Matrix Plainification Leads to High Thermoelectric Performance in Plastic Cu2Se/SnSe Composites

Matrix Plainification Leads to High Thermoelectric Performance in Plastic Cu2Se/SnSe Composites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Matrix Plainification Leads to High Thermoelectric Performance in Plastic Cu2Se/SnSe Composites Guodong Tang, Pan Ying, Qingyang Jian, Yaru Gong, Tong Song, yuxuan yang, and 15 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5735896/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Apr, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Thermoelectric technology exhibits significant potential for applications in power generation and electronic cooling. In this study, we report the achievement of exceptional thermoelectric performance and high plasticity in stable Cu 2 Se/SnSe composites. A novel matrix plainification strategy was employed to eliminate lattice vacancies within the Cu 2 Se matrix of the Cu 2 Se/SnSe composites, resulting in a marked improvement in carrier mobility. This increase in carrier mobility corresponds to a substantial enhancement of the power factor. Furthermore, the presence of quasi-coherent interfaces induces strong phonon scattering, which effectively reduces lattice thermal conductivity without compromising carrier mobility. Consequently, an outstanding figure of merit (ZT) of 3.3 was attained in the Cu 2 Se/SnSe composite. Additionally, the presence of high-density nanotwins imparts remarkable plasticity to the composite, yielding a compressive strain of 12%. The secondary phase contributes to the stability of the composite by hindering the extensive migration of Cu ions through bonding interactions. Our findings present a novel strategy for significantly enhancing the thermoelectric performance of composite semiconductors, with potential applicability to other thermoelectric systems. Physical sciences/Materials science/Materials for energy and catalysis Physical sciences/Energy science and technology/Thermoelectric devices and materials Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Thermoelectric materials can directly convert waste heat into electricity and vice versa without mechanical transmission, noise, and pollution based on carrier and phonon transport. 1, 2 Development of highly efficient thermoelectric materials has become increasingly critical as the world seeks sustainable solutions to alleviate energy and environmental crisis. 3, 4 The thermoelectric energy conversion efficiency is primarily determined by the dimensionless figure of merit, \(\:\text{ZT}\text{=}\text{σ}{S}^{2}\text{T}\text{/}{\text{}}_{\text{tot}}\:\) 5, 6, 7 , where σ , S , and T denote the electrical conductivity, the Seebeck coefficient and absolute temperature, respectively. κ tot is the total thermal conductivity, which is the sum of the lattice thermal conductivity ( κ lat ) and the electronic thermal conductivity ( κ ele ). The thermoelectric parameters σ , S , κ ele are strongly coupled via carrier concentration, which is quite difficult to decouple the electron and phonon transport and limits thermoelectric optimization. 8, 9 To date, several approaches have been emerged to substantially enhance ZT values, which include maximizing power factor ( PF = S 2 σ ) through engineering carrier concentration 10, 11, 12 , manipulating band structure 13, 14, 15 and modulating the phonon transport through nanostructuring 16, 17, 18, 19 , phase separation 20, 21, 22 , and all-scale hierarchical architecturing 23, 24, 25 . Cu 2 Se-based materials are of great potential due to their earth-abundant and nontoxic elements, high ZT value, and wide service temperature range 26 . It undergoes a structural transition from low symmetry monoclinic phase ( α -phase) to high symmetry cubic phase ( β -phase) at around 400 K. 27 The high temperature β -phase Cu 2 Se is classified as a superionic conductor, exemplifying the “electron-crystal, phonon-liquid” concept. 27 The high thermoelectric performance derives from its intrinsically low thermal conductivity and superior electrical transport properties due to highly mobile and diffusive Cu ions. 28 The mobile and diffusive Cu ions cause strong phonon scattering, leading to low lattice thermal conductivity. 27, 29 Meanwhile, enhanced carrier concentration induced by mobile and diffusive Cu ions and formation of abundant conductive framework contribute to high electrical transport properties. 27 However, stability and carrier mobility were seriously deteriorated by their superionic feature. The Cu ion migration leads to the deposition of Cu to the interface at the high temperature end of the material device under large external electric fields and gradients 30 , which adversely affects the stability and damages its thermoelectric performance 31, 32 . High intrinsic carrier concentration coupled with low solubility limits of dopants prevents the hole concentration of Cu 2 Se from being optimized to the optimal level 33, 34 , significantly constraining ZT optimization. Therefore, it is a great challenge for achieving a high ZT while improving the stability of Cu 2 Se. Ion confinement effect was demonstrate to inhibit the long-range migration of Cu ions and obtain highly stable Cu 2 Se based material. 26 Additionally, phase interface engineering has been shown to be an effective strategy to an ion-blocking interface to hinder Cu ion migration. 26, 35, 36 Furthermore, the composite phase can serve as phonon scattering centre, reducing the lattice thermal conductivity and partially decoupling electron-phonon transport. 28, 37 However, the introduction of secondary phases and interfaces in composite materials contribute strong carrier scattering, thereby leading to deterioration of carrier mobility. 3 Moreover, plenty of Cu vacancies exists in Cu 2 Se due to the weak chemical bonds and low vacancy formation energy. 27 The intrinsic Cu vacancies and mobile Cu ions significantly diminish carrier mobility at high temperatures. The reduction in carrier mobility leads to lower electrical conductivity and thus compromise the power factor. 38 Synergistic approach of boosting carrier mobility while suppress the lattice thermal conductivity is the key point to achieve optimal thermoelectric performance. Here, matrix planification was firstly proposed to fill matrix vacancy defects and boost carrier mobility in composite materials. We successfully achieved ultrahigh thermoelectric performance in Cu 2 Se by introducing Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase. Sn atoms of Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase effectively fill Cu vacancies of matrix Cu 2 Se, plainifizing the crystal lattice of Cu 2 Se matrix and significantly enhance carrier mobility of composite (Fig. 1 a,b). Furthermore, the large difference in work functions (Cu 2 Se: 5.16 eV and Sn 0.96 Pb 0.01 Zn 0.03 Se: 4.38 eV) effectively optimizes the carrier concentration (Supplementary Fig. 1) and enhances the Seebeck coefficient. The sharp increase in carrier mobility and the enhanced Seebeck coefficient leads to a marked increase of power factor. Meanwhile, the observed smooth and quasi-coherent interfaces cause strong phonon scattering, leading to substantial reduction in the lattice thermal conductivity without carrier mobility deterioration. These synergistic effects contribute to a record-high ZT value of 3.3 at 973 K in Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composite, which is the highest value among utmost reported thermoelectric systems (Fig. 1 c) 39, 40, 41, 42, 43, 44, 45, 46 . First-principles calculations found that the migrating Cu ions are effectively captured by the exposed Se atoms in SnSe, facilitating charge transfer between Cu and Se atoms. This effectively hinders the long-range migration of Cu ions and improves the stability of the Cu 2 Se based material. These findings provide a comprehensive framework for designing high-performance, stable, and mechanically robust thermoelectric materials with superionic characteristics. Results and Discussions Crystal structure and phase description The XRD patterns of the synthesized Cu 2 Se/x wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se (x = 0, 1, 3, 5 and 10) are shown in Supplementary Fig. 2a. The Bragg diffraction peaks of the primary phase align well with the monoclinic α -Cu 2 Se fingerprint peaks, except for the detection of the high-temperature β -Cu 2 Se phase in the pristine Cu 2 Se sample. Cu 2 Se has two energetically similar structures under ambient condition: a monoclinic structure ( α -Cu 2 Se) at room temperature and a cubic structure ( β -Cu 2 Se) above 375 K (Supplementary Fig. 3) 47 . The structural transition was evidenced by Differential Scanning Calorimeter (DSC) tests (Supplementary Fig. 4). According to the Cu-Se binary phase diagram, even a slight Cu deficiency can induce the β -Cu 2 Se phase, which arises from Cu deposition during the preparation process. We can speculate that the addition of Sn 0.96 Pb 0.01 Zn 0.03 Se during this process might hinder the migration and deposition of copper 48 , thus preventing the appearance of the β -Cu 2 Se phase. Due to the detection limits of X-ray characterization, secondary phases related to Sn 0.96 Pb 0.01 Zn 0.03 Se are only observed at doping levels above 3%. Rietveld refinement of the X-ray diffraction data (Supplementary Fig. 5) provides precise crystallographic information, indicating minimal variation in lattice parameters (Supplementary Fig. 2b). X-ray photoelectron spectroscopy (XPS) was performed on the Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample to determine the valence states of elements. The peaks with binding energy of 932.8 eV, and 940.6 eV can be assigned to Cu + (Supplementary Fig. 2c) 49 . The peaks with binding energies of 486.6 eV and 495 eV can be attributed to Sn 2+ (Supplementary Fig. 2d). Electrical transport properties Figure 2 a presents the temperature dependence of electrical conductivity ( s ) for Cu 2 Se/x wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composites. Temperature-dependent s demonstrates a degenerate semiconducting behavior, which primarily originates from intrinsic high Cu deficiency. The composites exhibit a noticeable reduction in s as compared with the pristine Cu 2 Se. The temperature-dependent carrier concentration ( n ) and mobility ( µ ) were measured and illustrated in Fig. 2 b and Fig. 2 c, respectively. It is found that the decrease of s is attributed to a significantly reduced carrier concentration ( n ) after the introduction of Sn 0.96 Pb 0.01 Zn 0.03 Se (Fig. 2 b). This phenomenon can be explained by examining their work functions: Cu 2 Se has a work function of 5.16 eV 36 , while Sn 0.96 Pb 0.01 Zn 0.03 Se has a work function of 4.38 eV (Supplementary Fig. 6). The large difference in work function would drive holes from Cu 2 Se matrix to Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase until their Fermi levels reach equilibrium (Supplementary Fig. 1), which ultimately leads to a reduction in carrier concentration. Hall mobility ( µ ) displays a negative correlation with carrier concentration ( n ) and decreases with increasing temperature (Fig. 2 c). Notably, carrier mobility ( µ ) shows a remarkable enhancement as compared with pristine Cu 2 Se in the whole investigated temperature range. At room temperature, the Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample achieves a remarkable carrier mobility of 33.7 cm 2 ·V − 1 ·s − 1 , which is about three times higher than that of pristine Cu 2 Se (11.5 cm 2 ·V − 1 ·s − 1 ). This value is significantly surpassing previously reported Cu 2 Se-based composites (4.65–16.60 cm 2 ·V − 1 ·s − 1 ) 36, 50, 51, 52, 53, 54 (Fig. 1 b). At 973 K, the carrier mobility of the Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample reduces to 4.57 cm 2 ·V − 1 ·s − 1 , which is still more than four times bigger than that of the pristine Cu 2 Se (1.07 cm 2 ·V − 1 ·s − 1 ). The significantly enhanced carrier mobility facilitates electrical transport, leading to high power factor. To understand the mechanism of the large enhancement of carrier mobility in the composites, we performed a systematical analysis combining theoretical calculations and experimental characterization. We first carried out the defect formation energy calculations using the density-function theory (DFT) to understand the defect behaviors in Cu 2 Se (Supplementary Table 1 and Supplementary Fig. 7). It is found that the defect formation energy of Cu vacancy (V Cu ) is very low (-0.66 eV). The negative formation energy indicates the spontaneously forming Cu vacancies in the Cu 2 Se matrix, which is consistent with the previously observed large amount of Cu vacancies in Cu 2 Se 27, 55 . When Sn fills Cu vacancies or substituting the Cu site (Sn Cu ), its formation energy is low (0.73 eV) as well, suggesting that the defect can be highly formed in the Cu 2 Se/x wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composites. Additionally, once the Sn Cu defect binding with the neighboring V Cu , it forms a complex defect (Sn Cu +V Cu ) and its formation energy is as low as 0.07 eV, which is lower than that of Sn Cu . Obviously, the formation of such complex defect further facilitates the Sn Cu formation. This indicates that Sn can easily fill the Cu vacancies to plain lattice of matrix Cu 2 Se in the composites. This leads to large enhancement of carrier mobility, as evidenced by experimental results. Aberration-corrected STEM characterization provides compelling evidence that the high-density Cu vacancies in the pristine Cu 2 Se matrix are filled by Sn atoms from the secondary phase (Sn 0.96 Pb 0.01 Zn 0.03 Se) in the composite. Figures 3 a- 3 d depict atomic-resolution HAADF images of pristine Cu 2 Se along two distinct zone axes, accompanied by fast Fourier transform (FFT) patterns and atomic configuration diagrams. These results precisely define the crystal structure of the room-temperature α -Cu 2 Se phase. To reveal subtle distinctions in the atomic structure of the Cu 2 Se matrix between pristine Cu 2 Se and Cu 2 Se/Sn 0.96 Pb 0.01 Zn 0.03 Se composites, Figs. 3 e- 3 j present representative atomic-resolution HAADF images alongside quantitative analyses of individual atomic intensities. The calculation method is to divide the intensity α of Cu/Se sites by the average contrast β of the surrounding Se atoms to obtain the numerical value ϒ , and then obtain the figure using the ratio of α and the average value ϒ ( ϒ avg ), in order to eliminate the effect of the sample thickness. Among them, blue and red points represent lighter/fewer and heavy/more atoms, respectively. Thus, the atomic columns that contain a large fraction of vacancies will show as blue contrast. These analyses provide precise determinations of atomic coordinates and intensity values. In pristine Cu 2 Se, the Cu atoms exhibit weak intensities at various lattice sites, indicating the presence of Cu vacancies due to the intrinsic low vacancy formation energy of Cu 2 Se (Figs. 3f1-3f 4 ). And Se atoms exhibit a uniform intensity distribution across all positions. The high density of Cu vacancies induces significant lattice distortions (Supplementary Figs. 8a-8c), disrupting the regular lattice periodicity, intensifying carrier scattering, and severely impairing charge carrier mobility. Upon incorporating Sn 0.96 Pb 0.01 Zn 0.03 Se, these Cu vacancies are effectively eliminated, as evidenced by the absence of low-intensity sites in the Cu 2 Se matrix (Fig. 3 g). Further magnified HAADF intensity images demonstrate that heterovalent cations with higher atomic mass have occupied the regions previously deficient in Cu (Figs. 3h1-3j). Energy-dispersive X-ray spectroscopy (EDS) line scan confirms that these sites are predominantly occupied by Sn atoms originating from the Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase (Supplementary Figs. 8d-8f). The intensity statistics of individual Cu atomic columns and regional atomic planes in STEM images also confirm that the incorporation of Sn atoms from the secondary phase Sn 0.96 Pb 0.01 Zn 0.03 Se into the Cu vacancies, leading to matrix plainification. Matrix plainification significantly boosts carrier mobility within the Cu 2 Se/x wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composites through weaken carrier scattering. The positive Seebeck coefficient (Fig. 2 d) indicates the dominant p -type charge transport. Compared to pristine Cu 2 Se, the composites samples exhibit enhanced Seebeck coefficients at entire temperature range due to reduced carrier concentration. At 973 K, the Seebeck coefficient increases from 168.3 µV·K − 1 for pristine Cu 2 Se to 228 µV·K − 1 for Cu 2 Se/3% wt. Sn 0.96 Pb 0.01 Zn 0.03 Se. Enhanced carrier mobility and the optimized carrier concentration result in a substantial increase in power factor ( PF ) (Fig. 2 e). The highest PF of 16.22 µW·cm − 1 ·K − 2 is achieved in Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample at 973 K. More comparisons of the PF of Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample with those of previously reported Cu 2 Se-based thermoelectrics is presented in Supplementary Fig. 9. Significantly enhanced PF indicates that incorporation of Sn 0.96 Pb 0.01 Zn 0.03 Se markedly optimizes electrical transport property of Cu 2 Se matrix. The intrinsic electrical transport characteristics can be further evaluated by the weighted mobility ( µ w ) provides a direct assessment of the intrinsic electrical transport characteristics (Fig. 2 f). The Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample exhibits the highest µ W among the investigated samples, reflecting its better electrical transport properties. Thermal transport properties Figure 2 g illustrates the temperature-dependent total thermal conductivity ( κ tot ) of Cu 2 Se/x wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se (x = 0, 1, 3, 5 and 10) composites. Introducing Sn 0.96 Pb 0.01 Zn 0.03 Se significantly reduced the total thermal conductivity in the whole temperature range. In particular, the composite with 5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se exhibits lowest total thermal conductivities ( κ tot ) among all investigated samples. To gain deeper insights into the exceptionally low thermal conductivity of the composites, we calculated the carrier thermal conductivity ( κ ele ) (Supplementary Fig. 10a) using the Wiedemann–Franz relation κ e = LsT , where Lorenz number ( L ) was calculated by a two-band model (Supplementary Fig. 10b). The lattice thermal conductivity ( κ lat ) was obtained by subtracting κ ele from the total thermal conductivity (Fig. 2 h). The reduction in κ ele is primarily due to the regulation of carrier concentration and carrier mobility, optimizing electrical conductivity within a reasonable value. The κ lat of Cu 2 Se/x wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composites markedly decreases compared with that of pristine Cu 2 Se. The sound velocities including both longitudinal and transverse sound velocities were measured for Cu 2 Se/x wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composites (Supplementary Fig. 11). The calculated average sound velocity ( v a ) and the phonon mean free path ( l ph ) were illustrated in Fig. 2 i. With increasing content of Sn 0.96 Pb 0.01 Zn 0.03 Se, the average sound velocity gradually decreases, and correspondingly, the phonon mean free path decreases from 2.52 nm for pure Cu 2 Se to 0.79 nm for the high-performance Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample. The reduction in sound velocity and phonon mean free path suggests that the incorporation of Sn 0.96 Pb 0.01 Zn 0.03 Se induces phonon softening and enhances phonon scattering in Cu 2 Se, thereby significantly reducing κ lat . Microstructural characterization Scanning electron microscopy (SEM) image shows that numerous pores present in the composite (Supplementary Fig. 12), which originate from Se volatilization during sintering. Some bright domains disperse within the composite, as illustrated by the back scattered electron (BSE) image of the polished surface (Supplementary Fig. 13a). SEM-EDS elemental mapping (Supplementary Fig. 13b-13d) confirms Sn enrichment at the domains, indicating the presence of Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase. A line scan of the secondary phase region was also performed, and the increase in the Sn elemental intensity as well as the decrease in the Cu content prove the presence of the Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase (Supplementary Fig. 14). Figure 4 a displays a low-magnification HAADF image of the synthesized Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composite. Micropores can be found in the sample, consistent with the SEM observation (Supplementary Fig. 12). Grains with different contrasts from the matrix were identified. STEM-EDS analysis confirmed the presence of submicron Sn 0.96 Pb 0.01 Zn 0.03 Se grains embedded within the composite, indicating the existence of Sn 0.96 Pb 0.01 Zn 0.03 Se (Fig. 4 b). When the sample is oriented along the [10 − 1] zone axis of Sn 0.96 Pb 0.01 Zn 0.03 Se (Fig. 4 c, 4 d), the atomic arrangement closely aligns with SnSe. Focused observations were carried out to investigate the interfaces between composite phase (Sn 0.96 Pb 0.01 Zn 0.03 Se) and matrix (Cu 2 Se), which reveal a prevalence of smooth, planar phase interfaces (Fig. 4 e- 4 h). These heterointerfaces exhibit atomic-scale flatness, contrasting with the commonly observed rough interfaces, and demonstrate quasi-coherence across different zone axes. Moreover, extensive nanotwins substructures were observed within both Cu 2 Se and Sn 0.96 Pb 0.01 Zn 0.03 Se grains of the synthesized composite (Fig. 4 i, 4 j). A noticeable presence of dislocations in the Cu 2 Se matrix is also detected (Fig. 4 k), which induce slight lattice strain (Fig. 4 l). The smooth and quasi-coherent interfaces between the Sn 0.96 Pb 0.01 Zn 0.03 Se and the Cu 2 Se matrix, in contrast to traditional rough interfaces, is very beneficial for the migration of Sn ions from Sn 0.96 Pb 0.01 Zn 0.03 Se to Cu 2 Se due to the virtually nonexistent of defects and dislocations, thereby facilitating matrix plainification. Meanwhile, the smooth and quasi-coherent interfaces has minimal adverse effects on carrier transport, but cause strong phonon scattering, leading to substantial reduction of lattice thermal conductivity without carrier mobility deterioration. Nanotwins and dislocations provide extra phonon scattering sources leading to further decreased lattice thermal conductivity in the composite. The strong phonon scattering was proved by the decline trend of sound velocity and phonon mean free. Enhanced thermoelectric performance and mechanical properites Incorporation of Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase can efficiently enhance ZT of Cu 2 Se thanks to the enhanced electrical transport properties and significantly reduced lattice thermal conductivity (Fig. 5 a). A maximum ZT of 3.3 is achieved at 973 K in Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composite, which surpasses utmost reported Cu 2 Se thermoelectrics 26, 28, 35, 50, 51, 52, 53, 56 (Fig. 5 b). This value presents the highest reported among any thermoelectric systems (Fig. 1 c). Good experimental repeatability for this high ZT is achieved, which is evidenced by the reproducible results from the measurements on several samples independently prepared (Supplementary Fig. 15). Furthermore, the Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se sample exhibits better mechanical properties than pristine Cu 2 Se (Fig. 5 c, 5 d). Vickers hardness and nanoindentation hardness are both improved over pristine Cu 2 Se. Figure 5 d illustrates the compressive strength profile of the Cu 2 Se/x %wt. Sn 0.96 Pb 0.01 Zn 0.03 Se. (x = 0, 5). The composite sample exhibits higher compressive strengths of 172.45 MPa, which is more than four times larger than that of pristine Cu 2 Se (41.95 MPa). It is worth to note that the compressive strain increases form 3% for pristine Cu 2 Se to 12% for Cu 2 Se/5%wt. Sn 0.96 Pb 0.01 Zn 0.03 Se composite. Large plastic deformation is achieved in the composite, which is higher than the most of traditional thermoelectric semiconductors and ceramics (usually have compressive strain below 3%) 57, 58, 59, 60 , and closes to strain of the plastic semiconductor Ag 2 Se. This significantly enhanced plastic deformability is most likely associated with the observed high density of nanotwin boundaries in the introduced composite component (Fig. 4 h, 4 i), i.e. , Sn 0.96 Pb 0.01 Zn 0.03 Se. The nanotwin boundaries act as additional slip planes within the material, particularly in the densely twinned Sn 0.96 Pb 0.01 Zn 0.03 Se, effectively increasing the number of active slip systems. Under applied stress, the twin boundaries facilitate slip, allowing for greater strain energy absorption. This thus results in significantly improved plasticity because the material can accommodate more deformation before failure. In the composite, the presence of high-density nanotwins in Sn 0.96 Pb 0.01 Zn 0.03 Se grains are also likely to play a pivotal role in enhancing dislocation mobility. These nanotwin boundaries act as efficient sites for dislocation nucleation and propagation, reducing the energy barrier for slip and providing a pathway for dislocation migaration through the material. The increased dislocation mobility leads to a more pronounced plastic response under compressive stress, allowing the composite to deform more easily. Additionally, these dense nanotwins effectively refine the microstructural characteritic size of the material, resulting in a hardening effect. This hardening is typically accompanied by an enhanced ability of the material to withstand higher stresses without fracturing, thereby exhibiting greater compressive strain. Moreover, the high-density nanotwin boundaries in Sn 0.96 Pb 0.01 Zn 0.03 Se grains are likely to facilitate stress relaxation in the heterointerfaces between Cu 2 Se and Sn 0.96 Pb 0.01 Zn 0.03 Se, creating efficient stress transfer zones. These zones help dissipate applied stress more uniformly throughout the composite, preventing localized strain accumulation and mitigating the risk of interfacial delamination or fracture. Collectively, the high-density nanotwins in Sn 0.96 Pb 0.01 Zn 0.03 Se, combined with the reinforcing effect at these interfaces, empower the material to endure higher compressive stresses without localized fracture or slip, thus substantially enhancing the overall compressive strain of the composites. The significantly enhanced plasticity grants the material with large deformability, processibility, and machinability, which increases the impact resistance of thermoelectric components, thus significantly increasing their service life. 57 The discovered composite with large plasticity has great potential in flexible thermoelectric technology. This work sheds light to advance highly effective thermoelectrics. Stability Test We conducted a detailed investigation into the stability of Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composite. Thermogravimetric analysis (TGA) was performed to assess the thermal stability of the material (Supplementary Fig. 16), and the results indicated negligible weight loss over a wide temperature range, confirming that elemental volatilization is igorable. Further compositional analysis before and after thermoelectric property measurements at high temperature provided robust evidence for the enhanced stability of the composites. The pristine Cu 2 Se sample exhibits pronounced Cu enrichment on its surface due to the intrinsic long-range migration of Cu ions after thermoelectric property measurements at high temperature (Supplementary Fig. 17a). Stoichiometric changes in pristine Cu 2 Se after thermoelectric properties measurements were evidenced by SEM-EDS analysis. In stark contrast, no Cu enrichment on the composite sample surface and no alterations in the composition are observed after thermoelectric properties measurements (Supplementary Fig. 17b), indicating its stability is enhanced. XRD analysis reveals that the pure sample undergoes stoichiometric changes due to Cu loss of the matrix, which facilitates the formation of β -Cu 2 Se after thermoelectric properties measurements (Supplementary Fig. 18a), whilst the composite samples maintain consistent phase components after the testing process (Supplementary Fig. 18b). To evaluate the stability under real operational conditions, we subjected the sample to simultaneous current field and temperature gradient field (Fig. 6 a,b). A pulsed current with a maximum current density of 25 A/cm 2 was applied (Fig. 6 c), and the relative resistance of the sample was monitored for up to 20,000 s. As shown in Fig. 6 e, the relative resistance of pristine Cu 2 Se exhibits a steep increase with test time, indicating substantial Cu ions migration and subsequent accumulation at the interface, which significantly affects the resistance. 31 In contrast, the relative resistance of the composite containing x = 5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se remains almost unchanged under the same conditions, suggesting that the addition of Sn 0.96 Pb 0.01 Zn 0.03 Se effectively hinders the long-range migration of Cu ions and improves the stability of the Cu 2 Se based material. First-principles calculations was conducted to delve deeper into the mechanism why Sn 0.96 Pb 0.01 Zn 0.03 Se suppresses the migration of Cu ions in Cu 2 Se. Charge density difference analysis reveals a strong interaction between Cu ions and Se atoms in SnSe upon Cu ions migrate at elevated temperatures (Fig. 6 g). Specifically, the migrating Cu ions are effectively captured by the exposed Se atoms in SnSe, facilitating charge transfer between Cu and Se atoms. This interaction leads to bonding between Cu and Se atoms, which plays a crucial role in inhibiting the long-range migration of Cu ions in the Cu 2 Se matrix. The secondary phase thus acts as a stabilizing agent, preventing the migration of Cu ions and thereby enhancing the stability of the composite material, exemplifying the maintenance of the stability of the composite by our meticulously targeted additives. The improved stability is essential for extending the service lifetime of thermoelectric materials. Conclusion We demonstrated a fascinating strategy of matrix planification to successfully enhanced carrier mobility and electrical transport property of composites. We reveals that Cu vacancies in matrix Cu 2 Se are filled by Sn atoms of secondary phase, leading to matrix planification. Moreover, the carrier concentration can be optimized by large difference in different work functions between matrix Cu 2 Se and the Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase, contributing to enhanced Seebeck coefficient. The sharp increase of carrier mobility and Seebeck coefficient contribute to substantial increase in power factor. Strong phonon scattering is induced by a prevalence of smooth and quasi-coherent interfaces, which greatly reduces lattice thermal conductivity without carrier mobility deterioration. Ultimately, an unprecedented high ZT value of 3.3 is achieved at 973 K in Cu 2 Se/5 wt.% Sn 0.96 Pb 0.01 Zn 0.03 Se composite. Notably, high-density nanotwins in the composite significantly enhance plasticity (compressive strain of 12%). The high plasticity grants the material with large deformability, processibility, and machinability, which significantly increasing their service life and has great potential in flexible thermoelectrics. We simultaneously improve the stability of Cu 2 Se due to inhibition the long-range migration of Cu ions by through bonding through introducing the Sn 0.96 Pb 0.01 Zn 0.03 Se secondary phase. These findings pave the way for designing of high-performance, stable, and durable liquid-like thermoelectric materials. Declarations Acknowledgments: Funding: This work was supported by The work was supported by the National Natural Science Foundation of China (No. 52071182, 52202049 and 52472250), the National Key R&D Program of China (2021YFB3201100), “Qinglan Project” of the Young and Middle aged Academic Leader of Jiangsu Province, the Fundamental Research Funds for the Central Universities (No. 30921011107, 30924010206). The authors thank the Instrument Analysis Center of Xi’an Jiaotong University for the assistance of aberration-corrected STEM. Author contributions: G.D.T. conceived and supervised the project. G.D.T., P.Y., H.J.W. and Q.Y.J. designed and carried out the experiments, analyzed the results, and wrote the paper. Q.Y.J. and Y.R.G. carried out the XRD, XPS experiments and electrical property measurements. C.C. and T.S. measured the thermal transport properties. T.S., R.X.S., Y.X.Y., J.Q.H., Y.Z., and H.J.W. conducted the microstructural characterization. P.Y. and Y.S.Z carried out the DFT calculations. T.F. performed the mechanical property measurements. K.S. performed the TEG fabrication and measured the stability. All authors analyzed the results and coedited the manuscript. Competing interests: The authors declare no other competing interests. Data and materials availability: All data are provided in the main text or the supplementary materials. References 1. Bell LE. Cooling, Heating, Generating Power, and Recovering Waste Heat with Thermoelectric Systems. Science 321 , 1457–1461 (2008). 2. He J, Tritt TM. 