Thermoelectric Materials Assembled from Nanocrystals

Nano- and mesostructuring of thermoelectric (TE) materials have emerged recently as a new paradigm to enhance the efficiency and manufacturability of TE modules. Switching from materials with large crystal grains to nano- and mesostructured compounds brings to the spotlight fundamentally important problems of morphological stability, grain growth, and inter-grain transport. The chemistry and physics of interfaces in TE devices remain largely underexplored. This is in stark contrast to, e.g., thin-film photovoltaics where grain boundaries have been studied in-depth for many years.<br/>We will first discuss the effect of interfaces on charge and heat transport in arrays of semiconductor nanocrystals (NCs) that represent a convenient model of nanostructured TE materials. Next, we will cover new chemical approaches for the rational design of the interfaces in nanostructured TE materials. The NCs themselves can serve as a “solder” for nano- and mesoscopic grains. During mild heat treatment, NCs fill up the voids between particles and act as a “glue” joining grains in hot-pressed pellets or solution-processed films. The chemical design of NC glue allowed for the selective enhancement or reduction of the majority carrier concentration near the grain boundaries, and thus resulted in doped or de-doped interfaces in granular TE materials. Chemically engineered interfaces can be further designed to optimize power factor and thermal conductivity.