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A synthetic method for uniform and pure Cs3Sb2Br9 NCs has been developed. Cs3Sb2Br9 NCs exhibit a 10-fold increase in activity for the photocatalytic CO2 reduction reaction compared to CsPbBr3 NCs, achieving 510 μmol CO g-1 cat. after 4 h. Density functional theory shows that Cs3Sb2Br9 surfaces sufficiently expose Sb to allow reactivity, as opposed to the unreactive CsPbBr3 surface.

Solution processing of organic semiconductors offers key advantages, including low-cost and compatibility with large-area flexible substrates. Controlling film crystallization from solution, however, is not trivial. This is particularly important since the device properties are highly dependent on the film microstructure, which, in turn, can vary significantly with processing. In this work, we tuned the small molecule organic semiconductor film microstructure by using a binary solvent consisting of a host solvent and a high-boiling point solvent additive and studied the effect of additive content on charge transport. Spin coated 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene films processed from a mixture of chlorobenzene and dichlorobenzene, in various ratios, were investigated by using Polarized Optical Microscopy, Scanning Electron Microscopy and Atomic Force Microscopy analysis and their electrical properties were evaluated from bottom-contact bottom-gate organic field-effect transistors. We found that the mobility increased by three times for a 8% dichlorobenzene content as a result of reducing the density of the grain boundaries within the device channel.

In the colloidal synthesis of inorganic perovskite materials, cesium oleate (CsOL) is the most commonly used Cs precursor. Yet, despite its ubiquitous use in literature, CsOL has been observed to be insoluble at room temperature and leads to surprisingly inconsistent results in CsPbX3 nanocrystal synthesis, depending on the Cs salt from which the precursor is derived. We show that under the conditions used in most reports, the amount of oleic acid (OA) added, while stoichiometrically sufficient, still leads to incomplete conversion of the Cs salts to CsOL. This results in a mixture of Cs sources being present during the reaction, causing decreased homogeneity and reproducibility. When a 1:5 Cs:OA ratio is used, complete conversion is readily obtained, even under mild conditions, resulting in a precursor solution that is soluble at room temperature and yields identical synthetic results, regardless of the initial Cs source. Furthermore, 1H nuclear magnetic resonance (NMR) of solutions prepared using varyin...

Two-dimensional (2D) materials have recently opened a new avenue to flexible thermoelectric materials with enhanced performance because of their unique electronic transport properties. Here, we report a feasible approach to improve the thermoelectric performance of transition-metal dichalcogenides by effectively decorating 2D MoS2 with Au nanoparticles using in situ growth. The present Au-decorated MoS2-assembled heterojunction system shows a certain decoupled phenomenon, that is, the Seebeck coefficient and conductivity increased simultaneously. This is due to the occurrence of p-type doping of the MoS2 2H phase and injection energy filtering of dopant-originated carriers around the local band bending at the interface. The composite flexible films can achieve a power factor value of 166.3 μW m–1 K–2 at room temperature, which have great potential for harvesting human body heat.

Self-assembly has proven to be a powerful method of preparing structurally intricate nanostructures. In this work, we design a nanoscale “Chinese Coin” based on Bi2Te3 nanoplates (NPs) by using a simple and scalable solution process; i.e., a single pore is introduced on a hexagonal/round plate similar to a fender washer. The diameter of the nanopores is well controlled within the range of 5–100 nm and depends strongly on the reaction time and heating temperatures, suggesting a kinetics related mechanism. Moreover, the thermal evolution of stable Bi2Te3 plate-pore structures was systematically explored to elucidate the underlying energetics of the V2-VI3 chalcogenides. We found that the nanopore is initiated near the middle of the plate, followed by the successive removal of Bi2Te3 slices from the high edge-energy pore with increased temperatures (70–150 °C), leading finally to the formation of a stable nanopore. The morphology of the pore as well as the local lattice crystallinity was studied using high-r...

