Poly(3,4-Ethylenedioxythiophene), a transparent conducting polymer with the acronym PEDOT that exhibits characteristics of Green Chemistry. PEDOT displays many qualities that make it considerable for use in applications as an environmentally friendly polymer. PEDOT has favorable properties of a low band gap, high conductivity, periodic dielectric modulation, low redox potential and it is self assembling.
Evolving from the monomer 3,4-
Ethylenedioxythiophene (EDOT), this polymer is unique in its ability to conduct. In the latter half of the 1980’s scientists from the Bayer AG research laboratories were first able to develop the polythiophere derivative,
Poly(3,4-Ethylenedioxythiophene.
PEDOT can be synthesized via two methods, either electrochemically or oxidatively. Under the principle of Prevention PEDOT has been considered for use in solar cells due to its favorable properties including high flexibility, low process temperature, and easy handling. Currently solar cells are coated with a transparent conductive material Indium Tin Oxide or Zinc Oxide. The coating is applied via sputtering of an argon plasma which causes damage to the emitter.
The MSDS lists the acceptable blood level of ITO to be 0.1 µg per L. A 30-year-0ld factory engineer who was “previously healthy, visited Tokyo’s Toranomon Hospital because of coughing and shortness of breath. He was diagnosed with pulmonary fibrosis and emphysema. His lungs also showed deposition of brown particles that turned out, in X-ray spectrometric analysis, to be indium and tin. His blood level of indium was 51 µg per L” It is clear why PEDOT would be considered as a replacement for ITO or ZnO. It exhibits the same or better properties than ITO or ZnO and it is not listed as a hazardous substance in the MSDS.
For a polymer, PEDOT has a very high conductivity (300 S/cm) and a boiling point of, 225°C respectively. It is also resistant to thermal degradation. Films of PEDOT/PSS can be heated in air to 100°C for over 1000 hours with only a minimal change in conductivity. PEDOT has also been considered to reduce static build up of plastics in dry air. Due to PEDOT’s ability to conduct charge and flexible nature it has been incorporated into many plastics including synthetic carpet.
A human being walking over synthetic carpet has the potential to create several thousand volts which is discharged when the individual touches a metal object. A similar effect is observed during the process of photographic film. During the winding cycle, a film that isn’t coated with PEDOT can develop a similar charge buildup. PEDOT is also instrumental in the packing industry and film VHS production. Primarily it is used to prevent static charging of electronic components as they are shipped.
Further improvements were made in 1992 when Chevrot found a way to synthesize the monomer unit using a four step process. This synthesis removes the particularly unpleasant reaction with CuO featured in the first synthesis (step 4). PEDOT’s transparency is related to its π-resonance chemical structure. Due to its extreme electron richness, pure PEDOT oxidizes in air and is stored under argon at low temperatures to avoid spontaneous polymerization.
With an ever increasing electronic world it seems the future of PEDOT and its derivatives will be bright. PEDOT has been considered for applications in carbon nanotubes and conductive rechargeable glassware. PEDOT has also been considered for applications in OLED devices such as televisions, and flat panel displays. It remains a prominent material for the dispersion of charge in anti-static bags used for shipping of sensitive electronic materials even currently. A more recent application of PEDOT was considered in terms of data storage. Researchers at Princeton University and HP Labs created a material that mimics a traditional CD that undergoes a permanent physical change when data is written to it.
However, instead of using a traditional laser read/write system, the material “plugs” into a circuit and contains no moving parts. This feature makes it extremely applicable for potable electronic devices that need to consume very little power. It was estimated that a gigabyte of data could be stored in a 1 cm cube. This is comparable to a modern (2008) flash drive in terms of storage versus size. The most modern application of PEDOT can be traced to flexible paper.
There have been previous reports of a novel type of flexible electronic paper that incorporates liquid powder technology. PEDOT is superior to ITO in this area because ITO is often cracked by mechanical deformation due to its inorganic crystalline structure. The current electronic paper of QR-LPD works by the formation of a large number of line-shaped electrodes (passive matrix driving) but high resolution patterns have not yet been developed . In terms of the future of this polymer, once high resolution displays become available these PEDOT based electrodes will replace tradition types of LCD panels reducing the amount of ITO and ZnO and replacing it with PEDOT, a more environmentally respected materials with better properties overall.
