@article{14734, abstract = {Developing cost-effective and high-performance thermoelectric (TE) materials to assemble efficient TE devices presents a multitude of challenges and opportunities. Cu3SbSe4 is a promising p-type TE material based on relatively earth abundant elements. However, the challenge lies in its poor electrical conductivity. Herein, an efficient and scalable solution-based approach is developed to synthesize high-quality Cu3SbSe4 nanocrystals doped with Pb at the Sb site. After ligand displacement and annealing treatments, the dried powders are consolidated into dense pellets, and their TE properties are investigated. Pb doping effectively increases the charge carrier concentration, resulting in a significant increase in electrical conductivity, while the Seebeck coefficients remain consistently high. The calculated band structure shows that Pb doping induces band convergence, thereby increasing the effective mass. Furthermore, the large ionic radius of Pb2+ results in the generation of additional point and plane defects and interphases, dramatically enhancing phonon scattering, which significantly decreases the lattice thermal conductivity at high temperatures. Overall, a maximum figure of merit (zTmax) ≈ 0.85 at 653 K is obtained in Cu3Sb0.97Pb0.03Se4. This represents a 1.6-fold increase compared to the undoped sample and exceeds most doped Cu3SbSe4-based materials produced by solid-state, demonstrating advantages of versatility and cost-effectiveness using a solution-based technology.}, author = {Wan, Shanhong and Xiao, Shanshan and Li, Mingquan and Wang, Xin and Lim, Khak Ho and Hong, Min and Ibáñez, Maria and Cabot, Andreu and Liu, Yu}, issn = {2366-9608}, journal = {Small Methods}, publisher = {Wiley}, title = {{Band engineering through Pb-doping of nanocrystal building blocks to enhance thermoelectric performance in Cu3SbSe4}}, doi = {10.1002/smtd.202301377}, year = {2023}, } @article{13235, abstract = {AgSbSe2 is a promising thermoelectric (TE) p-type material for applications in the middle-temperature range. AgSbSe2 is characterized by relatively low thermal conductivities and high Seebeck coefficients, but its main limitation is moderate electrical conductivity. Herein, we detail an efficient and scalable hot-injection synthesis route to produce AgSbSe2 nanocrystals (NCs). To increase the carrier concentration and improve the electrical conductivity, these NCs are doped with Sn2+ on Sb3+ sites. Upon processing, the Sn2+ chemical state is conserved using a reducing NaBH4 solution to displace the organic ligand and anneal the material under a forming gas flow. The TE properties of the dense materials obtained from the consolidation of the NCs using a hot pressing are then characterized. The presence of Sn2+ ions replacing Sb3+ significantly increases the charge carrier concentration and, consequently, the electrical conductivity. Opportunely, the measured Seebeck coefficient varied within a small range upon Sn doping. The excellent performance obtained when Sn2+ ions are prevented from oxidation is rationalized by modeling the system. Calculated band structures disclosed that Sn doping induces convergence of the AgSbSe2 valence bands, accounting for an enhanced electronic effective mass. The dramatically enhanced carrier transport leads to a maximized power factor for AgSb0.98Sn0.02Se2 of 0.63 mW m–1 K–2 at 640 K. Thermally, phonon scattering is significantly enhanced in the NC-based materials, yielding an ultralow thermal conductivity of 0.3 W mK–1 at 666 K. Overall, a record-high figure of merit (zT) is obtained at 666 K for AgSb0.98Sn0.02Se2 at zT = 1.37, well above the values obtained for undoped AgSbSe2, at zT = 0.58 and state-of-art Pb- and Te-free materials, which makes AgSb0.98Sn0.02Se2 an excellent p-type candidate for medium-temperature TE applications.