Controllable Colloidal Synthesis of Tin(II) Chalcogenide Nanocrystals and Their Solution‐Processed Flexible Thermoelectric Thin Films

Abstract

A systematic colloidal synthesis approach to prepare tin(II, IV) chalcogenide nanocrystals with controllable valence and morphology is reported, and the preparation of solution-processed nanostructured thermoelectric thin films from them is then demonstrated. Triangular SnS nanoplates with a recently-reported π-cubic structure, SnSe with various shapes (nanostars and both rectangular and hexagonal nanoplates), SnTe nanorods, and previously reported Sn(IV) chalcogenides, are obtained using different combinations of solvents and ligands with an Sn precursor. These unique nanostructures and the lattice defects associated with their Sn-rich composition allow the production of flexible thin films with competitive thermoelectric performance, exhibiting room temperature Seebeck coefficients of 115, 81, and 153 μV K for SnS, SnSe, and SnTe films, respectively. Interestingly, a p-type to n-type transition is observed in SnS and SnSe due to partial anion loss during post-synthesis annealing at 500 °C. A maximum figure of merit (ZT) value of 0.183 is achieved for an SnTe thin film at 500 K, exceeding ZT values from previous reports on SnTe at this temperature. Thus, a general strategy to prepare tin(II) chalcogenide nanocrystals is provided, and their potential for use in high-performance flexible thin film thermoelectric generators is demonstrated.

3D Conformal Printing and Photonic Sintering of High‐Performance Flexible Thermoelectric Films Using 2D Nanoplates

“…Solution‐printable and shape‐conformable thermoelectric (TE) devices have attracted considerable attentions due to their broad applications in cooling and energy harvesting for powering flexible electronics and sensors . Compared with early strategies like vacuum filtration and spin/spray coating that have been utilized to fabricate flexible TE films, ink‐based printing method can directly transform TE particles into complete device pattern without the need of other complex fabrication processes. However, it has been a major challenge to achieve outstanding TE properties and mechanical flexibility in printed films due to the reduced density of printed films and the restricted sintering temperature when printing on flexible substrate with low melting point .…”

Binary and Ternary Colloidal Cu‐Sn‐Te Nanocrystals for Thermoelectric Thin Films

“…Preparation of Trioctylphosphine-Te: TOP-Te precursor was prepared according to the previous report: 2 mmol of Te powder was mixed with 2 mL of TOP and the mixture was heated to 350 °C with stirring under nitrogen protection until a clear solution formed. [7] Synthesis of Binary and Ternary Metal (Cu and Sn) Tellurides: In a typical synthesis, a total of 1 mmol of CuCl and SnCl 2 powder at a specified molar ratio (1:0, 3:1, 1:1, 2:3, 3:7, 1:3, or 0:1) was mixed with 10 mL of OAm, and the mixture was degassed at 110 °C for 1 h under nitrogen protection. The solution was then heated to 280 °C, followed by injection of 1 mL of TOP-Te precursor.…”

“…[6] The tin telluride (SnTe) class of materials, which have band structures related to PbTe-based alloys, are typically narrow-gap semiconductors that can have high hole concentrations arising from inherent Sn vacancies. [7,8] As a TE material, SnTe suffers from a relatively low Seebeck coefficient due to its typically high carrier concentration (≈10 22 cm −3 ), although the room temperature electrical conductivity of bulk SnTe reaches 7.6 × 10 5 S m −1 . Previously, copper sulfide (Cu 2−x S) and copper selenide (Cu 2−x Se) were reported to have an ultralow thermal conductivity and high TE figure of merit.…”

“…Hot injection and ion exchange provide established effective and robust methods to produce copper or tin telluride NCs with controlled shape and size. [6,7,32,33] In this report, we employ trioctylphosphine-tellurium (TOP-Te) as Te precursor to synthesize binary Cu 2−x Te and SnTe and ternary Cu 2 SnTe 3 NCs. Hexagonal plate-like Cu 1.43 Te NCs and Cu 2 SnTe 3 nanocubes are reported for the first time.…”

Fiber Composites Made of Low-Dimensional Carbon Materials

“…Among all kinds of low-dimensional materials [1][2][3][4][5][6][7][8], using carbon-based lowdimensional materials to improve their physical, mechanical, and electrical properties has become a trend [9]. These carbon-based nano/micron additives include carbon fibers (CF), single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) [10][11][12], graphene oxide (GO) [13][14][15], and graphene nanoplates (GNP) [16].…”