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Hole-transport Layer (hole-transport + layer)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Long-Lifetime Polymer Light-Emitting Electrochemical Cells Fabricated with Crosslinked Hole-Transport Layers

ADVANCED MATERIALS, Issue 19 2009
Yan Shao
By inserting a crosslinkable hole-transport layer as the buffer layer between the single-phase polymer active layer and the anode of this new type of polymer light-emitting electrochemical cells (PLECs), the interface properties are improved and the PLECs can be operated with enhanced stability. [source]

Stable, Glassy, and Versatile Binaphthalene Derivatives Capable of Efficient Hole Transport, Hosting, and Deep-Blue Light Emission

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2010
Bin Wei
Abstract Organic light-emitting diodes (OLEDs) have great potential applications in display and solid-state lighting. Stability, cost, and blue emission are key issues governing the future of OLEDs. The synthesis and photoelectronics of a series of three kinds of binaphthyl (BN) derivatives are reported. BN1,3 are "melting-point-less" and highly stable materials, forming very good, amorphous, glass-like films. They decompose at temperatures as high as 485,545,°C. At a constant current density of 25,mA,cm,2, an ITO/BN3/Al single-layer device has a much-longer lifetime (>80,h) than that of an ITO/NPB/Al single-layer device (8,h). Also, the lifetime of a multilayer device based on BN1 is longer than a similar device based on NPB. BNs are efficient and versatile OLED materials: they can be used as a hole-transport layer (HTL), a host, and a deep-blue-light-emitting material. This versatility may cut the cost of large-scale material manufacture. More importantly, the deep-blue electroluminescence (emission peak at 444 nm with CIE coordinates (0.16, 0.11), 3.23 cd A,1 at 0.21,mA cm,2, and 25200,cd,m,2 at 9,V) remains very stable at very high current densities up to 1000,mA,cm,2. [source]

Long-Lifetime Polymer Light-Emitting Electrochemical Cells Fabricated with Crosslinked Hole-Transport Layers

Synthesis and properties of nitrogen-linked poly(2,7-carbazole)s as hole-transport material for organic light emitting diodes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2009
Tsuyoshi Michinobu
Abstract A novel class of carbazole polymers, nitrogen-linked poly(2,7-carbazole)s, was synthesized by polycondensation between two bifunctional monomers using the palladium-catalyzed amination reaction. The polymers were characterized by 1H NMR, Infrared, Gel permeation chromatography, and MALDI-TOF MS and it was revealed that the combination of the monomer structures is important for producing high molecular weight polymers. Thermal analysis indicated a good thermal stability with high glass transition temperatures, e.g., 138 °C for the higher molecular weight polymer P2. To pursue the application possibilities of these polymers, their optical properties and energy levels were investigated by UV-Vis absorption and fluorescence spectra as well as their electrochemical characteristics. Although the blue light emission was indeed observed for all polymers in solution, the quantum yields were very low and the solid films were not fluorescent. On the other hand, the HOMO levels of the polymers estimated from the onset potentials for the first oxidation in the solid thin films were relatively high in the range of ,5.12 to ,5.20 eV. Therefore, light emitting diodes employing these polymers as a hole-transport layer and iridium(III) complex as a triplet emitter were fabricated. The device of the nitrogen-linked poly(2,7-carbazole) P3 with p,p,-biphenyl spacer, which has a higher HOMO level and a higher molecular weight, showed a much better performance than the device of P2 with m -phenylene spacer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3880,3891, 2009 [source]

Tuning the Optoelectronic Properties of Carbazole/Oxadiazole Hybrids through Linkage Modes: Hosts for Highly Efficient Green Electrophosphorescence

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2010
Youtian Tao
Abstract A series of bipolar transport host materials: 2,5-bis(2-(9H -carbazol-9-yl)phenyl)-1,3,4-oxadiazole (o -CzOXD) (1), 2,5-bis(4-(9H -carbazol-9-yl)phenyl)-1,3,4-oxadiazole (p -CzOXD) (2), 2,5-bis(3-(9H -carbazol-9-yl)phenyl)-1,3,4-oxadiazole (m -CzOXD) (3) and 2-(2-(9H -carbazol-9-yl)phenyl)-5-(4-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (op -CzOXD) (4) are synthesized through simple aromatic nucleophilic substitution reactions. The incorporation of the oxadiazole moiety greatly improves their morphological stability, with Td and Tg in the range of 428,464,°C and 97,133,°C, respectively. The ortho and meta positions of the 2,5-diphenyl-1,3,4-oxadiazole linked hybrids (1 and 3) show less intramolecular charge transfer and a higher triplet energy compared to the para-position linked analogue (2). The four compounds exhibit similar LUMO levels (2.55,2.59,eV) to other oxadiazole derivatives, whereas the HOMO levels vary in a range from 5.55,eV to 5.69,eV, depending on the linkage modes. DFT-calculation results indicate that 1, 3, and 4 have almost complete separation of their HOMO and LUMO levels at the hole- and electron-transporting moieties, while 2 exhibits only partial separation of the HOMO and LUMO levels possibly due to intramolecular charge transfer. Phosphorescent organic light-emitting devices fabricated using 1,4 as hosts and a green emitter, Ir(ppy)3 or (ppy)2Ir(acac), as the guest exhibit good to excellent performance. Devices hosted by o -CzOXD (1) achieve maximum current efficiencies (,c) as high as 77.9,cd A,1 for Ir(ppy)3 and 64.2,cd A,1 for (ppy)2Ir(acac). The excellent device performance may be attributed to the well-matched energy levels between the host and hole-transport layers, the high triplet energy of the host and the complete spatial separation of HOMO and LUMO energy levels. [source]