数(CRI)稳定在64—65之间.
图 9 白光器件W2的亮度从1000 cd/m2增至5000 cd/m2过程中的归一化电致发光光谱和相应CIE色度坐标及显色指数的变化Fig. 9. Normalized EL spectra and the corresponding CIE coordinates, CRI of the device W2 at brightness of 1000−5000 cd/m2.4. 总结与展望
综上所述, 我们在对双发光层结构磷光OLEDs的发光机制和载流子传输过程进行系统研究的基础上, 制备了互补色发光的多发光层结构磷光WOLED. 该器件不仅实现了高亮度下的高发光效率, 同时还实现了在较宽亮度范围内稳定的白光发射, 并且制备工艺相对简单. WOLED的最大电流效率和外量子效率分别为34.6 cd/A和13.5%; 亮度为1000 cd/m2时, 其电流效率和外量子效率分别为33.9和13.3%, 外量子效率滚降仅为1.5%; 亮度从1000 cd/m2增至10000 cd/m2的过程中, 其CIE色度坐标从(0.342, 0.403)变化至(0.326, 0.392), 变化量ΔCIE为(0.016, 0.011), 显色指数稳定在64—65之间. 该实验结果为制备达到商业化应用目标的高性能磷光WOLEDs提供了一种有效方法.
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图 1 器件中所使用材料的能级示意图及Firpic和PO-01-TB的化学结构
Figure 1. Energy level diagram of materials used in the devices, and the chemical structures of Firpic and PO-01-TB.
图 2 器件A−D的结构示意图
Figure 2. Structure schematic of devices A−D.
图 3 薄膜的紫外-可见光吸收光谱和光致发光光谱
Figure 3. UV-vis absorption and PL spectra of the deposited films.
图 4 器件A−D的归一化电致发光光谱(电流密度为20 mA/cm2)
Figure 4. Normalized EL spectra of devices A−D at 20 mA/cm2
图 5 (a) 单空穴器件H1−H4和单电子器件E1−E4的结构示意图; (b) 单空穴器件H1−H4和(c) 单电子器件E1−E4的电流密度-电压关系特性曲线
Figure 5. (a) Structure schematic of hole-only devices H1−H4 and electron-only devices E1-E4; current density-voltage characteristics of (b) hole-only devices H1−H4 and (c) electron-only devices E1−E4.
图 6 (a)器件A和(b)器件B在不同电压下的归一化电致发光光谱; 插图为波长在540−570 nm之间的光谱放大图
Figure 6. Normalized EL spectra of devices A(a) and B(b) with different voltage. Inset is the corresponding enlarged spectra at 540−570 nm.
图 7 器件A和B的亮度-电压关系特性曲线; 插图为器件A和B的外量子效率-亮度关系特性曲线
Figure 7. Luminance-voltage characteristics of devices A and B. Inset is EQE-luminance characteristic of devices A and B
图 8 白光器件W1和W2的 (a) 能级结构和发光层中激子复合过程示意图, 蓝色虚线框为载流子复合区, S1和S0分别代表单线态能级和基态(○), T1代表三线态能级(△); (b) 亮度-电压和关系特性曲线和归一化电致发光光谱(插图); (c) 电流效率-亮度-外量子效率关系特性曲线; (d) 器件B和W2的外量子效率-电流密度关系特性曲线, 图中红线和蓝线分别为的器件B和W2拟合曲线(TTA模型)
Figure 8. (a) Energy diagram and exciton dynamics of the WOLEDs W1 and W2. S1 and T1 are respectively the singlet (○) and triplet (△) energy levels, and S0 is the ground state (○). The blue dashed box depicts the main region of carrier recombination. Luminance-voltage characteristics and the normalized EL spectra (b), and current efficiency-Luminance-external quantum efficiency characteristics (c) of the WOLEDs W1 and W2; (d) EQE-current density of the OLEDs B and W2. The red and blue lines are corresponding fitting curves based on the TTA model, respectively.
图 9 白光器件W2的亮度从1000 cd/m2增至5000 cd/m2过程中的归一化电致发光光谱和相应CIE色度坐标及显色指数的变化
Figure 9. Normalized EL spectra and the corresponding CIE coordinates, CRI of the device W2 at brightness of 1000−5000 cd/m2.
表 1 器件A, B和器件W1, W2的电致发光性能参数
Table 1. EL performance parameters of the OLEDs in our studies.