}, author = {Liu, Yu and Li, Mingquan and Wan, Shanhong and Lim, Khak Ho and Zhang, Yu and Li, Mengyao and Li, Junshan and Ibáñez, Maria and Hong, Min and Cabot, Andreu}, issn = {1936-086X}, journal = {ACS Nano}, number = {12}, pages = {11923–11934}, publisher = {American Chemical Society}, title = {{Surface chemistry and band engineering in AgSbSe₂: Toward high thermoelectric performance}}, doi = {10.1021/acsnano.3c03541}, volume = {17}, year = {2023}, } @article{12915, abstract = {Cu2–xS and Cu2–xSe have recently been reported as promising thermoelectric (TE) materials for medium-temperature applications. In contrast, Cu2–xTe, another member of the copper chalcogenide family, typically exhibits low Seebeck coefficients that limit its potential to achieve a superior thermoelectric figure of merit, zT, particularly in the low-temperature range where this material could be effective. To address this, we investigated the TE performance of Cu1.5–xTe–Cu2Se nanocomposites by consolidating surface-engineered Cu1.5Te nanocrystals. This surface engineering strategy allows for precise adjustment of Cu/Te ratios and results in a reversible phase transition at around 600 K in Cu1.5–xTe–Cu2Se nanocomposites, as systematically confirmed by in situ high-temperature X-ray diffraction combined with differential scanning calorimetry analysis. The phase transition leads to a conversion from metallic-like to semiconducting-like TE properties. Additionally, a layer of Cu2Se generated around Cu1.5–xTe nanoparticles effectively inhibits Cu1.5–xTe grain growth, minimizing thermal conductivity and decreasing hole concentration. These properties indicate that copper telluride based compounds have a promising thermoelectric potential, translated into a high dimensionless zT of 1.3 at 560 K.}, author = {Xing, Congcong and Zhang, Yu and Xiao, Ke and Han, Xu and Liu, Yu and Nan, Bingfei and Ramon, Maria Garcia and Lim, Khak Ho and Li, Junshan and Arbiol, Jordi and Poudel, Bed and Nozariasbmarz, Amin and Li, Wenjie and Ibáñez, Maria and Cabot, Andreu}, issn = {1936-086X}, journal = {ACS Nano}, number = {9}, pages = {8442--8452}, publisher = {American Chemical Society}, title = {{Thermoelectric performance of surface-engineered Cu1.5–xTe–Cu2Se nanocomposites}}, doi = {10.1021/acsnano.3c00495}, volume = {17}, year = {2023}, } @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{10809, abstract = {Thermoelectric materials are engines that convert heat into an electrical current. Intuitively, the efficiency of this process depends on how many electrons (charge carriers) can move and how easily they do so, how much energy those moving electrons transport, and how easily the temperature gradient is maintained. In terms of material properties, an excellent thermoelectric material requires a high electrical conductivity σ, a high Seebeck coefficient S (a measure of the induced thermoelectric voltage as a function of temperature gradient), and a low thermal conductivity κ. The challenge is that these three properties are strongly interrelated in a conflicting manner (1). On page 722 of this issue, Roychowdhury et al. (2) have found a way to partially break these ties in silver antimony telluride (AgSbTe2) with the addition of cadmium (Cd) cations, which increase the ordering in this inherently disordered thermoelectric material.}, author = {Liu, Yu and Ibáñez, Maria}, issn = {1095-9203}, journal = {Science}, keywords = {multidisciplinary}, number = {6530}, pages = {678--679}, publisher = {American Association for the Advancement of Science}, title = {{Tidying up the mess}}, doi = {10.1126/science.abg0886}, volume = {371}, year = {2021}, } @article{10858, abstract = {The cost-effective conversion of low-grade heat into electricity using thermoelectric devices requires developing alternative materials and material processing technologies able to reduce the currently high device manufacturing costs. In this direction, thermoelectric materials that do not rely on rare or toxic elements such as tellurium or lead need to be produced using high-throughput technologies not involving high temperatures and long processes. Bi2Se3 is an obvious possible Te-free alternative to Bi2Te3 for ambient temperature thermoelectric applications, but its performance is still low for practical applications, and additional efforts toward finding proper dopants are required. Here, we report a scalable method to produce Bi2Se3 nanosheets at low synthesis temperatures. We studied the influence of different dopants on the thermoelectric properties of this material. Among the elements tested, we demonstrated that Sn doping resulted in the best performance. Sn incorporation resulted in a significant improvement to the Bi2Se3 Seebeck coefficient and a reduction in the thermal conductivity in the direction of the hot-press axis, resulting in an overall 60% improvement in the thermoelectric figure of merit of Bi2Se3.