In this work we demonstrate a solution-based approach to the synthesis of ternary metal chalcogenide nanowires (NWs) with high thermoelectric figure of merit (ZT) and power factors. Utilizing templates of Te1−xSex alloys to balance the chemical reactivity between Te and Se atoms, we have been able to add a number of different metal species while maintaining a single-phase ternary metal chalcogenide NW with small diameter (

Thermoelectric materials that can generate electricity from waste heat will play an important role in the global sustainable energy solution. Low dimensional materials open new routes to high performance thermoelectric properties due to their unique density of states with confined electrons and holes. Here, we report that the phase engineered two dimensional transition metal dichalcogenides represent a new class of high performance thermoelectric materials. The organolithium chemically exfoliated nanosheets of MoS2 containing a high concentration of metallic 1T phase MoS2 show superior thermoelectric properties, with a room temperature power factor of 73.1 μW m−1 K−2, which is much higher than the pristine graphene or single wall carbon nanotubes can yield. Our first principle calculations on monolayer 1T phase MoS2 provide physical insight of their metallic and hole conductive nature, which happens to be important origins of their advantageous thermoelectric properties. These metallic 1T phase MoS2 nanosheets also reveal interesting moisture sensitive thermoelectric properties, indicating their potential diverse applications not only as thermoelectric energy harvesting devices but also as self-powered gas sensors.

A new spray doping method is presented that allows for easily tunable thermoelectric properties of thin film carbon nanotube (CNT) polymer composites. An airbrush introduces small molecule Polyethyleneimine into existing p-type CNT films converting it to an n-type composite. This technique allows for the conversion of a single p-type film into a multi-section device of alternating p- and n-type segments. A thermoelectric generator (TEG) design is presented with the effort to address current design issues facing thin film thermoelectric devices as a commercially viable TEG. The Seebeck coefficient and electrical conductivity were tested under different dopant concentrations and compared with traditional solution based methods.

Two-dimensional (2D) materials have recently opened a new avenue to flexible thermoelectric materials with enhanced performance because of their unique electronic transport properties. Here, we report a feasible approach to improve the thermoelectric performance of transition-metal dichalcogenides by effectively decorating 2D MoS

We report on the fabrication of flexible and freestanding n-type thermoelectric Cu intercalated Bi 2 Se 3 nanoplatelet/Polyvinylidene Fluoride (PVDF) composite films. The optimized power factor and figure of merit (ZT) of the Cu 0.1 Bi 2 Se 3 nanoplatelet/PVDF composites are 103 μW m −1 K −2 and 0.10 at 290 K, respectively, which are one of the highest values for n-type thermoelectric films. The mechanism by which the Seebeck coefficient and electrical conductivity can be partially decoupled is explained in details: PVDF can not only grantee the robust and flexibility but also create a high trap-state by introducing the energy barrier at the organic/inorganic interface, thus a high level of Seebeck coefficient is maintained for the composite system while a remarkable improvement on electrical conductivity was achieved. The thermoelectric films show high mechanical durability with only a 13% decrease in performance after 5000 bending cycles (bending curvature 1/2 mm −1 ). The overall performance of the n-type thermoelectric films approaches the values required for efficient flexible thermoelectric power generators.

Highly-flexible thermoelectric fabrics were fabricated based on a layered structure, composed of a thin active layer of self-assembled tellurium nanorods and a substrate layer of polyvinylidene fluoride. The resulting thermoelectric fabrics show a high room temperature power factor of 45.8 μW m(-1) K(-2), which opens a new avenue to fabricate highly-flexible sustainable energy sources.

A suite of complementary high-throughput screening systems for combinatorial films was developed at National Institute of Standards and Technology to facilitate the search for efficient thermoelectric materials. These custom-designed capabilities include a facility for combinatorial thin film synthesis and a suite of tools for screening the Seebeck coefficient, electrical resistance (electrical resistivity), and thermal effusivity (thermal conductivity) of these films. The Seebeck coefficient and resistance are measured via custom-built automated apparatus at both ambient and high temperatures. Thermal effusivity is measured using a frequency domain thermoreflectance technique. This paper will discuss applications using these tools on representative thermoelectric materials, including combinatorial composition-spread films, conventional films, single crystals, and ribbons.

Precise control of the selective growth of heterostructures with specific composition and functionalities is an emerging and extremely challenging topic. Here, the first investigation of the difference in binding energy between a series of metal-semiconductor heterostructures based on layered V

Engineered atomic dislocations have been used to create a novel, Sb2 Te3 nanoplate-like architecture that exhibits a unique antisymmetric chirality. High-resolution transmission electron microscopy (HRTEM) coupled with atomic force microscopy and X-ray photoelectron spectroscopy reveals the architectures to be extremely well ordered with little residual strain. Surface modification of these topologically complex macrostructures (≈3 µm) has been achieved by direct growth of metallic Ag nanoparticles onto the edge sites of the Sb2 Te3 . Again, HRTEM shows this nanoparticle decoration to be atomically sharp at the boundaries and regularly spaced along the selvedge of the nanostructure. Transport experiments of densified films of these assemblies exhibit marked increases in carrier density after nanoengineering, yielding 3.5 × 104 S m-1 in electrical conductivity. An increased Seebeck coefficient by 20% in parallel with electrical conductivity is also observed. This gives a thermoelectric power factor of 371 µW m-1 K-2 , which is the highest value for a flexible, freestanding film to date. These results suggest an entirely new direction in the search for wearable power harvesters based on topologically complex, low-dimensional nanoassemblies.

