Cesium hydroxide doped tris-(8-hydroxyquinoline) aluminum as an effective electron injection layer in inverted bottom-emission organic light emitting diodes

We demonstrate highly efficient inverted bottom-emission organic light-emitting diodes (IBOLEDs) by using cesium hydroxide (CsOH) doped tris-(8-hydroxyquinoline) aluminum (Alq(3)) as the electron injection layer on indium tin oxide cathode, which could significantly enhance the electron injection, resulting in a large increase in luminance and efficiency. The maximum luminance, current efficiency, and power efficiency reach 21 000 cd/cm(2), 6.5 cd/A, and 3.5 lm/W, respectively, which are 40%-50% higher in efficiency than that of IBOLEDs with cesium carbonate (Cs2CO3) doped Alq(3) as the electron injection layer, where the efficiencies are only 4.5 cd/A and 2.2 lm/W.

The modification of self-assembled monolayer on indium tin oxide as cathode in inverted bottom-emitting organic light-emitting diodes

Self-assembled monolayers (SAMs) of a series of p-substituted benzoyl chlorides were formed on indium tin oxide as the cathode for the fabrication of inverted bottom-emitting organic light-emitting diodes (IBOLEDs). The studies on the efficiency of electron injection and device performances showed that the direct tunneling of electron and the formation of dipole associated with the monolayer-forming molecule lead to significant enhancement in electron injection. Consequently, the device efficiency is greatly improved.

Efficient white organic light-emitting diodes using europium complex as the red unit

Efficient white organic light-emitting diodes (WOLEDs) using europium complex as the red unit are presented. The WOLEDs were fabricated by using the structure of indium tin oxide (ITO)/N, N'-di(naphthalene-1-yl)-N, N'-diphenyl-benzidine (NPB)/4,4-N, N-dicarbazolebiphenyl (CBP) : bis(2,4-diphenylquinolyl-N, C-2) iridium (acetylacetonate) ((PPQ)(2)Ir(acac)) : Eu (III) tris(thenoyltrifluoroacetone) 3,4,7,8-tetramethyl-1,10-phenanthroline (Eu(TTA)(3)(Tmphen))/NPB/2-methyl-9,10-di(2-naphthyl)anthracene (MADN) : p-bis (p-N, N-di-phenyl-aminostyryl)benzene (DSA-Ph)/9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris(8-hydroxyquinoline) aluminium (Alq3)/LiF/Al.

Al/WO3/Au as the interconnecting layer for efficient tandem white organic light-emitting diodes

White light emission from tandem organic light-emitting diodes consisting of blue and red light units separated by a transparent interconnecting layer of Al/WO3/Au has been realized. The devices have a structure of indium-tin-oxide (ITO)/molybdenum oxide (MoO3) (8 nm)/N, N'-di(naphthalene-1-yl)-N, N'-diphenyl-benzidine (NPB)(100 nm)/p-bis(p-N, N-diphenyl-aminostyryl) benzene) (DSA-ph): 2-methyl-9,10-di(2-naphthyl) anthracene (MADN)(40 nm)/tris(8-hydroxylquinoline) aluminium (Alq(3)) (10 nm)/LiF(1 nm)/Al(2 nm)/WO3(3 nm)/Au(16 nm)/MoO3(5 nm)/NPB(60 nm)/Alq(3): 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)(30 nm)/Alq3(30 nm)/LiF(1 nm)/Al(150 nm).

Realization of blue, green and red emission from top-emitting white organic light-emitting diodes with exterior tunable optical films

We developed an approach to realize blue, green and red emission from top-emitting white organic light-emitting diodes (OLEDs) through depositing exterior tunable optical films on top of the OLEDs. Three primary colors for full color display including blue, green and red emission are achieved by controlling the wavelength-dependent transmittance of the multilayer optical films overlaid on the emissive layer.

Tuning the emissive colour of top-emitting organic light-emitting diodes by using exterior multilayer films

We demonstrate an approach for realizing colour-controllable light emission from top-emitting organic light-emitting diodes (TEOLEDs) by utilizing exterior multilayer films overlaid on them. The emissive colour varies from blue to red for the TEOLED with green tris(8-quinolinolato) aluminium as the emissive layer by tuning the exterior multilayer films. The theoretical simulation of the electroluminescence for the colour tunable TEOLEDs is demonstrated and accords well with experimental results. The advantage of this approach is that the optical and electrical characteristics of the TEOLED can be controlled individually and hence provides the feasibility to realize a full-colour display by using white TEOLEDs.

