High efficiency pure white organic light-emitting diodes using a diphenylaminofluorene-based blue fluorescent material

High efficiency pure white organic light-emitting diodes (WOLEDs) were developed using a highly efficient diphenylaminofluorene-based deep blue fluorescent material (DAF). A high quantum efficiency of 7.1% with color coordinates of (0.15, 0.18) were obtained from the DAF-doped blue device, which was then combined with phosphorescent red/green devices. A mixed interlayer was used to control the color coordinates and charge balance in the emitting layer of the WOLEDs. The pure white hybrid WOLEDs showed a high quantum efficiency of 12.3%.     

Simplified single-emitting-layer hybrid white organic light-emitting diodes with high efficiency,low efficiency roll-off,high color rendering index and superior color stability

Single-emitting-layer hybrid white organic light-emitting diodes (SEL-hybrid-WOLEDs) are promising candidates for large-area lightings, however, ideal hybrid WOLEDs with a simple structure and high-efficiency, low roll-off, high color rendering index (CRI) and superior CIE coordinates have been rarely reported. In this paper, high-performance SEL-hybrid-WOLEDs are demonstrated by utilizing a thermally activated delayed fluorescence (TADF) host emitter combined with green and red phosphors. The optimized WOLED exhibits an external quantum efficiency (EQE) of 20.2%, CIE coordinates of (0.360, 0.390) and a CRI of 85. Remarkably, an extremely low efficiency roll-off is also realized, with an EQE of 19.4% remained even at the practical luminance of 1000 cd/m², resulting from the wide recombination zone as well as the well-tuned energy transfer in the emitting layer. Moreover, benefited from the stable recombination zone, superior color stability was also achieved. The intriguing results, we believe, greatly manifest the great potential of such a strategy and may pave the way towards real applications.     

白光有机电致发光器件发光稳定性研究

基于红绿/蓝双发光层,制作了结构为ITO/MoO ₃(10nm)/NPB(40nm)/TCTA(10nm)/CBP:R-4B(2%):GIR1(14%,X nm)/mCP:Firpic(8%,Y nm/BCP(10nm)/Alq₃(40nm)/LiF(1nm)/Al( 100nm)的白色全磷光有机电致发光器件(OLED),通过 调节红绿发光层的厚度X与蓝光发光层的厚度Y,研究了不同发光层厚度器件发 光性能的影响。研究发现:当X 为23nm、Y为7nm时,器件的光效和色坐标都具有 很高的稳定性,在电压分别为5、 10和15V时,色坐标分别为(0.33,0.37)、(0.33,0. 37)和(0.34,0.38);在电压为 5V时,电流密度为0.674mA,亮度为158.7cd ,最大电流效率为26.87cd/A;利用电子阻 挡材料TCTA和空穴阻挡材料BCP能够显著提高载流子的复合效率。分析认为:发光层顺序 为红绿/蓝时,更有利于蓝光的出射,从而使白光的色坐标更稳定。     

Investigation and optimization of each organic layer: A simple but effective approach towards achieving high-efficiency hybrid white organic light-emitting diodes

A highly efficient hybrid white organic light-emitting diode based on a simple structure has been successfully fabricated and characterized. By systematically investigating the influence of the emissive layer thickness, electron transporting layer thickness, spacer and hole transporting layer, the forward-viewing current efficiency and power efficiency of the resulting device without any out-coupling schemes or n-doping strategies can be as high as 59.4 cd/A and 58.4 lm/W, respectively. Besides, a Commission International de l’Eclairage of (0.412, 0.393) and a color rendering index of 60 are obtained at the current density of 11 mA/cm². Through the optimization and investigation, the origin of this unique device is explored comprehensively. Undoubtedly, such presented results will be beneficial to the design of both material and device architecture for ultra high-performance white organic light-emitting diodes.     

Deep blue phosphorescent organic light-emitting diodes with excellent external quantum efficiency

Highly efficient deep blue phosphorescent organic light-emitting diodes (PHOLEDs) using two heteroleptic iridium compounds, (dfpypy)₂Ir(acac) and (dfpypy)₂Ir(dpm), as a dopant and 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazol-3-yl)diphenylphosphine oxide as a host material have been developed. The electroluminescent device of (dfpypy)₂Ir(dpm) at the doping level of 3 wt% shows the best performance with external quantum efficiency of 18.5–20.4% at the brightness of 100–1000 cd/m² and the color coordinate of (0.14, 0.18) at 1000 cd/m².     

