New research by Faculty of Science professors Thomas Baumgartner and Christopher Caputo is challenging a long-held assumption about how electronic materials should be designed, opening a potential path toward lighter, more flexible and better-performing technologies for everyday life.
Silicon has been the foundation of modern electronics for decades, powering everything from computers to smartphones. Around the turn of the century, however, Baumgartner says researchers discovered that carbon-based materials, including some plastics, could be engineered to conduct electricity.
The finding led to a class of materials known as organic semiconductors, which are lightweight, flexible and potentially less expensive to manufacture than conventional electronic materials.
Despite their promise, and existing use in OLED displays in televisions and phones, they still lag behind silicon in many applications because they do not move electricity as efficiently. Scientists are working to overcome that limitation, including by refining a process known as doping, which involves introducing small amounts of another material to enable electricity to move more efficiently through a semiconductor.
While doping is widely used in traditional silicon-based electronics, researchers are still working to understand exactly how it functions in organic materials and how it can be made more effective. Improving that process could enhance the performance of carbon-based semiconductors and expand their use in future electronic devices.
鈥淒oping is one of the few levers to enhance the electronic performance of semiconductors,鈥 says Baumgartner. 鈥淒iscovering new ways of doping is critical to further drive this technology into our daily lives.鈥
For Baumgartner, Caputo and their collaborators, one of the biggest unanswered questions involved dopants known as Lewis acids. Researchers have known these materials can significantly boost the performance of organic semiconductors. One Lewis acid in particular, tris(pentafluorophenyl)borane (BCF), has repeatedly delivered better results than existing theories would predict, making it one of the field's enduring puzzles.
鈥淭here have been considerable inconsistencies in the literature,鈥 says Baumgartner. 鈥淭he parameters point to a different, yet unknown, mechanism for the doping with Lewis acids that we set out to unravel.鈥
In work in Nature Materials, Baumgartner and Caputo brought their chemistry expertise to a collaboration with researchers from Concordia University and the institut national de la recherche scientifique (INRS) specializing in device physics. Together, the interdisciplinary and inter-university team investigated why certain Lewis-acid dopants appeared to perform better than existing theories could explain.
鈥淲e have approached the work as a truly integrated team allowing us to leverage each of the different disciplinary pillars of the project to the fullest extent,鈥 says Caputo.
Researchers wanted to know why BCF performs so well and whether an overlooked process might be at work. They proposed and tested a new method called degradation-assisted doping, which suggests that the very process scientists typically try to avoid, a dopant breaking down, might help the material conduct electricity more effectively.
To investigate that possibility, the team combined laboratory experiments with theoretical modelling and computer simulations. By tracking what happened during the doping process and comparing the results against existing theories, they looked for evidence of the missing mechanism they suspected was at work.
Conventional wisdom suggests dopants should remain as stable as possible while they do their job. Instead, the researchers found evidence that the partial breakdown of the molecule can help the process continue. In effect, the breakdown removes a roadblock that would otherwise limit how much electrical charge can move through the material.
The discovery explains why BCF has consistently outperformed expectations and provides support for a new method the researchers call degradation-assisted doping. Beyond solving an ongoing puzzle, the finding provides a framework for developing future dopants. The team has already identified additional candidate materials for future study and believes the approach could guide the design of more effective organic electronic materials.
鈥淲ith this initial project, we have only scratched the surface of what is possible,鈥 says Baumgartner. 鈥淲hat sets organic semiconductors apart from traditional silicon-based systems is their inherent flexibility in molecular design using chemical synthesis. In essence, we can play molecular Lego庐 with suitable building blocks and assemble an almost infinite number of different semiconductor materials.鈥
That flexibility creates opportunities to develop new semiconductors and tailor-made dopants that take advantage of the newly identified mechanism. Over time, those advances could improve the performance of organic electronics and expand their use in technologies where lightweight, flexible materials offer advantages over conventional electronics.
鈥淪ince our work established a comprehensive understanding of the doping mechanism with Lewis acids, this has now opened the door to considerably expanding this strategy to different types of organic semiconductors and Lewis acids,鈥 says Caputo. 鈥淲e hope that our biggest impact will be stimulating the design and development of more powerful organic electronics with semiconductors whose performance is significantly enhanced by Lewis-acid doping.鈥