Facile Surfactant‐Free Synthesis of p‐Type SnSe Nanoplates with Exceptional Thermoelectric Power Factors

Abstract

As urfactant-free solution methodology,s imply using water as as olvent, has been developed for the straightforwards ynthesis of single-phase orthorhombic SnSe nanoplates in gram quantities.Individual nanoplates are composed of {100} surfaces with {011} edge facets.H ot-pressed nanostructured compacts (E g % 0.85 eV) exhibit excellent electrical conductivity and thermoelectric power factors (S 2 s)a t5 50 K. S 2 s values are 8-fold higher than equivalent materials prepared using citric acid as as tructure-directing agent, and electrical properties are comparable to the best-performing,extrinsically doped p-type polycrystalline tin selenides.T he method offers an energy-efficient, rapid route to p-type SnSe nanostructures.Growing global energy demands,together with the negative impacts resulting from combustion of fossil fuels,h ave diverted attention to technologies for sustainable energy generation and conversion.[1] Thermoelectrics realize direct inter-conversion between thermal and electrical energy and provide opportunities to harvest useful electricity from waste heat (and conversely to perform refrigeration). Thet hermoelectric conversion efficiencyo famaterial is determined by its dimensionless figure of merit, ZT= S 2 sT/k,where S, s, T, and k represent the Seebeck coefficient, electrical conductivity,a bsolute temperature,a nd thermal conductivity,r espectively.[2] Extensive efforts have been devoted to the improvement of the thermoelectric performance of state-of-the-art materials, [3] and to the discovery of new thermoelectrics [4] with ZT values > 2. Single-crystalline SnSe combines ah ighZTwith arelatively low toxicity and high Earth-abundance of the component elements.[4] SnSe crystals possess very low thermal conductivity owing to lattice anharmocity,y ielding record high ZTvalues of 2.6 and 2.3 at 923 Kalong the b and c crystallographic directions,r espectively.[4] Polycrystalline SnSe materials have been fabricated to improve mechanical properties, [5] but ZT has been limited to 1, owing to both increased electrical resistivity and thermal conductivity. [5] Unfortunately,t he synthesis of SnSe is protracted and energy-intensive,i nvolving heating, melting, and annealing at high temperatures ( % 800-1223 K). [4][5] Before the potential of SnSe can be realized, afast, cost-effective,and large-scale synthesis route to the pure selenide that does not sacrifice performance is essential.Nanostructuring very effectively enhances ZT. Theh igh density of interfaces improves phonon scattering, decreasing the lattice thermal conductivity. [2,3] Bottom-up solution synthesis methods facilitate control of size,m orphology,c rystal structure,and defects.[6] However,the organic surfactants that can control morphology through surface modification are commonly electrically insulating, which can drastically reduce the electrical conductivity of the materials.[7] Ligand replacement methods switch smaller species for long chain surfactant molecules, [7] but sometimes involve using high toxicity chemicals, ...

High-performance SnSe thermoelectric materials: Progress and future challenge

“…In this respect, HT and ST methods are useful to fabricate nanostructured products. In terms of the aqueous solution method [82,235], it is similar to HT/ST methods. The difference is that for aqueous solution method, the boiling solution is always under normal pressure, and the reaction time is shorter than traditional HT/ST methods.…”

“…The heat capacity (C p ) of SnSe in both temperature ranges from 373 to 1135 K and from 233 to 573 K was measured [61,77], which is important to determine the stability of the SnSe compounds. Besides, the thermodynamic data can be used as the guidance for designing their fabrications, especially for the growth of SnSe crystals via the Bridgman method [61,[78][79][80] or solvothermal method [81][82][83][84][85][86].…”

Few‐Layer Nanosheets of n‐Type SnSe2

“…Single crystals of SnSe have been discovered to be as uperior thermoelectric material resultingf rom ultralow thermal conductivity. [7] Other than SnSe, tin diselenide (SnSe 2 )i sa na dditional layered compound belonging to Sn-Se phase diagram (Figure 1a). [6a] Recently,n anoplates of p-type SnSe was synthesized by colloidal synthesis, which showsa ne xcellent thermoelectric power factor.…”

“…[6a] Recently,n anoplates of p-type SnSe was synthesized by colloidal synthesis, which showsa ne xcellent thermoelectric power factor. [7] Other than SnSe, tin diselenide (SnSe 2 )i sa na dditional layered compound belonging to Sn-Se phase diagram (Figure 1a). [8] SnSe 2 is as emiconductor with layered CdI 2 -type structure, where the Se 2À anionsf ormahexagonal close-packing (hcp) arrangement with the Sn 4 + cationso ccupying alternatinglayers of octahedral sites (Figure 1a).…”

Large-Scale Surfactant-Free Synthesis of p-Type SnTe Nanoparticles for Thermoelectric Applications

“…Such surfactants are adsorbed on the surfaces of the synthesised nanostructures and influence their electrical conductivity [ 42 , 44 ]. In contrast, surfactant-free solution synthesis can produce chalcogenide nanomaterials with cleaner surfaces, ensuring a higher electrical conductivity [ 45 , 46 ]. To date, the reported solution approaches for SnTe normally use surfactants and only produce small amounts of samples (<500 mg) [ 47 , 48 , 49 , 50 , 51 ].…”