@article{13092, abstract = {There is a need for the development of lead-free thermoelectric materials for medium-/high-temperature applications. Here, we report a thiol-free tin telluride (SnTe) precursor that can be thermally decomposed to produce SnTe crystals with sizes ranging from tens to several hundreds of nanometers. We further engineer SnTe–Cu2SnTe3 nanocomposites with a homogeneous phase distribution by decomposing the liquid SnTe precursor containing a dispersion of Cu1.5Te colloidal nanoparticles. The presence of Cu within the SnTe and the segregated semimetallic Cu2SnTe3 phase effectively improves the electrical conductivity of SnTe while simultaneously reducing the lattice thermal conductivity without compromising the Seebeck coefficient. Overall, power factors up to 3.63 mW m–1 K–2 and thermoelectric figures of merit up to 1.04 are obtained at 823 K, which represent a 167% enhancement compared with pristine SnTe.}, author = {Nan, Bingfei and Song, Xuan and Chang, Cheng and Xiao, Ke and Zhang, Yu and Yang, Linlin and Horta, Sharona and Li, Junshan and Lim, Khak Ho and Ibáñez, Maria and Cabot, Andreu}, issn = {1944-8252}, journal = {ACS Applied Materials and Interfaces}, number = {19}, pages = {23380–23389}, publisher = {American Chemical Society}, title = {{Bottom-up synthesis of SnTe-based thermoelectric composites}}, doi = {10.1021/acsami.3c00625}, volume = {15}, year = {2023}, } @article{13093, abstract = {The direct, solid state, and reversible conversion between heat and electricity using thermoelectric devices finds numerous potential uses, especially around room temperature. However, the relatively high material processing cost limits their real applications. Silver selenide (Ag2Se) is one of the very few n-type thermoelectric (TE) materials for room-temperature applications. Herein, we report a room temperature, fast, and aqueous-phase synthesis approach to produce Ag2Se, which can be extended to other metal chalcogenides. These materials reach TE figures of merit (zT) of up to 0.76 at 380 K. To improve these values, bismuth sulfide (Bi2S3) particles also prepared in an aqueous solution are incorporated into the Ag2Se matrix. In this way, a series of Ag2Se/Bi2S3 composites with Bi2S3 wt % of 0.5, 1.0, and 1.5 are prepared by solution blending and hot-press sintering. The presence of Bi2S3 significantly improves the Seebeck coefficient and power factor while at the same time decreasing the thermal conductivity with no apparent drop in electrical conductivity. Thus, a maximum zT value of 0.96 is achieved in the composites with 1.0 wt % Bi2S3 at 370 K. Furthermore, a high average zT value (zTave) of 0.93 in the 300–390 K range is demonstrated.}, author = {Nan, Bingfei and Li, Mengyao and Zhang, Yu and Xiao, Ke and Lim, Khak Ho and Chang, Cheng and Han, Xu and Zuo, Yong and Li, Junshan and Arbiol, Jordi and Llorca, Jordi and Ibáñez, Maria and Cabot, Andreu}, issn = {2637-6113}, journal = {ACS Applied Electronic Materials}, publisher = {American Chemical Society}, title = {{Engineering of thermoelectric composites based on silver selenide in aqueous solution and ambient temperature}}, doi = {10.1021/acsaelm.3c00055}, year = {2023}, } @article{12331, abstract = {High carrier mobility is critical to improving thermoelectric performance over a broad temperature range. However, traditional doping inevitably deteriorates carrier mobility. Herein, we develop a strategy for fine tuning of defects to improve carrier mobility. To begin, n-type PbTe is created by compensating for the intrinsic Pb vacancy in bare PbTe. Excess Pb2+ reduces vacancy scattering, resulting in a high carrier mobility of ∼3400 cm2 V–1 s–1. Then, excess Ag is introduced to compensate for the remaining intrinsic Pb vacancies. We find that excess Ag exhibits a dynamic doping process with increasing temperatures, increasing both the carrier concentration and carrier mobility throughout a wide temperature range; specifically, an ultrahigh carrier mobility ∼7300 cm2 V–1 s–1 is obtained for Pb1.01Te + 0.002Ag at 300 K. Moreover, the dynamic doping-induced high carrier concentration suppresses the bipolar thermal conductivity at high temperatures. The final step is using iodine to optimize the carrier concentration to ∼1019 cm–3. Ultimately, a maximum ZT value of ∼1.5 and a large average ZTave value of ∼1.0 at 300–773 K are obtained for Pb1.01Te0.998I0.002 + 0.002Ag. These findings demonstrate that fine tuning of defects with <0.5% impurities can remarkably enhance carrier mobility and improve thermoelectric performance.