White Organic Light-emitting Diode Device Research Articles

Color-Tunable All-Fluorescent White Organic Light-Emitting Diodes with a High External Quantum Efficiency Over 30% and Extended Device Lifetime.

White organic light-emitting diodes (WOLEDs) with high efficiencies and tunable colors attracts considerable interest from the industry and academia. Thermally activated delayed-fluorescence (TADF) emitters can revolutionize such WOLED devices; however, they still suffer from poor performances. In this study, an advanced double-emissive-layer device architecture capable of hole-trapping TADF-sensitized emissions is proposed to not only achieve a recombination zone shift for the tunable colors but also accelerate exciton emission dynamics for high efficiency and alleviated roll-off. The proof-of-concept WOLEDs exhibit significant shifts in their Commission Internationale de l'Eclairage (CIE) coordinates and correlated color temperatures from (0.40, 0.47) and 4088 K at 100cd m-2 to (0.27, 0.33) and 9269 K at 5000cd m-2 . Additionally, the maximum external quantum efficiency (EQE) reaches 30.7% and remains >25%over a wide luminance range of 500-5000cd m-2 , along with an extended LT80 of over 20000 h at an initial luminance of 100cd m-2 . This is the first time that all-fluorescent WOLEDs have been used to realize an EQE exceeding 30%, thereby establishing a new benchmark in this field.

Solution-processed white organic light-emitting diodes with blue fluorescent and orange-red thermally activated delayed fluorescent dendritic luminogens

In this work, dendritic luminogens, namely, 3ICz-Tr as a blue emitter and Tri-tNID as an orange-red emitter, were synthesized and used for the application of white organic light-emitting diodes (WOLEDs). These molecules have appropriately high molecular weights, which are favorable for the fabrication of thin films with fine surface morphologies. Interestingly, the blue emitting 3ICz-Tr displays fluorescent character and the orange-red emitting Tri-tNID exhibited thermally activated delayed fluorescence, which was confirmed by steady state and transient photoluminescence (TRPL) spectroscopy. Eventually, WOLED devices could be realized by mixing the two molecules and optimizing their mixture composition. Among the devices we fabricated, the device with Tri-tNID and 3ICz-Tr (0.5:99.5 wt ratio) without additional host material demonstrated nearly pure white emission, with the maximum EQE of 8.32% and CIE coordinate of (0.32, 0.30). Furthermore, by changing the composition of the two dendritic molecules, the emission color can be adjusted from a warm white to a cool white in the corresponding WOLED.

Molecular and Device Design Strategies for Ideal Performance White Organic Light-Emitting Diodes.

The progress of white organic light-emitting diodes (WOLEDs) via adopting fluorescent and phosphorescent organic materials have attracted commercial interest for their broad range of visible spectrum and potential of 100 % internal quantum efficiency. In this account, smart molecular designs for developing efficient phosphorescent host and good color purity blue fluorescent emitters are prepared to be discussed, especially donor-acceptor modification to regulate their triplet states and bipolar transport properties. Rational device configuration design strategies were also introduced by cooperating with efficient conventional fluorescent and thermally activated delayed fluorescent emitting molecules to achieve full exciton utilization and simplified device structures, further suggesting perspectives of potentially low-cost, ideal performance and promoted operational lifetime in WOLED devices.

Polymer-based scattering layers for internal light extraction from organic light emitting diodes

Efficient light extraction for organic light emitting diodes (OLED) using scalable processes and low-cost materials are important prerequisites for the future commercialization of OLED lighting devices. The light-extraction technology exhibited in this paper uses polymer-based high-refractive index scattering layers processed from solution. The scatter matrix formulation incorporates two types of nanoparticles for refractive index tuning and scattering, respectively. Planarization by the same material in order to reduce surface defects was critical for achieving highly increased device yield. Highly efficient and defect-free large-area (1.8 cm2) white OLED devices were fabricated on top of the scattering layer in a bottom emitter configuration. Light extraction enhancement leads to an overall efficiency gain of up to 81% for luminances of 5000 cd m−2.

White organic light-emitting diodes with single active layer using a solution process based on a co-host emitter system.

A two-color white organic light-emitting diode (WOLED) with a co-host system in solution process method was demonstrated. The device configuration was ITO/PEDOT:PSS (40 nm)/emitting layer (50 nm)/TPBi (20 nm)/LiF (1 nm)/Al. The emitting layer consisted of TAT, (α- or β-) NPB, DPAVBi (blue dopant), and Rubrene (yellow dopant). The device using α-NPB or β-NPB showed a white color of CIE (0.29, 0.40) and (0.28, 0.39). The device using the α-NPB co-host showed a luminance efficiency of 3.39 cd/A, which is 21% higher than β-NPB (2.80 cd/A). Power efficiency was increased by 16% in α-NPB (2.34 Im/W) compared to β-NPB (2.02 Im/W). The Co-host emitter system of HTL and single blue emitter using a solution process for WOLED was shown before, but the HTL role was not understood clearly. From this study, the WOLED device efficiency can be attributed to the HTL's energy transfer property in the emitter mixing system.