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Supplementary Files SupportingInformation.docx Matrix Plainification Leads to High Thermoelectric Performance in Plastic Cu2Se/SnSe Composites Cite Share Download PDF Status: Published Journal Publication published 07 Apr, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5735896","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":396870543,"identity":"c5e5847a-82e1-4a49-8207-e60ff2be2c0d","order_by":0,"name":"Guodong 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University","correspondingAuthor":false,"prefix":"","firstName":"Yang","middleName":"","lastName":"Zhang","suffix":""},{"id":396870563,"identity":"c04ae427-a974-46e3-a090-4964c7714b13","order_by":20,"name":"Haijun Wu","email":"","orcid":"https://orcid.org/0000-0002-7303-379X","institution":"Xi'an Jiaotong University","correspondingAuthor":false,"prefix":"","firstName":"Haijun","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2024-12-30 13:25:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5735896/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5735896/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-58484-0","type":"published","date":"2025-04-07T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":73150982,"identity":"ebdaa62a-ded1-42da-91aa-4c84f8f65d83","added_by":"auto","created_at":"2025-01-07 08:24:53","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":566273,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMatrix plainification\u003c/strong\u003e \u003cstrong\u003ein composite\u003c/strong\u003e \u003cstrong\u003eleads to high carrier mobility and ultrahigh \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eZT\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e values.\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e) The presence of high-density Cu vacancies in pristine Cu\u003csub\u003e2\u003c/sub\u003eSe strongly scatters carriers and reduces carrier mobility (\u003cem\u003em\u003c/em\u003e). Cu vacancies of the matrix Cu\u003csub\u003e2\u003c/sub\u003eSe are filled by Sn atoms of SnSe secondary phase, leading to matrix planification. The matrix plainification strategy leads to high carrier mobiliy (\u003cem\u003em\u003c/em\u003e) and thermoelectric performance. (\u003cstrong\u003eb\u003c/strong\u003e) The comparison of the carrier mobility (\u003cem\u003em\u003c/em\u003e) with reported values in the literatures, which demonstrates significant enhanced \u003cem\u003em \u003c/em\u003evia matrix plainification. (\u003cstrong\u003ec\u003c/strong\u003e) The comparison of \u003cem\u003eZT\u003c/em\u003e value with other reported promising thermoelectric materials.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/03e26a1d67d7b835d4890dd8.png"},{"id":73152748,"identity":"f1957cd5-98ef-4a96-90ec-f86033453889","added_by":"auto","created_at":"2025-01-07 08:40:53","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2180809,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTransport properties of Cu\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe/x wt.% Sn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.96\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePb\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.01\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eZn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.03\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe composites.\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e) Electrical conductivity (\u003cem\u003es\u003c/em\u003e). (\u003cstrong\u003eb\u003c/strong\u003e) Temperature dependent carrier concentration (\u003cem\u003en\u003c/em\u003e). (\u003cstrong\u003ec\u003c/strong\u003e) Temperature dependent carrier mobility (\u003cem\u003em\u003c/em\u003e). (\u003cstrong\u003ed\u003c/strong\u003e) Seebeck coefficient (\u003cem\u003eS\u003c/em\u003e). (\u003cstrong\u003ee\u003c/strong\u003e) Power factor (\u003cem\u003ePF\u003c/em\u003e). (\u003cstrong\u003ef\u003c/strong\u003e) Weighted carriermobility (\u003cem\u003em\u003c/em\u003e\u003csub\u003eW\u003c/sub\u003e). (\u003cstrong\u003eg\u003c/strong\u003e) Total thermal conductivity (\u003cem\u003ek\u003c/em\u003e\u003csub\u003etot\u003c/sub\u003e). (\u003cstrong\u003eh\u003c/strong\u003e) Lattice thermal conductivity (\u003cem\u003ek\u003c/em\u003e\u003csub\u003elat\u003c/sub\u003e). (\u003cstrong\u003ei\u003c/strong\u003e) Average sound velocity (\u003cem\u003eV\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e) and phonon mean free path (MFP) at 300 K.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/c7e15d3e4ab469d7a7c54a9c.png"},{"id":73150985,"identity":"9527aed2-d847-4373-ac79-8d24f00527f1","added_by":"auto","created_at":"2025-01-07 08:24:53","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1215283,"visible":true,"origin":"","legend":"\u003cp\u003eAtomic-resolution HAADF images of pure Cu\u003csub\u003e2\u003c/sub\u003eSe sample along [010] (\u003cstrong\u003ea\u003c/strong\u003e) and [110] (\u003cstrong\u003ec\u003c/strong\u003e) zone axes. Inset: Corresponding FFT images. Atomic configuration diagrams along [010] (\u003cstrong\u003eb\u003c/strong\u003e) and [110] (\u003cstrong\u003ed\u003c/strong\u003e) zone axes of Cu\u003csub\u003e2\u003c/sub\u003eSe. (\u003cstrong\u003ee\u003c/strong\u003e) Intensity mapping of Se of pristine Cu\u003csub\u003e2\u003c/sub\u003eSe sample. (\u003cstrong\u003ef1\u003c/strong\u003e-\u003cstrong\u003ef4\u003c/strong\u003e) Intensity mapping of different Cu sites relative to the surrounding Se atoms in pristine Cu\u003csub\u003e2\u003c/sub\u003eSe sample. (\u003cstrong\u003eg\u003c/strong\u003e) HADDF image of the Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite, showing Sn filling regions. (\u003cstrong\u003eh1\u003c/strong\u003e-\u003cstrong\u003eh2\u003c/strong\u003e) Intensity mapping of different Cu sites relative to the surrounding Se atoms in Cu\u003csub\u003e2\u003c/sub\u003eSe/Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite. (\u003cstrong\u003ei\u003c/strong\u003e, \u003cstrong\u003ej\u003c/strong\u003e) Atomic intensity profile for the red line in \u003cstrong\u003eh1\u003c/strong\u003e and all atoms in \u003cstrong\u003eg, \u003c/strong\u003eindicating the Sn filling in Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/ae6bb6f2c4250f27788a5fa2.png"},{"id":73150997,"identity":"59966e03-2b9d-4710-b7b1-794a42855c7a","added_by":"auto","created_at":"2025-01-07 08:24:53","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1050518,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMicrostructural characterization on Cu\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe/5 wt.% Sn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.96\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePb\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.01\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eZn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.03\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe composite.\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e) Low-magnification HAADF image. (\u003cstrong\u003eb\u003c/strong\u003e) ADF image and corresponding EDS mapping showing SnSe grain embedded in the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix. (\u003cstrong\u003ec\u003c/strong\u003e) HAADF image of the Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe grain view along the [01-1] zone axis. Inset: atomic configuration diagram. (\u003cstrong\u003ed\u003c/strong\u003e) Corresponding SAED image of \u003cstrong\u003ec\u003c/strong\u003e. (\u003cstrong\u003ee\u003c/strong\u003e) Medium-magnification HAADF image of the Cu\u003csub\u003e2\u003c/sub\u003eSe–Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe interface. (\u003cstrong\u003ef\u003c/strong\u003e) High-magnification HAADF image in \u003cstrong\u003ee\u003c/strong\u003e. (\u003cstrong\u003eg\u003c/strong\u003e) Medium-magnification HAADF image of the Cu\u003csub\u003e2\u003c/sub\u003eSe–Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe interface. (\u003cstrong\u003eh\u003c/strong\u003e) High-magnification HAADF image in \u003cstrong\u003eg\u003c/strong\u003e. (\u003cstrong\u003ei, j\u003c/strong\u003e) High-magnification HAADF image of the nanotwin substructures in the Cu\u003csub\u003e2\u003c/sub\u003eSe and Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe gains, respectively. (\u003cstrong\u003ek\u003c/strong\u003e) High-magnification HAADF image of \u0026nbsp;Cu\u003csub\u003e2\u003c/sub\u003eSe grain showing high-density dislocations. (\u003cstrong\u003el)\u003c/strong\u003e Strain mapping of boxed area in \u003cstrong\u003ek\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/2d5eb4202ef87156acd4bbf6.png"},{"id":73150990,"identity":"e6c1c554-5d5a-480a-8568-208f7ce8e448","added_by":"auto","created_at":"2025-01-07 08:24:53","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":514207,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDimensionless figure of merit \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eZT\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e and mechanical properties of the Cu\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe/5 wt.% Sn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.96\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePb\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.01\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eZn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.03\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe composite. \u003c/strong\u003e(\u003cstrong\u003ea\u003c/strong\u003e) \u003cem\u003eZT\u003c/em\u003e as a function of temperature for Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe. (\u003cstrong\u003eb\u003c/strong\u003e) Comparison of \u003cem\u003eZT\u003c/em\u003e between Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe in this work with reported Cu\u003csub\u003e2\u003c/sub\u003eSe-based materials. (\u003cstrong\u003ec\u003c/strong\u003e) The Vickers microhardness (HV) and nanoindentation hardness (H). (\u003cstrong\u003ed\u003c/strong\u003e) The compressive strain-stress curves.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/55ca9211540d22bf3604e9d2.png"},{"id":73151378,"identity":"af58b1b4-64e9-4679-94e8-006eff8c8c50","added_by":"auto","created_at":"2025-01-07 08:32:53","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":273267,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStability tests of Cu\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe/x wt.% Sn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.96\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePb\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.01\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eZn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.03\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSe (x = 0, 5) and mechanism diagram of trapping effect of SnSe on Cu ions.\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e)\u003cstrong\u003e \u003c/strong\u003ePower supply unit. (\u003cstrong\u003eb\u003c/strong\u003e) Photograph of TEGs fabricated.\u003cstrong\u003e \u003c/strong\u003e(\u003cstrong\u003ec\u003c/strong\u003e) Current density used for testing. (\u003cstrong\u003ed\u003c/strong\u003e) Temperature gradient field. (\u003cstrong\u003ee\u003c/strong\u003e) Variation of relative resistance (R/R\u003csub\u003e0\u003c/sub\u003e) with time. (\u003cstrong\u003ef\u003c/strong\u003e) Variation of voltage with time at the applied current density. (\u003cstrong\u003eg\u003c/strong\u003e) Differential charge density plot of Cu ions interacting with SnSe.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/1061890c8e362c33bc6c0cd1.png"},{"id":80118977,"identity":"f6ac0eb5-cd86-4da1-b70f-182d6202229f","added_by":"auto","created_at":"2025-04-08 07:06:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7109351,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/944b58f0-f691-40ba-8bc2-165bae970a65.pdf"},{"id":73151375,"identity":"355cda49-a598-43fb-bb66-7869cfa09b8f","added_by":"auto","created_at":"2025-01-07 08:32:53","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5073267,"visible":true,"origin":"","legend":"Matrix Plainification Leads to High Thermoelectric Performance in Plastic Cu2Se/SnSe Composites","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-5735896/v1/20d64f968541fa32d352b544.