In this chapter, we discuss a number of optical and opto-electronic device applications such as light-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.
The field of organic semiconductors, has existed for several decades. Molecular crystals of acenes, phthalocyanines, small molecules and metal-organic complexes such as Alq3 were studied because of their photoconductive and semiconducting properties and also as an approach to probe the optoelectronic properies of biological membranes. Small organic semiconductor molecules blended in polymer hosts have already found a major application in xerography. Recently, there has been renewed commercial interest and research activity into organic semiconductors with the development of conducting and semiconducting conjugated polymers. These offer scope for preparing large area conducting films for lightweight conductors, electromagnetic shielding and large area semiconducting films for displays, solar cells and transistor arrays.
Since this book deals with thiophenes, we will not dwell on the more established small molecular organic semiconductors but will focus on oligo(thiophene)s and poly(thiophene)s. Oligo(thiophene)s can be viewed both as materials with great potentialfor devices, partly because of their high field-effect mobilities, and also as finite model systems for the poly(thiophene)s.
Mark Harrison email@example.com, Marburg, February 11, 1999