Flexible thermoelectrics is a synergy of flexible electronics and thermoelectric energy conversion. In this work, we fabricated flexible full-inorganic thermoelectric power generation modules based on doped silver chalcogenides.

The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe2 ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe2 from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.

Among the Mo-and W-based two-dimensional (2D) transition metal dichalcogenides, MoTe 2 is particularly interesting for phase-engineering applications, because it has the smallest free energy difference between the semiconducting 2H phase and metallic 1T′ phase. In this work, we reveal that, under the proper circumstance, Mo and Te atoms can rearrange themselves to transform from a polycrystalline 1T′ phase into a single-crystalline 2H phase in a large scale. We manifest the mechanisms of the solid-to-solid transformation by conducting density functional theory calculations, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The phase transformation is well described by the time−temperature−transformation diagram. By optimizing the kinetic rates of nucleation and crystal growth, we have synthesized a single-crystalline 2H-MoTe 2 domain with a diameter of 2.34 mm, a centimeter-scale 2H-MoTe 2 thin film with a domain size up to several hundred micrometers, and a seamless 1T′−2H MoTe 2 coplanar homojunction. The 1T′−2H MoTe 2 homojunction provides an elegant solution for ohmic contact of 2D semiconductors. The controlled solid-to-solid phase transformation in 2D limit provides a new route to realize wafer-scale single-crystalline 2D semiconductor and coplanar heterostructure for 2D circuitry.

Flexible thermoelectrics provide a different solution for developing portable and sustainable flexible power supplies. The discovery of silver sulfide–based ductile semiconductors has driven a shift in the potential for flexible thermoelectrics, but the lack of good p-type ductile thermoelectric materials has restricted the reality of fabricating conventional cross-plane π-shaped flexible devices. We report a series of high-performance p-type ductile thermoelectric materials based on the composition-performance phase diagram in AgCu(Se,S,Te) pseudoternary solid solutions, with high figure-of-merit values (0.45 at 300 kelvin and 0.68 at 340 kelvin) compared with other flexible thermoelectric materials. We further demonstrate thin and flexible π-shaped devices with a maximum normalized power density that reaches 30 μW cm −2 K −2 . This output is promising for the use of flexible thermoelectrics in wearable electronics.

Hetero‐shaped thermoelectric (TE) generators (TEGs) can power the sensors used in safety monitoring systems of undersea oil pipelines, but their development is greatly limited by the lack of materials with both good shape‐conformable ability and high TE performance. In this work, a new ductile inorganic TE material, Ag20S7Te3, with high TE performance is reported. At 300–600 K, Ag20S7Te3 crystallizes in a body‐centered cubic structure, in which S and Te atoms randomly occupy the (0, 0, 1) site. Due to the smaller generalized stacking fault energy in the (101¯)[010] slip system, Ag20S7Te3 shows better ductility than Ag2S, yielding excellent shape‐conformability. The high carrier mobility and low lattice thermal conductivity observed in Ag20S7Te3 result in a maximum dimensionless figure of merit (zT) of 0.80 at 600 K, which is comparable with the best commercial Bi2Te3‐based alloys. The prototype TEG consisting of 10 Ag20S7Te3 strips displays an open‐circuit voltage of 69.2 mV and a maximum power output of 17.1 µW under the temperature difference of 70 K. This study creates a new route toward hetero‐shaped TEG.

Two-dimensional (2D) layered semiconductors, with their ultimate atomic thickness, have shown promise to scale down transistors for modern integrated circuitry. However, the electrical contacts that connect these materials with external bulky metals are usually unsatisfactory, which limits the transistor performance. Recently, contacting 2D semiconductors using coplanar 2D conductors has shown promise in reducing the problematic high resistance contacts. However, many of these methods are not ideal for scaled production.Here, we report on the large-scale, spatially controlled chemical assembly of the integrated 2H-MoTe 2 field-effect transistors (FETs) with coplanar metallic 1T′-MoTe 2 contacts via phase engineered approaches. We demonstrate that the heterophase FETs exhibit ohmic contact behavior with low contact resistance, resulting from the coplanar seamless contact between 2H and 1T′ MoTe 2 confirmed by transmission electron microscopy characterizations. The average mobility of the heterophase FETs was measured to be as high as 23 cm 2 V −1 s −1 (comparable with those of exfoliated single crystals), due to the large 2H MoTe 2 single-crystalline domain (486±187 μm). By developing a patterned growth method, we realize the 1T′ MoTe 2 gated heterophase FET array whose components of channel, gate, and contacts are all 2D materials. Finally, we transfer the heterophase device array onto a flexible substrate and demonstrate the near-infrared photoresponse with high photoresponsivity (~1.02 A/W). Our study provides a basis for the large-scale application of phase-engineered coplanar MoTe 2 semiconductors-meter structure in advanced electronics and optoelectronics.

