Ligand-Mediated Band Engineering in Bottom-Up Assembled SnTe Nanocomposites for Thermoelectric Energy Conversion

Abstract

The bottom-up assembly of colloidal nanocrystals is a versatile methodology to produce composite nanomaterials with precisely tuned electronic properties. Beyond the synthetic control over crystal domain size, shape, crystal phase, and composition, solution-processed nanocrystals allow exquisite surface engineering. This provides additional means to modulate the nanomaterial characteristics and particularly its electronic transport properties. For instance, inorganic surface ligands can be used to tune the type and concentration of majority carriers or to modify the electronic band structure. Herein, we report the thermoelectric properties of SnTe nanocomposites obtained from the consolidation of surface-engineered SnTe nanocrystals into macroscopic pellets. A CdSe-based ligand is selected to (i) converge the light and heavy bands through partial Cd alloying and (ii) generate CdSe nanoinclusions as a secondary phase within the SnTe matrix, thereby reducing the thermal conductivity. These SnTe-CdSe nanocomposites possess thermoelectric figures of merit of up to 1.3 at 850 K, which is, to the best of our knowledge, the highest thermoelectric figure of merit reported for solution-processed SnTe.

Enhanced Thermoelectric Performance by Surface Engineering in SnTe-PbS Nanocomposites

“…Combining the enhanced power factor and the significantly reduced thermal conductivity allowed achieving a remarkable ZT enhancement with respect to bare SnTe at high temperatures, increasing from 0.47 to 0.82 at 873 K, Figure 7 c. Compared with other bottom-up assembled SnTe [ 14 ], SnTe-PbS nanocomposites revealed moderately high ZT while utilizing more facile and inexpensive synthetic methods.…”

“…Recently, the bottom-up assembly of solution-processed nanoparticles (NPs) has provided the possibility to design alternative nanostructured materials while utilizing mild synthesis methods and inexpensive equipment [ 13 , 14 ]. Most metal chalcogenides thermoelectric materials have been produced by bottom-up solution methods, such as PbQ, Bi 2 Q 3 , SnQ (Q = Te, Se, S), etc.…”

Enhanced Thermoelectric Performance of n-Type Bi2Se3 Nanosheets through Sn Doping

“…However, the strong correlation between these parameters makes the optimization of the material performance extremely difficult. Several strategies have been developed to maximize ZT, including engineering the electronic band structure of the TE material through doping [7], the use of energy filtering interphases [8], and the reduction in lattice thermal conductivity through the introduction of abundant grain boundaries [9]. Commercial devices use large amounts of highly crystalline Bi 2 Te 3 -based alloys as the active TE material, which accounts for a significant part of the total cost of the device.…”

Synthesis of small Ag–Sb–Te nanocrystals with composition control

“…In the context of thermoelectrics, such bottom-up fabrication of semiconductors has been shown to increase interface scattering 20,21 and thus improve thermoelectric performance. Thermoelectrics assembled from nanocrystals of Bi 2 Te 3 22,23 , PbS-Ag 21,24 , CuFeSe 2 25 and other materials 26,27 , which are then sintered, show lower thermal conductivity compared to bulk materials. Achieving better control of the individual nanocrystal building blocks and nanocrystal surface (i.e., which often become the grain boundaries of sintered films) allow highly flexible design of thermoelectric devices.…”