Doping electroluminescence devices

Polyfarylene vinylene)s form an important class of conducting polymers. Two representative examples of this class of materials will be discussed in some detail here. There are poly(l,4-phenylene vinylcne) (PPV) 1, poly(l,4-thienylene viny-lenc) (PTV) 2 and their derivatives. The polymers are conceptually similar PTV may be considered as a heterocyclic analog of PPV, but has a considerably lowci band gap and exhibits higher conductivities in both its doped and undoped stales. The semiconducting properties of PPV have been shown to be useful in the manufacture of electroluminescent devices, whereas the potential utility of PTV has yet to be fully exploited. This account will provide a review of synthetic approaches to arylene vinylene derivatives and will give details an how the structure of the materials relate to their performance in real devices. 

Electroluminescent devices were made to demonstrate the possible application of these a-Si H materials. Er-doped p-n diodes in c-Si show electroluminescence, both in forward and reverse bias [670-672]. Under forward bias the electrolu-... 

J Kido, M Kohda, K Okuyama, and K Nagai, Organic electroluminescent devices based on molecularly doped polymers, Appl. Phys. Lett., 61 761-763, 1992. 

J. Kido and T. Matsumoto, Bright organic electroluminescent devices having a metal doped electron injection layer, Appl. Phys. Lett., 73 2866-2868 (1998). 

A. Fukase and J. Kido, Organic electroluminescent devices having self-doped cathode interface layer, Jpn. J. Appl. Phys., 41 L334-L336 (2002). 

J. Shi and C.W. Tang, Doped organic electroluminescent devices with improved stability, Appl. Phys. Lett., 70 1665-1667 (1997). 

M. Lee, H. Chen, C. Liao, C. Tsai, and C.H. Chen, Stable styrylamine-doped blue organic electroluminescent device based on 2-methyl-9,10-di(2-naphthyl)anthracene, Appl. Phys. Lett., 85 3301-3303 (2004). 

T Sano, H Fijii, Y Nishio, Y Hamada, H Takahashi, and K Shibata, Organic electroluminescent devices doped with condensed polycyclic aromatic compounds, Synth. Met., 91 27-30, 1997. 

Strontium thiogallate SrGa S iCe, doped with 4 mol% of cerium, gives a very good blue phosphor 455 nm), which has found to be useful in thin-film electroluminescent devices (see section 3.8.3.2). 

Although there are several potentially volatile cyclopentadienyl compounds for other transition metals [123], which could be utilised for AID processing, only a few have been studied in this respect. For example, volatile (C5H5)2Mn and (C5MeH4)Mn(CO)3 have been used as manganese sources for doping ZnS thin films to produce yellow-emitting thin-film electroluminescent devices [156]. 

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. ... 

Several examples have been reported recently of solution-processed multilayer electroluminescence devices incorporating semiconductor nanocrystals as the active recombination centers (16-18, 164). Recently, attention has also turned to hybrid electroluminescent devices involving transition metal-doped nanocrystals (104, 165-167). Although many challenges remain, including more specific exploitation of the dopants in many cases, the devices demonstrated to date represent a new direction in application of doped semiconductor nanocrystals made possible by the compatibility of these luminescent nanocrystals with solution processing methodologies. 

In one recent study, Mn2+-doped CdS nanocrystals grown with a ZnS passivating shell were used as the recombination centers in direct current (dc) electroluminescent devices (104). The Mn2+ CdS/ZnS nanocrystals were prepared by the inverse micelle procedure (102) (see Section II.C) and these colloids were incorporated into a multilayer device structure by spin-coat... 

Figure 120 The spectra of the two electroluminescent devices (I and II) containing organic phosphors, Ir(ppy)3 (a) (adapted from Ref. 304), and PtOEP (b) (see Ref. 493a, reprinted from Ref. 493a, Copyright 1998 Macmillan Publishers Ltd. [http //www.nature. com/]). The latter is compared with the EL spectrum of a device with no phosphor inside (III). For the chemical structures of the phosphors, see Fig. 31. The spectra from device I and II are characteristic of molecular phosphorescence as clearly seen from their comparison at different voltages with the PL spectrum (a). The DCM2-doped Alq3 layer of device III becomes dominated by their phosphorescene from the PtOEP-doped Alq3 layer in device II.

---