Electroluminescence polysilanes

J Kido, K Nagai, Y Okamoto, and T Skotheim, Electroluminescence from polysilane film doped with europium complex, Chem. Lett., 20 1267-1270, 1991. 

V. Cimrova and D. Vyprachticky, Enhanced electroluminescence from light-emitting devices based on poly(9,9-dihexadecylfluorene- 2,7-diyl) and polysilane blends, Appl. Phys. Lett., 82 642-644, 2003. 

Polysilanes are cr-conjugated polymers composed of Si-Si skeletons and organic pendant groups. They are insulators with filled intramolecular valence bands and empty intramolecular conduction bands. However, because of strong cr conjugation, they have rather narrow band gaps of less than 4 eV [24,25] and are converted to conductors by photoexcitation or by doping electron donors or acceptors. Recently they have attracted much attention because of their potential utility as one-dimensional conductors, nonlinear optical materials, and electroluminescent materials [26-28]. 

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. ... 

The fluorescence of polysilanes has received much attention in recent years, in part because of the discovery that some poly silanes are electroluminescent, and so may have applications in display technology. Fluorescence spectra, quantum yields, lifetimes and other properties for dialkylpolysilanes have been thoroughly investigated by Sun and coworkers.98 Dialkylpolysilanes exhibit fluorescence of a rather normal type, in which the emission is a mirror image of the absorption, with a rather small Stokes shift. This suggests that the emission takes place from a highly delocalized state, probably an... 

The discovery that polysilanes show luminescence in an electric field, electroluminescence, has aroused considerable interest in the possible use of polysilanes in light-emitting diodes and other electronic devices.101102... 

The photoconductivity of polysilanes was described in Section 5.8, and their electroluminescence is covered in Section 5.9.2. These properties make polysilanes possible components of polymer light-emitting diodes, either as charge transport layers or as the actual emissive materials.146 A drawback of the polysilanes is their photodegradation under ultraviolet irradiation, a problem which must be overcome if polysilanes are to become commercially useful. 

Polysilanes are air-stable Si-Si backbone polymers that exhibit efficient emission in the UV spectral region, high hole mobility, and high nonlinear optical susceptibility [28]. These properties arise from delocalization of a electrons along the Si-Si chain. Polysilanes have been employed as fluorescent materials for radiation detection, as electroluminescent materials for display devices, and as photorelractive materials for holographic data storage [28]. 

The HTL enhances exciton formation and recombination in the emissive layer by blocking the electrons away from the ITO anode and efficiently injecting holes into the electroluminescent layer. Polysilanes which are insulators for electrons have a good hole mobility of around lO cm A s due to a-conjugation of the electrons along the polymer chain. Moreover they are usually transparent in the whole visible region. These properties make them interesting candidates for application as hole transport layers in LEDs. 

Silicon-based materials with unique (opto)electronic properties photoluminescent materials for flat panel technology, displays, light-emitting diodes, sensors electroluminescence, nonmetallic conductors, e.g. siloles, polysilanes, 2,3-diphenyl-1-silacyclobutene chemistry design and application of liquid crystals. 

Suzuki, H., and Hoshino, S., Behavior of charge-carriers and excitons in multilayer organic light-emitting diodes made from a polysilane polymer as monitored with electroluminescence, J. Appl. Phys., 79, 858-865 (1996). 

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). 

Another intensively studied area of research with numerous contributions from Japan is the use of polysilanes as UV emitters in OLEDs. In polysilane based UV OLEDs with a layered design, the polysilane acts as semiconducting and emitting layer. The first UV OLED using polymethylphenylsilane was published in 1995 [119] but electroluminescence was only detectable at very low temperatures (77 K). Luminescence was drastically reduced at higher temperatures, the reason for this being a thermally induced conformational change of the silicon... 

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