Hole-transporting layer conductivity

A typical vaponr deposited EL device consists of a glass snbstrate coated with a conducting transparent indinm tin oxide electrode, on top of which is a 100-500 A hole transport layer (HTL), followed by a thin (= 100 A) light emitting layer (EML), then a 100-500 A electron transport layer (ETL) and finally a cathode of an alloy such as Mg Ag. This is illustrated in Fignre 3.32. 

Jung JW, Lee JU, Jo WH (2009) High-efficiency polymer solar cells with water-soluble and self-doped conducting polyaniline graft copolymer as hole transport layer. J Phys Chem C 114 633... 

Fehse K, Olthof S, Walzer K, Leo K, Johnson RL, Glowatzki H, Broker B, Koch N (2007) Energy level alignment of electrically doped hole transport layers with transparent and conductive indium tin oxide and polymer anodes. J Appl Phys 102 073719... 

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. ... 

A solid-state solar cell was assembled with an ionic liquid—l-ethyl-3-methylimidazolium bis(trifluoromethanesulfone)amide (EMITFSA) containing 0.2 M lithium bis(trifluoromethanesulfone)amide and 0.2 M 4-tert-butylpyridine—as the electrolyte and Au or Pt sputtered film as the cathode.51,52 The in situ PEP of polypyrrole and PEDOT allows efficient hole transport between the ruthenium dye and the hole conducting polymer, which was facilitated by the improved electronic interaction of the HOMO of the ruthenium dye and the conduction band of the hole transport material. The best photovoltaic result ( 7p=0.62 %, 7SC=104 pA/cm2, FOC=0.716 V, and FF=0.78) was obtained from the ruthenium dye 5 with polypyrrole as the hole transport layer and the carbon-based counterelectrode under 10 mW/cm2 illumination. The use of carbon-based materials has improved the electric connectivity between the hole transport layer and the electrode.51... 

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]. 

As you can see, the fabrication is rather simple. Yet, the light output rivals many of the LED s and is certainly more than the output of phosphor screens in certain devices. A conductive layer is required for electron injection into the electron transport layer (ETL). The metal electrode (ME) is composed of Al, Ag or Ag-Mg, and is usualfy light reflective. The hole transport layer (HTL) Injects holes from the transparent electrode (TE) into the HIL. The point where the excitons, i.e.- pairs of holes electrons, recombine is the b ht emitting (LE) region. This can vary according to the type of compounds used to form the two organic layers. These devices can be classified as ... 

The basic structure of a typical OLED is shown in Fig. 3.1 [35]. It consists of a transparent conducting anode, typically indium tin oxide (ITO) coated on a glass or plastic mechanical support, the organic layers, and a metal cathode. The thickness of OLEDs (excluding the mechanical support) is typically <0.5 j,m. Under forward bias electrons are injected from the low-workfunction cathode into the electron-transport layer (ETL). Similarly, holes are injected from the high-workfunction ITO into the hole-transport layer (HTL). Due to the applied bias, the electrons and holes drift toward each other, and typically recombine in a recombination zone near, or at, the ETL/HTL interface. A fraction of the recombination events forms radiative excited states. The radiative decay of these states provides the electroluminescence (EL) of the device. 

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. ... 

Adsorption of small redox-active molecules (e.g. ferrocene [326]) on ITO can be used to probe changes in electrochemical activity of ITO surface as a function of surface pretreatment [314]. Adsorption of ferrocene dicarboxylic add (Fc(COOH)2) and 3-thiophene acetic acid (3-TAA) onto ITO was achieved by soaking ITO in a 1 mM solution of these small molecules in pure ethanol for 10 min and then rinsing briefly with acetonitrile [314-316]. To ensure reproducibility, the adsorption of Fc(COOH)2 on pretreated ITO was repeated a minimum of three times on three separate ITO samples, for each pretreatment condition [314]. Chemisorbed small molecules on ITO will provide for better direct contact of added conducting polymer layers and/or hole transport layers (HTLs) in the devices [316],... 

The low oxidation (p-doping) potential of poly(oxythiophene)s along with high conductivity, transparency and stability of doped state make them ideal as a transparent conductor and as a hole-transport layer in various optoelectronic devices. On the other hand, alkyl-substituted EDOT and ProDOT derivatives are suitable for electrochromic applications. However, PEDOT remains one of the most extensively studied polymers in this class due to the easy commercial access of EDOT monomer and processable PEDOT polymers (Clevios-P). 

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