A Solution Processable High-Performance Thermoelectric Copper Selenide Thin Film

Multiple Phase Transition Induced Enhancement of Low-Temperature Thermoelectric Power in Ductile AgCuS-Based Thin Films

The increasing demand for energy autonomy in microscale and wearable electronics has intensified research interest in thermoelectric thin-film-based power generators. However, the development of such devices is challenging due to the intrinsic brittleness of inorganic materials and the poor performance of thin films. Recently, Ag2S-based compounds have emerged as ductile thermoelectric semiconductors. Nonetheless, the thermoelectric performance of their thin films remains constrained, especially at low temperatures. Herein, we present a solution-processed fabrication of a high-performance AgCuS/Cu2S composite thin film operable below 100 °C. These composite thin films underwent multiple phase transitions below 100 °C, notably increasing the thermoelectric power factors. Furthermore, the films exhibited significant intrinsic stretchability up to a strain of 16.1% owing to their intrinsic ductility. Wrinkled thin-film-based devices demonstrated enhanced power generation owing to multiple phase transitions and retained properties under 30% stretching, highlighting the potential of these films as viable energy harvesters for emerging electronic systems.

Morphology-Guided Phase-Controlled Synthesis of Nickel Selenide Nanocrystals through Cation Exchange Reactions

The precise control of the crystal phase during the synthesis of nickel selenide (NixSey) nanocrystals is crucial, as crystal structure and composition significantly influence their reactivity, growth kinetics, and properties. The cation exchange (CE) method provides a versatile and robust approach for synthesizing nanomaterials, enabling precise control over phase, composition, and morphology. However, the application of this method for phase-controlled synthesis of NixSey nanocrystals has received limited research attention. Here, we present a morphology-guided CE method for the synthesis of spinel Ni3Se4 nanoparticles (NPs) and rhombic Ni3Se2 nanorods (NRs), wherein berzelianite Cu2-xSe NPs and NRs are employed as sacrificial templates for CE with Ni2+. This phase-controlled behavior, which is guided by morphology and dependent on the stacking length of the close-packed facets, relies on the rearrangement of the Se2- sublattice accompanied by CE, providing a unique and precise approach to controlling phase during nanocrystal synthesis. Additionally, the obtained Ni3Se4 NPs and Ni3Se2 NRs exhibit structure-dependent catalytic activities in the oxygen evolution reaction.

Solar-Driven Sulfide Oxidation Paired With CO2 Reduction Based on Vacancies Engineering of Copper Selenide

Photovoltaic-driven electrochemical (PV-EC) carbon dioxide reduction (CO2R) coupled with sulfide oxidation (SOR) can efficiently convert the solar energy into chemical energy, expanding its applications. However, developing low-cost electrocatalysts that exhibit high selectivity and efficiency for both CO2R and SOR remains a challenge. Herein, a bifunctional copper selenide catalyst is developed with copper vacancies (v-CuSe2) for the CO2R-SOR. The Faradaic efficiency (FE) of 62.4% for methane at -200 mA cm-2 is achieved in the cathodic CO2R. In a two-electrode CO2R-SOR system with 16 h of long-term operation at a current density of 200 mA cm-2, an average Faradaic efficiency of 57.2% for methane and 97.7% for sulfur powder generation is achieved at cathode and anode, respectively. Compared to the coupling of CO2R with oxygen evolution reaction (OER), the energy efficiency (EE) of the CO2R-SOR system can be increased to 22.9%. The mechanism study has found that the synergistic effect of copper vacancies and introduced Se significantly enhances the selectivity toward methane. Driven by silicon solar cells, a solar-to-methane conversion efficiency of 2% is achieved.