Efficient deep-blue emitters based on triphenylamine-linked benzimidazole derivatives for nondoped fluorescent organic light-emitting diodes

Two triphenylamine-substituted benzimidazole derivatives were synthesized for use as efficient deep-blue emitters in nondoped fluorescent organic light-emitting diodes (FLOLEDs). The molecular design of 4′,4′′-(1H-benzo[d]imidazole-1,2-diyl)bis(N,N-diphenylbiphenyl-4-amine) (T2B) to limit the molecular packing density enabled T2B-based devices to suppress the exciton quenching by a bulky three-dimensional structure. Nondoped FLOLEDs fabricated using T2B as a blue emitter exhibited an external quantum efficiency of 4.67% with color coordinates of (0.15, 0.08).     

Efficient non-doped monochrome and white phosphorescent organic light-emitting diodes based on ultrathin emissive layers

Efficient red, orange, green and blue monochrome phosphorescent organic light-emitting diodes (OLEDs) with simplified structure were fabricated based on ultrathin emissive layers. The maximum efficiencies of red, orange, green and blue OLEDs are 19.3 cd/A (17.3 lm/W), 45.7 cd/A (43.2 lm/W), 46.3 cd/A (41.6 lm/W) and 11.9 cd/A (9.2 lm/W). Moreover, efficient and color stable white OLEDs based on two complementary colors of orange/blue, three colors of red/orange/blue, and four colors of red/orange/green/blue were demonstrated. The two colors, three colors and four colors white OLEDs have maximum efficiencies of 30.9 cd/A (27.7 lm/W), 30.3 cd/A (27.2 lm/W) and 28.9 cd/A (26.0 lm/W), respectively. And we also discussed the emission mechanism of the designed monochrome and white devices.     

Design of white tandem organic light-emitting diodes for full-color microdisplay with high current efficiency and high color gamut

Microdisplays based on organic light-emitting diodes (OLEDs) have a small form factor, and this can be a great advantage when applied to augmented reality and virtual reality devices. In addition, a high-resolution microdisplay of 3000 ppi or more can be achieved when applying a white OLED structure and a color filter. However, low luminance is the weakness of an OLED-based microdisplay as compared with other microdisplay technologies. By applying a tandem structure consisting of two separate emission layers, the efficiency of the OLED device is increased, and higher luminance can be achieved. The efficiency and white spectrum of the OLED device are affected by the position of the emitting layer in the tandem structure and calculated via optical simulation. Each white OLED device with optimized efficiency is fabricated according to the position of the emitting layer, and red, green, and blue spectrum and efficiency are confirmed after passing through color filters. The optimized white OLED device with color filters reaches 97.8% of the National Television Standards Committee standard.     

Above 20% external quantum efficiency in green and white phosphorescent organic light-emitting diodes using an electron transport type green host material

Highly efficient green and white phosphorescent organic light emitting diodes were developed using a green phosphorescent host material based on phenyl substituted spirobifluorene. A high quantum efficiency of 25.3% was achieved in the green phosphorescent device and a high quantum efficiency of 21.6% was obtained in the white device with a stacked emitting structure of deep blue and red:green emitting layers.     

Color temperature tunable white organic light-emitting diodes

In this work, we demonstrated color-tunable white organic light-emitting diodes by stacking upper orange transparent and lower blue bottom emission organic light-emitting diodes (OLEDs). By independently operating each OLED, it was possible to tune the color temperature in a range of 1500–10,000 K, which covers the full Planckian locus in the 1931 CIE space. In designing stable and efficient OLEDs, in addition to the electrical characteristics, the importance of internal microcavity was emphasized and implemented. In fabricating the upper transparent OLED, special attention was paid to the capping layer for enhancing the emission. Our results presented a general guideline that is practically useful in designing high-performance color-tunable OLEDs with transparent OLEDs.     

An ideal host-guest system to accomplish high-performance greenish yellow and hybrid white organic light-emitting diodes

Greenish yellow organic light-emitting diodes (GYOLEDs) have steadily attracted researcher's attention since they are important to our life. However, their performance significantly lags behind compared with the three primary colors based OLEDs. Herein, for the first time, an ideal host-guest system has been demonstrated to accomplish high-performance phosphorescent GYOLEDs, where the guest concentration is as low as 2%. The GYOLED exhibits a forward-viewing power efficiency of 57.0 lm/W at 1000 cd/m², which is the highest among GYOLEDs. Besides, extremely low efficiency roll-off and voltages are achieved. The origin of the high performance is unveiled and it is found that the combined mechanisms of host-guest energy transfer and direct exciton formation on the guest are effective to furnish the greenish yellow emission. Then, by dint of this ideal host-guest system, a simplified but high-performance hybrid white OLED (WOLED) has been developed. The WOLED can exhibit an ultrahigh color rendering index (CRI) of 92, a maximum total efficiency of 27.5 lm/W and a low turn-on voltage of 2.5 V (1 cd/m²), unlocking a novel avenue to simultaneously achieve simplified structure, ultrahigh CRI (>90), high efficiency and low voltage.     