}, author = {Li, Mengyao and Zhang, Yu and Zhang, Ting and Zuo, Yong and Xiao, Ke and Arbiol, Jordi and Llorca, Jordi and Liu, Yu and Cabot, Andreu}, issn = {2079-4991}, journal = {Nanomaterials}, keywords = {General Materials Science, General Chemical Engineering}, number = {7}, publisher = {MDPI}, title = {{Enhanced thermoelectric performance of n-type Bi2Se3 nanosheets through Sn doping}}, doi = {10.3390/nano11071827}, volume = {11}, year = {2021}, } @article{9118, abstract = {Cesium lead halides have intrinsically unstable crystal lattices and easily transform within perovskite and nonperovskite structures. In this work, we explore the conversion of the perovskite CsPbBr3 into Cs4PbBr6 in the presence of PbS at 450 °C to produce doped nanocrystal-based composites with embedded Cs4PbBr6 nanoprecipitates. We show that PbBr2 is extracted from CsPbBr3 and diffuses into the PbS lattice with a consequent increase in the concentration of free charge carriers. This new doping strategy enables the adjustment of the density of charge carriers between 1019 and 1020 cm–3, and it may serve as a general strategy for doping other nanocrystal-based semiconductors.}, author = {Calcabrini, Mariano and Genc, Aziz and Liu, Yu and Kleinhanns, Tobias and Lee, Seungho and Dirin, Dmitry N. and Akkerman, Quinten A. and Kovalenko, Maksym V. and Arbiol, Jordi and Ibáñez, Maria}, issn = {2380-8195}, journal = {ACS Energy Letters}, number = {2}, pages = {581--587}, publisher = {American Chemical Society}, title = {{Exploiting the lability of metal halide perovskites for doping semiconductor nanocomposites}}, doi = {10.1021/acsenergylett.0c02448}, volume = {6}, year = {2021}, } @article{9206, abstract = {The precise engineering of thermoelectric materials using nanocrystals as their building blocks has proven to be an excellent strategy to increase energy conversion efficiency. Here we present a synthetic route to produce Sb-doped PbS colloidal nanoparticles. These nanoparticles are then consolidated into nanocrystalline PbS:Sb using spark plasma sintering. We demonstrate that the introduction of Sb significantly influences the size, geometry, crystal lattice and especially the carrier concentration of PbS. The increase of charge carrier concentration achieved with the introduction of Sb translates into an increase of the electrical and thermal conductivities and a decrease of the Seebeck coefficient. Overall, PbS:Sb nanomaterial were characterized by two-fold higher thermoelectric figures of merit than undoped PbS. }, author = {Cadavid, Doris and Wei, Kaya and Liu, Yu and Zhang, Yu and Li, Mengyao and Genç, Aziz and Berestok, Taisiia and Ibáñez, Maria and Shavel, Alexey and Nolas, George S. and Cabot, Andreu}, issn = {1996-1944}, journal = {Materials}, number = {4}, publisher = {MDPI}, title = {{Synthesis, bottom up assembly and thermoelectric properties of Sb-doped PbS nanocrystal building blocks}}, doi = {10.3390/ma14040853}, volume = {14}, year = {2021}, } @article{9235, abstract = {Cu2–xS has become one of the most promising thermoelectric materials for application in the middle-high temperature range. Its advantages include the abundance, low cost, and safety of its elements and a high performance at relatively elevated temperatures. However, stability issues limit its operation current and temperature, thus calling for the optimization of the material performance in the middle temperature range. Here, we present a synthetic protocol for large scale production of covellite CuS nanoparticles at ambient temperature and atmosphere, and using water as a solvent. The crystal phase and stoichiometry of the particles are afterward tuned through an annealing process at a moderate temperature under inert or reducing atmosphere. While annealing under argon results in Cu1.8S nanopowder with a rhombohedral crystal phase, annealing in an atmosphere containing hydrogen leads to tetragonal Cu1.96S. High temperature X-ray diffraction analysis shows the material annealed in argon to transform to the cubic phase at ca. 400 K, while the material annealed in the presence of hydrogen undergoes two phase transitions, first to hexagonal and then to the cubic structure. The annealing atmosphere, temperature, and time allow adjustment of the density of copper vacancies and thus tuning of the charge carrier concentration and material transport properties. In this direction, the material annealed under Ar is characterized by higher electrical conductivities but lower Seebeck coefficients than the material annealed in the presence of hydrogen. By optimizing the charge carrier concentration through the annealing time, Cu2–xS with record figures of merit in the middle temperature range, up to 1.41 at 710 K, is obtained. We finally demonstrate that this strategy, based on a low-cost and scalable solution synthesis process, is also suitable for the production of high performance Cu2–xS layers using high throughput and cost-effective printing technologies.