Use as hole transport layer

An important application of polydimethylsilane is as a source of silicon carbide (SiC) fibres, which are manufactured under the trade-name Nicalon by Nippon Carbon in Japan. Heating in an autoclave under pressure converts polydimethylsilane to spinnable polycarbosilane (-Me2Si-CH2-) with elimination of methane. The spun fibres are then subjected to temperatures of 1200-1400 °C to produce silicon carbide fibres with very high tensile strengths and elastic moduli." As a result of their conductivity, polysilanes have also been used as hole transport layers in electroluminescent devices. In addition, the photoconductivity of polymethylphenylsilane doped with Cgo has been found to be particularly impressive. ... 

Polythiophenes and MEH-PPV have been used as hole-transporting layers to replace the electrolyte in cells with TiC>2 electrodes (Gratzel cells). Bulk hetero-junction devices have been made by the hydrolysis in air of titanium(IV) wopropoxide, co-deposited in MDMO-PPV spin-coated films, to form TiC>2 nanoparticles (van Hal et al., 2003). While reasonable peak performance under monochromatic illumination has been reported, the performance as a solar cell does not match that of the photo-electrochemical cells. 

C.iii.c. Preparation of Small Molecules for Materials Science. Pd-catalyzed amination has also been used to prepare small molecules that are useful as hole-transport materials, selective metal-cation detection systems, and dyestuffs. As mentioned briefly in the section on reacting diarylamines with aryl halides, Marder and co-workers used palladium chemistry to form triarylamines, which are useful as hole-transport layers. Reactions of primary arylamines with aryl halides using DPPF-hgated palladium as catalyst allows for the selective addition of one aryl halide, followed by the addition of a second aryl halide to form mixed triarylamines, as shown in Eq. 42. This procedure has been used to generate unsymmetrical triarylamines that are analogs of TPD, as shown in Eq. 43. hi addition, they have used aminoferrocene as a substrate to conduct diarylations to form N, A-diarylaminoferrocenes. ... 

Fig. 11. Structure of LEDs. Poly silanes are used as hole transport layer or emissive layer.

K. Yamashita, T. Mori, T. Mizutani, H. Miyazaki, and T. Takeda, EL properties of organic light-emitting-diode using TPD derivatives with diphenylstylyl groups as hole transport layer, Thin Solid Films, 363 33-36 (2000). 

The emission maxima were at 2.39 and 2.21 eV for 4a and 4b respectively with photoluminescence (PL) quantum efficiencies of 5-8%. Monolayer devices using these materials showed non-uniform emission, but two-layer devices with PPV as hole-transport layer and aluminum or calcium cathodes showed bright and uniform emission with internal efficiencies of 0.01%. The EL emission is slightly red-shifted with respect to the PL emission. No increase in efficiency was detected from substitution of calcium for aluminum, indicating that the polymers were efficient electron acceptors, and the low efficiencies reflect the modest fluorescence efticiencies of the polymers 4. 

All the polymers containing aromatic oxadiazoles were found to be easily n-doped whereas they were difficult to p-dope as revealed by cyclic voltamme, indicating that they possess electron injection and hole blocking properties which make them suitable for use as charge transporting layers in multilayer polymer LEDs. It was also shown that oxadiazole polymers can used as emissive materials. 

Summary The use of differently substituted polysilanes as hole transport layers (HTL) in organic light-emitting diodes (OLEDs) was investigated. While hydrogen-substituted polysilanes deteriorate the diode behavior amino-substituted polysilanes lead to a significant improvement of the diode performance compared to a single-layer OLED. 

Spiro-TAD 56 has been used as hole-transport material in combination with Alqs as emitting layer, replacing TPD or a-NPE, which have been used in the original KODAK structures, but have substantially lower TgS than Spiro-TAD. Consequently, the devices are more stable against thermal treatment (Fig. 30). Whereas the performance of the TPD device breaks down at 70 °C, which cor-... 

USGS. The delocalization of a electrons in polysilanes gives rise to unique electronic and optical properties. Also, several polysilanes have been foimd to function as useful thermal precursors to silicon carbide fibers and these materials have attracted attention with respect to microlithographic applications and as polymerization initiators (1,27,28). The use of these materials as hole transport layers in electroluminescent devices has also been explored (42). Indeed, the photoconductivity of poly(methylphenylsilane) doped with Geo has been studied and has been found to be comparable with the best materials available (43). 

Adachi A, Manhart SA, Okita K, Kido J, OhsMta J, Kunai A (1997) Multilayer electroluminescent device using organosUicon polymer as hole transport layer. Synth Met 91 333-334... 

PVK doped with the appropriate substances can also exhibit some other useful properties. PVK containing blue, green or orange emitting fluorescent dyes was recently demonstrated to be useful as hole transport and emitting layer in organic electroluminescent devices [77,78]. 

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