Conducting organic polymers (COPs) possess many of the useful properties of organic polymers while exhibiting electrical conductivity like semiconductors, making them well-suited to a wide range of optoelectronic applications. With the support of the Marie Skłodowska-Curie programme, the Tuning COPs project set out to enhance the potential of these materials with ways to tune their conductive and optical properties.
Harnessing a unique paradox
Electrons and photons are interdependent. Absorption of light (photons) can excite electrons to higher energy levels. As the electrons relax to lower energy levels, photons are often emitted. This process is typically well defined by the electron configurations of the materials or molecules and their atoms. Poly(3,4-ethylenedioxythiophene) (PEDOT), is an intensely studied COP. Unlike most conductors that are opaque exactly because the free electrons that make them good conductors also favour absorption of photons, PEDOT is a transparent conductor. In its commercially available forms including those doped with the polymer polystyrene sulfonate (PEDOT:PSS), PEDOT can exhibit photoluminescence and electrical conductivity. This makes it useful in applications including displays, antistatic films, photovoltaics, printed wiring, and sensors. One way to change these properties is by adding or removing electrons (reduction or oxidation, respectively). Clara Viñas i Teixidor, professor of the Institute of Materials Science of Barcelona, project supervisor, explains: “The photoluminescence and electrical conductivity of PEDOT-based materials are dependent only on the physical deposition method and cannot be tuned. We sought to exploit application of a redox potential to tune both the polymer and the doping agent.”
Leaving no stone unturned
Viñas’s research produced impressive results. She demonstrated a simple and efficient way to achieve tuning by focusing on the accompanying cations of the doping anions, which determine the stoichiometries of the COPs that, in turn, influence the electrochemical properties. This outcome was featured on the cover of ‘Chemistry – A European Journal’. While investigating the intended use of metallacarboranes as tuneable doping anions, Viñas also serendipitously discovered their photoredox catalytic property and apparent thermoelectrical capacity. Experimental and computational studies of metallacarboranes led to papers regarding photoluminescence in bivalent and trivalent metallacarboranes.
Paving the way to future applications
“It was exciting to find that, after so many years of COPs research, something as trivial as the accompanying cation – usually considered innocent, or having a clear and predictable oxidation state – was able to modify the stoichiometry of the conducting polymer and alter its physicochemical properties,” says Viñas. Importantly, this capacity to tune photoluminescence and conductivity properties is not possible in these same polymers with other doping anions and should spur advances in applications including light emitting diodes, electroluminescent materials, and organic solar cells, to name a few. Exploiting the possible thermoelectrical properties of these materials could also encourage their use in heat recovery devices. Viñas concludes: “The next steps involve finding ways to produce the same materials in a processable way. This has been, and is, the weak link for the sustainable development of these extremely attractive materials. Overcoming this barrier will open the door to tremendous opportunities for commercialisation.” Establishing collaborations with industrial partners could ensure a bright future for European leadership in the field of tuneable COPs for numerous cutting-edge applications.
Tuning COPs, photoluminescence, conductivity, conducting organic polymers (COPs), electrons, poly(3,4-ethylenedioxythiophene) (PEDOT), photons, doping, anions, metallacarboranes, photoredox, thermoelectrical