}, author = {Li, Mengyao and Liu, Yu and Zhang, Yu and Han, Xu and Zhang, Ting and Zuo, Yong and Xie, Chenyang and Xiao, Ke and Arbiol, Jordi and Llorca, Jordi and Ibáñez, Maria and Liu, Junfeng and Cabot, Andreu}, issn = {1936-086X}, journal = {ACS Nano}, keywords = {General Engineering, General Physics and Astronomy, General Materials Science}, number = {3}, pages = {4967–4978}, publisher = {American Chemical Society }, title = {{Effect of the annealing atmosphere on crystal phase and thermoelectric properties of copper sulfide}}, doi = {10.1021/acsnano.0c09866}, volume = {15}, year = {2021}, } @article{9304, abstract = {The high processing cost, poor mechanical properties and moderate performance of Bi2Te3–based alloys used in thermoelectric devices limit the cost-effectiveness of this energy conversion technology. Towards solving these current challenges, in the present work, we detail a low temperature solution-based approach to produce Bi2Te3-Cu2-xTe nanocomposites with improved thermoelectric performance. Our approach consists in combining proper ratios of colloidal nanoparticles and to consolidate the resulting mixture into nanocomposites using a hot press. The transport properties of the nanocomposites are characterized and compared with those of pure Bi2Te3 nanomaterials obtained following the same procedure. In contrast with most previous works, the presence of Cu2-xTe nanodomains does not result in a significant reduction of the lattice thermal conductivity of the reference Bi2Te3 nanomaterial, which is already very low. However, the introduction of Cu2-xTe yields a nearly threefold increase of the power factor associated to a simultaneous increase of the Seebeck coefficient and electrical conductivity at temperatures above 400 K. Taking into account the band alignment of the two materials, we rationalize this increase by considering that Cu2-xTe nanostructures, with a relatively low electron affinity, are able to inject electrons into Bi2Te3, enhancing in this way its electrical conductivity. The simultaneous increase of the Seebeck coefficient is related to the energy filtering of charge carriers at energy barriers within Bi2Te3 domains associated with the accumulation of electrons in regions nearby a Cu2-xTe/Bi2Te3 heterojunction. Overall, with the incorporation of a proper amount of Cu2-xTe nanoparticles, we demonstrate a 250% improvement of the thermoelectric figure of merit of Bi2Te3.}, author = {Zhang, Yu and Xing, Congcong and Liu, Yu and Li, Mengyao and Xiao, Ke and Guardia, Pablo and Lee, Seungho and Han, Xu and Moghaddam, Ahmad and Roa, Joan J and Arbiol, Jordi and Ibáñez, Maria and Pan, Kai and Prato, Mirko and Xie, Ying and Cabot, Andreu}, issn = {1385-8947}, journal = {Chemical Engineering Journal}, number = {8}, publisher = {Elsevier}, title = {{Influence of copper telluride nanodomains on the transport properties of n-type bismuth telluride}}, doi = {10.1016/j.cej.2021.129374}, volume = {418}, year = {2021}, } @article{9305, abstract = {Copper chalcogenides are outstanding thermoelectric materials for applications in the medium-high temperature range. Among different chalcogenides, while Cu2−xSe is characterized by higher thermoelectric figures of merit, Cu2−xS provides advantages in terms of low cost and element abundance. In the present work, we investigate the effect of different dopants to enhance the Cu2−xS performance and also its thermal stability. Among the tested options, Pb-doped Cu2−xS shows the highest improvement in stability against sulfur volatilization. Additionally, Pb incorporation allows tuning charge carrier concentration, which enables a significant improvement of the power factor. We demonstrate here that the introduction of an optimal additive amount of just 0.3% results in a threefold increase of the power factor in the middle-temperature range (500–800 K) and a record dimensionless thermoelectric figure of merit above 2 at 880 K.