Bright White Organic Light-emitting Diode Research Articles

Highly efficient green and white fluorescent organic electroluminescent devices with co-doped electron transport material as both supplementary host and blue emitter

An alternative approach was exploited to achieve high performance fluorescent organic light-emitting diodes (OLEDs) by co-doping traditional electron transport material into hole dominant light-emitting layer as supplementary host and blue emitter. Experimental results demonstrated that in this device structure, the co-doping of supplementary host was beneficial in broadening recombination zone, improving carriers trapping and facilitating the balance of holes and electrons, due to its well matched energy levels and high electron mobility. Based on this device design strategy, the optimized green electroluminescent (EL) device obtained the maximum brightness and external quantum efficiency up to 21176 cd/m2 and 5.4%, respectively, which are higher than those of reference devices. In addition, bright white OLED with the maximum brightness, current efficiency and external quantum efficiency up to 17207 cd/m2, 10.47 cd/A and 4.4%, respectively, was realized by modulating the doping concentrations of blue-emitting electron transport material and orange-emitting material. Thus, our investigation provides a chance to construct high performance white OLEDs with simplified device structure.

Bright design

In all likelihood, cheap and bright white organic light-emitting diodes will someday light up our homes. Three-dimensional models can now simulate the dynamics of charges and excitons governing the operation of these light sources and predict their performance with molecular precision.

White organic light-emitting diodes based on blue fluorescent bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb) 2] doped with DCM dye

Bright white organic light-emitting diodes (WOLEDs) with single active layer has been demonstrated from blue emitting zinc complex bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb) 2] doped with orange luminescent 4-(dicyanomethylene)-2-methyl-6-( p-dimethyl-aminostyryl)-4H-pyran (DCM) dye. White light electroluminescence (EL) spectrum from Zn(hpb) 2 has been achieved by adjusting the concentration of DCM dye. WOLED with a structure of ITO/α-NPD/Zn(hpb) 2:DCM ( x%)/BCP/Alq 3/LiF/Al has been fabricated. The EL spectra covering the whole visible spectra range of 400–700 nm, with two peaks at 446 and 555 nm has been measured. The device emits white light at 10 V with Commission Internationale de I’ Eclairage (CIE) coordinates (0.27, 0.31) and brightness 1083 Cd/m 2. The maximum current efficiency of the device was 1.23 Cd/A at 9.5 V and maximum luminance reaches 2210 Cd/m 2 at 12 V.

Efficient bright white organic light-emitting diode based on non-doped ultrathin 5,6,11,12-tetraphenylnaphthacene layer

High-performance undoped white organic light-emitting diode (OLED) has been fabricated using an ultrathin yellow-emitting layer of 5,6,11,12-tetraphenylnaphthacene (rubrene) inserted at two sides of interface between two N,N′-bis-(1-naphthyl)-N,N′- biphenyl-1,1′-biphenyl-4,4′- diamine (NPB) layers as a hole transporting and blue emissive layer, respectively. The results showed that a maximum luminance of the device reached to as high as 21,500 cd/m 2 at 15 V. The power efficiencies of 2.5 and 1.6 lm/W at a luminance of 1000 and 10000 cd/m 2, respectively, were obtained. The peaks of electroluminescent (EL) spectra locate at 429 and 560 nm corresponding to the Commissions Internationale De L’Eclairage (CIE) coordinates of (0.32, 0.33), which is independent of bias voltage. The performance enhancement of the device may result from direct charge carrier trapping in rubrene. Energy transfer mechanism was also found in the EL process.

