Transparent Conducting Polymers

Abstract

A conjugated polymer in neutral state is semiconductive. It becomes conductive after it is doped by oxidation or reduction. The optical properties of neutral conjugated polymers are predominantly determined by the electron transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), whereas the optical properties of conducting polymers are related to new energy levels, polaron and bipolaron levels, which are generated during oxidation or reduction. The appearance of the new energy levels significantly changes the optical properties. Some conjugated polymers with low energy band gap can have high transparency in the visible range after they are oxidized and become conductive. Poly(3,4-ethylenedioxythiophene) (PEDOT), its derivatives and analogues are the most popular transparent conducting polymers. This chapter reviews the preparation, structure, properties, and application of transparent conducting polymers, particularly the PEDOTs. PEDOTs can be prepared by solution chemical polymerization, vapor-phase polymerization, or electrochemical polymerization of its monomer. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) prepared by chemical polymerization in solution is particularly interesting because it can be dispersed in water and some polar organic solvents. High-quality PEDOT:PSS films can be readily prepared through solution processing techniques. Less conductive PEDOT:PSS has been used as the buffer layer in optoelectronic devices, such as organic and polymer light-emitting diodes (OLEDs and PLEDs) and organic and polymer solar cells (OSCs and PSCs). However, as-prepared PEDOT:PSS films from aqueous solution cannot be directly used as the transparent electrode of optoelectronic devices because its conductivity is below 1 S cm −1 . This conductivity is lower than the conductivity of indium tin oxide (ITO), the conventional transparent electrode material, by three to four orders of magnitude. A couple of methods have been developed to improve significantly

Conducting Polymers in the Fields of Energy, Environmental Remediation, and Chemical–Chiral Sensors

“…Band theory is based on Hückel’s molecular orbital theory (HMO) and was used at the end of the 1970s by Brédas to understand the CP properties known until then. , It has been continuously invoked to explain several CP properties. , Theoretical calculations suggest three absorption bands for the polaron and two for the bipolaron states, , and they have been experimentally observed in numerous CP absorption spectra (Figure ). − …”

“…Many of the interesting properties of CPs like optical response, − ionic and electronic conductivity, − surface tension, volume change, and tunable band-gaps , are direct consequences of the solid state redox reactions known as polymer charging/discharging (see section , Figure ), and have been exploited for technological applications (Table ). These properties can be controlled with the doping level of the material, and new possibilities for a wide range of industrial applications , are being developed.…”

Carbon Allotropes as ITO Electrode Replacement Materials in Liquid Crystal Devices

“…The chemistry, structure, and electronic transport properties have been reviewed in detail in some recent publications by Xia et al [63], Kayser and Lipomi [64], and very recently by Gueye et al [65] and by Huseynova et al [66].…”

Electrical Characterization of Thin PEDOT:PSS Films on Alumina and Thiol–Ene Substrates

“…One of the main drawbacks of PEDOT:PSS is associated with its relatively low inherent conductivity, which is usually below 1 S/cm. To improve conductivity, several methods, such as the addition of high-boiling-point polar organic solvents, ionic liquids, or surfactants; post-treatment with organic solvents, polar solvent vapor, salts, zwitterions, or acids; and combinations of these, have been explored, resulting in an increase in conductivity by two or three orders of magnitude [15][16][17][18][19][20]. Recently reported results demonstrated that it is possible to enhance the conductivity of PEDOT:PSS films to more than 4000 S/cm [21], which is comparable to that of indium tin oxide (ITO) and allows the PEDOT:PSS films to be used as transparent electrodes of touchscreens and solar cells.…”