Bing Yao

High‐Efficiency Single Emissive Layer White Organic Light‐Emitting Diodes Based on Solution‐Processed Dendritic Host and New Orange‐Emitting Iridium Complex

An extremely high-efficiency solution-processed white organic light-emitting diode (WOLED) is successfully developed by simultaneously using an ideal dendritic host material and a novel efficient orange phosphorescent iridium complex. The optimized device exhibits forward-viewing efficiencies of 70.6 cd A(-1) , 26.0%, and 47.6 lm W(-1) at a luminance of 100 cd m(-2) , respectively, promising the low-cost solution-processed WOLEDs a bright future as the next generation of illumination sources.

Multifunctional metallophosphors with anti-triplet-triplet annihilation properties for solution-processable electroluminescent devices

With the goal to provide organometallic triplet emitters with good hole-injection/hole-transporting properties, highly amorphous character for simple solution-processed organic light-emitting diodes, and negligible triplet–triplet (T–T) annihilation, a series of new phosphorescent cyclometalated IrIII and PtII complexes with triphenylamine-anchored fluorenylpyridine dendritic ligands were synthesized and characterized. The photophysical, thermal, electrochemical and electroluminescent properties of these molecules are reported. The incorporation of two sterically hindered electron-rich triphenylamino groups to the 9-position of the fluorene skeleton was found not only to afford triplet emitters in the glassy state with high Tg, but also to elevate the HOMO levels and confer the hole-injection ability to the phosphorescent center. These highly amorphous metal phosphors can serve as doped emitters in a small molecular host for spin-coated emission layer in suitable OLED structures to achieve good device performance with a maximum luminance of 29380 cd m−2 at 23 V, a peak external quantum efficiency of 7.0%, a luminance efficiency of 21.4 cd A−1 and a power efficiency of 2.9 lm W−1. Both the electrophosphorescent device characterization as well as the theoretical simulation results show that these iridium electrophosphors show negligible T–T annihilation even at high operating current densities and moderately high doping levels. Our investigations indicate that attaching the triphenylamino moieties to the fluorene ring is an effective way to overcome the T–T annihilation caused by the strong interactions among the emitting molecules.

Solution-Processed Phosphorescent Organic Light-Emitting Diodes with Ultralow Driving Voltage and Very High Power Efficiency

To realize power efficient solution-processed phosphorescent organic light-emitting diodes (s-PhOLEDs), the corresponding high driving voltage issue should be well solved. To solve it, efforts have been devoted to the exploitation of novel host or interfacial materials. However, the issues of charge trapping of phosphor and/or charge injection barrier are still serious, largely restraining the power efficiency (PE) levels. Herein, with the utilization of an exciplex-forming couple 4, 4′, 4″ -tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), the efficient charge injection and transporting, barrier-free hole-electron recombination for the formation of the interfacial exciplex, and elimination of charge traps of phosphors in the emissive layer are realized simultaneously, resulting in a turn-on voltage of 2.36u2009V, a record high PE of 97.2u2009lm W−1, as well as extremely low driving voltage of 2.60u2009V at 100u2009cd m−2, 3.03u2009V at 1000u2009cd m−2 and 4.08u2009V at 10000u2009cd m−2. This report is the first time that the PE performance of s-PhOLED approaches 100u2009lm W−1 high level, even superior to the corresponding state-of-the-art performance of the same color vacuum-deposited PhOLED (v-PhOLED) counterpart. We anticipate this report opens a new avenue for achieving power efficient monochromatic and white s-PhOLEDs with simple structures.

White polymeric light-emitting diodes with high color rendering index

The efficient white polymeric light-emitting diodes based on a white emissive polymer doped with a red phosphorescent dopant were fabricated by spin-coating method. The emission spectrum of the device is broadened to cover the full visible region by doping the red phosphorescent dye and thereby realizes white emission with high color-rendering index (CRI). By controlling the contents of the doped electron-transporting 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and the red phosphorescent dopant, a luminous efficiency as high as 5.3cd∕A and a power efficiency of 3lm∕W were obtained with a CRI of 92.

Electrophosphorescent Heterobimetallic Oligometallaynes and Their Applications in Solution-Processed Organic Light-Emitting Devices

By combining the iridium(III) ppy-type complex (Hppy=2-phenylpyridine) with a square-planar platinum(II) unit, some novel phosphorescent oligometallaynes bearing dual metal centers (viz. Ir(III) and Pt(II)) were developed by combining trans-[Pt(PBu(3))(2)Cl(2)] with metalloligands of iridium possessing bifunctional pendant acetylene groups. Photophysical and computational studies indicated that the phosphorescent excited states arising from these oligometallaynes can be ascribed to the triplet emissive Ir(III) ppy-type chromophore, owing to the obvious trait (such as the longer phosphorescent lifetime at 77 K) also conferred by the Pt(II) center. So, the two different metal centers show a synergistic effect in governing the photophysical behavior of these heterometallic oligometallaynes. The inherent nature of these amorphous materials renders the fabrication of simple solution-processed doped phosphorescent organic light-emitting diodes (PHOLEDs) feasible by effectively blocking the close-packing of the host molecules. Saliently, such a synergistic effect is also important in affording decent device performance for the solution-processed PHOLEDs. A maximum brightness of 3,356 cd m(-2) (or 2,708 cd m(-2)), external quantum efficiency of 0.50% (or 0.67%), luminance efficiency of 1.59 cd A(-1) (or 1.55 cd A(-1)), and power efficiency of 0.60 Lm W(-1) (or 0.55 Lm W(-1)) for the yellow (or orange) phosphorescent PHOLEDs can be obtained. These results show the great potential of these bimetallic emitters for organic light-emitting diodes.

