Solution-based synthesis and processing of Sn- and Bi-doped Cu₃SbSe₄nanocrystals, nanomaterials and ring-shaped thermoelectric generators

Abstract

Copper-based chalcogenides that comprise abundant, low-cost, and environmental friendly elements are excellent materials for a number of energy conversion applications, including photovoltaics, photocatalysis, and thermoelectrics (TE). In such applications, the use of solution-processed nanocrystal (NC) to produce thin films or bulk nanomaterials has associated several potential advantages, such as high material yield and throughput, and composition control with unmatched spatial resolution and cost. Here we report on the production of Cu3SbSe4 (CASe) NCs with tuned amounts of Sn and Bi dopants. After proper ligand removal, as monitored by nuclear magnetic resonance and infrared spectroscopies, these NCs were used to produce dense CASe bulk nanomaterials for solid state TE energy conversion. By adjusting the amount of extrinsic dopants, dimensionless TE figures of merit (ZT) up to 1.26 at 673 K were reached. Such high ZT values are related to an optimized carrier concentration by Sn doping, a minimized lattice thermal conductivity due to efficient phonon scattering at point defects and grain boundaries, and to an increase of the Seebeck coefficient obtained by a modification of the electronic band structure with the Bi doping. Nanomaterials were further employed to fabricate ring-shaped TE generators to be coupled to hot pipes and which provided 20 mV and 1 mW per TE element when exposed to a 160 °C temperature gradient. The simple design and good thermal contact associated with the ring geometry and the potential low cost of the material solution processing may allow the fabrication of TE generators with short payback times.Peer ReviewedPostprint (author's final draft

Colloidal Synthesis and Thermoelectric Properties of CuFeSe2 Nanocrystals

“…However, these peaks disappeared after the sample had undergone washing treatment by a mixed solution of hydrazine hydrate and hexane, indicating that the organic groups on the NCs’ surface were removed completely. In addition, using other non-toxic inorganic salts can be considered for the ligand removal in order to implement this material in TE devices in future work, such as sodium salts [47] and ammonium salts [18]. …”

“…In this contribution, copper-based chalcogenide multinary semiconductors, containing abundant, low-cost and environmentally-friendly elements have recently emerged as some of the best performing p -type TE materials [12], such as Cu 2 CdSnSe 4 [13,14], Cu 2 ZnGeSe 4 [15], Cu 3 SbSe 4 [16,17,18], Cu 2 SnSe 3 [19,20,21], etc. One potentially attractive, yet not well-studied, copper-based material is CuFeSe 2 , which represents a well-known class of I-III-VI 2 group ternary chalcogenides.…”

Copper chalcogenide thermoelectric materials

“…. . [35,36,112,113]. Quaternary I 2 -II-IV-VI 4 (I=Cu; II=Zn, Cd, Fe, Co, Mn, Hg, Mg; IV=Ge, Sn; VI=S, Se, Te) compounds generally exhibit a larger band gap and lower mobility than the ternary counterparts, which is likely due to the localized d-orbitals of the transition metal elements.…”

“…3a, Cu 2 Se possesses two sublattices: the rigid FCC framework of Se atoms and the disordered and flowing sublattice of Cu. At high temperatures, Cu ions migrate from one site (interstitial one formed by Se) to another, exhibiting a flowing character that is Figure 1 Timeline of zT for selected Cu-based superionic conductors [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] (red), tetragonal [28][29][30][31][32][33][34][35][36][37] (blue) and distorted [38][39][40][41][42][43][44][45][46][47][48][49] (green) diamond-like materials and BiCuSeO oxyselenides (purple) [50][51][52][53][54][55][56][57][58][59]…”

“…Doping was widely employed to improve the carrier concentration and the electrical conductivity, such as CuIn(Ga) 1−x M x Te 2 (M=Zn, Mn, Cd, Hg, Ni, Ag, Gd) [114][115][116][117][118], Cu 1−x Fe 1+x S 2 [119], Cu 3 Sb 1−x M x Se 4 (M=Al, In, Sn, Ge, Bi) [35,[120][121][122] and Cu 2 Cd 1−x In x SnSe 4 [123]. Introducing vacancies is another practical way for the electrical transport optimization as well as the lattice thermal conductivity minimizing.…”