Device Max EQE/CE/Luminance/(%/[cd/A]/[cd/m2]) At 1000 cd/m2 At 5000 cd/m2 EQE/CE/(%/[cd/A]) CIE/(x, y) CRI EQE/CE/(%/[cd/A]) CIE/(x, y) CRI A 7.3/16.5/8589 6.1/13.8 0.209, 0.351 44 4.2/9.6 0.215, 0.354 46 B 11.9/31.2/13890 11.7/30.8 0.303, 0.413 56 9.0/23.4 0.294, 0.408 56 W1 11.7/29.4/17260 11.4/28.3 0.320, 0.390 64 9.8/23.7 0.309, 0.383 65 W2 13.5/34.6/18340 13.3/33.9 0.342, 0.403 64 11.7/29.3 0.331, 0.395 65 
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[1] Kido J, Hongawa K, Okuyama K, Nagai K 1994 Appl. Phys. Lett. 64 815
Google Scholar
[2] Liu Y C, Li C S, Ren Z J, Yan S K, Bryce M R 2018 Nat. Rev. Mater. 3 18020
Google Scholar
[3] Ai X, Evans E W, Dong S, Gillett A J, Guo H, Chen Y, Hele T J H, Friend R H, Li F 2018 Nature 563 536
Google Scholar
[4] Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C 2012 Nature 492 234
Google Scholar
[5] Reineke S, Lindner F, Schwartz G, Seidler N, Walzer K, Lüssem B, Leo K 2009 Nature 459 234
Google Scholar
[6] Zhang X, Pan T, Zhang J, Zhang L, Liu S, Xie W 2019 ACS Photonics 6 2350
Google Scholar
[7] Baldo M A, O'Brien D F, You Y, Shoustikov A, Sibley S, Thompson M E, Forrest S R 1998 Nature 395 151
Google Scholar
[8] Zaen R, Park K M, Lee K H, Lee J Y, Kang Y J 2019 Adv. Opt. Mater. 190138 7
[9] Udagawa K, Sasabe H, Igarashi F, Kido J 2016 Adv. Opt. Mater. 4 86
Google Scholar
[10] Liu D, Deng L J, Li W, Yao R J, Li D L, Wang M, Zhang S F 2016 Adv. Opt. Mater. 4 864
Google Scholar
[11] Zhu L P, Wu Z B, Chen J S, Ma D G 2015 J. Mater. Chem. C 3 3304
Google Scholar
[12] Lee C W, Lee J Y 2013 Adv. Mater. 25 5450
Google Scholar
[13] Baldo M A, Adachi C, Forrest S R 2000 Phys. Rev. B 62 10967
Google Scholar
[14] Reineke S, Walzer K, Leo K 2007 Phys. Rev. B 75 125328
Google Scholar
[15] Giebink N C, Forrest S R 2008 Phys. Rev. B 77 235215
Google Scholar
[16] Zhao C Y, Yan D H, Ahamad T, Alshehri S M, Ma D G 2019 J. Appl. Phys. 125 045501
Google Scholar
[17] Yu Z W, Zhang J X, Liu S H, Zhang L T, Zhao Y, Zhao H Y, Xie W F 2019 ACS Appl. Mater. Interaces 11 6292
Google Scholar
[18] Wang F, Zhao Y P, Xu H X, Zhang J, Miao Y Q, Guo K P, Shinar R, Shinar O S, Wang H, Xu B S 2019 Org. Electron. 70 272
Google Scholar
[19] Maheshwaran A, Sree V G, Park H Y, Kim H, Han S H, Lee J Y, Jin S H 2018 Adv. Funct. Mater. 28 1802945
Google Scholar
[20] Lee S, Kim K H, Limbach D, Park Y S, Kim J J 2013 Adv. Funct. Mater. 23 4105
Google Scholar
[21] Gather M C, Alle R, Becker H, Meerholz K 2007 Adv. Mater. 19 4460
Google Scholar
[22] Chen S F, Wu Q, Kong M, Zhao X F, Yu Z, Jia P P, Huang W 2013 J. Mater. Chem. C 1 3508
Google Scholar
[23] Kim S H, Jang J, Lee J Y 2009 Synth. Met. 159 1295
Google Scholar
[24] Liu B Q, Wang L, Xu M, Tao H, Xia X H, Zou J H, Su Y J, Gao D Y, Lan L F, Peng J J 2014 J. Mater. Chem. C 2 5870
[25] Ying S A, Xiao S, Yao J W, Sun Q, Dai Y F, Yang D Z, Qiao X F, Chen J S, Zhu T F, Ma D G 2019 Adv. Opt. Mater. 7 1901291
Google Scholar
[26] 俞浩健, 姚方男, 代旭东, 曹进, 田哲圭 2019 物理学报 68 017202
Google Scholar
Yu H J, Yao F N, Dai X D, Cao J, Jhun C 2019 Acta Phys. Sin. 68 017202
Google Scholar
[27] Tanaka I, Tokito S 2004 Jpn. J. Appl. Phys. 43 7733
Google Scholar
[28] Jou J H, Wang W B, Chen S Z, Shyue J J, Hsu M F, Lin C W, Shen S M, Wang C J, Liu C P, Chen C T, Wu M F, Liu S W 2010 J. Mater. Chem. 20 8411
Google Scholar
[29] Su S J, Chiba T, Takeda T, Kido J 2008 Adv. Mater. 20 2125
Google Scholar
[30] Sun N, Wang Q, Zhao Y B, Chen Y H, Yang D Z, Zhao F C, Chen J S, Ma D G 2014 Adv. Mater. 26 1617
Google Scholar
[31] Xu Z, Gong Y B, Dai Y F, Sun Q, Qiao X F, Yang D Z, Zhan X J, Li Z, Tang B Z, Ma D G 2019 Adv. Opt. Mater. 7 1801539
Google Scholar
[32] Wu Z B, Wang Q, Yu L, Chen J S, Qiao X F, Ahamad T, Alshehri S M, Yang C L, Ma D G 2016 ACS Appl. Mater. Interfaces 8 28780
Google Scholar
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百度学术2. 柴源，李铭睿，袁曦，华杰，汪津. 基于混合主体结构的暖白色荧光有机电致发光器件的制备. 光源与照明. 2022(06): 46-48 . 百度学术3. 徐冲，牛连斌，钱雅翠，文林，熊元强，彭浩南，关云霞. Fe(NH_2trz)_3·(BF_4)_2掺杂聚芴的有机电致发光器件. 物理学报. 2021(07): 306-314 . 百度学术其他类型引用(1)
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