The intrinsic magnetic layered topological insulator MnBi 2 Te 4 with nontrivial topological properties and magnetic order has become a promising system for exploring exotic quantum phenomena such as quantum anomalous Hall effect. However, the layer-dependent magnetism of MnBi 2 Te 4 , which is fundamental and crucial for further exploration of quantum phenomena in this system, remains elusive. Here, we use polar reflective magnetic circular dichroism spectroscopy, combined with theoretical calculations, to obtain an in-depth understanding of the layer-dependent magnetic properties in MnBi 2 Te 4 . The magnetic behavior of MnBi 2 Te 4 exhibits evident odd-even layer-number effect, i.e. the oscillations of the coercivity of the hysteresis loop (at μ 0 H c ) and the spinflop transition (at μ 0 H 1 ), concerning the Zeeman energy and magnetic anisotropy energy. In the even-number septuple layers, an anomalous magnetic hysteresis loop is observed, which is attributed to the thickness-independent surface-related magnetization. Through the linear-chain model, we can clarify the odd-even effect of the spin-flop field and determine the evolution of magnetic states under the external magnetic field. The mean-field method also allows us to trace the experimentally observed magnetic phase diagrams to the magnetic fields, layer numbers and especially, temperature. Overall, by harnessing the unusual layerdependent magnetic properties, our work paves the way for further study of quantum properties of MnBi 2 Te 4 .

Deformable and flexible thermoelectrics is quite appealing in both academic and industrial communities because it can directly generate electricity by utilizing heat from various non-flat, hetero-shaped hot surfaces such as human body and hot pipes. [1] Deformable thermoelectric (TE) semiconductors should possess both good deformability and high TE performance. The latter one can be evaluated by the dimensionless figure of merit zT = S 2 sT/k, where S, s, k, and T are Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. [2] Semiconducting organic polymers are candidate materials for flexible thermoelectrics due to their inherent softness and flexibility, but their zT values are generally low. [3] In contrast, inorganic TE materials (e.g., Bi 2 Te 3 , PbTe, and SiGe) have high zTs, [4] but they are inherently brittle to bear deformation or mechanical processing. It is thus urgent to develop new materials with both high deformability and superior zT values.Recently, a series of inorganic semiconductors with exceptional room-temperature plasticity have been discovered, including Ag 2 S, [5] ZnS single crystals in darkness, [6] and InSe single crystals, [7] providing a new solution to the dilemma between deformability and TE performance. The Ag 2 S-based alloys simultaneously demonstrate noticeable plasticity and high zTs (e.g., 0.26 for Ag 2 S 0.5 Se 0.5 at 300 K, 0.63 for Ag 2 S 0.8 Te 0.2 at 450 K, and 0.75 for Ag 2 Te 0.6 S 0.4 at 725 K). [8] Particularly, the power factors of these materials are at least one order of magnitude higher than those of organic counterparts, [9] offering the possibility to fabricate full-inorganic deformable TE devices with high power density.High performance TE device simultaneously requires n-type and p-type TE materials with matching physical and chemical properties. [10] Nonetheless, as shown in Figure 1a, all the currently known plastic inorganic semiconductors are n-type materials. The lack of p-type counterparts severely restricts the development of full-inorganic high performance TE devices. Consequently, the exploration of p-type inorganic plastic semiconductors will not only enrich the scientific connotation of this newly emerging field, but also promise a broad application in flexible and deformable thermoelectrics. It has been well recognized that most Ag-based TE materials exhibit an n-type conduction behavior. On the contrary, most Cu-containing TE materials show a p-type conduction behavior. Such Cu-and Deformable thermoelectrics have great potential in self-powered flexible or hetero-shaped electronics. The exceptional room-temperature plasticity recently discovered in several inorganic semiconductors makes it possible to develop new thermoelectric (TE) materials with both high performance and intrinsic deformability. Nonetheless, all the known plastic or ductile TE materials are n-type semiconductors. It is urgent to explore p-type counterparts for device design and fabrication. In this study, the first p-ty...