Infoscience

Thesis

Synthesis of Cyanine Polyelectrolytes and Anions for Organic Electronic Devices

Many practical applications among organic electronic devices have been demonstrated over the last decades. They are considered as promising alternatives to inorganic semiconductor technologies due to the potential of cost-effective fabrication, excellent performance and versatile functionalities such as flexibility, portability and transparency. In this work, we mainly focused on the investigation of a special class of organic semiconductors, cyanine dyes. Starting with the synthesis of cyanine polyelectrolytes (Cy-Poly) and novel anions, new functionalities such as orthogonal solubility, crosslinking capability and photosensitizing ability were introduced and the corresponding materials as active components in organic electronic devices were explored. The utilization of cyanines allows for the mixed ionic/electronic conduction in solid organic semiconducting thin films. Due to the presence of mobile anions, an ionic junction is created as a result of the ionic motion towards respective metal electrodes. This leads to electrochemical oxidation and reduction within the organic thin film and the establishment of a built-in electric field across the intrinsic region with potential energy shifts. The electronic conductivity is considerably enhanced in the doped zones, which facilitates charge injection from the electrodes. The remarkable potential drop in the intrinsic region enables light emission of the electroluminescent materials as well as a photovoltaic response upon white light illumination. A special interest was given to the stabilization of ionic junctions in cyanine dye organic electronic devices by chemically fixing the ionic carriers in the desired position. Unexpected exciton quenching behavior was observed in the devices containing the immobilizable phenyl azide anions, which was attributed to the triplet sensitization effect of trimethine cyanines on the photodecomposition of 4-azido benzoate ions.

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