The Importance of Surface Adsorbates in Solution‐Processed Thermoelectric Materials: The Case of SnSe

Abstract

Solution synthesis of particles emerges as an alternative to prepare thermoelectric materials with less demanding processing conditions than conventional solid‐state synthetic methods. However, solution synthesis generally involves the presence of additional molecules or ions belonging to the precursors or added to enable solubility and/or regulate nucleation and growth. These molecules or ions can end up in the particles as surface adsorbates and interfere in the material properties. This work demonstrates that ionic adsorbates, in particular Na+ ions, are electrostatically adsorbed in SnSe particles synthesized in water and play a crucial role not only in directing the material nano/microstructure but also in determining the transport properties of the consolidated material. In dense pellets prepared by sintering SnSe particles, Na remains within the crystal lattice as dopant, in dislocations, precipitates, and forming grain boundary complexions. These results highlight the importance of considering all the possible unintentional impurities to establish proper structure–property relationships and control material properties in solution‐processed thermoelectric materials.

Solution-Processed Inorganic Thermoelectric Materials: Opportunities and Challenges

“…Surface atoms have a different atomic environment that can significantly alter the particle’s surface energy and reactivity, both crucial parameters for the transformation that occurs during consolidation. The surface chemistry of the NPs is comprised of two different structural features: first, the termination atoms of the NPs, which are usually determined by the synthesis, and second, the adsorbates connected to the under-coordinated termination atoms. , The adsorption of species on the surface of the NPs occurs during synthesis or during postsynthetic treatments; such adsorbates can vary from molecules with long aliphatic chains to molecular or ionic species. , Such surface species can be viewed as an added tunable feature in guiding sintering and solid-state reactions during consolidation rather than an inescapable detriment (Figure ).…”

“…It should be noted that truly “naked” surfaces actually do not exist in solution. In order to be colloidally stable, particles need either to be sterically stabilized by bulky ligands or electrostatically charged, inevitably leading to the coprecipitation of ions when the particles are removed from solution . However, if suitable species are placed on the surface in combination with mild thermal treatments, “naked” surfaces might become possible.…”

Upcycling Silicon Photovoltaic Waste into Thermoelectrics

“…[ 21–25 ] Strategies such as band‐engineering, carrier scattering modulation, nanostructuring, resonant doping, and energy filtering have been well reported to enhance various aspects of thermoelectrics. [ 17,26–31 ]…”

“…[21][22][23][24][25] Strategies such as band-engineering, carrier scattering modulation, nanostructuring, resonant doping, and energy filtering have been well reported to enhance various aspects of thermoelectrics. [17,[26][27][28][29][30][31] In this work, we turn waste silicon PV into thermoelectrics by pulverizing polycrystalline silicon into powder, followed by pelletization into ingot. Germanium and phosphorus doping were carried out before the pelletization using spark plasma sintering.…”

In Situ Investigation of the Phase Transition at the Surface of Thermoelectric PbTe with van der Waals Control

“…Most studies of the PbTe phase transition mainly focused on the internal structure of the material [ 20 – 22 ], while the phase transition near the surface was rarely investigated. In addition, it is possible that surface state is closely related to their thermoelectric properties [ 23 , 24 ], and the phase transition near the surface could play an important part of the whole phase-transition process.…”