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Matrix Plainification Leads to High Thermoelectric Performance in Plastic Cu2Se/SnSe Composites","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThermoelectric materials can directly convert waste heat into electricity and vice versa without mechanical transmission, noise, and pollution based on carrier and phonon transport. \u003csup\u003e1, 2\u003c/sup\u003e Development of highly efficient thermoelectric materials has become increasingly critical as the world seeks sustainable solutions to alleviate energy and environmental crisis. \u003csup\u003e3, 4\u003c/sup\u003e The thermoelectric energy conversion efficiency is primarily determined by the dimensionless figure of merit, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{ZT}\\text{=}\\text{\u0026sigma;}{S}^{2}\\text{T}\\text{/}{\\text{}}_{\\text{tot}}\\:\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e5, 6, 7\u003c/sup\u003e, where \u003cem\u003eσ\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e, and \u003cem\u003eT\u003c/em\u003e denote the electrical conductivity, the Seebeck coefficient and absolute temperature, respectively. \u003cem\u003eκ\u003c/em\u003e\u003csub\u003etot\u003c/sub\u003e is the total thermal conductivity, which is the sum of the lattice thermal conductivity (\u003cem\u003eκ\u003c/em\u003e\u003csub\u003elat\u003c/sub\u003e) and the electronic thermal conductivity (\u003cem\u003eκ\u003c/em\u003e\u003csub\u003eele\u003c/sub\u003e). The thermoelectric parameters \u003cem\u003eσ\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e, \u003cem\u003eκ\u003c/em\u003e\u003csub\u003eele\u003c/sub\u003e are strongly coupled via carrier concentration, which is quite difficult to decouple the electron and phonon transport and limits thermoelectric optimization. \u003csup\u003e8, 9\u003c/sup\u003e To date, several approaches have been emerged to substantially enhance \u003cem\u003eZT\u003c/em\u003e values, which include maximizing power factor (\u003cem\u003ePF\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eS\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003cem\u003eσ\u003c/em\u003e) through engineering carrier concentration \u003csup\u003e10, 11, 12\u003c/sup\u003e, manipulating band structure \u003csup\u003e13, 14, 15\u003c/sup\u003e and modulating the phonon transport through nanostructuring \u003csup\u003e16, 17, 18, 19\u003c/sup\u003e, phase separation \u003csup\u003e20, 21, 22\u003c/sup\u003e, and all-scale hierarchical architecturing \u003csup\u003e23, 24, 25\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eCu\u003csub\u003e2\u003c/sub\u003eSe-based materials are of great potential due to their earth-abundant and nontoxic elements, high \u003cem\u003eZT\u003c/em\u003e value, and wide service temperature range \u003csup\u003e26\u003c/sup\u003e. It undergoes a structural transition from low symmetry monoclinic phase (\u003cem\u003eα\u003c/em\u003e-phase) to high symmetry cubic phase (\u003cem\u003eβ\u003c/em\u003e-phase) at around 400 K. \u003csup\u003e27\u003c/sup\u003e The high temperature \u003cem\u003eβ\u003c/em\u003e-phase Cu\u003csub\u003e2\u003c/sub\u003eSe is classified as a superionic conductor, exemplifying the \u0026ldquo;electron-crystal, phonon-liquid\u0026rdquo; concept. \u003csup\u003e27\u003c/sup\u003e The high thermoelectric performance derives from its intrinsically low thermal conductivity and superior electrical transport properties due to highly mobile and diffusive Cu ions. \u003csup\u003e28\u003c/sup\u003e The mobile and diffusive Cu ions cause strong phonon scattering, leading to low lattice thermal conductivity. \u003csup\u003e27, 29\u003c/sup\u003e Meanwhile, enhanced carrier concentration induced by mobile and diffusive Cu ions and formation of abundant conductive framework contribute to high electrical transport properties. \u003csup\u003e27\u003c/sup\u003e However, stability and carrier mobility were seriously deteriorated by their superionic feature. The Cu ion migration leads to the deposition of Cu to the interface at the high temperature end of the material device under large external electric fields and gradients \u003csup\u003e30\u003c/sup\u003e, which adversely affects the stability and damages its thermoelectric performance \u003csup\u003e31, 32\u003c/sup\u003e. High intrinsic carrier concentration coupled with low solubility limits of dopants prevents the hole concentration of Cu\u003csub\u003e2\u003c/sub\u003eSe from being optimized to the optimal level \u003csup\u003e33, 34\u003c/sup\u003e, significantly constraining \u003cem\u003eZT\u003c/em\u003e optimization. Therefore, it is a great challenge for achieving a high \u003cem\u003eZT\u003c/em\u003e while improving the stability of Cu\u003csub\u003e2\u003c/sub\u003eSe.\u003c/p\u003e \u003cp\u003eIon confinement effect was demonstrate to inhibit the long-range migration of Cu ions and obtain highly stable Cu\u003csub\u003e2\u003c/sub\u003eSe based material. \u003csup\u003e26\u003c/sup\u003e Additionally, phase interface engineering has been shown to be an effective strategy to an ion-blocking interface to hinder Cu ion migration. \u003csup\u003e26, 35, 36\u003c/sup\u003e Furthermore, the composite phase can serve as phonon scattering centre, reducing the lattice thermal conductivity and partially decoupling electron-phonon transport. \u003csup\u003e28, 37\u003c/sup\u003e However, the introduction of secondary phases and interfaces in composite materials contribute strong carrier scattering, thereby leading to deterioration of carrier mobility. \u003csup\u003e3\u003c/sup\u003e Moreover, plenty of Cu vacancies exists in Cu\u003csub\u003e2\u003c/sub\u003eSe due to the weak chemical bonds and low vacancy formation energy. \u003csup\u003e27\u003c/sup\u003e The intrinsic Cu vacancies and mobile Cu ions significantly diminish carrier mobility at high temperatures. The reduction in carrier mobility leads to lower electrical conductivity and thus compromise the power factor. \u003csup\u003e38\u003c/sup\u003e Synergistic approach of boosting carrier mobility while suppress the lattice thermal conductivity is the key point to achieve optimal thermoelectric performance. Here, matrix planification was firstly proposed to fill matrix vacancy defects and boost carrier mobility in composite materials.\u003c/p\u003e \u003cp\u003eWe successfully achieved ultrahigh thermoelectric performance in Cu\u003csub\u003e2\u003c/sub\u003eSe by introducing Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase. Sn atoms of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase effectively fill Cu vacancies of matrix Cu\u003csub\u003e2\u003c/sub\u003eSe, plainifizing the crystal lattice of Cu\u003csub\u003e2\u003c/sub\u003eSe matrix and significantly enhance carrier mobility of composite (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea,b). Furthermore, the large difference in work functions (Cu\u003csub\u003e2\u003c/sub\u003eSe: 5.16 eV and Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe: 4.38 eV) effectively optimizes the carrier concentration (Supplementary Fig.\u0026nbsp;1) and enhances the Seebeck coefficient. The sharp increase in carrier mobility and the enhanced Seebeck coefficient leads to a marked increase of power factor. Meanwhile, the observed smooth and quasi-coherent interfaces cause strong phonon scattering, leading to substantial reduction in the lattice thermal conductivity without carrier mobility deterioration. These synergistic effects contribute to a record-high \u003cem\u003eZT\u003c/em\u003e value of 3.3 at 973 K in Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite, which is the highest value among utmost reported thermoelectric systems (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) \u003csup\u003e39, 40, 41, 42, 43, 44, 45, 46\u003c/sup\u003e. First-principles calculations found that the migrating Cu ions are effectively captured by the exposed Se atoms in SnSe, facilitating charge transfer between Cu and Se atoms. This effectively hinders the long-range migration of Cu ions and improves the stability of the Cu\u003csub\u003e2\u003c/sub\u003eSe based material. These findings provide a comprehensive framework for designing high-performance, stable, and mechanically robust thermoelectric materials with superionic characteristics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussions","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eCrystal structure and phase description\u003c/h2\u003e \u003cp\u003eThe XRD patterns of the synthesized Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe (x\u0026thinsp;=\u0026thinsp;0, 1, 3, 5 and 10) are shown in Supplementary Fig.\u0026nbsp;2a. The Bragg diffraction peaks of the primary phase align well with the monoclinic \u003cem\u003eα\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe fingerprint peaks, except for the detection of the high-temperature \u003cem\u003eβ\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe phase in the pristine Cu\u003csub\u003e2\u003c/sub\u003eSe sample. Cu\u003csub\u003e2\u003c/sub\u003eSe has two energetically similar structures under ambient condition: a monoclinic structure (\u003cem\u003eα\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe) at room temperature and a cubic structure (\u003cem\u003eβ\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe) above 375 K (Supplementary Fig.\u0026nbsp;3) \u003csup\u003e47\u003c/sup\u003e. The structural transition was evidenced by Differential Scanning Calorimeter (DSC) tests (Supplementary Fig.\u0026nbsp;4). According to the Cu-Se binary phase diagram, even a slight Cu deficiency can induce the \u003cem\u003eβ\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe phase, which arises from Cu deposition during the preparation process. We can speculate that the addition of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe during this process might hinder the migration and deposition of copper \u003csup\u003e48\u003c/sup\u003e, thus preventing the appearance of the \u003cem\u003eβ\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe phase. Due to the detection limits of X-ray characterization, secondary phases related to Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe are only observed at doping levels above 3%. Rietveld refinement of the X-ray diffraction data (Supplementary Fig.\u0026nbsp;5) provides precise crystallographic information, indicating minimal variation in lattice parameters (Supplementary Fig.\u0026nbsp;2b). X-ray photoelectron spectroscopy (XPS) was performed on the Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample to determine the valence states of elements. The peaks with binding energy of 932.8 eV, and 940.6 eV can be assigned to Cu\u003csup\u003e+\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;2c) \u003csup\u003e49\u003c/sup\u003e. The peaks with binding energies of 486.6 eV and 495 eV can be attributed to Sn\u003csup\u003e2+\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;2d).