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We present a study of the electrical properties of electrochemically doped conjugated polymers using polymeric light-emitting electrochemical cells (PLECs) and interpreting the results according to a phenomenological model (PM) which assumes that, above the device turn-on voltage, the bulk transport properties of the doped organic semiconductor are responsible for the main contribution to the whole device conductivity. To confirm the predictions of this model, the dependence of the conductivity of PLECs with different parameters is evaluated and compared with the behavior expected for a doped semiconducting polymeric material. The organic semiconductor doping level, the blend concentration of organic semiconducting molecules, the device thickness, the charge carrier mobility, and the temperature are the parameters varied to perform this analysis. We observed that the device conductivity is independent of the active layer thickness, weakly dependent on the temperature, but strongly dependent on the semiconductor doping level, on the semiconductor fraction in the blend, and on the intrinsic charge carrier mobility. These results were well described by the variable range hopping (VRH) model, which has been widely employed to describe the charge transport in doped semiconducting polymeric materials, confirming the prediction of the phenomenological model. The current analysis demonstrates that PLECs are a suitable system for studying, in situ, the electrochemical doping of semiconducting polymers, permitting the evaluation of material properties as, for instance, the density of electronic charge carriers (and, consequently, the ionic charge carrier concentration) necessary to achieve the maximum electrochemical doping level of the organic semiconductor. [ABSTRACT FROM AUTHOR]

Cationic iridium(III) complexes represent the single largest class of emitters used in light emitting electrochemical cells (LEECs). In this chapter, we highlight the state-of-the-art emitters in terms of efficiency and stability in LEEC devices, highlighting blue, green, yellow/orange, red and white devices, and provide an outlook to the future of LEECs. [ABSTRACT FROM AUTHOR]

A phenomenological model has been developed to account for the results of impedance/admittance spectroscopy measurements from light-emitting electrochemical cells (LECs) comprising a polymer electrolyte and two different conjugated polymers used as organic semiconductor. The application of a d.c. offset bias superimposed to the a.c. modulation voltage was used to observe the transition from the behavior prior to device operation and after the formation of the electrochemical p-i-n junction. The analysis of the whole device 'conductivity' as a function of the applied bias and of the frequency was used to support the assumptions considered to develop the model. The results show that the device, after the p-i-n junction formation, can be considered as composed by two highly conductive electrochemically doped ( n and p) regions and a thin (few tens nanometers), insulating layer, where the electrical current is dominated by electronic charge carrier injection via tunneling through a rectangular energy barrier. Before the p-i-n junction formation, there is no doping of semiconductor material, and the device electrical properties are dominated by the intrinsic electronic charge carriers in the organic semiconductor. Results from devices made of organic semiconductors with different band gap energy and different layer thicknesses are used to corroborate the proposed model. [ABSTRACT FROM AUTHOR]

Light-emitting electrochemical cells (LECs) are a promising type of electroluminescent device for display and lighting applications. In this study, LECs based on ionic iridium complexes utilizing a tetrazole based ancillary ligand were fabricated and their electrical properties were investigated. Two new iridium(III) complexes with tetrazole based ancillary ligands, namely, [Ir(ppy)(tetrazole)]PF (complex 1) and [Ir(dfppy)(tetrazole)]PF (complex 2) (where ppy is 2-phenylpyridine, dfppy is 2-(2,4-difluorophenyl)pyridine, tetrazole is 5-bromo-2-(2-methyl-2H-tetrazol-5-yl)-pyridine and PF is hexafluorophosphate), have been synthesized and characterized. These synthesized complexes were used for the fabrication of LEC devices. LECs based on complex 1 result in orange light emission (576 nm) with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.45, 0.49), while complex 2 emits green (518 nm) electroluminescence with the CIE coordinates of (0.33, 0.49). Our work suggests that the light emission of cationic iridium complexes can easily be tuned by the substituents on the cyclometalated ligands. [ABSTRACT FROM AUTHOR]

Conjugated ployfluorene with 2-(2-(2-methoxyethoxy)ethoxy)ethyl groups (EO-PF) is prepared by the palladium-catalyzed Suzuki coupling reaction. The polymer is purified carefully by a simple chemical procedure. The inductively coupled plasma (ICP) test shows palladium-catalyst in the polymer can be removed by this procedure. The thermal properties, electrochemical properties, UV-Vis absorption properties, photoluminescence properties and electroluminescent properties of the polymer without (EO-PF1) or with purification (EO-PF2) are studied. EO-PF2 shows better PL CIE coordinates in THF solutions as blue light-emitting materials and better photoluminescence stability in thin solid films. Polymer light emitting diodes and electrochemical cells based on EO-PF2 exhibit somewhat improved optoelectronic performance than control devices of EO-PF1. [ABSTRACT FROM AUTHOR]