A solution-processed, all-phosphor, three-color (i.e., blue, green, and red), alternating current-driven white field-induced polymer electroluminescent device (WFIPEL), with low operational voltage, high luminance, high efficiency, high color-rendering index (CRI), and excellent color-stability, was demonstrated. The devices employed poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) [P(VDF–TrFE–CFE)] dielectric modified by single-walled carbon nanotubes (SWNTs) to further improve the dielectric characteristics, as the insulating layer. This significantly lowers the driving voltage of the device. Moreover, hole-generation layer and electron-transporting layer with high conductivity were used to more efficiently form and confine excitons in the emissive layer. The resulting WFIPEL devices show significant improvements in performance as compared to previous reports. Specifically, the devices exhibit a low turn-on voltage of 10 V, a maximum luminance of 7210 cd m −2 , a maximum current efficiency and power efficiency of 33.8 cd A −1 and 10.5 lm W −1 , and a CRI of 82. The power efficiency is even 10 times higher than the highest previous report (1 lm W −1 ).

We report a simple way of enhancing blue emission in Poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO) based alternating current field driven electroluminescence devices by mixing graphite nano platelets in the emission layer. Significantly strong and well resolved blue peaks at 437 nm and 470 nm are observed both in the devices’ electroluminescence and photoluminescence spectra with the presence of graphite nano platelets. The origin of this strong blue emission has been identified as the PFO’s beta-phase formation confirmed by transmission electron microscopy images and UV–Vis absorption spectra. The nano platelets loading in PFO solution can be controlled by the dispersion time in organic solvents. When the loading increases, the green emission in the electroluminescence spectrum can be reduced. This technique has been found useful in the generation of bright white light when illuminating through down conversion phosphor.

The high-color-quality white emission in an AC-driven field-induced electroluminescence (FIPEL) device consisting of a white emitting ter-polymer: poly(fluorene–benzothiadiazole–quinoline) PF–BT–QL combined with a red emitting dye: Bis(2-methyl-dibenzof,hquinoxaline)(acetylacetonate)iridium (III) Ir(MDQ)2(acac) was achieved. The wide EL emission effectively covered the visible spectral region at the concentration of 5% Ir(MDQ)2(acac) in PF–BT–QL and largely enriched the color rendering capability with a CIE (0.36, 0.38) close to the ideal equal-energy white (0.33, 0.33) and a CRI as high as 97.4, close to the blackbody curve characteristic and CCT between 3034 K and 5334 K which are required for high-quality white-light illumination. When further increasing the concentration of Ir(MDQ)2(acac) to 10%, leading to a more pure white with CIE (0.36, 0.37) and a CRI as high as 97.1. Surprisingly, the FIPEL devices containing 20% and 30% Ir(MDQ)2(acac) in PF–BT–QL still exhibit high-quality white emission with CIE (0.42, 0.37) and (0.32, 0.38) and CRI 93.9 and 88.9 at high electric field, respectively. To the best of our knowledge, there are no reports of two-component FIPELs with a CRI > 90, especially with such a high concentration of the phosphor dopant. We attribute this to the unique carrier injection characteristics of the AC-driven field induced device. This further suggests its great potential application in display and solid state lighting.

The thermoelectric properties of large diameter multiwalled carbon nanotubes synthesized by chemical vapor deposition have been measured after successively longer periods of high energy probe sonication. Electrical conductivity decreases with increased sonication time due to shortening of the nanotubes. The initial Seebeck coefficient before sonication is −2.5 μV/K, but increases to 12 μV/K for sonication periods longer than 12 h. This effect is attributed to the introduction of defects and shortening of the nanotubes during sonication which exposes previously shielded carbon from internal walls to oxygen doping from exposure to atmosphere which results in increased p-type doping and a positive thermoelectric power. Temperature dependent measurements indicate that this oxygen doping of the exposed nanotube ends has a thermally activated charge transfer energy since low temperature thermoelectric power measurements of the sonicated samples approach that of the raw n-type nanotubes.

