@article{22734, abstract = {Silver selenide (Ag2Se) is a promising near-room-temperature thermoelectric material, but its narrow stoichiometric window and β–α phase transition complicate reproducible microstructure control. Here, we present a mismatch-assisted microstructure engineering strategy in which Ag2Se particles are treated with polyanionic ZnSe complexes and consolidated through the β–α transition to introduce ZnSe nanoprecipitates, Ag2Se/ZnSe interfaces, and local strain fields. The crystallographic mismatch between ZnSe and Ag2Se, together with the Zn2+/Ag+ size difference, amplifies phase-transition-induced deformation and promotes high-density dislocations with periodic strain modulations. This defect architecture suppresses grain coarsening, removes excess Ag, limits Ag-interstitial formation, and reduces lattice thermal conductivity through lattice softening and multiscale phonon scattering. Ag2Se–4%ZnSe nanocomposites achieve a peak zTmax of 1.13 at 369 K and a zTavg of 1.08 from 300 to 380 K, demonstrating mismatch-driven defect engineering through the β–α phase transition as a route for optimizing Ag2Se-based thermoelectrics.}, author = {Liu, Yu and Kleinhanns, Tobias and Spadaro, Maria Chiara and Genç, Aziz and Horta, Sharona and Navita, Navita and Costanzo, Tommaso and Dutkiewicz, Ewelina and Arbiol, Jordi and Hong, Min and Ibáñez, Maria}, issn = {2380-8195}, journal = {ACS Energy Letters}, number = {8}, pages = {5752--5762}, publisher = {American Chemical Society}, title = {{Exploiting mismatch strain and the β–α phase transition for microstructural engineering in thermoelectric Ag2Se}}, doi = {10.1021/acsenergylett.6c01499}, volume = {11}, year = {2026}, } @article{22967, abstract = {Alkali salts are widely used in solution processing, yet the corresponding cations are often assumed to remain in the liquid phase. Here, we show that alkali ions introduced during the solution synthesis of SnSe are retained through particle isolation and continue to influence the material during subsequent thermal processing, where they shape the evolution of the final polycrystalline material. Different SnSe powders were prepared using Li+, Na+, and K+ precursors, as well as tetramethylammonium (TMA+) precursors as a nonalkali reference for comparison, and all samples were consolidated under identical conditions. Although all three alkali ions were found in the matrix, at grain boundaries, and in segregated nanoscale regions, they partitioned differently and resulted in distinct grain sizes, defect distributions, and therefore transport properties. Li induced the strongest grain size heterogeneity and the lowest energy barriers, Na the best overall balance between carrier concentration and mobility, and K the broadest alkali-rich grain boundary regions along with the strongest interfacial penalty to charge carrier transport. These results show that residual alkali ions are not just remnants of solution synthesis but active determinants of microstructure and thermoelectric performance in SnSe.}, author = {Fiedler, Christine and Horta, Sharona and Navita, Navita and Maji, Krishnendu and Kleinhanns, Tobias and Llorca, Jordi and Wang, Qi and Ramon, Maria Garcia and Das, Sambit and Gavini, Vikram and Liu, Yu and Ibáñez, Maria}, issn = {1520-5002}, journal = {Chemistry of Materials}, number = {18}, pages = {9323–9332}, publisher = {American Chemical Society}, title = {{Alkali ions retained from synthesis govern microstructure and transport in solution-processed SnSe}}, doi = {10.1021/acs.chemmater.6c01284}, volume = {38}, year = {2026}, } @phdthesis{22017, author = {Kleinhanns, Tobias}, isbn = {978-3-99078-081-7}, issn = {2663-337X}, pages = {59}, publisher = {Institute of Science and Technology Austria}, title = {{Unraveling the origin and evolution of defects to enable advanced thermoelectric performance}}, doi = {10.15479/AT-ISTA-22017}, year = {2026}, } @article{20326, abstract = {Ag2Se is a promising n-type thermoelectric material, but its performance is limited by excessive carrier concentration, compositional inhomogeneity, and phase instability, challenges rooted in a narrow homogeneity range and uncontrolled Ag+ diffusion in the superionic phase. Here, we address these issues by exploiting liquid–solid interface reactions using CdSe complexes that remove surface excess Ag to yield stoichiometric Ag2Se and generate CdSe nanodomains that inhibit Ag+ diffusion and constrain grain growth. The resulting Ag2Se-CdSe nanocomposites exhibit a reproducible, stable figure of merit (zT) of 1.04 between 300 and 390 K. Beyond demonstrating high performance, we elucidate the interfacial chemical reactions that give rise to the observed microstructure and transport properties, providing a foundation for rationally engineering interfacial chemistry to tailor transport properties across diverse thermoelectric material systems.