Semiconductors, conjugated polyme

The tunability of a Shottky diode based on a semiconductor/conjugated polymer (doped) interface has been explored electrochemically manipulating the work function of the conjugated polymer [66]. In the above case, the work function along with the charge carrier concentration and the nature of interface decide the LED characteristics. 

The apphcation of a high electric field across a thin conjugated polymer film has shown the materials to be electroluminescent (216—218). Until recentiy the development of electroluminescent displays has been confined to the use of inorganic semiconductors and a limited number of small molecule dyes as the emitter materials. Expansion to the broad array of conjugated polymers available gives advantages in control of emission frequency (color) and facihty in device fabrication as a result of the ease of processibiUty of soluble polymers (see Chromogenic materials,electrochromic). 

The opportunity to synthesize new conjugated polymers with improved properties began to attract the attention of a larger number of synthetic chemists in the 1980s. Equally important was the subsequent development of stable, processible metallic polymers. As a result of these efforts, we now have a class of materials which exhibit a unique combination of properties the electronic and optical properties of metals and semiconductors in combination with the processing advantages and mechanical properties of polymers. 

Despite the scientific progress and the demonstration of novel device concepts, there was considerable skepticism that semiconducting polymers would ever reach the levels of purity required for long-lifetime commercial devices. In the context of the last 50 years of semiconductor physics, conjugated polymers were often... 

Primary Photoexcitations in Conjugated Polymers Molecular Exciton versus Semiconductor Band Model (Ed. N.S. Sariciftci) World Scientific, Singapore 1997. 

For spin-1/2 excitations such as electrons and holes in normal semiconductors or polarons in conjugated polymers, a single resonance is found centered at the Field... 

In low-dimensional systems, such as quantum-confined. semiconductors and conjugated polymers, the first step of optical absorption is the creation of bound electron-hole pairs, known as excitons [34). Charge photogcncration (CPG) occurs when excitons break into positive and negative carriers. This process is of essential importance both for the understanding of the fundamental physics of these materials and for applications in photovoltaic devices and photodctcctors. Since exciton dissociation can be affected by an external electric field, field-induced spectroscopy is a powerful tool for studying CPG. 

Several attempts to use otganic polymeric semiconductors as the active component in photovoltaic devices have been reported during the last two decades. Interest in the photovoltaic properties of conjugated polymers like polyacelylcne, various derivatives of polythiophenes and poly(para-phenylene vinylene)s arose from... 

In a first approximation, conjugated polymers with a high charge earner concentration can be described as p-lype semiconductors whereby holes seem to be the majority charge earners. Depending on the workfunction of the polymer rela-... 

Conjugated polymers doped with C60 become p-type semiconductors [305,306] some LB films of two polyalkylthiophenes mixed with arachidic acid and doped with C60 have been prepared [307]. The films of polyalkylthiophene + arachidic acid -l- C60 (spread from mixtures of 1.0 0.33 0.1 ratio) on ITO glass had a well-defined layer structure, as confirmed by x-ray diffraction. The bilayer distance obtained from the Bragg equation was 5.6 nm, the same as for arachidic acid LB films. Since the films were spread on subphases containing... 

Preliminary measurements of electrical conductivity of the conjugated derivatives of PBTAB, PBTB and PTTB obtained by the above treatment with bromine vapor are poor semiconductors with a conductivity of the order 10 °S/cm which apparently is not due to doping. Subsequent electrochemical or chemical doping of these polymers lead to 4-6 orders of magnitude increase in conductivity. Ongoing studies of the electrical properties of these conjugated polymers with alternating aromatic/quinonoid units will be reported elsewhere. 

The partial oxidation of conjugated polymers is generally referred to as p-doping, again in analogy to other semiconductor materials, but the basic process is the removal of electrons as in any other branch of chemistry, i.e.,... 

Agrawal, G. P. Cojan, C. Flytzanis, C. "Nonlinear Optical Properties of One-Dimensional Semiconductors and Conjugated Polymers," Phys. Rev. 1978, B17, 776. 

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