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1. High-performance thermoelectric silver selenide thin films cation exchanged from a copper selenide template

   https://doi.org/10.1039/C9NA00605B  

   Chen, Nan ; Scimeca, Michael R. ; Paul, Shlok J. ; Hafiz, Shihab B. ; Yang, Ze ; Liu, Xiangyu ; Yang, Fan ; Ko, Dong-Kyun ; Sahu, Ayaskanta ( January 2020 , Nanoscale Advances)

   Over the past decade, Ag 2 Se has attracted increasing attention due to its potentially excellent thermoelectric (TE) performance as an n-type semiconductor. It has been considered a promising alternative to Bi–Te alloys and other commonly used yet toxic and/or expensive TE materials. To optimize the TE performance of Ag 2 Se, recent research has focused on fabricating nanosized Ag 2 Se. However, synthesizing Ag 2 Se nanoparticles involves energy-intensive and time-consuming techniques with poor yield of final product. In this work, we report a low-cost, solution-processed approach that enables the formation of Ag 2 Se thin films from Cu 2−x Se template films via cation exchange at room temperature. Our simple two-step method involves fabricating Cu 2−x Se thin films by the thiol-amine dissolution of bulk Cu 2 Se, followed by soaking Cu 2−x Se films in AgNO 3 solution and annealing to form Ag 2 Se. We report an average power factor (PF) of 617 ± 82 μW m −1 K −2 and a corresponding ZT value of 0.35 at room temperature. We obtained a maximum PF of 825 μW m −1 K −2 and a ZT value of 0.46 at room temperature for our best-performing Ag 2more »Se thin-film after soaking for 5 minutes. These high PFs have been achieved via full solution processing without hot-pressing.« less
2. Synthetic versatility, reaction pathway, and thermal stability of tetrahedrite nanoparticles

   https://doi.org/10.1039/d0tc03599h  

   Fasana, Christine D. ; Jensen, Mitchel S. ; García Ponte, Graciela E. ; MacAlister, Tyler R. ; Kunkel, Grace E. ; Rogers, John P. ; Ochs, Andrew M. ; Stevens, Daniel L. ; Weller, Daniel P. ; Morelli, Donald T. ; et al ( October 2020 , Journal of Materials Chemistry C)

   Copper-antimony-sulfide compounds have desirable earth-abundant compositions for application in renewable energy technologies, such as solar energy and waste heat recycling. These compounds can be synthesized by bottom-up, solution-phase techniques that are more energy and time efficient than conventional solid-state methods. Solution-phase methods typically produce nanostructured materials, which adds another dimension to control optical, electrical, and thermal material properties. This study focuses on a modified-polyol, solution-phase synthesis for tetrahedrite (Cu 12 Sb 4 S 13 ), a promising thermoelectric material with potential also for photovoltaic applications. To dope the tetrahedrite and tune material properties, the utility of the modified polyol synthetic approach has been demonstrated as a strategy to produce phase-pure tetrahedrite that incorporates transition metal (Fe, Co, Ni, Zn, Ag) dopants for Cu, Te dopant for Sb, and Se for S. Six of these reported tetrahedrite compounds have not previously been made by solution-phase methods. For the bottom-up formation of the tetrahedrite nanomaterials, the evolution of the chemical phases has been determined by an investigation of the reaction progress as a function of temperature and time. Digenite (Cu 1.8 S), covellite (CuS), and famatinite (Cu 3 SbS 4 ) are identified as key intermediates and are consistently observed for bothmore »undoped and doped tetrahedrites. The effect of nanostructuring and doping tetrahedrite on thermal properties has been investigated. It was found that nanostructured undoped tetrahedrite has reduced thermal stability relative to samples made by solid-state methods, while the addition of dopants for Cu increased the thermal stability of the material. Crystallinity, composition, and nanostructure of products and intermediates were characterized by powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and transmission electron microscopy. Thermal properties were investigated by differential scanning calorimetry and thermal gravimetric analysis. This synthetic study with thermal property analysis demonstrates the potential of the modified polyol method to produce tetrahedrite and other copper-antimony-sulfide compounds for thermoelectric and photovoltaic applications.« less
3. Zintl Phase Compounds Mg3Sb2−xBix (x = 0, 1, and 2) Monolayers: Electronic, Phonon and Thermoelectric Properties From ab Initio Calculations

   https://doi.org/10.3389/fmech.2022.876655  

   Chang, Zheng ; Ma, Jing ; Yuan, Kunpeng ; Zheng, Jiongzhi ; Wei, Bin ; Al-Fahdi, Mohammed ; Gao, Yufei ; Zhang, Xiaoliang ; Shao, Hezhu ; Hu, Ming ; et al ( April 2022 , Frontiers in Mechanical Engineering)

