Periodic Reporting for period 2 - 3DALIGN (Enhancing the performance of 3D-printed organic thermoelectrics by electric field-assisted molecular alignment)
Reporting period: 2022-08-01 to 2024-01-31
Thermoelectrics (TEs) are important because they can convert heat directly into electrical energy and enable efficient heating/cooling. As such, they can contribute to mitigating the energy shortage of our society, enable new applications in the fields of wearable electronics, and provide powering solutions for the internet of things. However, the popularization of TEs has been hindered by 1) their low efficiency (especially at room temperature), 2) the use of rare/toxic materials, and 3) the difficulty to process those materials. In 3DALIGN, I target a 3-in-1 solution to these challenges by using for the first time electric-field-assisted molecular alignment of 3D-printed TE polymers. High electrical/low thermal conductivity is required for efficient TEs, but both conductivities go hand in hand in traditional inorganic TE materials. This paradigm can shift for polymers, which possess complicated molecular structures. Despite their relatively low electrical conductivity, conducting polymers are appealing for TEs due to their much lower thermal conductivity than inorganic TE materials. Existing studies of organic TEs have focused on finding new materials, but not much attention has been paid to molecular ordering, a known strategy to improve performance in organic transistors. I have recently developed a versatile method to induce molecular alignment in solution-processed polymers by using externally applied electric fields. In 3DALIGN, I propose to use this new method to boost the electrical conductivity of polymer TEs while inducing minimal alteration in their thermal conductivity. The high risk of this goal is mitigated by other advantages of using polymer TEs: polymers are less toxic and more abundant than inorganic TE materials; and they are easy to 3D print, enabling a simple fabrication route for large-area through-plane TE structures that will lead to novel applications. In conclusion, this project will shed light on the relationship between molecular ordering and transport properties of organic electronic materials. If successful, it will also introduce a breakthrough in the performance and feasibility of TEs.
Within the last 1.5 years of the project, I have built a promising team of young researchers, who are now experts in the field of organic thermoelectric (OTE). I have built from scratch a new lab to study OTE materials that is now smoothly running, and brought expertise in thermoelectrics to my institution, KU Leuven. My group has shown our latest results in the 9th Forum on New Materials (CIMTEC Congress, 2022) in Italy last June 2022. Those results include demonstrating the improvement of TE performance upon molecular alignment in thin films of a commercial benchmark material. We have also demonstrated the 3D printability of such material and have preliminary evidence of the effect of applying an external electric field in the morphology of the 3D printed parts.
We expect to demonstrate direct ink writing of OTE materials, which are highly aligned at a multiscale level (from molecular to mesoscopic level), and in which this specific imparted morphology leads to improved TE performance by increasing the ratio between electrical and thermal conductivity. At the same time, we will tackle the viability of the integration of such materials on flexible substrates to produce a prototype of a TE generator able to harvest heat from human skin to power electronic systems.