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eElectrical transport properties\u003c/h3\u003e\n\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea presents the temperature dependence of electrical conductivity (\u003cem\u003es\u003c/em\u003e) for Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composites. Temperature-dependent \u003cem\u003es\u003c/em\u003e demonstrates a degenerate semiconducting behavior, which primarily originates from intrinsic high Cu deficiency. The composites exhibit a noticeable reduction in \u003cem\u003es\u003c/em\u003e as compared with the pristine Cu\u003csub\u003e2\u003c/sub\u003eSe. The temperature-dependent carrier concentration (\u003cem\u003en\u003c/em\u003e) and mobility (\u003cem\u003e\u0026micro;\u003c/em\u003e) were measured and illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, respectively. It is found that the decrease of \u003cem\u003es\u003c/em\u003e is attributed to a significantly reduced carrier concentration (\u003cem\u003en\u003c/em\u003e) after the introduction of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). This phenomenon can be explained by examining their work functions: Cu\u003csub\u003e2\u003c/sub\u003eSe has a work function of 5.16 eV \u003csup\u003e36\u003c/sup\u003e, while Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe has a work function of 4.38 eV (Supplementary Fig.\u0026nbsp;6). The large difference in work function would drive holes from Cu\u003csub\u003e2\u003c/sub\u003eSe matrix to Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase until their Fermi levels reach equilibrium (Supplementary Fig.\u0026nbsp;1), which ultimately leads to a reduction in carrier concentration. Hall mobility (\u003cem\u003e\u0026micro;\u003c/em\u003e) displays a negative correlation with carrier concentration (\u003cem\u003en\u003c/em\u003e) and decreases with increasing temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Notably, carrier mobility (\u003cem\u003e\u0026micro;\u003c/em\u003e) shows a remarkable enhancement as compared with pristine Cu\u003csub\u003e2\u003c/sub\u003eSe in the whole investigated temperature range. At room temperature, the Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample achieves a remarkable carrier mobility of 33.7 cm\u003csup\u003e2\u003c/sup\u003e\u0026middot;V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is about three times higher than that of pristine Cu\u003csub\u003e2\u003c/sub\u003eSe (11.5 cm\u003csup\u003e2\u003c/sup\u003e\u0026middot;V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). This value is significantly surpassing previously reported Cu\u003csub\u003e2\u003c/sub\u003eSe-based composites (4.65\u0026ndash;16.60 cm\u003csup\u003e2\u003c/sup\u003e\u0026middot;V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) \u003csup\u003e36, 50, 51, 52, 53, 54\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). At 973 K, the carrier mobility of the Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample reduces to 4.57 cm\u003csup\u003e2\u003c/sup\u003e\u0026middot;V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is still more than four times bigger than that of the pristine Cu\u003csub\u003e2\u003c/sub\u003eSe (1.07 cm\u003csup\u003e2\u003c/sup\u003e\u0026middot;V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The significantly enhanced carrier mobility facilitates electrical transport, leading to high power factor. To understand the mechanism of the large enhancement of carrier mobility in the composites, we performed a systematical analysis combining theoretical calculations and experimental characterization. We first carried out the defect formation energy calculations using the density-function theory (DFT) to understand the defect behaviors in Cu\u003csub\u003e2\u003c/sub\u003eSe (Supplementary Table\u0026nbsp;1 and Supplementary Fig.\u0026nbsp;7). It is found that the defect formation energy of Cu vacancy (V\u003csub\u003eCu\u003c/sub\u003e) is very low (-0.66 eV). The negative formation energy indicates the spontaneously forming Cu vacancies in the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix, which is consistent with the previously observed large amount of Cu vacancies in Cu\u003csub\u003e2\u003c/sub\u003eSe \u003csup\u003e27, 55\u003c/sup\u003e. When Sn fills Cu vacancies or substituting the Cu site (Sn\u003csub\u003eCu\u003c/sub\u003e), its formation energy is low (0.73 eV) as well, suggesting that the defect can be highly formed in the Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composites. Additionally, once the Sn\u003csub\u003eCu\u003c/sub\u003e defect binding with the neighboring V\u003csub\u003eCu\u003c/sub\u003e, it forms a complex defect (Sn\u003csub\u003eCu\u003c/sub\u003e+V\u003csub\u003eCu\u003c/sub\u003e) and its formation energy is as low as 0.07 eV, which is lower than that of Sn\u003csub\u003eCu\u003c/sub\u003e. Obviously, the formation of such complex defect further facilitates the Sn\u003csub\u003eCu\u003c/sub\u003e formation. This indicates that Sn can easily fill the Cu vacancies to plain lattice of matrix Cu\u003csub\u003e2\u003c/sub\u003eSe in the composites. This leads to large enhancement of carrier mobility, as evidenced by experimental results. Aberration-corrected STEM characterization provides compelling evidence that the high-density Cu vacancies in the pristine Cu\u003csub\u003e2\u003c/sub\u003eSe matrix are filled by Sn atoms from the secondary phase (Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe) in the composite. Figures\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed depict atomic-resolution HAADF images of pristine Cu\u003csub\u003e2\u003c/sub\u003eSe along two distinct zone axes, accompanied by fast Fourier transform (FFT) patterns and atomic configuration diagrams. These results precisely define the crystal structure of the room-temperature \u003cem\u003eα\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe phase. To reveal subtle distinctions in the atomic structure of the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix between pristine Cu\u003csub\u003e2\u003c/sub\u003eSe and Cu\u003csub\u003e2\u003c/sub\u003eSe/Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composites, Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej present representative atomic-resolution HAADF images alongside quantitative analyses of individual atomic intensities. The calculation method is to divide the intensity \u003cem\u003eα\u003c/em\u003e of Cu/Se sites by the average contrast \u003cem\u003eβ\u003c/em\u003e of the surrounding Se atoms to obtain the numerical value \u003cem\u003eϒ\u003c/em\u003e, and then obtain the figure using the ratio of \u003cem\u003eα\u003c/em\u003e and the average value \u003cem\u003eϒ\u003c/em\u003e (\u003cem\u003eϒ\u003c/em\u003e\u003csub\u003eavg\u003c/sub\u003e), in order to eliminate the effect of the sample thickness. Among them, blue and red points represent lighter/fewer and heavy/more atoms, respectively. Thus, the atomic columns that contain a large fraction of vacancies will show as blue contrast. These analyses provide precise determinations of atomic coordinates and intensity values. In pristine Cu\u003csub\u003e2\u003c/sub\u003eSe, the Cu atoms exhibit weak intensities at various lattice sites, indicating the presence of Cu vacancies due to the intrinsic low vacancy formation energy of Cu\u003csub\u003e2\u003c/sub\u003eSe (Figs.\u0026nbsp;3f1-3f\u003cb\u003e4\u003c/b\u003e). And Se atoms exhibit a uniform intensity distribution across all positions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe high density of Cu vacancies induces significant lattice distortions (Supplementary Figs.\u0026nbsp;8a-8c), disrupting the regular lattice periodicity, intensifying carrier scattering, and severely impairing charge carrier mobility. Upon incorporating Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe, these Cu vacancies are effectively eliminated, as evidenced by the absence of low-intensity sites in the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). Further magnified HAADF intensity images demonstrate that heterovalent cations with higher atomic mass have occupied the regions previously deficient in Cu (Figs.\u0026nbsp;3h1-3j). Energy-dispersive X-ray spectroscopy (EDS) line scan confirms that these sites are predominantly occupied by Sn atoms originating from the Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase (Supplementary Figs.\u0026nbsp;8d-8f). The intensity statistics of individual Cu atomic columns and regional atomic planes in STEM images also confirm that the incorporation of Sn atoms from the secondary phase Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe into the Cu vacancies, leading to matrix plainification. Matrix plainification significantly boosts carrier mobility within the Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composites through weaken carrier scattering.\u003c/p\u003e \u003cp\u003eThe positive Seebeck coefficient (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) indicates the dominant \u003cem\u003ep\u003c/em\u003e-type charge transport. Compared to pristine Cu\u003csub\u003e2\u003c/sub\u003eSe, the composites samples exhibit enhanced Seebeck coefficients at entire temperature range due to reduced carrier concentration. At 973 K, the Seebeck coefficient increases from 168.3 \u0026micro;V\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for pristine Cu\u003csub\u003e2\u003c/sub\u003eSe to 228 \u0026micro;V\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Cu\u003csub\u003e2\u003c/sub\u003eSe/3% wt. Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe. Enhanced carrier mobility and the optimized carrier concentration result in a substantial increase in power factor (\u003cem\u003ePF\u003c/em\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). The highest \u003cem\u003ePF\u003c/em\u003e of 16.22 \u0026micro;W\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e is achieved in Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample at 973 K. More comparisons of the \u003cem\u003ePF\u003c/em\u003e of Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample with those of previously reported Cu\u003csub\u003e2\u003c/sub\u003eSe-based thermoelectrics is presented in Supplementary Fig.\u0026nbsp;9. Significantly enhanced \u003cem\u003ePF\u003c/em\u003e indicates that incorporation of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe markedly optimizes electrical transport property of Cu\u003csub\u003e2\u003c/sub\u003eSe matrix. The intrinsic electrical transport characteristics can be further evaluated by the weighted mobility (\u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003ew\u003c/sub\u003e) provides a direct assessment of the intrinsic electrical transport characteristics (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). The Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample exhibits the highest \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003eW\u003c/sub\u003e among the investigated samples, reflecting its better electrical transport properties.\u003c/p\u003e\n\u003ch3\u003eThermal transport properties\u003c/h3\u003e\n\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg illustrates the temperature-dependent total thermal conductivity (\u003cem\u003eκ\u003c/em\u003e\u003csub\u003etot\u003c/sub\u003e) of Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe (x\u0026thinsp;=\u0026thinsp;0, 1, 3, 5 and 10) composites. Introducing Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe significantly reduced the total thermal conductivity in the whole temperature range. In particular, the composite with 5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe exhibits lowest total thermal conductivities (\u003cem\u003eκ\u003c/em\u003e\u003csub\u003etot\u003c/sub\u003e) among all investigated samples. To gain deeper insights into the exceptionally low thermal conductivity of the composites, we calculated the carrier thermal conductivity (\u003cem\u003eκ\u003c/em\u003e\u003csub\u003eele\u003c/sub\u003e) (Supplementary Fig.