}, author = {Zhang, Yu and Xing, Congcong and Liu, Yu and Spadaro, Maria Chiara and Wang, Xiang and Li, Mengyao and Xiao, Ke and Zhang, Ting and Guardia, Pablo and Lim, Khak Ho and Moghaddam, Ahmad Ostovari and Llorca, Jordi and Arbiol, Jordi and Ibáñez, Maria and Cabot, Andreu}, issn = {2211-2855}, journal = {Nano Energy}, number = {7}, publisher = {Elsevier}, title = {{Doping-mediated stabilization of copper vacancies to promote thermoelectric properties of Cu2-xS}}, doi = {10.1016/j.nanoen.2021.105991}, volume = {85}, 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}, } @article{10327, abstract = {Composite materials offer numerous advantages in a wide range of applications, including thermoelectrics. Here, semiconductor–metal composites are produced by just blending nanoparticles of a sulfide semiconductor obtained in aqueous solution and at room temperature with a metallic Cu powder. The obtained blend is annealed in a reducing atmosphere and afterward consolidated into dense polycrystalline pellets through spark plasma sintering (SPS). We observe that, during the annealing process, the presence of metallic copper activates a partial reduction of the PbS, resulting in the formation of PbS–Pb–CuxS composites. The presence of metallic lead during the SPS process habilitates the liquid-phase sintering of the composite. Besides, by comparing the transport properties of PbS, the PbS–Pb–CuxS composites, and PbS–CuxS composites obtained by blending PbS and CuxS nanoparticles, we demonstrate that the presence of metallic lead decisively contributes to a strong increase of the charge carrier concentration through spillover of charge carriers enabled by the low work function of lead. The increase in charge carrier concentration translates into much higher electrical conductivities and moderately lower Seebeck coefficients. These properties translate into power factors up to 2.1 mW m–1 K–2 at ambient temperature, well above those of PbS and PbS + CuxS. Additionally, the presence of multiple phases in the final composite results in a notable decrease in the lattice thermal conductivity. Overall, the introduction of metallic copper in the initial blend results in a significant improvement of the thermoelectric performance of PbS, reaching a dimensionless thermoelectric figure of merit ZT = 1.1 at 750 K, which represents about a 400% increase over bare PbS. Besides, an average ZTave = 0.72 in the temperature range 320–773 K is demonstrated.}, author = {Li, Mengyao and Liu, Yu and Zhang, Yu and Han, Xu and Xiao, Ke and Nabahat, Mehran and Arbiol, Jordi and Llorca, Jordi and Ibáñez, Maria and Cabot, Andreu}, issn = {1944-8252}, journal = {ACS Applied Materials and Interfaces}, keywords = {CuxS, PbS, energy conversion, nanocomposite, nanoparticle, solution synthesis, thermoelectric}, number = {43}, pages = {51373–51382}, publisher = {American Chemical Society }, title = {{PbS–Pb–CuxS composites for thermoelectric application}}, doi = {10.1021/acsami.1c15609}, volume = {13}, year = {2021}, } @article{8039, abstract = {In the present work, we report a solution-based strategy to produce crystallographically textured SnSe bulk nanomaterials and printed layers with optimized thermoelectric performance in the direction normal to the substrate. Our strategy is based on the formulation of a molecular precursor that can be continuously decomposed to produce a SnSe powder or printed into predefined patterns. The precursor formulation and decomposition conditions are optimized to produce pure phase 2D SnSe nanoplates. The printed layer and the bulk material obtained after hot press displays a clear preferential orientation of the crystallographic domains, resulting in an ultralow thermal conductivity of 0.55 W m–1 K–1 in the direction normal to the substrate. Such textured nanomaterials present highly anisotropic properties with the best thermoelectric performance in plane, i.e., in the directions parallel to the substrate, which coincide with the crystallographic bc plane of SnSe. This is an unfortunate characteristic because thermoelectric devices are designed to create/harvest temperature gradients in the direction normal to the substrate. We further demonstrate that this limitation can be overcome with the introduction of small amounts of tellurium in the precursor. The presence of tellurium allows one to reduce the band gap and increase both the charge carrier concentration and the mobility, especially the cross plane, with a minimal decrease of the Seebeck coefficient. These effects translate into record out of plane ZT values at 800 K.