Acid treatment of carbon nanotubes is a post synthesis processing step used to clean carbon nanotubes. We show that exposure of the nanotubes to oxygen rich reagents including nitric and sulfuric acid results in an increase of the thermoelectric power. Improving dispersion through the use of the surfactant triton-x results in a further increase in TEP of up to 21%. Additionally, refluxing in an oxygen rich acidic solution results in improved dispersion and an increased TEP. These results indicate that improved dispersion of the nanotubes by either sonication or reflux leads to increased oxygenation and thermopower.

An evaluation of methods is represented to extract parameters from the current–voltage ( I – V ) characteristics of solar cells. This evaluation includes five aspects: applicability, convergence, stability, calculation speed, and error on various types of I – V data. Six current popular extraction methods are discussed and evaluated in this work. We find that the widely adopted method using the reciprocals of slope at two points is the fastest and simplest approach to estimating resistances, but it is an incomplete method to obtain the other parameters. Of the five complete methods, the Ishibashi–Kimura method shows the best accuracy (4.5% average error) while having bad applicability. Generally speaking, the Lambert W-function method is the best comprehensive method with good accuracy, applicability, and convergence, though the calculation speed is relatively lower than the other four methods.

Freestanding few layer graphene platelet/polyvinylidene fluoride composites have been synthesized, resulting in flexible, light weight, and durable electrically conducting films. These composites exhibit reasonable thermoelectric properties including a maximum electrical conductivity of 2005 S m−1, Seebeck coefficient of 18.3 μV K−1, and power factor of 0.52 μW m−1 K−2. The temperature dependent behavior of these properties is also investigated. The electrical conductivity of the composites exhibits thermal fluctuation-assisted tunneling behavior coupled with a high energy phonon scattering term, while the thermoelectric power is characterized by electron-phonon enhanced metallic diffusion thermopower plus a phonon drag term. This results in a characteristic change in majority charge carrier type from hole to electron as the temperature decreases below 60 K. These composites have the potential to be used in low power applications where sufficient waste heat is available.

Graphene containing thin film polymer composites possess favorable thermoelectric properties that allow them to be considered for use in low powered applications where durability and weight are important considerations. The use of these materials will be subject to the properties of the specific application, making it necessary to quantify the dependence of the thermoelectric power output on these extrinsic properties. In this study, we show that the power output for a 60 wt% few layer graphene/polyvinylidene composite is dependent on the absolute temperature, temperature difference, and dimensions of the heat source and magnitude of the load resistance. Additionally, the peak power output is achieved when the load resistance matches the internal resistance of the composite. These results demonstrate that it is necessary to optimize the extrinsic properties of the specific application when designing a thermoelectric module to maximize the power output.

Thermoelectrics are materials capable of the solid-state conversion between thermal and electrical energy. Carbon nanotube/polymer composite thin films are known to exhibit thermoelectric effects, however, have a low figure of merit (ZT) of 0.02. In this work, we demonstrate individual composite films of multiwalled carbon nanotubes (MWNT)/polyvinylidene fluoride (PVDF) that are layered into multiple element modules that resemble a felt fabric. The thermoelectric voltage generated by these fabrics is the sum of contributions from each layer, resulting in increased power output. Since these fabrics have the potential to be cheaper, lighter, and more easily processed than the commonly used thermoelectric bismuth telluride, the overall performance of the fabric shows promise as a realistic alternative in a number of applications such as portable lightweight electronics.

The topological nature of two-dimensional (2D) chalcogenide platelets, can present novel opportunities in thin, flexible thermoelectrics. In this work, metal dopants are added to the reactive edges of 2D Bi2Te3 platelets. We show that along this active edge, an atomically well-ordered heterojunction is formed and facile charge exchange is created, onto the platelet and proximal to its known topological states. Temperature dependent conductivity suggests that local band bending across the interface may act as an injection energy filter for dopant-originated carriers. Moreover, as carrier density increases with increasing edge-dopant, carrier scattering does not appear to increase dramatically. As a result, an apparent decoupling between electrical conductivity and Seebeck coefficient occurs, leading to a surprisingly high power factors (PF): For example, the PF increases in Bi2Te3 platelets by eight times when doped with Cu. First principles calculations show that the electronics of the semiconductor-metal interfaces are quite different for edge and facial configurations, thus the site of metal dopant is believed to play an important role in the expected thermoelectric performance. Finally, this work suggests that the topological sensitivity of dopant placement should be considered in the rational design of high performance thermoelectric composites.