Interfacial triplet confinement for achieving efficient solution-processed deep-blue and white electrophosphorescent devices with underestimated poly(N-vinylcarbazole) as the host

Highly efficient deep-blue and white PhOLEDs with FIr6 as a blue emitter and PVK as a host are developed by using a high triplet level interfacial layer to confine triplet excitons within the emissive layer. Incorporation of an interfacial layer with a higher triplet level such as TPCz can effectively cut off the potential loss pathways of the triplet excitons within the PVK:FIr6 emissive layer. The resultant PVK:FIr6-based deep-blue and white solution-processed PhOLEDs exhibit an unprecedented forward-viewing EQE of 16.1% and a total EQE of 28.0% (38.4 lm W−1) at a practical luminance of 1000 cd m−2, respectively.

Power-efficient solution-processed red organic light-emitting diodes based on an exciplex host and a novel phosphorescent iridium complex

High power-efficiency solution-processed red phosphorescent organic light-emitting diodes (s-PhOLEDs) are urgently needed in OLED displays and lighting applications. Herein, we have synthesized a novel solution-processable red heteroleptic iridium complex bis[2-di(p-methoxyphenyl) amino (9,9-diethylfluoren-2-yl)-5-(trifluoromethyl) pyridine][acetylacetonate] iridium(III), i.e. Ir(DPA-Flpy-CF3)2acac, which shows efficient red photoluminescence with an emission peak located at 602 nm. This novel red phosphor possesses a high absorption coefficient in the long wavelength region, ensuring the efficient energy transfer from the interfacial exciplex host to the phosphor guest at low phosphor-doping concentration. The optimized red s-PhOLED based on the red Ir(DPA-Flpy-CF3)2acac shows a maximum external quantum efficiency of 19.3% and a power efficiency of 44.5 lm W−1 with Commission International de LEclairage (CIE) coordinates of (0.64, 0.36). It is so far the highest power efficiency ever reported for red s-PhOLEDs and is comparable to state-of-the-art red PhOLEDs prepared by thermal evaporation.

Highly Efficient TADF Polymer Electroluminescence with Reduced Efficiency Roll-off via Interfacial Exciplex Host Strategy

Solution-processed organic light-emitting diodes (s-OLED) consisting of TAPC/TmPyPB interfacial exciplex host and polymer PAPTC TADF emitter are prepared, simultaneously displaying ultralow voltages (2.50/2.91/3.51/4.91 V at luminance of 1/100/1000/1000 cd m-2), high efficiencies (14.9%, 50.1 lm W-1), and extremely low roll-off rates (J50 of 63.16 mA cm-2, L50 of ca. 15000 cd m-2). Such performance is distinctly higher than that of pure-PAPTC s-OLED. Compared to pure-PAPTC, the advanced emissive layer structure of TAPC:PAPTC/TmPyPB is unique in much higher PL quantum yield (79.5 vs 36.3%) and nearly 4-fold enhancement in kRISC of the PAPTC emitter to 1.48 × 107 s-1.

Highly efficient top-emitting organic light-emitting devices with aluminium electrodes

Top-emitting organic light-emitting diodes (OLEDs) using aluminium (Al) and nickel (Ni) as the anode and Al as the semitransparent cathode were developed. Hole injection was largely improved by spin coating poly(ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT) on the metal anode. For top-emitting OLEDs with a configuration of metal anode/PEDOT/NPB/Alq3/LiF/Al/Alq3, both devices using Al and Al/Ni anodes showed efficient green light emission with a narrow emission peak. Current efficiency was increased from 4.32 cd A−1 to 6.45 cd A−1 when replacing high work function Ni with low work function Al as the anode. A luminance of 20 000 cd m−2 can be achieved for these top-emitting OLEDs. The device made with the Al/Ni anode showed a low driving voltage and high power efficiency as compared to that made with the Al anode. The improvement on light-emitting efficiency was attributed to balanced charge carrier injection and utilization of the high reflective semitransparent Al cathode.

Thermally activated delayed fluorescence in Cu(I) complexes originating from restricted molecular vibrations.

The mechanism of thermally activated delayed fluorescence (TADF) in molecules in aggregated or condensed solid states has been rarely studied and is not well understood. Nevertheless, many applications of TADF emitters are strongly affected by their luminescence properties in the aggregated state. In this study, two new isomeric tetradentate CuI complexes which simultaneously show aggregation induced emission (AIE) and TADF characteristics are reported for the first time. We provide direct evidence that effectively restricting the vibrations of individual molecules is a key requisite for TADF in these two CuI complexes through in-depth photophysical measurements combined with kinetic methods, single crystal analysis and theoretical calculations. These findings should stimulate new molecular engineering endeavours in the design of AIE-TADF active materials with highly emissive aggregated states.