}, author = {Zhang, Yu and Liu, Yu and Xing, Congcong and Zhang, Ting and Li, Mengyao and Pacios, Mercè and Yu, Xiaoting and Arbiol, Jordi and Llorca, Jordi and Cadavid, Doris and Ibáñez, Maria and Cabot, Andreu}, issn = {19448252}, journal = {ACS Applied Materials and Interfaces}, number = {24}, pages = {27104--27111}, publisher = {American Chemical Society}, title = {{Tin selenide molecular precursor for the solution processing of thermoelectric materials and devices}}, doi = {10.1021/acsami.0c04331}, volume = {12}, year = {2020}, } @article{8747, abstract = {Appropriately designed nanocomposites allow improving the thermoelectric performance by several mechanisms, including phonon scattering, modulation doping and energy filtering, while additionally promoting better mechanical properties than those of crystalline materials. Here, a strategy for producing Bi2Te3–Cu2xTe nanocomposites based on the consolidation of heterostructured nanoparticles is described and the thermoelectric properties of the obtained materials are investigated. We first detail a two-step solution-based process to produce Bi2Te3–Cu2xTe heteronanostructures, based on the growth of Cu2xTe nanocrystals on the surface of Bi2Te3 nanowires. We characterize the structural and chemical properties of the synthesized nanostructures and of the nanocomposites produced by hot-pressing the particles at moderate temperatures. Besides, the transport properties of the nanocomposites are investigated as a function of the amount of Cu introduced. Overall, the presence of Cu decreases the material thermal conductivity through promotion of phonon scattering, modulates the charge carrier concentration through electron spillover, and increases the Seebeck coefficient through filtering of charge carriers at energy barriers. These effects result in an improvement of over 50% of the thermoelectric figure of merit of Bi2Te3.}, author = {Zhang, Yu and Liu, Yu and Calcabrini, Mariano and Xing, Congcong and Han, Xu and Arbiol, Jordi and Cadavid, Doris and Ibáñez, Maria and Cabot, Andreu}, journal = {Journal of Materials Chemistry C}, number = {40}, pages = {14092--14099}, publisher = {Royal Society of Chemistry}, title = {{Bismuth telluride-copper telluride nanocomposites from heterostructured building blocks}}, doi = {10.1039/D0TC02182B}, volume = {8}, year = {2020}, } @article{7467, abstract = {Nanomaterials produced from the bottom-up assembly of nanocrystals may incorporate ∼1020–1021 cm–3 not fully coordinated surface atoms, i.e., ∼1020–1021 cm–3 potential donor or acceptor states that can strongly affect transport properties. Therefore, to exploit the full potential of nanocrystal building blocks to produce functional nanomaterials and thin films, a proper control of their surface chemistry is required. Here, we analyze how the ligand stripping procedure influences the charge and heat transport properties of sintered PbSe nanomaterials produced from the bottom-up assembly of colloidal PbSe nanocrystals. First, we show that the removal of the native organic ligands by thermal decomposition in an inert atmosphere leaves relatively large amounts of carbon at the crystal interfaces. This carbon blocks crystal growth during consolidation and at the same time hampers charge and heat transport through the final nanomaterial. Second, we demonstrate that, by stripping ligands from the nanocrystal surface before consolidation, nanomaterials with larger crystal domains, lower porosity, and higher charge carrier concentrations are obtained, thus resulting in nanomaterials with higher electrical and thermal conductivities. In addition, the ligand displacement leaves the nanocrystal surface unprotected, facilitating oxidation and chalcogen evaporation. The influence of the ligand displacement on the nanomaterial charge transport properties is rationalized here using a two-band model based on the standard Boltzmann transport equation with the relaxation time approximation. Finally, we present an application of the produced functional nanomaterials by modeling, fabricating, and testing a simple PbSe-based thermoelectric device with a ring geometry.