Realization of high efficacy white organic light emitting diode by controlling internal light absorption and angular distribution

We investigated highly efficient organic light emitting diode (OLED) with advanced optical designs of organic layers to convert evanescent mode (internal absorption) into guided light and micro structure to extract the specifically distributed guided light dominated by wide angular substrate mode. White OLED device based on these optical designs realized high efficacy of 133 lm/W and external quantum efficiency of 56 % at 1000 cd/m2.

52.4: Highly Efficient Single‐Unit White OLED Device with Emission from Both Singlet and Triplet Excitons

AbstractWe succeeded in developing a single‐unit hybrid organic light‐emitting diode (OLED) device with efficient light emission from both a phosphorescent layer and a fluorescent layer. The single‐unit hybrid OLED achieved power efficiency higher than that of a two‐unit hybrid tandem OLED with a phosphorescent and fluorescent layers.

Study of energy transfer in single and multi-emissive layer using Gaussian peak fitting

White organic light-emitting diodes(WOLEDs) were fabricated with the device structure of ITO(1800Å)/NPB(700Å)/emissive layer(300Å)/Bphen(300Å)/Liq(20Å)/Al(1200Å) using the two complementary colors method. Then, we investigated their electrical and optical characteristics to determine luminous efficiency, luminance and color coordinates of single, double, triple and quadruple emissive layered-WOLED. Thickness of emissive layer was fixed at 30Å, and DPASN and BAlq were used for blue emissive host material and DCJTB was added as red dopant in the emissive layer. Then, we investigated the performance of OLEDs via its charge blocking structure and its different emissive region with emissive layers. Luminous efficiency of 5.30cd/A at 50mA/cm2 of current density is obtained in WOLED device with double emissive layer of DPASN:DCJTB-0.1% (150Å)/BAlq:DCJTB-0.1% (150Å) and these are 80% higher than WOLED device with single emissive layer of DPASN:DCJTB-0.1% (300Å).

Mechanoluminescent and efficient white OLEDs for Pt(ii) phosphors bearing spatially encumbered pyridinyl pyrazolate chelates

Three Pt(II) complexes with a formula of [Pt(Lx)2], x = 1, 2 and 3, in which the pyrazole chelate (Lx)H represents 4-(2,6-diisopropylphenyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (1), 5-(2,6-diisopropylphenyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (2) and 4-(tert-butyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (3), were synthesized, and their photophysical properties were examined. Single-crystal X-ray diffraction studies of 1 and 2 reveal a planar molecular geometry with both Lx chelates adopting a mutually trans configuration. Distinctive packing arrangements within the crystal lattices are observed, e.g., complex 2 shows structural repetitions that prohibit formation of intimate π–π stacking, while complex 1 exhibits an ordered alignment along the axis of the square planar core framework and, remarkably, shows mechanoluminescence and concentration dependent photoluminescence in the poly(methyl methacrylate) matrix (PMMA). In sharp contrast, derivatives 2 and 3 show only the luminescence derived from the monomeric and aggregated state, respectively, which is attributed to the imposed substituent effect. For application, organic light emitting diodes (OLEDs) were also fabricated using the aforementioned blue dopant 1, attaining the peak external quantum efficiency, current and power efficiencies of ηext = 9.1%, ηc = 18.4 cd A−1 and ηp = 16.6 lm W−1 respectively. With the same device structure, devices based on 3 exhibit an extremely high efficiency orange emission (20.0%, 47.6 cd A−1, 50.8 lm W−1) due to the occurrence of extensive π–π-stacking. Upon combining blue-emitting phosphor 1 and orange-emitting phosphor 3, two white OLED devices are fabricated, one of which obtained by sequentially doping 1, 3 and then 1 into separated layers exhibits performance efficiencies of 11.3%, 28.3 cd A−1, and 21.2 lm W−1, highly stable chromaticity (CIEx = 0.41–0.40 and CIEy = 0.43–0.41), and an adequate color-rendering index (CRI) of 80 at brightness of 370 to 10 800 cd m−2. The other device obtained by co-doping 1 and 3 into a single emissive layer shows improved efficiencies of 15.0%, 44.8 cd A−1, and 46.2 lm W−1, but with a lower CRI of 63.