Performance Enhancement of Polymer Light-Emitting Diodes by Using Ultrathin Fluorinated Polyimide Modifying the Surface of Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate)

Herein, an insulating fluorinated polyimide (F-PI) is utilized as an ultrathin buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in polymer light-emitting diodes to enhance the device performance. The selective solubility of F-PI in common solvents avoids typical intermixing interfacial problems during the sequential multilayer spin-coating process. Compared to the control device, the F-PI modification causes the luminous and power efficiencies of the devices to be increased by a factor of 1.1 and 4.7, respectively, along with almost 3-fold device lifetime enhancement. Photovoltaic measurement, single-hole devices, and X-ray photoelectron spectroscopy, are utilized to investigate the underlying, mechanisms, and it is found that the hole injection barrier is lowered owing to the interactions between the PEDOT:PSS and F-PI. The F-PI modified PEDOT:PSS layer demonstrates step-up ionization potential profiles from the intrinsic bulk PEDOT:PSS side toward the F-PI-modified PEDOT:PSS surface, which facilitate the hole injection.

Efficient inverted top-emitting organic light-emitting diodes using ultrathin MoO3/C-60 bilayer structure to enhance hole injection

Efficient inverted top-emitting organic light-emitting diodes with aluminum (Al) as both the cathode and semitransparent anode are investigated. It is found that introduction of the ultrathin molybdenum trioxide (MoO3)/fullerene (C-60) bilayer structure between the low work function Al top anode and the hole-transporting layer dramatically enhances the device performance as compared to the devices with sole MoO3 or C-60 buffer layer. The ultraviolet photoemission spectroscopy and x-ray photoelectron spectroscopy indicate that the hole injection barrier between Al anode and hole-transporting layer is effectively reduced via strong dipole effect at Al/MoO3/C-60 interfaces with its direction pointing from Al to C-60.

Formation of low surface energy separators with undercut structures via a full-solution process and its application in inkjet printed matrix of polymer light-emitting diodes

In this paper, low surface energy separators With undercut structures were fabricated through a full solution process, These low Surface energy separators are more suitable for application in inkjet printed passive-matrix displays of polymer light-emitting diodes. A patterned PS film was formed on the P4VP/photoresist film by microtransfer printing firstly. Patterned Au-coated Ni film was formed on the uncovered P4VP/photoresist film by electroless deposition. This metal film was used as mask to pattern the photoresist layer and form undercut structures with the patterned photoresist layer. The surface energy of the metal film also decreased dramatically from 84.6 mj/m(2) to 21.1 mJ/m(2) by modification of fluorinated mercaptan self-assemble monolayer on Au surface. The low surface energy separators were used to confine the flow of inkjet printed PFO solution and improve the patterning resolution of inkjet printing successfully. Separated PFO stripes, complement with the pattern of the separators, formed through inkjet printing.

High efficiency fluorescent white organic light-emitting diodes with red, green and blue separately monochromatic emission layers

Highly efficient fluorescent white organic light-emitting diodes (WOLEDs) have been fabricated by using three red, green and blue, separately monochromatic emission layers. The red and blue emissive layers are based on 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) doped N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) and p-bis(p-N,N-diphenyl-amino-styryl) benzene (DSA-ph) doped 2-methyl-9,10-di(2-naphthyl) anthracene (MADN), respectively; and the green emissive layer is based on tris(8-hydroxyquionline)aluminum(Alq(3)) doped with 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl- 1H,5H,1[H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-1]-one (C545T), which is sandwiched between the red and the blue emissive layers. It can be seen that the devices show stable white emission with Commission International de L'Eclairage coordinates of (0.41, 0.41) and color rendering index (CRI) of 84 in a wide range of bias voltages.

Origin of improvement in device performance via the modification role of cesium hydroxide doped tris(8-hydroxyquinoline) aluminum interfacial layer on ITO cathode in inverted bottom-emission organic light-emitting diodes

It has been found that cesium hydroxide (CsOH) doped tris(8-hydroxyquinoline) aluminum (Alq(3)) as an interfacial modification layer on indium-tin-oxide (ITO) is an effective cathode structure in inverted bottom-emission organic light-emitting diodes (IBOLEDs). The efficiency and high temperature stability of IBOLEDs with CsOH:Alq(3) interfacial layer are greatly improved with respect to the IBOLEDs with the case of Cs2CO3:Alq(3). Herein, we have studied the origin of the improvement in efficiency and high temperature stability via the modification role of CsOH:Alq(3) interfacial layer on ITO cathode in IBOLEDs by various characterization methods, including atomic force microscopy (AFM), ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS) and capacitance versus voltage (C-V). The results clearly demonstrate that the CsOH:Alq(3) interfacial modification layer on ITO cathode not only enhances the stability of the cathode interface and electron-transporting layer above it. which are in favor of the improvement in device stability, but also reduces the electron injection barrier and increases the carrier density for current conduction, leading to higher efficiency.