Enhancing Thermoelectric and Cooling Performance of Bi0.5Sb1.5Te3 through Ferroelectric Polarization in Flexible Ag/PZT/PVDF/Bi0.5Sb1.5Te3 Film

Bi2Te3-based thin films are gaining recognition for their remarkable room temperature thermoelectric performance. Beyond the conventional "process-composition-performance" paradigm, it is highly desirable to explore new methods to enhance their performance further. Here, we designed a sandwich-structured Ag/PZT/PVDF/Bi0.5Sb1.5Te3(BST) thin film device and effectively regulated the performance of the BST film by controlling the polarization state of the PZT/PVDF layers. Results indicate that polarization induces interlayer charge redistribution and charge transfer between PZT/PVDF and BST, thereby achieving the continuous modulation of the electrical transport characteristics of BST films. Finally, following polarization at a saturation voltage of 3 kV, the power factor of the BST film increased by 13% compared to the unpolarized condition, reaching 20.8 μW cm-1 K-2. Furthermore, a device with 7 pairs of P-N legs was fabricated, achieving a cooling temperature difference of 11.0 K and a net cooling temperature difference of 2.4 K at a current of 10 mA after the saturation polarization of the PZT/PVDF layer. This work reveals the critical effect of introducing ferroelectric layer polarization to achieve excellent thermoelectric performance of the BST film.

A Strategy for Fabricating Ultra-Flexible Thermoelectric Films Using Ag2Se-Based Ink

Flexible thermoelectric materials have drawn significant attention from researchers due to their potential applications in wearable electronics and the Internet of Things. Despite many reports on these materials, it remains a significant challenge to develop cost-effective methods for large-scale, patterned fabrication of materials that exhibit both excellent thermoelectric performance and remarkable flexibility. In this study, we have developed an Ag2Se-based ink with excellent printability that can be used to fabricate flexible thermoelectric films by screen printing and low-temperature sintering. The printed films exhibit a Seebeck coefficient of -161 μV/K and a power factor of 3250.9 μW/m·K2 at 400 K. Moreover, the films demonstrate remarkable flexibility, showing minimal changes in resistance after being bent 5000 times at a radius of 5 mm. Overall, this research offers a new opportunity for the large-scale patterned production of flexible thermoelectric films.

Hybrid Photovoltaic/Thermoelectric Systems for Round-the-Clock Energy Harvesting

Due to their emission-free operation and high efficiency, photovoltaic cells (PVCs) have been one of the candidates for next-generation “green” power generators. However, PVCs require prolonged exposure to sunlight to work, resulting in elevated temperatures and worsened performances. To overcome this shortcoming, photovoltaic–thermal collector (PVT) systems are used to cool down PVCs, leaving the waste heat unrecovered. Fortunately, the development of thermoelectric generators (TEGs) provides a way to directly convert temperature gradients into electricity. The PVC–TEG hybrid system not only solves the problem of overheated solar cells but also improves the overall power output. In this review, we first discuss the basic principle of PVCs and TEGs, as well as the principle and basic configuration of the hybrid system. Then, the optimization of the hybrid system, including internal and external aspects, is elaborated. Furthermore, we compare the economic evaluation and power output of PVC and hybrid systems. Finally, a further outlook on the hybrid system is offered.

Generalised optical printing of photocurable metal chalcogenides

Optical three-dimensional (3D) printing techniques have attracted tremendous attention owing to their applicability to mask-less additive manufacturing, which enables the cost-effective and straightforward creation of patterned architectures. However, despite their potential use as alternatives to traditional lithography, the printable materials obtained from these methods are strictly limited to photocurable resins, thereby restricting the functionality of the printed objects and their application areas. Herein, we report a generalised direct optical printing technique to obtain functional metal chalcogenides via digital light processing. We developed universally applicable photocurable chalcogenidometallate inks that could be directly used to create 2D patterns or micrometre-thick 2.5D architectures of various sizes and shapes. Our process is applicable to a diverse range of functional metal chalcogenides for compound semiconductors and 2D transition-metal dichalcogenides. We then demonstrated the feasibility of our technique by fabricating and evaluating a micro-scale thermoelectric generator bearing tens of patterned semiconductors. Our approach shows potential for simple and cost-effective architecturing of functional inorganic materials.

Optical 3D printing techniques are low-cost mask-less patterning methods, but their application is limited by the number of printable materials. Here, the authors report a generalized optical method to print 2D or micrometre-thick 2.5D architectures based on metal chalcogenides inks, showing the realization of micro-scale thermoelectric generators.