High quantum efficiency and color stability in white phosphorescent organic light-emitting diodes using carboline derivative as a host material

Highly efficient and color stable phosphorescent white organic light-emitting diodes were developed using a high triplet energy host material, 3,3′-bis(9H-pyrido[2,3-b]indol-9-yl)-1,1′-biphenyl (CbBPCb), derived from carboline. Two color phosphorescent white organic light-emitting diodes were fabricated by co-doping of blue and orange triplet emitters or double emitting layer structure of blue and orange emitting layers. High quantum efficiency above 20% and color stability were achieved in the white device by optimizing the doping concentration and emitting layer thickness.     

Low driving voltage white organic light-emitting diodes with high efficiency and low efficiency roll-off

Single emission layer white organic light-emitting diodes (WOLEDs) showing high color stability, low turn-on voltage, high efficiency and low efficiency roll-off by incorporating iridium(III) bis[(4,6-difluo-rophenyl)-pyridinato-N,C2] (FIrpic) and bis(2-phenylbenzothiazolato) (acetylacetonate)iridium(III) (Ir(BT)₂(acac)) phosphors dyes have been demonstrated. Our WOLEDs without any out-coupling schemes as well as n-doping strategies show low operating voltages, low turn-on voltage (defined for voltage to obtain a luminance of 1 cd/m²) of 2.35 V, 79.2 cd/m² at 2.6 V, 940.5 cd/m² at 3.0 V and 10 300 cd/m² at 4.0 V, respectively, and achieve a current efficiency of 40.5 cd/A, a power efficiency of 42.6 lm/W at a practical brightness of 1000 cd/m², and a low efficiency roll-off 14.7% calculated from the maximum efficiency value to that of 5000 cd/m². Such improved properties are attributed to phosphors assisted carriers transport for achieving charge carrier balance in the single light-emitting layer (EML). Meanwhile the host–guest energy transfer and direct exciton formation process are two parallel pathways serve to channel the overall excitons to dopants, greatly reduced the unfavorable energy losses.     

高效率非掺杂型白色有机电致发光器件

制备了基于rubrene超薄层和NPBX做激子阻挡层的高效率的非掺杂型白色有机电致发光器件.器件结构为:ITO/2T-NATA(20 nm)/NPBX(25-d nm)/rubrene(0.2 nm)/NPBX(d nm)/DPVBi(30 nm)/Alq(30 nm)/LiF(0.5 nm)/Al.器件的电致发光光谱依靠激子阻挡层NPBX厚度d的变化而变化,当NPBX厚度d为5 nm时,器件色坐标从7 V变化到16 V时均在白光的中心区域,有最大电流效率7.91 cd/A(V=7 V)和最大亮度13 540 cd/m2 (V=16 V).     

以Liq:rubrene为单发光层的白色OLED的制备与研究

以ITO玻璃基片为衬底,8-羟基喹啉锂(Liq)掺杂红荧烯 (Rubrene)作为单一发光层,制备结构为ITO/PTV:TPD/Liq:Rubrene/Alq3/Al的白色有机电致发光器件(OLED),其量度达到3 120 cd/m2.对4种不同掺杂浓度器件进行比较,分析了掺杂剂对器件发光亮度的影响,并对上述器件的发光和电学性能进行了研究和探讨.     

多层白色有机发光器件的结构和性能优化

以红、蓝、绿为基,制备了不同发光层组合次序的有机发光器件,研究了各发光层的顺序及厚度对器件性能的影响,并在此基础上构成了白色有机发光器件.通过改变关键发光层的厚度,来调节不同颜色之间的平衡,从而达到色度很好的向色;由于关键发光层的厚度很薄,因此得到的器件在高电压的色度漂移也很小.优化的白光器件在200 mA/cm2时,电流效率为3.78 cd/A,色坐标为x=0.345,y=0.323.根据激子产生和扩散理论,讨论了器件性能对于各发光层的厚度及激子扩散长度的依赖关系,拟合结果与实验结果吻合.     

