Single crystalline SnSe is one of the most intriguing new thermoelectric materials but the thermoelectric performance of polycrystalline SnSe seems to lag significantly compared to that of a single crystal. Here an effective strategy for enhancing the thermoelectric performance of p‐type polycrystalline SnSe by Ag/Na dual‐doping and Ag8SnSe6 (STSe) nanoprecipitates is reported. The Ag/Na dual‐doping leads to a two orders of magnitude increase in carrier concentration and a convergence of valence bands (VBM1 and VBM5), which in turn results in sharp enhancement of electrical conductivities and high Seebeck coefficients in the Ag/Na dual‐doped samples. Additionally, the SnSe matrix becomes nanostructured with dispersed nanoprecipitates of the compound Ag8SnSe6, which further strengthens the scattering of phonons. Specifically, ≈20% reduction in the already ultralow lattice thermal conductivity is realized for the Sn0.99Na0.01Se–STSe sample at 773 K compared to the thermal conductivity of pure SnSe. Consequently, a peak thermoelectric figure of merit ZT of 1.33 at 773 K with a high average ZT (ZTave) value of 0.91 (423–823 K) is achieved for the Sn0.99Na0.01Se–STSe sample.

Memristive systems present a low-power alternative to silicon-based electronics for neuromorphic and in-memory computation. 2D materials have been increasingly explored for memristive applications due to their novel biomimetic functions, ultrathin geometry for ultimate scaling limits, and potential for fabricating large-area, flexible, and printed neuromorphic devices. While the switching mechanism in memristors based on single 2D nanosheets is similar to conventional oxide memristors, the switching mechanism in nanosheet composite films is complicated by the interplay of multiple physical processes and the inaccessibility of the active area in a twoterminal vertical geometry. Here, the authors report thermally activated memristors fabricated from percolating networks of diverse solution-processed 2D semiconductors including MoS 2 , ReS 2 , WS 2 , and InSe. The mechanisms underlying threshold switching and negative differential resistance are elucidated by designing large-area lateral memristors that allow the direct observation of filament and dendrite formation using in situ spatially resolved optical, chemical, and thermal analyses. The high switching ratios (up to 10 3 ) that are achieved at low fields (≈4 kV cm −1 ) are explained by thermally assisted electrical discharge that preferentially occurs at the sharp edges of 2D nanosheets. Overall, this work establishes percolating networks of solutionprocessed 2D semiconductors as a platform for neuromorphic architectures.

Expected to become mainstream in the electronics industry, flexible electronics still face major challenging issues. For polymeric-based flexible electronic substrates in particular, these challenges include a lack of electromagnetic shielding capability and poor heat dissipation. Here, we report a highly flexible and thermally conductive macroscopic polydimethylsiloxane (PDMS) polymer film embedded with a copper-coated reduced graphene oxide (rGO) fiber mesh. The rGO fibers are assembled into 3D fiber meshes and electroplated with micrometer-thick copper coatings, displaying excellent electrical and thermal conductivities. Oriented in the horizontal and perpendicular directions within the PDMS polymeric matrix, the fiber mesh serves as a highly electrically and thermally conductive backbone through the in-plane direction. Meanwhile, the fiber mesh also effectively shields electromagnetic interference in the X-band without causing thermal damage. The macroscopic film remains electrically insulated in the through-plane direction. Utilizing both the favorable thermal and electrical properties of the graphene fiber-based mesh and the flexibility of the PDMS matrix, our film may exhibit potential for flexible electronics applications such as wearable electronic thermal management and flexible microwave identification devices.

Hybrid halide perovskites display a great tunability of optoelectronic properties and environmental stability by controlling the halogen anions (e.g., I, Cl, and Br). However, their water interaction and degradation mechanisms are not fully elucidated. In this work, the interaction of Cs2SnCl6 and Cl-enriched solid solution Cs2SnI0.9Cl5.1 with water was systematically studied by in situ synchrotron X-ray diffraction and micro-Raman spectra and compared with the isostructural Cs2SnI6. Unlike Cs2SnI6, which experiences a direct dissolution in water, Cs2SnCl6 displays an enhanced stability and the dissolution of the Cs2SnCl6 accompanies with the formation of an amorphous alteration phase.  Under controlled dehydration conditions, two-dimensional Cs2SnCl6 flakes can be precipitated out from water solution. Furthermore, the mixed halide perovskite (Cs2SnI0.9Cl5.1) experiences fast iodide dissolution in water solution and transforms to a more chloride-enriched perovskite which shows a behavior similar to Cs2SnCl6. The mechanistic understanding of the dissolution–precipitation process of Cs2SnI x Cl6–x perovskites is useful for developing new perovskites with varied halogen and controlled environmental stability.

