PEDOT: A Revolutionary Conducting Polymer

Introduction

Poly(3,4-ethylenedioxythiophene), commonly known as PEDOT, is a fascinating conducting polymer that has been a subject of extensive research over the past few decades. With its unique properties, PEDOT holds tremendous potential for applications across diverse fields ranging from electronic devices to biomedical technologies.

Chemical Structure and Properties

PEDOT is a thiophene-based polymer which in its oxidized state exists as polythiophene cation with a positively charged backbone. It has a monomer unit consisting of 3,4-ethylenedioxythiophene (EDOT) which provides solubility and processability due to polar ethylene dioxy groups. The presence of these side groups helps to overcome aggregation issues commonly seen in conducting polymers.

The backbone of PEDOT can adopt planar and rigid conformations enabling high carrier mobility. It has a low band gap of around 1.5 eV which makes it highly conductive even at low doping levels. PEDOT displays good environmental, thermal and electrochemical stability. It is less oxidatively and chemically reactive compared to other conducting polymers like polypyrrole and polyaniline.

PEDOT is usually processed from its oxidized form as PEDOT:PSS (polystyrene sulfonate), which enhances its solubility and film forming ability. The sulfonate anions in PSS act as counter ions to balance the positive charges on PEDOT backbone imparting high conductivity. PEDOT:PSS has high transparency, is solution processable and can be deposited easily on various substrates using techniques like spin coating, inkjet printing etc.

Production Methods

PEDOT can be synthesized using chemical and electrochemical polymerization techniques. However, the most common method employed commercially is chemical oxidative polymerization. In this process, EDOT monomer is oxidatively polymerized using chemical oxidizing agents like iron(III) salts in the presence of a polymerization mediator like pyridine.

The oxidized form of polymer (PEDOT) is then treated with PSS to obtain PEDOT:PSS dispersion. This dispersion has high thermal stability and remains stable for months without any precipitation. PSS not only aids in solubility but also prevents over-oxidation of PEDOT chains during processing. Commercially available PEDOT:PSS dispersions have conductivity in the range of 0.1-1000 S/cm.

Applications of PEDOT

With its low cost, good stability and film forming ability, PEDOT:PSS has become immensely popular for transparent electrode applications in recent times. It is being widely used as a replacement for expensive materials like indium tin oxide in touchscreen panels, OLED and LCD displays. PEDOT:PSS electrodes offer advantages such as flexibility, light weight and anti-glare properties.

PEDOT is also finding increasing use in bioelectronics and biomedical devices. Its native electrical conductivity and biocompatibility make it attractive for technologies like neural implants, biosensors, tissue engineering scaffolds. PEDOT coatings have been shown to enhance cell adhesion and growth on neural probes and enhances their performance. PEDOT coated neural probes cause minimal tissue damage and show great potential for brain-machine interfaces.

PEDOT is also a promising material for energy storage applications such as supercapacitors and batteries. PEDOT coated electrodes have high specific capacitance and cycling stability. PEDOT allows fast ion transport and reduces polarization effects improving electrochemical performance. Research is ongoing on PEDOT-based cathodes for lithium and sodium ion batteries.

PEDOT is an emerging material for thermoelectric applications as well. Doped and composite forms of PEDOT have demonstrated high Seebeck coefficients and electrical conductivity making it suitable for waste heat recovery. PEDOT nanostructures also show potential for efficient dye sensitized solar cells and organic photovoltaics due to its ability to transport photogenerated charges with minimum recombination losses.

PEDOT is a unique conducting polymer that has revolutionized fields ranging from electronics and energy storage to biomedical engineering, due to its excellent conductivity, environmental stability and film forming ability. Continuous efforts are being made to functionalize PEDOT structure and fabricate nanostructured forms to further enhance its properties. With rapid advancements in science and processing techniques, PEDOT promises to significantly impact technologies of the future.

For more insights, Read- PEDOT