Interlayer free hybrid white organic light-emitting diodes with red/blue phosphorescent emitters and a green thermally activated delayed fluorescent emitter

Two different hybrid white organic light-emitting diodes (WOLEDs) with red/blue phosphorescent emitters and a green thermally activated delayed fluorescent (TADF) emitter were designed to develop high efficiency hybrid WOLEDs. One hybrid WOLED (type I) had a device structure with a hybrid emitting layer of green TADF and red phosphorescent emitters stacked on a blue phosphorescent emitting layer and the other hybrid WOLED (type II) had a device architecture with the green TADF emitting layer stacked on a red and blue phosphorescent emitting layer. Efficient energy transfer from the green TADF emitter to the red phosphorescent emitter was observed and balanced white emission could be obtained by optimizing the device structure of the hybrid WOLEDs. A quantum efficiency of 16.2% with a color coordinate of (0.45,0.47) and a quantum efficiency of 18.0% with a color coordinate of (0.37,0.47) were achieved in the type I and type II hybrid WOLEDs, respectively.     

Simplified and high-efficiency warm/cold phosphorescent white organic light-emitting diodes based on interfacial exciplex co-host

Possessing the reverse intersystem crossing (RISC) process, exciplex system has vast potential to enhance the efficiency of the white organic light-emitting diodes (WOLEDs). Nevertheless, general structures of the emitting layer always employ triple-doping in a long range (20–30 nm) which is complicated on fabrication progress. In this paper, based on the interfacial exciplex co-host, a flexible and simplified structure design is proposed to realize both warm and cold phosphorescent WOLEDs. In the two devices, with strategically locating the ultrathin orange phosphorescent emitting layers at two sides of the blue phosphorescent emitting layer (2 nm), respectively, multiple energy transfer channels are created to carry out highly efficient exciton utilization. Owing to the different energy transfer mechanisms, different organic emission ratios are obtained in two WOLEDs. The cold WOLEDs exhibited superior maximum external quantum efficiency (EQE), current efficiency (CE) and power efficiency (PE) of 28.37%, 72.17 cd A⁻¹ and 87.17 lm W⁻¹, respectively. Also, the warm WOLEDs showed high values as EQE of 23.80%, CE of 67.70 cd A⁻¹ and PE of 81.10 lm W⁻¹. Furthermore, both the devices presented rather stable color output in the luminance range from 2000 cd m⁻² to 10000 cd m.⁻²     

High-efficiency orange and white phosphorescent organic light-emitting diodes based on homojunction structure

We demonstrate high-efficiency orange and white phosphorescent organic light-emitting diodes based on homojunction structure. Excellent performance is realized by using step-graded p- and n-type doping structure in orange homojunction device. The resulting orange homojunction device exhibits a maximum current efficiency of 30.0 cd/A and low efficiency roll-off. The improvements are mainly attributed to the utilization of step-graded doped profile, which facilitates balanced charge carrier injection and transport. Moreover, one optimized white homojunction device based on two complementary colors shows a maximum efficiency of 15.4 cd/A, and superior color-stability in a wide range of luminance.     

Green Ir(III) complexes with multifunctional ancillary ligands for highly efficient solution-processed phosphorescence organic light-emitting diodes with high current efficiency

Two new highly efficient green emitting heteroleptic Ir(III) complexes, namely, bis[5-(2-ethylhexyl)-8-(trifluoromethyl)benzo[c][1,5]naphthyridin-6(5H)-one]iridium-4-((3,5-di(9H-carbazol-9-yl)benzyl)oxy)picolinate (Ir-HT) and bis[5-(2-ethylhexyl)-8-(trifluoromethyl) benzo[c][1,5]naphthayridin-6(5H)-one]iridium-4-((4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzyl) oxy)picolinate (Ir-ET) were designed and synthesized for solution-processed phosphorescence organic light-emitting diodes (PHOLEDs). These new Ir(III) complexes are based on amide-bridged trifluoromethyl (-CF₃) substituted phenylpyridine unit as main ligand and 1,3-bis(N-carbazolyl)benzene (mCP) unit and 1,3,4-oxadiazole (OXD) unit functionalized picolinate (pic) as an ancillary ligand. These multifunctional groups were attached into the 4-position of pic ancillary ligands via ether linkage. Interestingly, the solution-processed PHOLED device using Ir-HT as a dopant exhibited a maximum external quantum efficiency (EQE_max) of 20.92% and a maximum current efficiency (CE_max) of 64.04 cd A⁻¹. Whereas PHOLED device using Ir-ET displayed a EQE_max of 20.68% and a CE_max of 65.02 cd A⁻¹. This is one of best CE with high EQE for green Ir(III) complexes via solution-processed PHOLEDs using multifunctional ancillary ligands so far.