Expeditious Electrochemical Synthesis of Mesoporous Chalcogenide Flakes: Mesoporous Cu2 Se as a Potential High-Rate Anode for Sodium-Ion Battery

Nanostructured copper selenide (Cu₂ Se) attracts much interest as it shows outstanding performance as thermoelectric, photo-thermal, and optical material. The mesoporous structure is also a promising morphology to obtain better performance for electrochemical and catalytic applications, thanks to its high surface area. A simple one-step electrochemical method is proposed for mesoporous chalcogenides synthesis. The synthesized Cu₂ Se material has two types of mesopores (9 and 18 nm in diameter), which are uniformly distributed inside the flakes. These materials are also implemented for sodium (Na) ion battery (NIB) anode as a proof of concept. The electrode employing the mesoporous Cu₂ Se exhibits superior and more stable specific capacity as a NIB anode compared to the non-porous samples. The electrode also exhibits excellent rate tolerance at each current density, from 100 to 1000 mA g^-1 . It is suggested that the mesoporous structure is advantageous for the insertion of Na ions inside the flakes. Electrochemical analysis indicates that the mesoporous electrode possesses more prominent diffusion-controlled kinetics during the sodiation-desodiation process, which contributes to the improvement of Na-ion storage performance.

Ultrahigh Power Factor of Ternary Composites with Abundant Se Nanowires for Thermoelectric Application

In this work, ultrahigh-performance single-walled carbon nanotube (SWCNT)/Se nanowire (NW)/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) ternary thermoelectric (TE) nanocomposite films are successfully designed by rational design of CNT/Se/PEDOT:PSS ternary nanocomposites. The addition of CNTs apparently improves the electrical conductivity of composite films, resulting in a relatively huge growth of the power factor. The PEDOT:PSS interface layers uniformly attach on both sides of the Se NWs and CNTs effectively, forming a tightly interleaving and interconnected three-dimensional network. As a consequence, a maximum power factor of 863.83 μW/(m·K2) has been achieved for the sample containing 26 wt % CNTs at 434 K. Ultimately, a flexible TE generator prototype consisting of 5-unit freestanding composite film strips is fabricated using the optimized composite films, which can generate a maximum output power of 206.8 nW at a temperature gradient of 44.7 K. Therefore, the present work has a further potential to be used for the flexible polymer/carbon TE nanocomposite films and devices.

Printed Thermoelectrics

The looming impact of climate change and the diminishing supply of fossil fuels both highlight the need for a transition to more sustainable energy sources. While solar and wind can produce much of the energy needed, to meet all our energy demands there is a need for a diverse sustainable energy generation mix. Thermoelectrics can play a vital role in this, by harvesting otherwise wasted heat energy and converting it into useful electrical energy. While efficient thermoelectric materials have been known since the 1950s, thermoelectrics have not been utilized beyond a few niche applications. This can in part be attributed to the high cost of manufacturing and the geometrical restraints of current commercial manufacturing techniques. Printing offers a potential route to manufacture thermoelectric materials at a lower price point and allows for the fabrication of generators that are custom built to meet the waste heat source requirements. This review details the significant progress that has been made in recent years in printing of thermoelectric materials in all thermoelectric material groups and printing methods, and highlights very recent publications that show printing can now offer comparable performance to commercially manufactured thermoelectric materials.

Flexible Thermoelectric Generator Based on Polycrystalline SiGe Thin Films

Flexible and reliable thermoelectric generators (TEGs) will be essential for future energy harvesting sensors. In this study, we synthesized p- and n-type SiGe layers on a high heat-resistant polyimide film using metal-induced layer exchange (LE) and demonstrated TEG operation. Despite the low process temperature (<500 °C), the polycrystalline SiGe layers showed high power factors of 560 µW m⁻¹ K⁻² for p-type Si_0.4Ge_0.6 and 390 µW m⁻¹ K⁻² for n-type Si_0.85Ge_0.15, owing to self-organized doping in LE. Furthermore, the power factors indicated stable behavior with changing measurement temperature, an advantage of SiGe as an inorganic material. An in-plane π-type TEG based on these SiGe layers showed an output power of 0.45 µW cm⁻² at near room temperature for a 30 K temperature gradient. This achievement will enable the development of environmentally friendly and highly reliable flexible TEGs for operating micro-energy devices in the future Internet of Things.