}, author = {Wang, Siqi and Chang, Cheng and Bai, Shulin and Qin, Bingchao and Zhu, Yingcai and Zhan, Shaoping and Zheng, Junqing and Tang, Shuwei and Zhao, Li Dong}, issn = {1520-5002}, journal = {Chemistry of Materials}, number = {2}, pages = {755--763}, publisher = {American Chemical Society}, title = {{Fine tuning of defects enables high carrier mobility and enhanced thermoelectric performance of n-type PbTe}}, doi = {10.1021/acs.chemmater.2c03542}, volume = {35}, year = {2023}, } @article{11142, abstract = {SnTe is a promising Pb-free thermoelectric (TE) material with high electrical conductivity. We discovered the synergistic effect of Bi2O3 on enhancing the average power factor (PF) and overall ZT value of the SnTe-based thermoelectric material. The introduction of Bi2O3 forms plenty of SnO2, Bi2O3, and Bi-rich nanoprecipitates. These interfaces between the SnTe matrix and the nanoprecipitates can enhance the average PF through the energy filtering effect. On the other hand, abundant and diverse nanoprecipitates can significantly diminish the lattice thermal conductivity (κlat) through enhanced phonon scattering. The synergistic effect of Bi2O3 resulted in a maximum ZT (ZTmax) value of 0.9 at SnTe-2% Bi2O3 and an average ZT (ZTave) value of 0.4 for SnTe-4% Bi2O3 from 300 K to 823 K. The work provides an excellent reference to develop non-toxic high-performance TE materials.}, author = {Hong, Tao and Guo, Changrong and Wang, Dongyang and Qin, Bingchao and Chang, Cheng and Gao, Xiang and Zhao, Li Dong}, issn = {2468-6069}, journal = {Materials Today Energy}, publisher = {Elsevier}, title = {{Enhanced thermoelectric performance in SnTe due to the energy filtering effect introduced by Bi2O3}}, doi = {10.1016/j.mtener.2022.100985}, volume = {25}, year = {2022}, } @article{11144, abstract = {Thermoelectric materials allow for direct conversion between heat and electricity, offering the potential for power generation. The average dimensionless figure of merit ZTave determines device efficiency. N-type tin selenide crystals exhibit outstanding three-dimensional charge and two-dimensional phonon transport along the out-of-plane direction, contributing to a high maximum figure of merit Zmax of ~3.6 × 10−3 per kelvin but a moderate ZTave of ~1.1. We found an attractive high Zmax of ~4.1 × 10−3 per kelvin at 748 kelvin and a ZTave of ~1.7 at 300 to 773 kelvin in chlorine-doped and lead-alloyed tin selenide crystals by phonon-electron decoupling. The chlorine-induced low deformation potential improved the carrier mobility. The lead-induced mass and strain fluctuations reduced the lattice thermal conductivity. Phonon-electron decoupling plays a critical role to achieve high-performance thermoelectrics.}, author = {Su, Lizhong and Wang, Dongyang and Wang, Sining and Qin, Bingchao and Wang, Yuping and Qin, Yongxin and Jin, Yang and Chang, Cheng and Zhao, Li Dong}, issn = {1095-9203}, journal = {Science}, number = {6587}, pages = {1385--1389}, publisher = {American Association for the Advancement of Science}, title = {{High thermoelectric performance realized through manipulating layered phonon-electron decoupling}}, doi = {10.1126/science.abn8997}, volume = {375}, year = {2022}, } @article{11356, author = {Chang, Cheng and Qin, Bingchao and Su, Lizhong and Zhao, Li Dong}, issn = {2095-9281}, journal = {Science Bulletin}, number = {11}, pages = {1105--1107}, publisher = {Elsevier}, title = {{Distinct electron and hole transports in SnSe crystals}}, doi = {10.1016/j.scib.2022.04.007}, volume = {67}, year = {2022}, } @article{11705, abstract = {The broad