In this study, we report the fabrication of n-type flexible thermoelectric fabrics using layered Bi2Se3 nanoplate/polyvinylidene fluoride (PVDF) composites as the thermoelectric material. These composites exhibit room temperature Seebeck coefficient and electrical conductivity values of -80 μV K(-1) and 5100 S m(-1), respectively, resulting in a power factor approaching 30 μW m(-1)K(-2). The temperature-dependent thermoelectric properties reveal that the composites exhibit metallic-like electrical conductivity, whereas the thermoelectric power is characterized by a heterogeneous model. These composites have the potential to be used in atypical applications for thermoelectrics, where lightweight and flexible materials would be beneficial. Indeed, bending tests revealed excellent durability of the thermoelectric fabrics. We anticipate that this work may guide the way for fabricating high performance thermoelectric fabrics based on layered V-VI nanoplates.

Freestanding, flexible/foldable, and wearable bifuctional ultrathin graphene paper for heating and cooling is fabricated as an active material in personal thermal management (PTM). The promising electrical conductivity grants the superior Joule heating for extra warmth of 42 °C using a low supply voltage around 3.2 V. Besides, based on its high out-of-plane thermal conductivity, the graphene paper provides passive cooling via thermal transmission from the human body to the environment within 7 s. The cooling effect of graphene paper is superior compared with that of the normal cotton fiber, and this advantage will become more prominent with the increased thickness difference. The present bifunctional graphene paper possesses high durability against bending cycles over 500 times and wash time over 1500 min, suggesting its great potential in wearable PTM.

Precise control of the selective growth of heterostructures with specific composition and functionalities is an emerging and extremely challenging topic. Here, the first investigation of the difference in binding energy between a series of metal-semiconductor heterostructures based on layered V-2-VI3 nanostructures is investigated by means of density functional theory. All lateral configurations show lower formation energy compared with that of the vertical ones, implying the selective growth of metal nanoparticles. The simulation results are supported by the successful fabrication of self-assembled Ag/Cu-nanoparticle-decorated p-type Sb2Te3 and n-type Bi2Te3 nanoplates at their lateral sites through a solution reaction. The detailed nucleation-growth kinetics are well studied with controllable reaction times and precursor concentrations. Accompanied by the preserved topological structure integrity and electron transfer on the semiconductor host, exceptional properties such as dramatically increased electrical conductivity are observed thanks to the pre-energy-filtering effect before carrier injection. A zigzag thermoelectric generator is built using Cu/Ag-decorated Sb2Te3 and Bi2Te3 as p-n legs to utilize the temperature gradient in the vertical direction. Synthetic approaches using similar chalcogenide nanoplates as building blocks, as well as careful control of the dopant metallic nanoparticles or semiconductors, are believed to be broadly applicable to other heterostructures with novel applications.

This work presents an integration of flexible thermoelectric and piezoelectric materials into a single device structure. This device architecture overcomes several prohibitive issues facing the combination of traditional thermoelectric and piezoelectric generators, while optimizing performance of the combined power output. The structure design uses a carbon nanotube/polymer thin film as a flexible thermoelectric generator that doubles as an electrode on a piezoelectric generator made of poly(vinylidene fluoride). An example 2 × 2 array of devices is shown to generate 89% of the maximum thermoelectric power, and provide 5.3 times more piezoelectric voltage when compared with a traditional device.

Multiwalled carbon nanotubes (MWNTs) have been grown using a standard chemical vapor deposition method, except for varying the growth temperature. Nanotubes grown below 770 °C exhibit typical positive thermoelectric powers, while those grown above have negative values. This behavior is attributed to the larger nanotube diameters observed at higher growth temperatures. Below 770 °C, the average nanotube diameter is about 50 nm, while above, nanotubes reach diameters of 300 nm. This increase in diameter and number of inner shells leads to the intrinsic negative thermoelectric power of the inner nanotube shells becoming larger than the positive thermoelectric power due to oxygen doping on the outer surface of the nanotube. The overall negative thermopower (about −6 μV/K, compared to +7 μV/K for smaller diameter nanotubes) can be understood in terms of a parallel conduction model. Our large-diameter multiwalled carbon nanotubes allow the intrinsic negative thermopower of MWNTs to be accessed without requiring specific deoxygenation treatment.

Resistivity and thermoelectric power (TEP) measurements were conducted on single walled carbon nanotube (SWNT), polyvinylidene fluoride composite thin films of varying SWNT concentrations. This heterogeneous material was used in order to utilize the good electrical conductance of the nanotubes and the poor thermal conductance of the polymer to increase the figure of merit (ZT). As the nanotube weight percent decreased from 100% to 5%, the beneficial effects of the TEP increase and thermal conductivity decrease outweighed the negative effect of decreased electrical conductivity, resulting in an increase in ZT by a factor of 100.