Synthesis of an electroluminescent polymer and its non‐doped light‐emitting diodes with stable green emission

An electroluminescent polymer was synthesized by Wittig condensation and characterized by the measurements of ¹H‐NMR, IR, gel permeation chromatography (GPC), UV–Vis, PL, and cyclic voltammetry (CV). The polymer can be dissolved in common organic solvents such as tetrahydrofuran (THF), chloroform, and dichloromethane. The electroluminescent investigation showed that the non‐doped devices with a double‐layer configuration (ITO/PEDOT:PSS/Polymer/Mg:Ag) have a stable green emission property. The maximum luminance of the annealed device reaches 2317 cd/m². The emission maximum and the CIE 1931 coordinate values are respectively stabilized at 552 nm and near (x, y) = (0.43, 0.55) with different voltages. Copyright © 2008 John Wiley & Sons, Ltd.     

Optically detected magnetic resonance studies of luminescence‐quenching processes in π‐conjugated materials and organic light‐emitting devices

It is widely recognized that nonradiative quenching of excitons by other excitons and polarons become the dominant decay mechanism of these excitons at high excitation densities. These quenching processes cause the roll‐off in the efficiency of organic light‐emitting devices (OLEDs) and prevent lasing at high injection current densities. This review presents the optically‐detected magnetic resonance (ODMR) evidence for these photoluminescence‐ and electroluminescence‐quenching processes. And while it provides such evidence for quenching of singlet excitons by polarons and triplet excitons, it reveals the central role of the strongly spin‐dependent annihilation of triplet excitons by polarons, since under normal excitation conditions the steady‐state polaron and triplet exciton populations are 100–10⁴ times the singlet exciton population. In addition, it also suggests that quenching of singlet excitons by bipolarons, likely stabilized by a counterpolaron or countercharge at specific sites, may also be a significant quenching mechanism that also affects the charge transport properties.     

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

Higher efficiency in the end‐use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid‐state electroluminescent materials and belong to the general area of solid‐state lighting (SSL). The two main technologies being developed in SSL are light‐emitting diodes (LEDs) and organic light‐emitting diodes (OLEDs), but in recent years, light‐emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition‐metal complexes (iTMCs). Cyclometalated complexes of Ir^III are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn‐on time, stability, efficiency, and color is presented.     

Spectral and Luminescent Properties and Electroluminescence of Polyvinylcarbazole with 1,8-Naphthalimide in the Side Chain

A novel copolymer with moieties capable of charge transport and light emission on the basis of polyvinylcarbazole and 1,8-naphthalimide is synthesized. A bright and stable electroluminescence from single layered structure is observed. White light emission can be easily realized by tuning the content of naphthalimide moieties or a number of naphthalimide derivatives. Such approach can be considered as a common way to create single layered light-emitting devices with a stable white emission.     

有机电致发光器件(OLED)的制备方法和工艺

有机发光器件经过40年的发展,特别是在近年,具有理想特性的有机电致发光器件(OLED)成为研究开发的热点.由于OLED具有超轻薄、低成本、低功耗、宽视角、全固化、自发光、驱动电压低(3～12V) 及可实现柔软显示等诸多突出的性能,OLED将成为很有前途的新一代的平板显示技术.本文首先回顾了有机电致发光显示器件的发展历史,对有机材料、发展现状和趋势等都做了简要的概括.然后对当前先进的OLED器件结构、显示的发光机理,特别是对实现全彩显示的方法及制备工艺进行了详细的描述.     

Electroluminescence and charge photogeneration in poly(9,9-dihexadecylfluorene-2,7-diyl) and its blends

Photoluminescence, electroluminescence (EL), charge photogeneration and transport were studied in poly(9,9-dihexadecylfluorene-2,7-diyl) (PFC16), poly[(2,5-dihexadecyl-1,4-phenylene)(1,4-phenylene)] (PPPC16) and their blends. Blending of PFC16 with PPPC16 led to a significant improvement of the EL efficiency and stability compared with the devices fabricated from the neat polymers. Efficient blue and white light-emitting devices (LEDs) were fabricated using the blends. The increase in the EL efficiency was attributed to modification of the charge injection, transport and recombination properties in the blend.     

Modification of poly(styrene-alt-maleic anhydride) with 1,3,4-oxadiazole units for electroluminescent devices

New copolymers of poly(styrene-alt-maleic anhydride) (PSMA) modified with 2-(4-aminophenyl)-5-(biphenyl-4-yl)-1,3,4-oxadiazole and hexylamine were prepared. The copolymers, characterized by UV-vis and FT IR spectroscopy, reached 1.22 mol % of the oxadiazole units relative to anhydride groups at the maximum (PSMA-4). Electric and optical properties of the copolymers were studied. The currents obtained depend strongly on the content of oxadiazole units in the copolymers. Currents measured in PSMA-4 were more than two orders of magnitude higher than those measured in the copolymers without oxadiazole. Using polymer blends made of poly(9,9-dihexadecylfluorene-2,7-diyl) and PSMA-4, blue light-emitting devices were fabricated and their photoluminescence and electroluminescence spectra were measured.     

Pyrazoloquinolines – alternative chromophores for organic LED fabrication

In this paper the synthesis of some new chromophores which could be used in polymer/organic LED fabrication are presented. All of them are pyrazoloquinoline (PAQ) derivatives. Their emission properties were tuned by side group substitution. They were characterized by absorption and photoemission spectroscopy. Some were used, dispersed in poly(N-vinylcarbazole) (PVK) matrix, as the emissive layer in LED structures.