implementation of thermoelectricity requires high-performance and low-cost materials. One possibility is employing surfactant-free solution synthesis to produce nanopowders. We propose the strategy of functionalizing “naked” particles’ surface by inorganic molecules to control the nanostructure and, consequently, thermoelectric performance. In particular, we use bismuth thiolates to functionalize surfactant-free SnTe particles’ surfaces. Upon thermal processing, bismuth thiolates decomposition renders SnTe-Bi2S3 nanocomposites with synergistic functions: 1) carrier concentration optimization by Bi doping; 2) Seebeck coefficient enhancement and bipolar effect suppression by energy filtering; and 3) lattice thermal conductivity reduction by small grain domains, grain boundaries and nanostructuration. Overall, the SnTe-Bi2S3 nanocomposites exhibit peak z T up to 1.3 at 873 K and an average z T of ≈0.6 at 300–873 K, which is among the highest reported for solution-processed SnTe.}, author = {Chang, Cheng and Liu, Yu and Lee, Seungho and Spadaro, Maria and Koskela, Kristopher M. and Kleinhanns, Tobias and Costanzo, Tommaso and Arbiol, Jordi and Brutchey, Richard L. and Ibáñez, Maria}, issn = {1521-3773}, journal = {Angewandte Chemie - International Edition}, number = {35}, publisher = {Wiley}, title = {{Surface functionalization of surfactant-free particles: A strategy to tailor the properties of nanocomposites for enhanced thermoelectric performance}}, doi = {10.1002/anie.202207002}, volume = {61}, year = {2022}, } @article{10042, abstract = {SnSe has emerged as one of the most promising materials for thermoelectric energy conversion due to its extraordinary performance in its single-crystal form and its low-cost constituent elements. However, to achieve an economic impact, the polycrystalline counterpart needs to replicate the performance of the single crystal. Herein, we optimize the thermoelectric performance of polycrystalline SnSe produced by consolidating solution-processed and surface-engineered SnSe particles. In particular, the SnSe particles are coated with CdSe molecular complexes that crystallize during the sintering process, forming CdSe nanoparticles. The presence of CdSe nanoparticles inhibits SnSe grain growth during the consolidation step due to Zener pinning, yielding a material with a high density of grain boundaries. Moreover, the resulting SnSe–CdSe nanocomposites present a large number of defects at different length scales, which significantly reduce the thermal conductivity. The produced SnSe–CdSe nanocomposites exhibit thermoelectric figures of merit up to 2.2 at 786 K, which is among the highest reported for solution-processed SnSe.}, author = {Liu, Yu and Calcabrini, Mariano and Yu, Yuan and Lee, Seungho and Chang, Cheng and David, Jérémy and Ghosh, Tanmoy and Spadaro, Maria Chiara and Xie, Chenyang and Cojocaru-Mirédin, Oana and Arbiol, Jordi and Ibáñez, Maria}, issn = {1936-086X}, journal = {ACS Nano}, keywords = {tin selenide, nanocomposite, grain growth, Zener pinning, thermoelectricity, annealing, solution processing}, number = {1}, pages = {78--88}, publisher = {American Chemical Society }, title = {{Defect engineering in solution-processed polycrystalline SnSe leads to high thermoelectric performance}}, doi = {10.1021/acsnano.1c06720}, volume = {16}, year = {2022}, } @article{10566, abstract = {A versatile, scalable, room temperature and surfactant-free route for the synthesis of metal chalcogenide nanoparticles in aqueous solution is detailed here for the production of PbS and Cu-doped PbS nanoparticles. Subsequently, nanoparticles are annealed in a reducing atmosphere to remove surface oxide, and consolidated into dense polycrystalline materials by means of spark plasma sintering. By characterizing the transport properties of the sintered material, we observe the annealing step and the incorporation of Cu to play a key role in promoting the thermoelectric performance of PbS. The presence of Cu allows improving the electrical conductivity by increasing the charge carrier concentration and simultaneously maintaining a large charge carrier mobility, which overall translates into record power factors at ambient temperature, 2.3 mWm-1K−2. Simultaneously, the lattice thermal conductivity decreases with the introduction of Cu, leading to a record high ZT = 0.37 at room temperature and ZT = 1.22 at 773 K. Besides, a record average ZTave = 0.76 is demonstrated in the temperature range 320–773 K for n-type Pb0.955Cu0.045S.