Jiangshan Chen

High‐Performance Hybrid White Organic Light‐Emitting Devices without Interlayer between Fluorescent and Phosphorescent Emissive Regions

By using mixed hosts with bipolar transport properties for blue emissive layers, a novel phosphorescence/fluorescence hybrid white OLED without using an interlayer between the fluorescent and phosphorescent regions is demonstrated. The peak EQE of the device is 19.0% and remains as high as 17.0% at the practical brightness of 1000 cd m(-2) .

Novel hole-transporting materials based on 1,4-bis(carbazolyl)benzene for organic light-emitting devices

Novel hole-transporting molecules containing 1,4-bis(carbazolyl)benzene as a central unit and different numbers of diphenylamine moieties as the peripheral groups have been synthesized and characterized. These compounds are thermally stable with high glass transition temperatures of 141–157 °C and exhibit chemically reversible redox processes. Their amorphous state stability and hole transport properties can be significantly improved by increasing the number of diphenylamine moieties in the outer part and by controlling the symmetry of the carbazole-based molecules. These compounds can be used as good hole-transporting materials for organic electroluminescent (EL) devices. The device performance based on tri- and tetra-substituted carbazole derivatives is comparable to that of a typical 4,4′-bis[N-(1-naphthyl)-N-phenylamino] biphenyl (NPB)-based device.

Solution-processable small molecules as efficient universal bipolar host for blue, green and red phosphorescent inverted OLEDs

Inverted organic light-emitting diodes (IOLEDs) with a bottom cathode are of great interest for large-size active-matrix displays due to their easy integration with n-type thin film transistors (TFTs) based on low-cost and highly-uniform amorphous silicon and oxide. In this work, a solution-processable electron transporting material 2,7-bis(diphenylphosphoryl)-9,9′-spirobi[fluorene] (SPPO13) is employed to blend with a solution-processable hole transporting material 4,4′,4′′-tri(9-carbazoyl)triphenylamine (TCTA) to be used as a universal bipolar co-host for blue, green and red phosphors, and for the first time, phosphorescent IOLEDs are fabricated by solution-processing small molecules. High efficiency and reduced efficiency roll-off are achieved in the solution-processed IOLEDs, which mainly contribute to the high quality of the solution-processed small molecule films as well as the balanced charge injection in the co-host system. Importantly, the solution process is advantageous over vacuum evaporation to deposit multi-component small molecule films, and can be expected to reduce manufacturing costs. Our results demonstrate a promising approach to fabricate low-cost and high-performance IOLEDs for n-type TFT-based displays.

A simple carbazole-N-benzimidazole bipolar host material for highly efficient blue and single layer white phosphorescent organic light-emitting diodes

A new simple carbazole-N-benzimidazole bipolar luminogen mNBICz was constructed and utilized as a host for an FIrpic-doped blue device, and exhibited high efficiencies with a ηEQE,max of 26.2%, a ηC,max of 54.5 cd A−1 and a ηP,max of 52.2 lm W−1. Furthermore, a two-color, all-phosphor single layer white device displayed a ηEQE,max of 22.9%, a ηC,max of 62.5 cd A−1 and a ηP,max of 60.4 lm W−1.

Ultrathin nondoped emissive layers for efficient and simple monochrome and white organic light-emitting diodes.

In this paper, highly efficient and simple monochrome blue, green, orange, and red organic light emitting diodes (OLEDs) based on ultrathin nondoped emissive layers (EMLs) have been reported. The ultrathin nondoped EML was constructed by introducing a 0.1 nm thin layer of pure phosphorescent dyes between a hole transporting layer and an electron transporting layer. The maximum external quantum efficiencies (EQEs) reached 17.1%, 20.9%, 17.3%, and 19.2% for blue, green, orange, and red monochrome OLEDs, respectively, indicating the universality of the ultrathin nondoped EML for most phosphorescent dyes. On the basis of this, simple white OLED structures are also demonstrated. The demonstrated complementary blue/orange, three primary blue/green/red, and four color blue/green/orange/red white OLEDs show high efficiency and good white emission, indicating the advantage of ultrathin nondoped EMLs on constructing simple and efficient white OLEDs.