   The Mg 3 Sb 2− x Bi x family has emerged as the potential candidates for thermoelectric applications due to their ultra-low lattice thermal conductivity ( κ L ) at room temperature (RT) and structural complexity. Here, using ab initio calculations of the electron-phonon averaged (EPA) approximation coupled with Boltzmann transport equation (BTE), we have studied electronic, phonon and thermoelectric properties of Mg 3 Sb 2− x Bi x (x = 0, 1, and 2) monolayers. In violation of common mass-trend expectations, increasing Bi element content with heavier Zintl phase compounds yields an abnormal change in κ L in two-dimensional Mg 3 Sb 2− x Bi x crystals at RT (∼0.51, 1.86, and 0.25 W/mK for Mg 3 Sb 2 , Mg 3 SbBi, and Mg 3 Bi 2 ). The κ L trend was detailedly analyzed via the phonon heat capacity, group velocity and lifetime parameters. Based on quantitative electronic band structures, the electronic bonding through the crystal orbital Hamilton population (COHP) and electron local function analysis we reveal the underlying mechanism for the semiconductor-semimetallic transition of Mg 3 Sb 2-− x Bi x compounds, and these electronic transport properties (Seebeck coefficient, electrical conductivity, and electronic thermal conductivity) were calculated.more »We demonstrate that the highest dimensionless figure of merit ZT of Mg 3 Sb 2− x Bi x compounds with increasing Bi content can reach ∼1.6, 0.2, and 0.6 at 700 K, respectively. Our results can indicate that replacing heavier anion element in Zintl phase Mg 3 Sb 2− x Bi x materials go beyond common expectations (a heavier atom always lead to a lower κ L from Slack’s theory), which provide a novel insight for regulating thermoelectric performance without restricting conventional heavy atomic mass approach.« less
4. Measured and simulated thermoelectric properties of FeAs _2−x Se _x ( x = 0.30–1.0): from marcasite to arsenopyrite structure

   https://doi.org/10.1039/d0ma00371a  

   Perez, Christopher J. ; Devlin, Kasey P. ; Skaggs, Callista M. ; Tan, Xiaoyan ; Frank, Corey E. ; Badger, Jackson R. ; Kang, Chang-Jong ; Emge, Thomas J. ; Kauzlarich, Susan M. ; Taufour, Valentin ; et al ( August 2020 , Materials Advances)

   FeAs 2−x Se x ( x = 0.30–1.0) samples were synthesized as phase pure powders by conventional solid-state techniques and as single crystals ( x = 0.50) from chemical vapor transport. The composition of the crystals was determined to be Fe 1.025(3) As 1.55(3) Se 0.42(3) , crystallizing in the marcasite structure type, Pnnm space group. FeAs 2−x Se x (0 < x < 1) was found to undergo a marcasite-to-arsenopyrite ( P 2 1 / c space group) structural phase transition at x ∼ 0.65. The structures are similar, with the marcasite structure best described as a solid solution of As/Se, whereas the arsenopyrite has ordered anion sites. Magnetic susceptibility and thermoelectric property measurements from 300–2 K were performed on single crystals, FeAs 1.50 Se 0.50 . Paramagnetic behavior is observed from 300 to 17 K and a Seebeck coefficient of −33 μV K −1 , an electrical resistivity of 4.07 mΩ cm, and a very low κ l of 0.22 W m −1 K −1 at 300 K are observed. In order to determine the impact of the structural transition on the high-temperature thermoelectric properties, polycrystalline FeAs 2−x Se x ( x = 0.30, 0.75, 0.85, 1.0) samplesmore »were consolidated into dense pellets for measurements of thermoelectric properties. The x = 0.85 sample shows the best thermoelectric performance. The electronic structure of FeAsSe was calculated with DFT and transport properties were approximately modeled above 500 K.« less
5. Enhanced thermoelectric performance of F4-TCNQ doped FASnI ₃ thin films

   https://doi.org/10.1039/D0TA09329G  

   Zheng, Luyao ; Zhu, Tao ; Li, Yifan ; Wu, Haodong ; Yi, Chao ; Zhu, Jiahua ; Gong, Xiong ( December 2020 , Journal of Materials Chemistry A)

   In the past decade, great efforts have been devoted to the development of organic–inorganic hybrid perovskites for achieving efficient photovoltaics, but less attention has been paid to their thermoelectric applications. In this study, for the first time, we report the thermoelectric performance of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped NH 2 CHNH 2 SnI 3 (FASnI 3 ) thin films. It is found that the electrical conductivities of the F4-TCNQ doped FASnI 3 thin films increase and then decrease along with increased doping levels of F4-TCNQ. Systematic studies indicate that enhanced electrical conductivities are attributed to the increased charge carrier concentrations and mobilities and superior film morphologies of the F4-TCNQ doped FASnI 3 thin films, and decreased electrical conductivities originate from the cracks and poor film morphology of the F4-TCNQ doped FASnI 3 thin films induced by excess F4-TCNQ dopants. The quantitative thermal conductivity scanning thermal microscopy studies reveal that the F4-TCNQ doped FASnI 3 thin films exhibit ultralow thermal conductivities. Moreover, the thermoelectric performance of the F4-TCNQ doped FASnI 3 thin films is investigated. It is found that the F4-TCNQ doped FASnI 3 thin films exhibit a Seebeck coefficient of ∼310 μV K −1 , a power factor of ∼130 μW mmore »−1 K −2 and a ZT value of ∼0.19 at room temperature. All these results demonstrate that our studies open a door for exploring cost-effective less-toxic organic–inorganic hybrid perovskites in heat-to-electricity conversion applications at room temperature.« less