}, author = {Cadavid, Doris and Ortega, Silvia and Illera, Sergio and Liu, Yu and Ibáñez, Maria and Shavel, Alexey and Zhang, Yu and Li, Mengyao and López, Antonio M. and Noriega, Germán and Durá, Oscar Juan and López De La Torre, M. A. and Prades, Joan Daniel and Cabot, Andreu}, issn = {2574-0962}, journal = {ACS Applied Energy Materials}, number = {3}, pages = {2120--2129}, publisher = {American Chemical Society}, title = {{Influence of the ligand stripping on the transport properties of nanoparticle-based PbSe nanomaterials}}, doi = {10.1021/acsaem.9b02137}, volume = {3}, year = {2020}, } @article{6566, abstract = {Methodologies that involve the use of nanoparticles as “artificial atoms” to rationally build materials in a bottom-up fashion are particularly well-suited to control the matter at the nanoscale. Colloidal synthetic routes allow for an exquisite control over such “artificial atoms” in terms of size, shape, and crystal phase as well as core and surface compositions. We present here a bottom-up approach to produce Pb–Ag–K–S–Te nanocomposites, which is a highly promising system for thermoelectric energy conversion. First, we developed a high-yield and scalable colloidal synthesis route to uniform lead sulfide (PbS) nanorods, whose tips are made of silver sulfide (Ag2S). We then took advantage of the large surface-to-volume ratio to introduce a p-type dopant (K) by replacing native organic ligands with K2Te. Upon thermal consolidation, K2Te-surface modified PbS–Ag2S nanorods yield p-type doped nanocomposites with PbTe and PbS as major phases and Ag2S and Ag2Te as embedded nanoinclusions. Thermoelectric characterization of such consolidated nanosolids showed a high thermoelectric figure-of-merit of 1 at 620 K.}, author = {Ibáñez, Maria and Genç, Aziz and Hasler, Roger and Liu, Yu and Dobrozhan, Oleksandr and Nazarenko, Olga and Mata, María de la and Arbiol, Jordi and Cabot, Andreu and Kovalenko, Maksym V.}, issn = {1936-086X}, journal = {ACS Nano}, keywords = {colloidal nanoparticles, asymmetric nanoparticles, inorganic ligands, heterostructures, catalyst assisted growth, nanocomposites, thermoelectrics}, number = {6}, pages = {6572--6580}, publisher = {American Chemical Society}, title = {{Tuning transport properties in thermoelectric nanocomposites through inorganic ligands and heterostructured building blocks}}, doi = {10.1021/acsnano.9b00346}, volume = {13}, year = {2019}, } @article{6586, abstract = {The bottom-up assembly of colloidal nanocrystals is a versatile methodology to produce composite nanomaterials with precisely tuned electronic properties. Beyond the synthetic control over crystal domain size, shape, crystal phase, and composition, solution-processed nanocrystals allow exquisite surface engineering. This provides additional means to modulate the nanomaterial characteristics and particularly its electronic transport properties. For instance, inorganic surface ligands can be used to tune the type and concentration of majority carriers or to modify the electronic band structure. Herein, we report the thermoelectric properties of SnTe nanocomposites obtained from the consolidation of surface-engineered SnTe nanocrystals into macroscopic pellets. A CdSe-based ligand is selected to (i) converge the light and heavy bands through partial Cd alloying and (ii) generate CdSe nanoinclusions as a secondary phase within the SnTe matrix, thereby reducing the thermal conductivity. These SnTe-CdSe nanocomposites possess thermoelectric figures of merit of up to 1.3 at 850 K, which is, to the best of our knowledge, the highest thermoelectric figure of merit reported for solution-processed SnTe.}, author = {Ibáñez, Maria and Hasler, Roger and Genç, Aziz and Liu, Yu and Kuster, Beatrice and Schuster, Maximilian and Dobrozhan, Oleksandr and Cadavid, Doris and Arbiol, Jordi and Cabot, Andreu and Kovalenko, Maksym V.}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {20}, pages = {8025--8029}, publisher = {American Chemical Society}, title = {{Ligand-mediated band engineering in bottom-up assembled SnTe nanocomposites for thermoelectric energy conversion}}, doi = {10.1021/jacs.9b01394}, volume = {141}, year = {2019}, }