Efficient triplet exciton confinement of white organic light-emitting diodes using a heavily doped phosphorescent blue emitter

We demonstrated efficient white electrophosphorescence with a heavily doped phosphorescent blue emitter and a triplet exciton blocking layer (TEBL) inserted between the hole transporting layer (HTL) and the emitting layer (EML). We fabricated white organic light-emitting diodes (WOLEDs) (devices A, B, C, and D) using a phosphorescent red emitter; bis(2-phenylquinolinato)-acetylacetonate iridium III (Ir(pq) 2acac) doped in the host material; N,N′-dicarbazolyl-3,5-benzene (mCP) as the red EML and the phosphorescent blue emitter; bis(3,5-Difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (FIrpic) doped in the host material; p-bis(triphenylsilyly)benzene (UGH2) as the blue EML. The properties of device B, which demonstrate a maximum luminous efficiency and external quantum efficiency of 26.83 cd/A and 14.0%, respectively, were found to be superior to the other WOLED devices. It also showed white emission with CIE x , y coordinates of ( x = 0.35, y = 0.35) at 8 V. Device D, which has a layer of P-type 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) material between the HTL and TEBL, was compared with device A to determine the 430 nm emission peak.

Fabrication of White Organic Light-Emitting Diodes Using Two Complementary Color Methods

White organic light-emitting diodes (WOLEDs) were fabricated using two complementary color methods with two emissive layer structure such as NPB (500 Å)/DPVBi (65 Å)/MADN:DCM2-0.5% (170 Å)/Bphen (300 Å)/Liq (20 Å)/Al (1000 Å). A deep blue and orange emissions were obtained from DPVBi layer and MADN host doped with a red fluorescent DCM2 dopant each. White emission was achieved through controlling hole-electron recombination by optimization of emissive layers thicknesses and DCM2 concentrations. Optimized WOLED device shows emission efficiency of 5.04 cd/A, current density of 2.64 mA/cm2 and luminance of 938 cd/m2 at 6 V with CIEx,y color coordinate of (0.338, 0.330). These results indicate that DPVBi layer effects on hole blocking and the exciton generation due to difference of energy level in highest occupied molecular orbital. The CIEx,y coordinates of device was slightly changed change from (0.338, 0.330) at 6 V to (0.341, 0.333) at 12 V, which is almost independent on driving voltages.

High Efficient White Organic Light-Emitting Diodes Using BCzVBi as Blue Fluorescent Dopant

Efficiency improvement and color optimization of white organic light-emitting diodes (WOLEDs) were achieved via employing blue host DPVBi doped with blue fluorescent, BCzVBi. The structure of high efficient WOLED device was composed of ITO/NPB/DPVBi:BCzVBi-6%/MADN:DCM2-0.5%/Bphen/Liq/Al. WOLED doped by blue fluorescent BCzVBi exhibits 6.19 cd/A of luminous efficiency and 15400 cd/m2 of maximum luminescence. It also performs 480 cd/m2 of luminance at 5.7 V and 15400 cd/m2 at 12.9 V with CIE(x,y) coordinates of (0.33, 0.32) and (0.32, 0.32), respectively. Hole carrier and energy transfer from DPVBi to BCzVBi are proposed to explain the observed phenomena.

Highly efficient p-i-n white organic light emitting devices with tandem structure

Highly efficient tandem p-i-n white organic light emitting devices have been fabricated. Utilizing an optical transparent bilayer with doped organic p-n junction that consists of 4,7-diphenyl-1,10-phenanthroline: 2% cesium carbonate (Cs2CO3)∕N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine: 50% v/v tungsten oxide (WO3) as the connecting layer, the tandem p-i-n white device achieved an electroluminescence efficiency of 23.9cd∕A and a power efficiency of 7.8lm∕W at 20mA∕cm2 with a Commission Internationale de l’Eclairage coordinates of (0.30, 0.43). The electroluminescent color of this tandem p-i-n white organic light-emitting diode device will not change significantly with respect to drive current variation and forward viewing angle.

White p-i-n organic light-emitting devices with high power efficiency and stable color

Highly efficient p-i-n two-component white organic light-emitting devices have been fabricated with a thin dual emission layer system comprised of one codeposited emitting layer with blue and yellow dyes and one blue emitting layer, which gives rise to a balance white emission. The p-i-n white device achieved an electroluminescence efficiency of 10cd∕A and a power efficiency of 9.3lm∕W at 1000cd∕m2 and a low voltage of 3.4V with a Commission Internationale de l’Eclairage coordinates of (0.32, 0.43). The electroluminescent color of this p-i-n white organic light-emitting diode device has been shown to be immune to drive current density variations.