High brightness OLED with dual emitting layers

The bright white organic light-emitting diode can be obtained by using two major organic layers which emit blue and orange-yellow light, respectively. The two emitting organic materials 4,4-Bis(2,2-diphenyl-ethen-1-yl)-biphenyl (DPVBi) and 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminost-yry)-4H-pyran (DCM) doped into Tris(8-quin olinolato) aluminum (DCM:Alq 3) are used as a blue emitting and a orange-yellow emitting layer, respectively. The ratios of co-evaporated rate for DCM and Alq 3 could be controlled and the thickness of DPVBi was changed to get optimum result for white light. We got the maximum luminance 12,000 cd/m 2 at 15 V. The CIE coordinates were (0.3520, 0.2956) operated at 12 V entirely within the white light region in CIE coordinates. The current efficiency at 15 V was 6.7 cd/A. The optimum co-evaporated rate for DCM relative to Alq 3 to get orange-yellow emission in co-evaporation was 0.01:1 and the thickness of DPVBi was 35 Å.

Stable and highly bright white organic light-emitting diode based on 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine

A stable and very bright white organic light-emitting diode (WOLED) was fabricated with the structure ITO/m-MTDATA (30nm)∕NPB (30nm)/DPVBi (11nm)∕Alq3:DCJTB(50nm)∕LiF(1nm)∕Al(250nm). White light emission was achieved by combining blue and orange emissions emitted from DPVBi and Alq3:DCJTB layers, respectively. Inserting an m-MTDATA layer between ITO and NPB improved the charge balance in the recombination zone, improving the stability of the emission color of WOLED. The maximum luminance was 20590cd∕m2 at 13V with CIE coordinates of x=0.30, y=0.31. The maximum power and current efficiencies were 6.01lm∕W at 5V and 6.2cd∕A at 5V, respectively. Conversely, the WOLED without an m-MTDATA buffer layer exhibited unstable emission characteristic.

High bright white organic light-emitting diode based on mixing orange and blue emission

White organic light-emitting diodes have been everyone's attention recently. Suitable combination of greenish-red and blue emission can get white light emission. The structure is ITO/NPB/DPVBi/Alq 3:DCM/LiF/Al. N, N′-diphenyl- N, N′- (2-napthyl)-(1,1′-phenyl)-4,4′-diamine (NPB) is used as a hole transport layer. 4,4-Bis(2,2-diphenyl-ethen-1-yl)-biphenyl (DPVBi) and 4- (dicyanomethylene)-2- methyl-6-(4-dimethylaminost- yry)-4H-pyran doped into Tris(8-quinolinolato) aluminum (DCM:Alq 3) layers are used as blue-emitting and orange-emitting layers, respectively. The optimum co-evaporated rate is 0.01:1 for DCM relative to Alq 3 to get orange-light emission in coevaporation. LiF layer inserted is used as a buffer layer to increase the electron injection efficiency. The maximum luminance is 15000 cd/m 2 at 20 V and 8010 cd/m 2 at 12 V, whose CIE coordinates are x = 0.3520 , y = 0.2956 .

Multi-color display and its model for a white OLED combined with optical color filters

A bright white organic light-emitting diode (OLED) has been successfully fabricated in which a greenish-white emitting host Bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTZ)2) is doped with an orange-red fluorescent dye 5,6,11,12-tetraphenylnaphthacene (rubrene). The pure white light emission with CIE coordinates of (0.341, 0.334) is achieved at the driving voltage of 20V, and the corresponding luminance and external quantum efficiency are 4000Cd/m2 and 0.63%. On the other hand, the pure red, green, and blue (RGB) emissions are obtained from the white OLED combined well with RGB custom-built optical color filters (CFs) with peaks at 616, 556, and 456nm, respectively. Moreover, based upon the color mixture principles, we build a model of multi-color display mixed by the pure RGB emissions under the controllable bias.

Bright white organic light-emitting diodes based on two blue emitters with similar molecular structures

We show that highly efficient and chromatically stable white organic electroluminescent devices can be obtained, based on two blue emitters with similar structures: 9,10-di-(2-naphthyl)-anthracene (ADN) and 9,10-di-(2-naphthyl)-2-terbutyl-anthracene doped with yellow-orange emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) at ultralow doping concentrations (0.01%–0.05%). The relative intensity of the blue and orange-yellow emissions could be fine-tuned by varying the doping concentrations of rubrene in the host to achieve pure white emission. The energy-transfer mechanism of ADN and rubrene with ultralow doping concentrations is discussed in terms of the long exciton diffusion distance of ADN.