Metal halide perovskites have excited tremendous research interests due to their extraordinary photovoltaic and optoelectronic performance. Cs2SnI6 has emerged as a promising lead-free perovskite in advanced optoelectronics due to its high stability, appropriate bandgap, and high absorption coefficient. The performance of two-dimensional (2D) Cs2SnI6-based photodetectors is limited as compared to lead-based perovskites. Here, we report a simple strategy for incorporating aliovalent metal ions (nickel and zinc) for doping or passivation of perovskites to improve their performance. Aliovalent metal ions are employed to break the inherent dark transition of the 2D Cs2SnI6, greatly increasing photoluminescence by two orders of magnitude than pristine Cs2SnI6. Density function calculation reveals the n-type doping of nickel ions without introducing any deep trap states. We further demonstrate that the surface passivation of 2D Cs2SnI6 by zinc ions can greatly reduce surface trap/defect density. Aliovalent metal ion-incorporated Cs2SnI6 perovskites exhibit broadband detection, high responsivity (1.6 × 103 A W–1, for Ni-incorporated Cs2SnI6) and high detectivity (1.56 × 1013 Jones, for Zn-incorporated Cs2SnI6). These results will prompt research on the influence of metal ions in perovskite materials that may afford novel properties for next-generation optoelectronics.

Cs2SnI6 perovskite displays excellent air stability and a high absorption coefficient, promising for photovoltaic and optoelectronic applications. However, Cs2SnI6‐based device performance is still low as a result of lacking optimized synthesis approaches to obtain high quality Cs2SnI6 crystals. Here, a new simple method to synthesize single crystalline Cs2SnI6 perovskite at a liquid–liquid interface is reported. By controlling solvent conditions and Cs2SnI6 supersaturation at the liquid–liquid interface, Cs2SnI6 crystals can be obtained from 3D to 2D growth with controlled geometries such as octahedron, pyramid, hexagon, and triangular nanosheets. The formation mechanisms and kinetics of complex shapes/geometries of high quality Cs2SnI6 crystals are investigated. Freestanding single crystalline 2D nanosheets can be fabricated as thin as 25 nm, and the lateral size can be controlled up to sub‐millimeter regime. Electronic property of the high quality Cs2SnI6 2D nanosheets is also characterized, featuring a n‐type conduction with a high carrier mobility of 35 cm2 V−1 s−1. The interfacial reaction‐controlled synthesis of high‐quality crystals and mechanistic understanding of the crystal growth allow to realize rational design of materials, and the manipulation of crystal growth can be beneficial to achieve desired properties for potential functional applications.

Perovskite-based ceramic composites were developed as potential waste form materials for immobilizing cesium (Cs) and iodine (I) with high waste loadings and chemical durability. The perovskite Cs3Bi2I9 has high Cs (22 wt%) and I (58 wt%) content, and thus can be used as a potential host phase to immobilize these critical radionuclides. In this work, the perovskite Cs3Bi2I9 phase was synthesized by a cost effective solution-based approach, and was embedded into a highly durable hydroxyapatite matrix by spark plasma sintering to form dense ceramic composite waste forms. The chemical durabilities of the monolithic Cs3Bi2I9 and Cs3Bi2I9—hydroxyapatite composite pellets were investigated by static and semi-dynamic leaching tests, respectively. Cs and I are incongruently released from the matrix for both pure Cs3Bi2I9 and composite structures. The normalized Cs release rate is faster than that of I, which can be explained by the difference in the strengths between Cs-I and Bi-I bonds as well as the formation of insoluble micrometer-sized BiOI precipitates. The activation energies of elemental releases based on dissolution and diffusion-controlled mechanisms are determined with significantly higher energy barriers for dissolution from the composite versus that of the monolithic Cs3Bi2I9. The ceramic-based composite waste forms exhibit excellent chemical durabilities and waste loadings, commensurate with the state-of-the-art glass-bonded perovskite composites for I and Cs immobilization.

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