Writing in the journal Energies, a team of researchers from MIT and the University of Mississippi has reviewed the latest advances in conducting and semiconducting polymers.
Study: Recent Progress in Conjugated Conducting and Semiconducting Polymers for Energy Devices. Image Credit: nevodka/Shutterstock.com
Semiconducting Polymers
Polymers have received increased research interest recently due to their potential as organic conducting materials. They have a rich history, but several critical challenges need to be addressed in research to fully understand them and unlock their potential.
To be considered for real-world applications, semiconducting polymers must be stable, cost-effective, and scalable. PEDOT is the most widely used polymer for this purpose so far.
These materials present a metal-free alternative for semiconductors to expensive and resource-critical electrocatalytic metals such as platinum. Polymers possess the potential to accelerate electron transfer at their surfaces, making them good electrocatalysts. Semiconducting and conducting polymers have attracted attention due to the existence of both electronic and ionic conduction in materials. Ionic transport mechanisms are multiple-step processes.
Several key factors govern ionic conduction behavior in conducting and semiconducting polymers. For instance, each process is unique and possesses its own dynamics. Additionally, localized backbone structural reorganization occurs, and conformational changes can change the polymer’s morphology.
Upon increased ionic intercalation, electrostatic forces increase. Furthermore, polymers interact with electrolytes, and surface charge transfer can occur in the presence of solvents and electrolytes.
Controlling Polymer Nanostructure, Surface Morphology, and Texture
Controlling the nanostructure and surface texture as well as the morphology of semiconducting polymers is central to tuning and enhancing their properties. Tuning the material’s nanostructure avoids localized charge carriers. Research has focused on developing new fabrication methods to achieve the desired polymer surface morphology and nanostructure, as fabrication methods play a vital role in achieving the desired material properties.
Recently developed methods to achieve this are based on chemical vapor deposition processes. These methods include iCVD and oCVD. Further research into modifying and optimizing chemical vapor deposition-based methods has the potential to expedite the commercial adoption of polymers for semiconducting applications.
Optimizing Semiconducting Polymer Parameters
As has been mentioned, the nanostructure, morphology, and texture of semiconducting polymers must be tuned to achieve the desired electrochemical properties and device performance.
The main parameters that need to be optimized are thin-film orientation, intra- and inter-chain couplings, crystallite size, π-π stacking distance, and doping level. Carrier mobility and density optimization is essential for enhancing the optoelectronic performance and electrical conductivity of materials.
One of the main challenges in semiconducting polymer design is achieving optimal carrier mobility in the presence of high carrier density. Again, this requires precise control of the polymer’s nanostructure to avoid carrier localization and reduced device performance.
Extending the polymer chains enhances carrier charge mobility by providing more bridges between neighboring crystallites, achieving a percolating pathway that improves charge transport. The high edge-on or face-on orientation of crystals in the polymeric structure yields low-angle grain boundaries. This crystalline orientation and short π-π stacking distance aid in enhancing the crystallite bridging and consequent charge transport improvements.
Potential Applications for Semiconducting Polymers
There has been a growing demand for semiconducting polymers in recent years due to their sustainability, non-toxicity, enhanced electrochemical properties, cost, durability, safety, and replacement of critical and expensive electrocatalytic metals.
Polymers have been explored for real-world applications such as photovoltaics, grid-scale energy storage, redox flow batteries, thin-film transistors, gas sensors, heat exchangers, supercapacitors, lithium-ion batteries, and wearable electronics. Numerous studies have concentrated on developing advanced polymer materials for these applications.
Other potential applications of semiconducting polymers include actuation, drug delivery, corrosion protection, and environmental remediation.
In Conclusion
The study has provided a comprehensive review of current perspectives and research progress in the field of conducting and semiconducting polymers and provides pertinent information for future studies in this area. A literature review of seventy-two studies has been performed by the authors.
The authors have highlighted the importance of tuning the nanostructure, texture, and surface morphology of polymers to optimize their mechanical, electrochemical, and optoelectronic properties. As noted by the authors, fabrication methods play a key role in the design of polymeric materials, and several fabrication methods have been explored recently based on chemical vapor deposition processes.
Semiconducting polymer design is a highly challenging area of materials science research, with potential benefits for the manufacture of several next-generation energy harvesting and storage components for devices from flexible, wearable electronics to grid-level energy storage for renewable electricity technologies.
Realizing the full potential of this important class of organic conductors will help to increase the electrification of industry and achieve net-zero carbon emission targets by 2050.
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Further Reading
Gharahcheshmeh, M.H & Gleason, K.K (2022) Recent Progress in Conjugated Conducting and Semiconducting Polymers for Energy Devices Energies 15(10) 3661 [online] mdpi.com. Available at: https://www.mdpi.com/1996-1073/15/10/3661
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