}, author = {Li, Mengyao and Liu, Yu and Zhang, Yu and Chang, Cheng and Zhang, Ting and Yang, Dawei and Xiao, Ke and Arbiol, Jordi and Ibáñez, Maria and Cabot, Andreu}, issn = {1385-8947}, journal = {Chemical Engineering Journal}, publisher = {Elsevier}, title = {{Room temperature aqueous-based synthesis of copper-doped lead sulfide nanoparticles for thermoelectric application}}, doi = {10.1016/j.cej.2021.133837}, volume = {433}, year = {2022}, } @article{10073, abstract = {Thermoelectric materials enable the direct conversion between heat and electricity. SnTe is a promising candidate due to its high charge transport performance. Here, we prepared SnTe nanocomposites by employing an aqueous method to synthetize SnTe nanoparticles (NP), followed by a unique surface treatment prior NP consolidation. This synthetic approach allowed optimizing the charge and phonon transport synergistically. The novelty of this strategy was the use of a soluble PbS molecular complex prepared using a thiol-amine solvent mixture that upon blending is adsorbed on the SnTe NP surface. Upon consolidation with spark plasma sintering, SnTe-PbS nanocomposite is formed. The presence of PbS complexes significantly compensates for the Sn vacancy and increases the average grain size of the nanocomposite, thus improving the carrier mobility. Moreover, lattice thermal conductivity is also reduced by the Pb and S-induced mass and strain fluctuation. As a result, an enhanced ZT of ca. 0.8 is reached at 873 K. Our finding provides a novel strategy to conduct rational surface treatment on NP-based thermoelectrics.}, author = {Chang, Cheng and Ibáñez, Maria}, issn = {1996-1944}, journal = {Materials}, number = {18}, publisher = {MDPI}, title = {{Enhanced thermoelectric performance by surface engineering in SnTe-PbS nanocomposites}}, doi = {10.3390/ma14185416}, volume = {14}, year = {2021}, } @article{10123, abstract = {Solution synthesis of particles emerged as an alternative to prepare thermoelectric materials with less demanding processing conditions than conventional solid-state synthetic methods. However, solution synthesis generally involves the presence of additional molecules or ions belonging to the precursors or added to enable solubility and/or regulate nucleation and growth. These molecules or ions can end up in the particles as surface adsorbates and interfere in the material properties. This work demonstrates that ionic adsorbates, in particular Na⁺ ions, are electrostatically adsorbed in SnSe particles synthesized in water and play a crucial role not only in directing the material nano/microstructure but also in determining the transport properties of the consolidated material. In dense pellets prepared by sintering SnSe particles, Na remains within the crystal lattice as dopant, in dislocations, precipitates, and forming grain boundary complexions. These results highlight the importance of considering all the possible unintentional impurities to establish proper structure-property relationships and control material properties in solution-processed thermoelectric materials.}, author = {Liu, Yu and Calcabrini, Mariano and Yu, Yuan and Genç, Aziz and Chang, Cheng and Costanzo, Tommaso and Kleinhanns, Tobias and Lee, Seungho and Llorca, Jordi and Cojocaru‐Mirédin, Oana and Ibáñez, Maria}, issn = {1521-4095}, journal = {Advanced Materials}, keywords = {mechanical engineering, mechanics of materials, general materials science}, number = {52}, publisher = {Wiley}, title = {{The importance of surface adsorbates in solution‐processed thermoelectric materials: The case of SnSe}}, doi = {10.1002/adma.202106858}, volume = {33}, year = {2021}, }