Electro-optical polythiophene devices

Magnus Granstrom, Mark G. Harrison, and Richard H. Friend 

In this chapter, we discuss a number of optical and optoelectronic device applications such as hght-emitting diodes (LEDs), photovoltaic and photoconductive devices, field-effect optical modulator devices and all-optical modulator devices made from thiophenes. Following an introduction to the basic operating principles of each device, we will assess progress in the development of each type of device and focus on the underlying semiconductor physics issues. 

Since this book deals with thiophenes, we will not dwell on the more estabUshed small molecular organic semiconductors but will focus on oligo(thiophenes) and poly(thiophenes). Oligo(thiophenes) can be viewed both as materials with great potentials for devices, partly because of their high field-effect mobilities, and also as finite model systems for the poly(thiophenes). Structures of some oligo(thio-phenes) are shown in Fig. 2. 

As mentioned above, we identify two main reasons for studying oligomers of conjugated polymers  

Oligomers are well-defined systems of monodisperse (uniform-length) molecules, with greatly reduced occurrence of defects within the molecular chains, in comparison with polymers. They therefore offer the possibility of better ordering of the molecules and consequently more well-defined optical properties. This renders them particularly appealing for both theoretical and experimental investigations 

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