Single-layer organic memory devices based on N,N′-di(naphthalene-l-yl)-N,N′-diphenyl-benzidine

We report a single-layer organic electrically bistable device made of N,N′-di(naphthalene-l-yl)-N,N′-diphenyl-benzidine sandwiched between two electrodes. The measured current-voltage characteristics show two states of different conductivities at the same applied voltage—high-conductance state (ON state) and low-conductance state (OFF state)—and the two states are reproducible by applying a negative writing voltage. It was found that the ratio of the ON∕OFF current depends strongly on the writing voltage, and the bistable characteristics were yet retained for up to hours and days before reading the device after applying a writing voltage. Furthermore, more than 106 write-read-erase-reread cycles have been performed in ambient conditions without degradation. These properties show the devices promising for high-density, low-cost memory application.

High power efficiency tandem organic light-emitting diodes based on bulk heterojunction organic bipolar charge generation layer

The significant enhancement in power efficiency of tandem organic light-emitting diodes (OLEDs) was achieved using bulk heterojunction organic bipolar charge generation layer (CGL), consisted of zinc phthalocyanine (ZnPc): fullerene (C60) blend. In addition to a significant enhancement in luminance and current efficiency this work yielded a maximum power efficiency of 21 lm W−1 for a tandem OLED, notably almost two times higher than that of a single-unit device, with a maximum power efficiency of 10.1 lm W−1. The enhancement in power efficiency at higher luminance is also over 50%. The remarkable enhancement in power efficiency has been attributed to the effective charge generation, transport and extraction due to the presence of interface-modified ZnPc:C60 CGL in tandem OLEDs. Our results demonstrate that the bulk heterojunction, consisting of two matched n- and p-type organic semiconductors, is a promising bipolar CGL for high power efficiency tandem OLEDs.

Tandem white phosphorescent organic light-emitting diodes based on interface-modified C60/pentacene organic heterojunction as charge generation layer

The significant improvement of power efficiency and efficiency roll-off in tandem white organic light-emitting diodes (WOLEDs) was achieved using interface-modified C60/pentacene organic heterojunction as charge generation layer (CGL). The resulting tandem WOLED exhibits a maximum power efficiency of 53.8 lm W−1 and a maximum current efficiency of 101.5 cd A−1 without any out-coupling techniques. More importantly, the efficiency roll-off is greatly improved, yet remaining power efficiency of 53 lm W−1 at 100 cd m−2 and 45 lm W−1 at 1000 cd m−2, which outperforms that of the conventional CGL-based tandem WOLED. This clearly demonstrates that the organic heterojunction is a promising CGL for high-performance tandem WOLEDs.

Negative differential resistance effect in organic devices based on an anthracene derivative

The authors observed a negative differential resistance (NDR) in organic devices consisting of 9,10-bis-(9,9-diphenyl-9H-fluoren-2-yl)-anthracene (DPFA) sandwiched between Ag and indium tin oxide electrodes. The large NDR shown in current-voltage characteristics is reproducible, resulting in that the organic devices can be electrically switched between a high conductance state (on state) and a low conductance state (off state). It can be found that the currents at both on to off states are space-charge limited and attributed to the electron traps at the Ag/DPFA interface. The large and reproducible NDR makes the devices of tremendous potential in low power memory and logic circuits.

A Small‐Molecule Zwitterionic Electrolyte without a π‐Delocalized Unit as a Charge‐Injection Layer for High‐Performance PLEDs

Small-molecule zwitterionic materials were found to be more efficient as charge-injection materials in an organic electronic device than a previously described polymer (see structures). Furthermore, the superior device performance observed for 1 indicates that it is not necessary to focus only on π-delocalized systems and that solid ionic liquids may be promising alternative candidates for charge-injection materials.