Surface Chemistry and Band Engineering in AgSbSe₂: Toward High Thermoelectric Performance

Abstract

AgSbSe 2 is a promising thermoelectric (TE) ptype material for applications in the middle-temperature range. AgSbSe 2 is characterized by relatively low thermal conductivities and high Seebeck coefficients, but its main limitation is moderate electrical conductivity. Herein, we detail an efficient and scalable hot-injection synthesis route to produce AgSbSe 2 nanocrystals (NCs). To increase the carrier concentration and improve the electrical conductivity, these NCs are doped with Sn 2+ on Sb 3+ sites. Upon processing, the Sn 2+ chemical state is conserved using a reducing NaBH 4 solution to displace the organic ligand and anneal the material under a forming gas flow. The TE properties of the dense materials obtained from the consolidation of the NCs using a hot pressing are then characterized. The presence of Sn 2+ ions replacing Sb 3+ significantly increases the charge carrier concentration and, consequently, the electrical conductivity. Opportunely, the measured Seebeck coefficient varied within a small range upon Sn doping. The excellent performance obtained when Sn 2+ ions are prevented from oxidation is rationalized by modeling the system. Calculated band structures disclosed that Sn doping induces convergence of the AgSbSe 2 valence bands, accounting for an enhanced electronic effective mass. The dramatically enhanced carrier transport leads to a maximized power factor for AgSb 0.98 Sn 0.02 Se 2 of 0.63 mW m −1 K −2 at 640 K. Thermally, phonon scattering is significantly enhanced in the NC-based materials, yielding an ultralow thermal conductivity of 0.3 W mK −1 at 666 K. Overall, a record-high figure of merit (zT) is obtained at 666 K for AgSb 0.98 Sn 0.02 Se 2 at zT = 1.37, well above the values obtained for undoped AgSbSe 2 , at zT = 0.58 and state-of-art Pb-and Te-free materials, which makes AgSb 0.98 Sn 0.02 Se 2 an excellent p-type candidate for medium-temperature TE applications.

A low-temperature thermoelectric transport study of non-stoichiometric AgSbTe2

“…The presence of peaks at 528.9 eV and 540 eV corresponds to the Sb 0 32 and Sb 5+ oxidation state; the O1s peak at binding energy 531.5 eV may be accompanied by the presence of Sb 2 O 5 due to the surface oxidation of the material. 34 The Te 3d spectra contain four sub-peaks; two of them centered at approximately 572.36 eV and 582.94 eV correspond to 3d 5/2 and 3d 3/2 of Te 2− , and the other two peaks are associated with the Te–Te bonds 32 of minor-phase monoclinic Ag 2 Te.…”

Harvesting Thermal Energy through Pyroelectric and Thermoelectric Nanomaterials for Catalytic Applications

“…The ZT of representative TE materials such as Bi 2 Te 3 and PbTe is ≈1, which is currently believed to be the standard requirement for practical applications [47,48]. In pursuit of high conversion efficiency, several materials with high ZT values have been proposed recently, most of which are semiconductors with ultralow κ, including Bi 2 Te 3 [49][50][51], PbTe [52,53], SnSe [7,54,55], BiCuSeO [56,57], AgSbSe 2 [58], etc.…”

Unveiling Crucial Chemical Processing Parameters Influencing the Performance of Solution‐Processed Inorganic Thermoelectric Materials

“…To date, there has been limited work explaining the effects of each of the processing steps on the final material. Most reports have focused on developing new synthetic strategies for the particles, implementing novel surface treatments [15][16][17] or exploring thermal treatments [18][19][20] to achieve high performance. However, one of the most crucial processes has been completely neglected: the purification process.…”