White organic light-emitting diodes based on 2,7-bis(2,2-diphenylvinyl)-9,9′-spirobifluorene: Improvement in operational lifetime

Very bright white organic light-emitting diodes were fabricated using 2,7-bis(2,2-diphenylvinyl)-9,9′-spirobifluorene (DPVSBF) doped with [4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran)] (DCJTB) as the emission layer. With a device configuration of ITO∕NPB(40nm)∕DPVSBF:0.2%DCJTB(11nm)∕Alq(30nm)∕LiF(1nm)∕Al(150nm), a brightness of 1575cd∕m2 with an external quantum efficiency of 3.31% and luminous efficiency of 8.00cd∕A, a power efficiency of 5.35lm∕W was achieved at a driving current of 20mA∕cm2 (4.7V). The brightness reached 66000cd∕m2 at 15V. The Commission Internationale de l’Eclairage coordinates stayed nearly constant, changed from (0.35, 0.36) to (0.32, 0.34) when the voltage increased from 6to12V. The relative operational lifetime of the device increased by a factor of ∼20 compared with a similar device based on 4,4′-bis-(2,2-diphenylvinyl)-1,1′-biphenyl as the source of the blue emission. The much extended half-lifetime was attributed to the higher morphological stability of the DPVSBF.

Highly-bright white organic light-emitting diodes based on a single emission layer

A very bright white organic light-emitting diode (OLED) was fabricated with a thin layer of 4-{4-[N-(1-naphthyl)-N-phenylaminophenyl]}-1,7-diphenyl-3,5-dimethyl-1,7-dihydro-dipyrazolo [3,4-b;4′3′-e]pyridine (PAP-NPA) doped with rubrene as the source of the white emission. Thus, with a simple three-layer structure of ITO/NPB(40 nm)/PAP-NPA:0.5% rubrene(20 nm)/TPBI(40 nm)/Mg:Ag, a white light with Commission Internationale de l’Eclairage (CIE) coordinates of (0.31, 0.33) were generated. The device gave a maximum brightness of ∼42 000 cd/m2 at 14 V, and maximum luminance efficiencies of 2.92 lm/W at 6.5 V and 6.11 cd/A at 7.0 V. The CIE coordinates stayed virtually constant when the voltage increased from 8 to 12 V. Furthermore, with a two-layer structure of ITO/PAP-NPA:0.4%rubrene(40 nm)/TPBI(40 nm)/Mg:Ag, the device also reached a stable white color with maximum brightness of ∼37 000 cd/m2 and maximum luminance efficiencies of 2.51 lm/W at 6.5 V and 5.57 cd/A at 8.5 V. The stability of the white color is attributed to the confinement of charge recombination zone in a single layer.

Bright white organic light-emitting diode

A very bright white organic light-emitting diode (OLED) was realized by using a bright blue-emitting layer, 1,7-diphenyl-4-biphenyl-3,5-dimethyl-1,7-dihydrodipyrazolo[3,4-b;4′,3′-e]pyridine (PAP-Ph), together with a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyry)-4H-pyran (DCM)-doped Alq [tris(8-hydroxyquinolinato) aluminum (III)] layer to provide blue, red, and green emission for color mixing. By appropriately controlling the layer thickness, the white light OLED achieved good performance of 24 700 cd/m2 at 15 V, 1.93 lm/W at 6.5 V, and >300 cd/m2 at 7.7 mA/cm2. The Commission Internationale de l’Eclairage coordinates of the emitted light are quite stable at voltages from 6 to 12 V, ranging from (0.35, 0.34) to (0.34, 0.35).