Facile synthesis of copper selenides with different stoichiometric compositions and their thermoelectric performance at a low temperature range

Copper selenide is widely considered to be a promising candidate for high-performance flexible thermoelectrics; however, most of the reported ZT values of copper selenides are unsatisfactory at a relatively low temperature range. Herein, we utilized some wet chemical methods to synthesize a series of copper selenides. XRD, SEM and TEM characterizations revealed that CuSe, Cu3Se2 and Cu2-x Se were prepared successfully and possessed different morphologies and sizes. Based on the analysis of their thermoelectric properties, Cu2-x Se exhibited the highest Seebeck coefficient and lowest thermal conductivity among the three samples owing to its unique crystal structure. After being sintered at 400 °C under N2 atmosphere, the electrical conductivity of Cu2-x Se enhanced considerable, resulting in a significant improvement of its ZT values from 0.096 to 0.458 at 30 to 150 °C. This result is remarkable for copper selenide-based thermoelectric materials at a relatively low temperature range, indicating its brilliant potential in the field of flexible thermoelectric devices.

Thermoelectric Materials for Textile Applications

Since prehistoric times, textiles have served an important role-providing necessary protection and comfort. Recently, the rise of electronic textiles (e-textiles) as part of the larger efforts to develop smart textiles, has paved the way for enhancing textile functionalities including sensing, energy harvesting, and active heating and cooling. Recent attention has focused on the integration of thermoelectric (TE) functionalities into textiles-making fabrics capable of either converting body heating into electricity (Seebeck effect) or conversely using electricity to provide next-to-skin heating/cooling (Peltier effect). Various TE materials have been explored, classified broadly into (i) inorganic, (ii) organic, and (iii) hybrid organic-inorganic. TE figure-of-merit (ZT) is commonly used to correlate Seebeck coefficient, electrical and thermal conductivity. For textiles, it is important to think of appropriate materials not just in terms of ZT, but also whether they are flexible, conformable, and easily processable. Commercial TEs usually compromise rigid, sometimes toxic, inorganic materials such as bismuth and lead. For textiles, organic and hybrid TE materials are more appropriate. Carbon-based TE materials have been especially attractive since graphene and carbon nanotubes have excellent transport properties with easy modifications to create TE materials with high ZT and textile compatibility. This review focuses on flexible TE materials and their integration into textiles.

Thermoelectric Properties of Cu2Se Nano-Thin Film by Magnetron Sputtering

Thermoelectric technology can achieve mutual conversion between thermoelectricity and has the unique advantages of quiet operation, zero emissions and long life, all of which can help overcome the energy crisis. However, the large-scale application of thermoelectric technology is limited by its lower thermoelectric performance factor (ZT). The thermoelectric performance factor is a function of the Seebeck coefficient, electrical conductivity, thermal conductivity and absolute temperature. Since these parameters are interdependent, increasing the ZT value has always been a challenge. Here, we report the growth of Cu₂Se thin films with a thickness of around 100 nm by magnetron sputtering. XRD and TEM analysis shows that the film is low-temperature α-Cu₂Se, XPS analysis shows that about 10% of the film’s surface is oxidized, and the ratio of copper to selenium is 2.26:1. In the range of 300–400 K, the maximum conductivity of the film is 4.55 × 10⁵ S m⁻¹, which is the maximum value reached by the current Cu₂Se film. The corresponding Seebeck coefficient is between 15 and 30 µV K⁻¹, and the maximum ZT value is 0.073. This work systematically studies the characterization of thin films and the measurement of thermoelectric properties and lays the foundation for further research on nano-thin-film thermoelectrics.