\u0026nbsp;10a) using the Wiedemann\u0026ndash;Franz relation \u003cem\u003eκ\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eLsT\u003c/em\u003e, where Lorenz number (\u003cem\u003eL\u003c/em\u003e) was calculated by a two-band model (Supplementary Fig.\u0026nbsp;10b). The lattice thermal conductivity (\u003cem\u003eκ\u003c/em\u003e\u003csub\u003elat\u003c/sub\u003e) was obtained by subtracting \u003cem\u003eκ\u003c/em\u003e\u003csub\u003eele\u003c/sub\u003e from the total thermal conductivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). The reduction in \u003cem\u003eκ\u003c/em\u003e\u003csub\u003eele\u003c/sub\u003e is primarily due to the regulation of carrier concentration and carrier mobility, optimizing electrical conductivity within a reasonable value. The \u003cem\u003eκ\u003c/em\u003e\u003csub\u003elat\u003c/sub\u003e of Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composites markedly decreases compared with that of pristine Cu\u003csub\u003e2\u003c/sub\u003eSe. The sound velocities including both longitudinal and transverse sound velocities were measured for Cu\u003csub\u003e2\u003c/sub\u003eSe/x wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composites (Supplementary Fig.\u0026nbsp;11). The calculated average sound velocity (\u003cem\u003ev\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e) and the phonon mean free path (\u003cem\u003el\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e) were illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei. With increasing content of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe, the average sound velocity gradually decreases, and correspondingly, the phonon mean free path decreases from 2.52 nm for pure Cu\u003csub\u003e2\u003c/sub\u003eSe to 0.79 nm for the high-performance Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample. The reduction in sound velocity and phonon mean free path suggests that the incorporation of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe induces phonon softening and enhances phonon scattering in Cu\u003csub\u003e2\u003c/sub\u003eSe, thereby significantly reducing \u003cem\u003eκ\u003c/em\u003e\u003csub\u003elat\u003c/sub\u003e.\u003c/p\u003e\n\u003ch3\u003eMicrostructural characterization\u003c/h3\u003e\n\u003cp\u003eScanning electron microscopy (SEM) image shows that numerous pores present in the composite (Supplementary Fig.\u0026nbsp;12), which originate from Se volatilization during sintering. Some bright domains disperse within the composite, as illustrated by the back scattered electron (BSE) image of the polished surface (Supplementary Fig.\u0026nbsp;13a). SEM-EDS elemental mapping (Supplementary Fig.\u0026nbsp;13b-13d) confirms Sn enrichment at the domains, indicating the presence of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase. A line scan of the secondary phase region was also performed, and the increase in the Sn elemental intensity as well as the decrease in the Cu content prove the presence of the Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase (Supplementary Fig.\u0026nbsp;14). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea displays a low-magnification HAADF image of the synthesized Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite. Micropores can be found in the sample, consistent with the SEM observation (Supplementary Fig.\u0026nbsp;12). Grains with different contrasts from the matrix were identified. STEM-EDS analysis confirmed the presence of submicron Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe grains embedded within the composite, indicating the existence of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). When the sample is oriented along the [10\u0026thinsp;\u0026minus;\u0026thinsp;1] zone axis of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed), the atomic arrangement closely aligns with SnSe. Focused observations were carried out to investigate the interfaces between composite phase (Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe) and matrix (Cu\u003csub\u003e2\u003c/sub\u003eSe), which reveal a prevalence of smooth, planar phase interfaces (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee-\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh). These heterointerfaces exhibit atomic-scale flatness, contrasting with the commonly observed rough interfaces, and demonstrate quasi-coherence across different zone axes. Moreover, extensive nanotwins substructures were observed within both Cu\u003csub\u003e2\u003c/sub\u003eSe and Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe grains of the synthesized composite (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ej). A noticeable presence of dislocations in the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix is also detected (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ek), which induce slight lattice strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003el). The smooth and quasi-coherent interfaces between the Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe and the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix, in contrast to traditional rough interfaces, is very beneficial for the migration of Sn ions from Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe to Cu\u003csub\u003e2\u003c/sub\u003eSe due to the virtually nonexistent of defects and dislocations, thereby facilitating matrix plainification. Meanwhile, the smooth and quasi-coherent interfaces has minimal adverse effects on carrier transport, but cause strong phonon scattering, leading to substantial reduction of lattice thermal conductivity without carrier mobility deterioration. Nanotwins and dislocations provide extra phonon scattering sources leading to further decreased lattice thermal conductivity in the composite. The strong phonon scattering was proved by the decline trend of sound velocity and phonon mean free.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eEnhanced thermoelectric performance and mechanical properites\u003c/h3\u003e\n\u003cp\u003eIncorporation of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase can efficiently enhance \u003cem\u003eZT\u003c/em\u003e of Cu\u003csub\u003e2\u003c/sub\u003eSe thanks to the enhanced electrical transport properties and significantly reduced lattice thermal conductivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). A maximum \u003cem\u003eZT\u003c/em\u003e of 3.3 is achieved at 973 K in Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite, which surpasses utmost reported Cu\u003csub\u003e2\u003c/sub\u003eSe thermoelectrics \u003csup\u003e26, 28, 35, 50, 51, 52, 53, 56\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). This value presents the highest reported among any thermoelectric systems (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Good experimental repeatability for this high \u003cem\u003eZT\u003c/em\u003e is achieved, which is evidenced by the reproducible results from the measurements on several samples independently prepared (Supplementary Fig.\u0026nbsp;15).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, the Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe sample exhibits better mechanical properties than pristine Cu\u003csub\u003e2\u003c/sub\u003eSe (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). Vickers hardness and nanoindentation hardness are both improved over pristine Cu\u003csub\u003e2\u003c/sub\u003eSe. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed illustrates the compressive strength profile of the Cu\u003csub\u003e2\u003c/sub\u003eSe/x %wt. Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe. (x\u0026thinsp;=\u0026thinsp;0, 5). The composite sample exhibits higher compressive strengths of 172.45 MPa, which is more than four times larger than that of pristine Cu\u003csub\u003e2\u003c/sub\u003eSe (41.95 MPa). It is worth to note that the compressive strain increases form 3% for pristine Cu\u003csub\u003e2\u003c/sub\u003eSe to 12% for Cu\u003csub\u003e2\u003c/sub\u003eSe/5%wt. Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite. Large plastic deformation is achieved in the composite, which is higher than the most of traditional thermoelectric semiconductors and ceramics (usually have compressive strain below 3%) \u003csup\u003e57, 58, 59, 60\u003c/sup\u003e, and closes to strain of the plastic semiconductor Ag\u003csub\u003e2\u003c/sub\u003eSe.\u003c/p\u003e \u003cp\u003eThis significantly enhanced plastic deformability is most likely associated with the observed high density of nanotwin boundaries in the introduced composite component (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei), \u003cem\u003ei.e.\u003c/em\u003e, Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe. The nanotwin boundaries act as additional slip planes within the material, particularly in the densely twinned Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe, effectively increasing the number of active slip systems. Under applied stress, the twin boundaries facilitate slip, allowing for greater strain energy absorption. This thus results in significantly improved plasticity because the material can accommodate more deformation before failure. In the composite, the presence of high-density nanotwins in Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe grains are also likely to play a pivotal role in enhancing dislocation mobility. These nanotwin boundaries act as efficient sites for dislocation nucleation and propagation, reducing the energy barrier for slip and providing a pathway for dislocation migaration through the material. The increased dislocation mobility leads to a more pronounced plastic response under compressive stress, allowing the composite to deform more easily. Additionally, these dense nanotwins effectively refine the microstructural characteritic size of the material, resulting in a hardening effect. This hardening is typically accompanied by an enhanced ability of the material to withstand higher stresses without fracturing, thereby exhibiting greater compressive strain. Moreover, the high-density nanotwin boundaries in Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe grains are likely to facilitate stress relaxation in the heterointerfaces between Cu\u003csub\u003e2\u003c/sub\u003eSe and Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe, creating efficient stress transfer zones. These zones help dissipate applied stress more uniformly throughout the composite, preventing localized strain accumulation and mitigating the risk of interfacial delamination or fracture. Collectively, the high-density nanotwins in Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe, combined with the reinforcing effect at these interfaces, empower the material to endure higher compressive stresses without localized fracture or slip, thus substantially enhancing the overall compressive strain of the composites. The significantly enhanced plasticity grants the material with large deformability, processibility, and machinability, which increases the impact resistance of thermoelectric components, thus significantly increasing their service life. \u003csup\u003e57\u003c/sup\u003e The discovered composite with large plasticity has great potential in flexible thermoelectric technology. This work sheds light to advance highly effective thermoelectrics.