Bernard TANGUY, Ph.D. Candidate 40th cycle, University of Trento, DICAM

A large share of global energy production depends on thermal processes, which result in the release of substantial amounts of waste heat into the environment. Currently, nearly 60% of primary energy is lost as residual heat. Recovering and harnessing this waste heat for energy generation could significantly improve the efficiency of these processes. Thermoelectric generators (TEGs) offer a promising avenue for sustainable energy conversion by harnessing the Seebeck effect to convert waste heat into electrical power. Typically constructed using both p- and n-type semiconductors, these generators are interconnected in series and configured in a π-type geometry to form a TEG module.

Conversely, by exploiting the Peltier effect, where an electric current is applied to generate a temperature gradient, thermoelectric materials can also be used for cooling applications across various applications, such as in electronic devices.

The efficiency of the heat-to-electric energy transformation of a TEG is proportional to its figure of merit, defined as zT=(S^2 σ)/κ T, where S is the Seebeck coefficient, σ is the electrical conductivity, T the absolute temperature, and κ is the thermal conductivity, which is composed of a lattice (κ_l) and electronic (κ_e) contributions (κ= κ_l+κ_e). However, since heat propagation is mainly governed by κ_l, an effective approach for reducing κ is producing thin film materials such that phonons with wavelengths larger than the thin film thickness are eliminated. Therefore, the performance of thin-film TEGs is only determined by the improvement of the electrical properties in the so-called power factor, PF=S^2  σ=S^2/ ρ, where ρ is the electrical resistivity.
Despite their potential, widespread adoption of TEGs is hindered by challenges in materials sustainability, fabrication scalability, and optimization of device performance. The present project aims to address these challenges through a multifaceted approach that combines advances in material science, fabrication techniques, and system integration strategies. 
During my PhD, I will focus on developing thin film TEG devices based on eco-friendly, available, non-toxic, and cost-effective materials such as copper-sulphide-based compounds, including, Cu2SnS3 (CTS), CuFeS2 (CFS), and Cu2ZnSnS4 (CZTS). By exploring the thermoelectric properties of these materials and optimizing device geometry, doping strategies, and material patterning techniques, the main goal is to achieve TEGs with enhanced efficiency compared to already reported devices in literature. 

Fabrication techniques will be explored, including wet ink deposition and dry route via thermal evaporation methods for material synthesis and TEG fabrication. Characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDXS), will be employed to analyse material properties. The thermoelectric properties of the thin films will be assessed using facilities available in our laboratories, such as Hall effect measurements and two-contact Seebeck coefficient measurements. Additionally, current-voltage-power measurements will be conducted to evaluate the performance of entire thin-film TEGs. Further analyses and measurements will be supported through collaborations with national and international research groups.
The objectives of this research include the development of sustainable p-n TEGs, optimization of fabrication techniques for scalability and commercial viability, systematic investigation of device geometry and doping strategies (using Ag, Mn, In, Na), and integration of TEGs with complementary sustainable technologies.
This research aims to advance the development of efficient, scalable, and environmentally friendly TEGs for diverse energy-harvesting applications and sustainable power generation. Part of the work is already published in the following publication [1]. 

[1]    T. Bernard, M. A. Malagutti, K. Lohani, M. D’Incau, N. Ataollahi, and P. Scardi, “Environmentally friendly p-type CTS-based thin-film thermoelectric generator,” J. Mater. Sci., vol. 59, no. 32, pp. 15491–15503, Aug. 2024, doi: 10.1007/s10853-024-10104-w.