A nanoscale Cu2-xSe ultrathin film deposited via atomic layer deposition and its memristive effects

An ultrathin film of copper selenide 50 nm thick was deposited using a home-made atomic layer deposition apparatus. Synthesized copper pivalate and bis(triethylsilyl) selenide precursors were used. The deposition rate at 160 °C was 0.48 Å per atomic layer deposition cycle. The thickness was monitored by an in situ ellipsometer and further analyzed by an atomic force microscope. The composition and structure of the film were confirmed by x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction to be Cu1.16Se. The fluorine-doped tin oxide/Cu1.16Se/tungsten wire memristor was fabricated and its memristive effect was investigated. The non-linear I-V curve and spike-timing-dependent plasticity of our Cu1.16Se memristor demonstrate that the short-term and long-term potentiation that occurs in a human brain can be mimicked by adjusting voltage-pulse intervals. A memristor is the electrical equivalent of a synapse. Our memristor has a 1 ms switching time, a 400 s retention time, Roff/on = 2, and reproducibility over 1000 cycles.

Synergistically enhanced thermoelectric performance by optimizing the composite ratio between hydrothermal Sb2Se3 and self-assembled β-Cu2Se nanowires

Sb₂Se₃ and β-Cu₂Se nanowires were synthesized via hydrothermal reaction and a water-evaporation induced self-assembly method, respectively, and a 70%-Sb₂Se₃ and 30%-β-Cu₂Se disk pellet shows enhanced thermoelectric performance.

Ultrahigh Performance of n-Type Ag2Se Films for Flexible Thermoelectric Power Generators

Due to the limited thermoelectric (TE) performance of conducting polymers and rigidity of inorganic materials, it is still a huge challenge to prepare low-cost, highly flexible, and high-performance TE materials. Herein, we fabricated n-type Ag₂Se films using a porous nylon membrane as a flexible substrate by vacuum-assisted filtration, followed by hot pressing. A very high power factor of ∼1882 μW m^-1 K^-2 at room temperature is obtained. The high power factor is mainly the result of the high density of the Ag₂Se film and the tuned grain orientation, which is realized by the synthesis of multisized Ag₂Se nanostructures. The film also exhibits excellent flexibility with 90.7% retention of the power factor after bending around a rod of 4 mm radius for 1000 times. A four-leg TE generator is assembled with the Ag₂Se film, and its maximum output power is up to 3.2 μW at a temperature difference of 30 K, corresponding to the maximum power density of 22.0 W m^-2 and a normalized maximum power density of 408 μW m^-1 K^-2. This work provides an effective route to achieve high-power-factor, high-flexibility, and low-cost TE films.

High-performance thermoelectric silver selenide thin films cation exchanged from a copper selenide template

Over the past decade, Ag₂Se has attracted increasing attention due to its potentially excellent thermoelectric (TE) performance as an n-type semiconductor. It has been considered a promising alternative to Bi-Te alloys and other commonly used yet toxic and/or expensive TE materials. To optimize the TE performance of Ag₂Se, recent research has focused on fabricating nanosized Ag₂Se. However, synthesizing Ag₂Se nanoparticles involves energy-intensive and time-consuming techniques with poor yield of final product. In this work, we report a low-cost, solution-processed approach that enables the formation of Ag₂Se thin films from Cu_2-x Se template films via cation exchange at room temperature. Our simple two-step method involves fabricating Cu_2-x Se thin films by the thiol-amine dissolution of bulk Cu₂Se, followed by soaking Cu_2-x Se films in AgNO₃ solution and annealing to form Ag₂Se. We report an average power factor (PF) of 617 ± 82 μW m^-1 K^-2 and a corresponding ZT value of 0.35 at room temperature. We obtained a maximum PF of 825 μW m^-1 K^-2 and a ZT value of 0.46 at room temperature for our best-performing Ag₂Se thin-film after soaking for 5 minutes. These high PFs have been achieved via full solution processing without hot-pressing.

Large-Area Laying of Soft Textile Power Generators for the Realization of Body Heat Harvesting Clothing

This paper presents the realization of a flexible thermoelectric (TE) generator as a textile fabric that converts human body heat into electrical energy for portable, low-power microelectronic products. In this study, an organic non-toxic conductive coating was used to dip rayon wipes into conductive TE fabrics so that the textile took advantage of the TE currents which were parallel to the temperature gradient. To this end, a dyed conductive cloth was first sewn into a TE unit. The TE unit was then sewn into an array to create a temperature difference between the human body and the environment for TE power harvesting. The prototype of the TE fabric consisted of 48 TE units connected by conductive wire over an area of 275 × 205 mm2, and the TE units were sewn on a T-shirt at the chest area. After fabrication and property tests, a Seebeck coefficient of approximately 20 μV/K was measured from the TE unit, and 0.979 mV voltage was obtained from the T-shirt with TE textile fabric. Since the voltage was generated at a low temperature gradient environment, the proposed energy solution in actual fabric applications is suitable for future portable microelectronic power devices.