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStability Test\u003c/h2\u003e \u003cp\u003eWe conducted a detailed investigation into the stability of Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite. Thermogravimetric analysis (TGA) was performed to assess the thermal stability of the material (Supplementary Fig.\u0026nbsp;16), and the results indicated negligible weight loss over a wide temperature range, confirming that elemental volatilization is igorable. Further compositional analysis before and after thermoelectric property measurements at high temperature provided robust evidence for the enhanced stability of the composites. The pristine Cu\u003csub\u003e2\u003c/sub\u003eSe sample exhibits pronounced Cu enrichment on its surface due to the intrinsic long-range migration of Cu ions after thermoelectric property measurements at high temperature (Supplementary Fig.\u0026nbsp;17a). Stoichiometric changes in pristine Cu\u003csub\u003e2\u003c/sub\u003eSe after thermoelectric properties measurements were evidenced by SEM-EDS analysis. In stark contrast, no Cu enrichment on the composite sample surface and no alterations in the composition are observed after thermoelectric properties measurements (Supplementary Fig.\u0026nbsp;17b), indicating its stability is enhanced. XRD analysis reveals that the pure sample undergoes stoichiometric changes due to Cu loss of the matrix, which facilitates the formation of \u003cem\u003eβ\u003c/em\u003e-Cu\u003csub\u003e2\u003c/sub\u003eSe after thermoelectric properties measurements (Supplementary Fig.\u0026nbsp;18a), whilst the composite samples maintain consistent phase components after the testing process (Supplementary Fig.\u0026nbsp;18b). To evaluate the stability under real operational conditions, we subjected the sample to simultaneous current field and temperature gradient field (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea,b). A pulsed current with a maximum current density of 25 A/cm\u003csup\u003e2\u003c/sup\u003e was applied (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec), and the relative resistance of the sample was monitored for up to 20,000 s. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee, the relative resistance of pristine Cu\u003csub\u003e2\u003c/sub\u003eSe exhibits a steep increase with test time, indicating substantial Cu ions migration and subsequent accumulation at the interface, which significantly affects the resistance. \u003csup\u003e31\u003c/sup\u003e In contrast, the relative resistance of the composite containing x\u0026thinsp;=\u0026thinsp;5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe remains almost unchanged under the same conditions, suggesting that the addition of Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe effectively hinders the long-range migration of Cu ions and improves the stability of the Cu\u003csub\u003e2\u003c/sub\u003eSe based material. First-principles calculations was conducted to delve deeper into the mechanism why Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe suppresses the migration of Cu ions in Cu\u003csub\u003e2\u003c/sub\u003eSe. Charge density difference analysis reveals a strong interaction between Cu ions and Se atoms in SnSe upon Cu ions migrate at elevated temperatures (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg). Specifically, the migrating Cu ions are effectively captured by the exposed Se atoms in SnSe, facilitating charge transfer between Cu and Se atoms. This interaction leads to bonding between Cu and Se atoms, which plays a crucial role in inhibiting the long-range migration of Cu ions in the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix. The secondary phase thus acts as a stabilizing agent, preventing the migration of Cu ions and thereby enhancing the stability of the composite material, exemplifying the maintenance of the stability of the composite by our meticulously targeted additives. The improved stability is essential for extending the service lifetime of thermoelectric materials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eWe demonstrated a fascinating strategy of matrix planification to successfully enhanced carrier mobility and electrical transport property of composites. We reveals that Cu vacancies in matrix Cu\u003csub\u003e2\u003c/sub\u003eSe are filled by Sn atoms of secondary phase, leading to matrix planification. Moreover, the carrier concentration can be optimized by large difference in different work functions between matrix Cu\u003csub\u003e2\u003c/sub\u003eSe and the Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase, contributing to enhanced Seebeck coefficient. The sharp increase of carrier mobility and Seebeck coefficient contribute to substantial increase in power factor. Strong phonon scattering is induced by a prevalence of smooth and quasi-coherent interfaces, which greatly reduces lattice thermal conductivity without carrier mobility deterioration. Ultimately, an unprecedented high \u003cem\u003eZT\u003c/em\u003e value of 3.3 is achieved at 973 K in Cu\u003csub\u003e2\u003c/sub\u003eSe/5 wt.% Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe composite. Notably, high-density nanotwins in the composite significantly enhance plasticity (compressive strain of 12%). The high plasticity grants the material with large deformability, processibility, and machinability, which significantly increasing their service life and has great potential in flexible thermoelectrics. We simultaneously improve the stability of Cu\u003csub\u003e2\u003c/sub\u003eSe due to inhibition the long-range migration of Cu ions by through bonding through introducing the Sn\u003csub\u003e0.96\u003c/sub\u003ePb\u003csub\u003e0.01\u003c/sub\u003eZn\u003csub\u003e0.03\u003c/sub\u003eSe secondary phase. These findings pave the way for designing of high-performance, stable, and durable liquid-like thermoelectric materials.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This work was supported by The work was supported by the National Natural Science Foundation of China (No. 52071182, 52202049\u0026nbsp;and 52472250), the National Key R\u0026amp;D Program of China (2021YFB3201100),\u0026nbsp;\u0026ldquo;Qinglan Project\u0026rdquo; of the Young and Middle\u0026nbsp;aged Academic Leader of Jiangsu Province, the Fundamental Research Funds for the Central Universities (No. 30921011107, 30924010206). The authors thank the Instrument Analysis Center of Xi\u0026rsquo;an Jiaotong University for the assistance of aberration-corrected STEM.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e G.D.T. conceived and supervised the project. G.D.T., P.Y., H.J.W. and Q.Y.J. designed and carried out the experiments, analyzed the results, and wrote the paper. Q.Y.J. and Y.R.G. carried out the XRD, XPS experiments and electrical property measurements. C.C. and T.S. measured the thermal transport properties. T.S., R.X.S., Y.X.Y., J.Q.H., Y.Z., and H.J.W. conducted the microstructural characterization. P.Y. and Y.S.Z carried out the DFT calculations. T.F. performed the mechanical property measurements. K.S. performed the TEG fabrication and measured the stability. All authors analyzed the results and coedited the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e The\u0026nbsp;authors declare no other competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData and materials availability:\u003c/strong\u003e All data are provided in the main text or the\u0026nbsp;supplementary materials.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e1. Bell LE. Cooling, Heating, Generating Power, and Recovering Waste Heat with Thermoelectric Systems. \u003cem\u003eScience\u003c/em\u003e \u003cb\u003e321\u003c/b\u003e, 1457\u0026ndash;1461 (2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e2. He J, Tritt TM. Advances in thermoelectric materials research: Looking back and moving forward. \u003cem\u003eScience\u003c/em\u003e \u003cb\u003e357\u003c/b\u003e, eaak9997 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e3. 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Ultrahigh Thermoelectric Performance in Environmentally Friendly SnTe Achieved through Stress-Induced Lotus‐Seedpod‐Like Grain Boundaries. \u003cem\u003eAdvanced Functional Materials\u003c/em\u003e \u003cb\u003e31\u003c/b\u003e, 2101554 (2021).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5735896/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5735896/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThermoelectric technology exhibits significant potential for applications in power generation and electronic cooling. In this study, we report the achievement of exceptional thermoelectric performance and high plasticity in stable Cu\u003csub\u003e2\u003c/sub\u003eSe/SnSe composites. A novel matrix plainification strategy was employed to eliminate lattice vacancies within the Cu\u003csub\u003e2\u003c/sub\u003eSe matrix of the Cu\u003csub\u003e2\u003c/sub\u003eSe/SnSe composites, resulting in a marked improvement in carrier mobility. This increase in carrier mobility corresponds to a substantial enhancement of the power factor. Furthermore, the presence of quasi-coherent interfaces induces strong phonon scattering, which effectively reduces lattice thermal conductivity without compromising carrier mobility. Consequently, an outstanding figure of merit (ZT) of 3.3 was attained in the Cu\u003csub\u003e2\u003c/sub\u003eSe/SnSe composite. Additionally, the presence of high-density nanotwins imparts remarkable plasticity to the composite, yielding a compressive strain of 12%. The secondary phase contributes to the stability of the composite by hindering the extensive migration of Cu ions through bonding interactions. Our findings present a novel strategy for significantly enhancing the thermoelectric performance of composite semiconductors, with potential applicability to other thermoelectric systems.\u003c/p\u003e","manuscriptTitle":"Matrix Plainification Leads to High Thermoelectric Performance in Plastic Cu2Se/SnSe Composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-07 08:24:48","doi":"10.21203/rs.3.rs-5735896/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ed850082-1392-437f-9390-31f68a55fdee","owner":[],"postedDate":"January 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":42282242,"name":"Physical sciences/Materials science/Materials for energy and catalysis"},{"id":42282243,"name":"Physical sciences/Energy science and technology/Thermoelectric devices and materials"}],"tags":[],"updatedAt":"2025-04-08T07:06:09+00:00","versionOfRecord":{"articleIdentity":"rs-5735896","link":"https://doi.org/10.1038/s41467-025-58484-0","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-04-07 04:00:00","publishedOnDateReadable":"April 7th, 2025"},"versionCreatedAt":"2025-01-07 08:24:48","video":"","vorDoi":"10.1038/s41467-025-58484-0","vorDoiUrl":"https://doi.org/10.1038/s41467-025-58484-0","workflowStages":[]},"version":"v1","identity":"rs-5735896","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5735896","identity":"rs-5735896","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}