(596b) Facile Fabrication of Lead Chalcogenide Thin Films with Controlled Structure and Composition

Lead chalcogenides can be utilized as thermoelectric generators to recover waste energy lost as heat, thus they offer a path towards the realization of a sustainable energy future. Literature has shown that these materials have excellent thermoelectric properties for mid-temperature applications¹; however, current materials and synthetic methods are not efficient enough to be economical in most applications. Common bulk synthetic methods of the best performing materials involve high temperature melt steps, milling, and sintering². These processing steps are both energy intensive and low-throughput by nature, making them disadvantageous to economical material production. To this end, recent work has explored solution-processed routes to lead chalcogenide material fabrication³, as solution-processing can offer a lower-intensity and higher throughput alternative. Unfortunately, literature reports of materials produced in this manner have shown figures of merit that still fall short of those needed for economic implementation^3,4. The challenge then is to develop a facile synthetic route to lead chalcogenide materials that can optimize the properties required for high thermoelectric performance. Two of these key properties are appropriate feature sizes within the material and optimum dopant/alloy compositions to positively tune the thermoelectric efficiency⁵.

Our group has identified a route to overcoming this challenge that utilizes a thiol-amine reaction system. We have shown that combining a lead halide solution and a chalcogen solution in select thiol-amine mixtures leads to the creation of lead chalcogenide nanoparticles and their microscale assemblies⁶. This synthesis occurs instantaneously at room temperature and allows for control over assembly size through thiol-amine variations, making it both facile and tunable.

Building off of that work, in this report we exploit these assembly properties of PbTe in thiol-amine mixtures to fabricate PbTe thin films from solution at room temperature within the order of minutes. These films exhibit features on the length scale of nanometers to micrometers and display intimate contact amongst nano/micro-particles. This contact shows promise towards overcoming the traditional electrical limitations of solution-processed thermoelectric materials and eliminates the need for further processing often required by other techniques. With the reduced complexity and feature size relevant to improved thermoelectric properties, this method of film formation offers a facile alternative to traditional PbTe synthetic techniques.

To further demonstrate the tunability of this fabrication method, we will also present a novel room-temperature method of introducing selenium into these PbTe materials. This introduction of selenium allows us to create films that closely mirror the composition of materials from literature that display some of the highest reported thermoelectric figures of merit. We will then present the thermoelectric properties of the PbTe thin films resulting from this fabrication method and their dependence on grain size and composition. The capabilities of this fabrication method then offer promise towards a tunable, low intensity route amenable to large scale production of lead chalcogenide thin film materials.

References

1. Zhu, T. et al. Compromise and Synergy in High-Efficiency Thermoelectric Materials. Adv. Mater. 29, (2017).
2. Biswas, K. et al. High-performance bulk thermoelectrics with all-scale hierarchical architectures. Nature 489, 414–418 (2012).
3. Ding, D., Lu, C. & Tang, Z. Bottom Up Chalcogenide Thermoelectric Materials from Solution-Processed Nanostructures. Adv. Mater. Interfaces 4, 1–16 (2017).
4. Ding, D. et al. Interface Engineering in Solution-Processed Nanocrystal Thin Films for Improved Thermoelectric Performance. Adv. Mater. 29, (2017).
5. Snyder, G. J. & Toberer, E. S. Complex thermoelectric materials. Nat. Mater. 7, 105–114 (2008).
6. Miskin, C. K. et al. Lead Chalcogenide Nanoparticles and Their Size-Controlled Self-Assemblies for Thermoelectric and Photovoltaic Applications. (2019). doi:10.1021/acsanm.8b02125