}, author = {Liu, Yu and Kleinhanns, Tobias and Horta, Sharona and Dutkiewicz, Ewelina and Lu, Shaoqing and Spadaro, Maria Chiara and Genç, Aziz and Chen, Lei and Lim, Khak Ho and Hong, Min and Arbiol, Jordi and Ibáñez, Maria}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {35}, pages = {32199--32208}, publisher = {American Chemical Society}, title = {{Liquid-solid interface reactions drive enhanced thermoelectric performance in Ag2Se}}, doi = {10.1021/jacs.5c11435}, volume = {147}, year = {2025}, } @article{15182, abstract = {Thermoelectric materials convert heat into electricity, with a broad range of applications near room temperature (RT). However, the library of RT high-performance materials is limited. Traditional high-temperature synthetic methods constrain the range of materials achievable, hindering the ability to surpass crystal structure limitations and engineer defects. Here, a solution-based synthetic approach is introduced, enabling RT synthesis of powders and exploration of densification at lower temperatures to influence the material's microstructure. The approach is exemplified by Ag2Se, an n-type alternative to bismuth telluride. It is demonstrated that the concentration of Ag interstitials, grain boundaries, and dislocations are directly correlated to the sintering temperature, and achieve a figure of merit of 1.1 from RT to 100 °C after optimization. Moreover, insights into and resolve Ag2Se's challenges are provided, including stoichiometry issues leading to irreproducible performances. This work highlights the potential of RT solution synthesis in expanding the repertoire of high-performance thermoelectric materials for practical applications.}, author = {Kleinhanns, Tobias and Milillo, Francesco and Calcabrini, Mariano and Fiedler, Christine and Horta, Sharona and Balazs, Daniel and Strumolo, Marissa J. and Hasler, Roger and Llorca, Jordi and Tkadletz, Michael and Brutchey, Richard L. and Ibáñez, Maria}, issn = {1614-6840}, journal = {Advanced Energy Materials}, number = {22}, publisher = {Wiley}, title = {{A route to high thermoelectric performance: Solution‐based control of microstructure and composition in Ag2Se}}, doi = {10.1002/aenm.202400408}, volume = {14}, year = {2024}, } @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{12237, abstract = {Thermoelectric technology requires synthesizing complex materials where not only the crystal structure but also other structural features such as defects, grain size and orientation, and interfaces must be controlled. To date, conventional solid-state techniques are unable to provide this level of control. Herein, we present a synthetic approach in which dense inorganic thermoelectric materials are produced by the consolidation of well-defined nanoparticle powders. The idea is that controlling the characteristics of the powder allows the chemical transformations that take place during consolidation to be guided, ultimately yielding inorganic solids with targeted features. Different from conventional methods, syntheses in solution can produce particles with unprecedented control over their size, shape, crystal structure, composition, and surface chemistry. However, to date, most works have focused only on the low-cost benefits of this strategy. In this perspective, we first cover the opportunities that solution processing of the powder offers, emphasizing the potential structural features that can be controlled by precisely engineering the inorganic core of the particle, the surface, and the organization of the particles before consolidation. We then discuss the challenges of this synthetic approach and more practical matters related to solution processing. Finally, we suggest some good practices for adequate knowledge transfer and improving reproducibility among different laboratories.}, author = {Fiedler, Christine and Kleinhanns, Tobias and Garcia, Maria and Lee, Seungho and Calcabrini, Mariano and Ibáñez, Maria}, issn = {1520-5002}, journal = {Chemistry of Materials}, keywords = {Materials Chemistry, General Chemical Engineering, General Chemistry}, number = {19}, pages = {8471--8489}, publisher = {American Chemical Society}, title = {{Solution-processed inorganic thermoelectric materials: Opportunities and challenges ∇}}, doi = {10.1021/acs.chemmater.2c01967}, volume = {34}, year = {2022}, } @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{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{8189, abstract = {Direct ethanol fuel cells (DEFCs) show a huge potential to power future electric vehicles and portable electronics, but their deployment is currently limited by the unavailability of proper electrocatalysis for the ethanol oxidation reaction (EOR). In this work, we engineer a new electrocatalyst by incorporating phosphorous into a palladium-tin alloy and demonstrate a significant performance improvement toward EOR. We first detail a synthetic method to produce Pd2Sn:P nanocrystals that incorporate 35% of phosphorus. These nanoparticles are supported on carbon black and tested for EOR. Pd2Sn:P/C catalysts exhibit mass current densities up to 5.03 A mgPd−1, well above those of Pd2Sn/C, PdP2/C and Pd/C reference catalysts. Furthermore, a twofold lower Tafel slope and a much longer durability are revealed for the Pd2Sn:P/C catalyst compared with Pd/C. The performance improvement is rationalized with the aid of density functional theory (DFT) calculations considering different phosphorous chemical environments. Depending on its oxidation state, surface phosphorus introduces sites with low energy OH− adsorption and/or strongly influences the electronic structure of palladium and tin to facilitate the oxidation of the acetyl to acetic acid, which is considered the EOR rate limiting step. DFT calculations also points out that the durability improvement of Pd2Sn:P/C catalyst is associated to the promotion of OH adsorption that accelerates the oxidation of intermediate poisoning COads, reactivating the catalyst surface.}, author = {Yu, Xiaoting and Liu, Junfeng and Li, Junshan and Luo, Zhishan and Zuo, Yong and Xing, Congcong and Llorca, Jordi and Nasiou, Déspina and Arbiol, Jordi and Pan, Kai and Kleinhanns, Tobias and Xie, Ying and Cabot, Andreu}, issn = {2211-2855}, journal = {Nano Energy}, number = {11}, publisher = {Elsevier}, title = {{Phosphorous incorporation in Pd2Sn alloys for electrocatalytic ethanol oxidation}}, doi = {10.1016/j.nanoen.2020.105116}, volume = {77}, year = {2020}, }