Tungsten oxide doped N,N-'-di(naphthalen-1-yl)-N,N-'-diphenyl-benzidine as hole injection layer for high performance organic light-emitting diodes

By introducing tungsten oxide (WO3) doped N,N-'-di(naphthalen-1-yl)-N,N-'-diphenyl-benzidine (NPB) hole injection layer, the great improvement in device efficiency and the organic film morphology stability at high temperature were realized for organic light-emitting diodes (OLEDs). The detailed investigations on the improvement mechanism by optical, electric, and film morphology properties were presented. The experimental results clearly demonstrated that using WO3 doped NPB as the hole injection layer in OLEDs not only reduced the hole injection barrier and enhanced the transport property, leading to low operational voltage and high efficiency, but also improved organic film morphology stability, which should be related to the device stability. It could be seen that due to the utilization of WO3 doped NPB hole injection layer in NPB/tris (8-quinolinolato) aluminum (Alq(3))-based device, the maximum efficiency reached 6.1 cd A(-1) and 4.8 lm W-1, which were much higher than 4.5 cd A(-1) and 1.1 lm W-1 of NPB/Alq(3) device without hole injection layer. The device with WO3 doped NPB hole injection layer yet gave high efficiency of 6.1 cd A(-1) (2.9 lm W-1) even though the device was fabricated at substrate temperature of 80 degrees C.

Lead(IV) dioxide: an effective electron injection material to realize high-efficiency inverted top-emitting organic light-emitting diodes

Lead(IV) dioxide (PbO2) has been used as the electron injection layer (EIL) to realize high-efficiency inverted top-emitting organic light-emitting diodes (I-TOLEDs). It can be seen that the inserting of the PbO2 EIL significantly reduces operational voltage, thus greatly improving the current efficiency and power efficiency of fabricated I-TOLEDs. The 10-(2-benzothiazolyl)-1, 1, 7, 7-tetramethyl-2, 3, 6, 7-tetrahydro-1H, 5H, 11H-[1] benzopyrano [6, 7, 8-ij] quinolizin-11-one (C545T)-based I-TOLEDs with the PbO2 EIL exhibit a maximum current efficiency of 31.6 cd A(-1) and a maximum power efficiency of 14.3 lm W-1, which are both higher than 22.5 cd A(-1) and 5.4 lm W-1 of the I-TOLEDs with LiF as the EIL respectively. A detailed analysis with respect to the role mechanism of PbO2 in electron injection has been presented. The improvement in EL performance is attributed to the formation of the interfacial dipoles at the electrode interface due to charge transfer between PbO2 and Alq(3).

Simple and Efficient Near-Infrared Organic Chromophores for Light-Emitting Diodes with Single Electroluminescent Emission above 1000 nm

A series of NIR organic chromophores with donor-pi-acceptor-pi-donor structure are synthesized. Good thermal stability and strong photoluminescence in solid state render them suitable for application in light-emitting diodes. Exclusive near-infrared emission at 1080 nm with external quantum efficiency of 0.28% is obtained from the nondoped OLEDs. The longest electroluminescence wave-length is 1220 nm.

Synthesis and Application of Thiadiazoloquinoxaline-Containing Chromophores as Dopants for Efficient Near-Infrared Organic Light-Emitting Diodes

series of a donor-acceptor-donor type of near-infrared (NIR) fluorescent chromophores based on [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) as an electron acceptor and triphenylamine as an electron donor are synthesized and characterized. By introducing pendent phenyl groups or changing the pi-conjugation length in the TQ core, we tuned tile energy levels of these chromophores, resulting in the NIR emission in a range from 784 to 868 nm. High thermal stability and glass transition temperatures allow these chromophores to be used as dopant emitters, which can be processed by vapor deposition for the fabrication of organic light-emitting diodes (OLEDs) having the multilayered structure of ITO/MoO3/NPB/Alq(3):dopant emitter/BCP/Alq(3)/LiF/Al. The electroluminescence spectra of the devices based on these new chromophores cover a range from 748 to 870 nm. With 2 wt % of dopant 1, the LED device shows an exclusive NIR emission at 752 nm with the external quantum efficiency (EQE) as high as 1.12% over a wide range of current density (e.g., around 200 mA cm(-2)).