3D Printing of Solution-Processable 2D Nanoplates and 1D Nanorods for Flexible Thermoelectrics with Ultrahigh Power Factor at Low-Medium Temperatures

Solution-processable semiconducting 2D nanoplates and 1D nanorods are attractive building blocks for diverse technologies, including thermoelectrics, optoelectronics, and electronics. However, transforming colloidal nanoparticles into high-performance and flexible devices remains a challenge. For example, flexible films prepared by solution-processed semiconducting nanocrystals are typically plagued by poor thermoelectric and electrical transport properties. Here, a highly scalable 3D conformal additive printing approach to directly convert solution-processed 2D nanoplates and 1D nanorods into high-performing flexible devices is reported. The flexible films printed using Sb2Te3 nanoplates and subsequently sintered at 400 °C demonstrate exceptional thermoelectric power factor of 1.5 mW m-1 K-2 over a wide temperature range (350-550 K). By synergistically combining Sb2Te3 2D nanoplates with Te 1D nanorods, the power factor of the flexible film reaches an unprecedented maximum value of 2.2 mW m-1 K-2 at 500 K, which is significantly higher than the best reported values for p-type flexible thermoelectric films. A fully printed flexible generator device exhibits a competitive electrical power density of 7.65 mW cm-2 with a reasonably small temperature difference of 60 K. The versatile printing method for directly transforming nanoscale building blocks into functional devices paves the way for developing not only flexible energy harvesters but also a broad range of flexible/wearable electronics and sensors.

Ink Processing for Thermoelectric Materials and Power-Generating Devices

The growing concern over the depletion of hydrocarbon resources, and the adverse environmental effects associated with their use, has increased the demand for renewable energy sources. Thermoelectric (TE) power generation from waste heat has emerged as a renewable energy source that does not generate any pollutants. Recently, ink-based processing for the preparation of TE materials has attracted tremendous attention because of the simplicity in design of power generators and the possibility of cost-effective manufacturing. In this progress report, recent advances in the development of TE inks, processing techniques, and ink-fabricated devices are reviewed. A summary of typical formulations of TE materials as inks is included, as well as a discussion on various ink-based fabrication methods, with several examples of newly designed devices fabricated using these techniques. Finally, the prospects of this field with respect to the industrialization of TE power generation technology are presented.

Solution-Based Synthesis and Processing of Metal Chalcogenides for Thermoelectric Applications

Metal chalcogenide materials are current mainstream thermoelectric materials with high conversion efficiency. This review provides an overview of the scalable solution-based methods for controllable synthesis of various nanostructured and thin-film metal chalcogenides, as well as their properties for thermoelectric applications. Furthermore, the state-of-art ink-based processing method for fabrication of thermoelectric generators based on metal chalcogenides is briefly introduced. Finally, the perspective on this field with regard to material production and device development is also commented upon.

Composition change-driven texturing and doping in solution-processed SnSe thermoelectric thin films

The discovery of SnSe single crystals with record high thermoelectric efficiency along the b-axis has led to the search for ways to synthesize polycrystalline SnSe with similar efficiencies. However, due to weak texturing and difficulties in doping, such high thermoelectric efficiencies have not been realized in polycrystals or thin films. Here, we show that highly textured and hole doped SnSe thin films with thermoelectric power factors at the single crystal level can be prepared by solution process. Purification step in the synthetic process produced a SnSe-based chalcogenidometallate precursor, which decomposes to form the SnSe₂ phase. We show that the strong textures of the thin films in the b-c plane originate from the transition of two dimensional SnSe₂ to SnSe. This composition change-driven transition offers wide control over composition and doping of the thin films. Our optimum SnSe thin films exhibit a thermoelectric power factor of 4.27 μW cm^-1 K^-2.

