Holes electroluminescence devices

X. Jiang, R.A. Register, K.A. Killeen, M.E. Thompson, F. Pschenitzka, and J.C. Sturm, Statistical copolymers with side-chain hole and electron transport groups for single-layer electroluminescent device applications, Chem. Mater., 12 2542-2549, 2000. 

I. 3,5-triazine ethers as hole-blocking materials in electroluminescent devices, Chem. Mater., 10 3620-3625 (1998). 

C. Adachi, T. Tsutsui, and S. Saito, Organic electroluminescent device having a hole conductor as an emitting layer, Appl. Phys. Lett., 55 1489-1491 (1989). 

M. Kinoshita, H. Kita, and Y. Shirota, A novel family of boron-containing hole-blocking amorphous molecular materials for blue- and blue-violet-emitting organic electroluminescent devices, Adv. Func. Mater., 12 780-786 (2002). 

J.X. Tang, Y.Q. Li, L.S. Hung, and C.S. Lee, Photoemission study of hole-injection enhancement in organic electroluminescent devices with Au/CF anode, Appl. Phys. Lett., 84 73-75, 2004. 

S Tokito, K Nada, and Y Taga, Metal oxides as a hole-injecting layer for an organic electroluminescent device, J. Phys. D Appl. Phys., 29 2750-2753, 1996. 

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. ... 

Mizusaki et al. (5) prepared triphenylamine copolymers, (VI), which had hole transport properties that were used in organic electroluminescent devices. 

Kepler et al. (1995) measured electron and hole mobilities of tris(8-hydroxyquinoline)aluminum (Alq). Alq is of interest for electroluminescent devices. The photocurrent transients for both carriers were highly dispersive. Transit times could be resolved only from double logarithmic transients. The electron mobilities were approximately two orders of magnitude higher than hole mobilities. Figure 46 compares the room temperature electron and hole mobilities. The dashed line represents electron mobilities reported by Hosokawa et al. (1994). At 4 x 105 V/cm, the electron and hole mobilities are 1.4 x 10-6 cm2/Vs and 2.0 x 10-8 cm2 Vs. The activation energy for the electron mobility was reported as 0.56 eV. Later results of Lin et al. (1996) were in excellent agreement with the hole mobilities reported by Kepler et al. 

It should be noted here for triarylamine networks and dendrimers [104], respectively, the radical cations have interesting properties like the formation of high-spin polyradicals with ferromagnetic coupling [105] or conducting polymers [106]. Very often, triarylamines have been used as the hole-transport layer in electroluminescent devices [107]. 

Figure 1-1. Schematic drawing of a single-layer electroluminescent device. An applied electric field leads to injection of holes (positive charges the majortiy charge carriers in polymers such as PPV) and electrons (usually the minority charge carriers) into the light-emitting polymer film from the two electrode contacts. Formation of an electron-hole pair within the polymer may then result in the emission of a photon. Since holes migrate much more easily through PPV than electrons, electron-hole recombination takes place in the vicinity of the cathode.

K Imai, (1994). Multilayered organic electroluminescent device using a novel starburst molecule, 4,4, 4 -tiis(3-methylphenylphenylamino)triphenylamine, as a hole transport mateiiaL Appl. Phys. Lett., VoL 65, No. 7, pp. 807-809. 

Application of triphenylene-based polymers as a hole transport layer in electroluminescence devices was also studied. The triphenylene polyacrylate was spun on ITO substrate, on which Alq3 and A1 cathode were vacuum-deposited a brightness of 1390 cdm-2 was obtained at 4.5 V [100]. 

HOMO-LUMO gap of CN-PPV XIII is about 2.1 eV (590 nm) and two-layer electroluminescent devices made of ITO/PPV (as a hole transporting layer)/CN-PPV (as emitter)/Al or Ca, exhibit a red electroluminescence with a peak at 710 nm and a i7ext) of about 1 % [31]. The same two-layer configuration devices based on MEH-CN-PPV XIV exhibit a red-orange electroluminescence peaking at ca. 600 nm, a rjext = 2.5%, a luminous effiency of 2.5 lm/W, and a luminance of 1000 cd/m2 at 6 V [166,189]. The blue-shifted emission of MEH-CN-PPV in comparison with that of CN-PPV has been ascribed to a steric effect of the branched ethylhexyl side-chain, which induced a slight twisting of the polymer backbone. 

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