A study of materials and devices for polymer electronics

University dissertation from Linköping : Linköpings universitet

Abstract: In recent years, much research has been conducted in the field of conjugated polymers. A very promising direction for applications of this research is toward polymerbased light emitting devices. Conjugated, semi-conducting polymers, otherwise known as "conducting polymers" in their oxidized or reduced states, have been shown to be very suitable for use as active material in light emitting devices. Thus, much of the research activity has been concentrated on the design and fabrication of light emitting devices. In such devices, there are many important parameters that determine device performance. In addition to the properties of materials, the interfaces between the different materials are very important in determining performance. In this work, we have studied organic materials, polymers and molecules, used in devices, as well as the devices themselves. The main experimental method to study the materials has been photoelectron spectroscopy. We have combined the experimental method with the results of quantum chemical calculations in order to obtain a better understanding of the chemical and electronic structure of the materials. Devices have also been made in attempts to extend the results from the basic studies of these materials and to get a better understanding of how the materials interact in a device.Much recent research has been focused on to increasing the quantum efficiency of the polymer based light emitting devices. In the first polymer based light emitting devices only one active emitting layer was used. In this thesis, one work is aimed at showing to increase the quantum efficiency of the device by using a polymer blend, with two different polymers in the emitting layer. Another way to increase the efficiency is to use several layers in the device. Normally there are two layers in common devices; one active emitting layer and one extra layer that decrease the energy barrier for the positive charges between the anode and the emitting polymer. The most common polymer used as a hole injecting layer is poly(3,4-ethylenedioxythiophene) blended with poly(4-styrenesulfonate), PEDOTPSS. Here we have studied the electronic structure of the monomer of PEDOT-PSS, namely ethylenedioxythiophene. The molecules have been studied in gas phase, in solid state, and interacting with a gold substrate. The understanding of interactions between polymers and metals is important for patterning, making printed circuits, in more advanced devices. Another way to increase the quantum efficiency is to incorporate an extra layer for injecting of electrons. This is normally the case in devices based on molecules. Here we have studied the electronic and chemical structure of some polymer very similar to some molecules that are used elsewhere in molecular based devices.

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