Materials and Designs for Power Supply Systems in Skin-Interfaced Electronics

Recent advances in materials chemistry and composite materials design establish the foundations for classes of electronics with physical form factors that bridge the gap between soft biological organisms and rigid microsystems technologies. Skin-interfaced platforms of this type have broad utility in continuous clinical-grade monitoring of physiological status, with the potential to significantly lower the cost and increase the efficacy of modern health care. Development of materials and device designs for power supply systems in this context is critically important, and it represents a rapidly expanding focus of research in the chemical sciences. Reformulating conventional technologies into biocompatible platforms and co-integrating them into skin-interfaced systems demand innovative approaches in materials chemistry and engineering. In terms of physical properties, the resulting devices must offer levels of flexibility, stretchability, thickness, and mass density that approach those of the epidermis itself, while maintaining operational characteristics and mechanical durability for practical use outside of a laboratory or hospital. While nearly all commercially available components for energy storage and harvesting are rigid and planar, recent research provides options in devices that are biocompatible not only at the level of the constituent materials but also in terms of the mechanics and geometrical forms, with resulting capabilities for establishing stable, nonirritating, intimate interfaces to the skin for extended periods of time. This Account highlights the range of materials choices and associated device architectures for skin-interfaced power supply systems. The Account begins with an overview of the main design strategies, ranging from one-, two-, and three-dimensional engineered composite structures to active materials that are intrinsically stretchable. The following sections describe a broad collection of devices based on these concepts, starting with batteries and supercapacitors for storage and then photovoltaic, piezoelectric, triboelectric, and thermoelectric devices for harvesting. Representative examples highlight recent advances, with a focus on the relationship between the materials and the performance during deformation. A final section discusses the challenges and opportunities in this area. Continued efforts in fundamental chemical research will be critically important to progress in this emerging field of technology. For example, understanding the mechanisms by which physical deformations affect the intrinsic materials properties and the system-level performance requires further study. The development of stretchable and biocompatible solid electrolytes with high ionic conductivity is an example of a specific area of interest for energy storage devices. Here and in other storage and harvesting systems advanced materials are needed to provide robust barriers to environmental factors. Work to address these and other interesting challenges will demand multidisciplinary collaborations between chemists, materials scientists, bioengineers, and clinicians, all oriented toward establishing the foundations for technologies that could help to address global grand challenges in human health care.

Tin Diselenide Molecular Precursor for Solution-Processable Thermoelectric Materials

In the present work, we detail a fast and simple solution-based method to synthesize hexagonal SnSe₂ nanoplates (NPLs) and their use to produce crystallographically textured SnSe₂ nanomaterials. We also demonstrate that the same strategy can be used to produce orthorhombic SnSe nanostructures and nanomaterials. NPLs are grown through a screw dislocation-driven mechanism. This mechanism typically results in pyramidal structures, but we demonstrate here that the growth from multiple dislocations results in flower-like structures. Crystallographically textured SnSe₂ bulk nanomaterials obtained from the hot pressing of these SnSe₂ structures display highly anisotropic charge and heat transport properties and thermoelectric (TE) figures of merit limited by relatively low electrical conductivities. To improve this parameter, SnSe₂ NPLs are blended here with metal nanoparticles. The electrical conductivities of the blends are significantly improved with respect to bare SnSe₂ NPLs, what translates into a three-fold increase of the TE Figure of merit, reaching unprecedented ZT values up to 0.65.

Realizing zT of 2.3 in Ge1-x-y Sbx Iny Te via Reducing the Phase-Transition Temperature and Introducing Resonant Energy Doping

GeTe with rhombohedral-to-cubic phase transition is a promising lead-free thermoelectric candidate. Herein, theoretical studies reveal that cubic GeTe has superior thermoelectric behavior, which is linked to (1) the two valence bands to enhance the electronic transport coefficients and (2) stronger enharmonic phonon-phonon interactions to ensure a lower intrinsic thermal conductivity. Experimentally, based on Ge_1-x Sb_x Te with optimized carrier concentration, a record-high figure-of-merit of 2.3 is achieved via further doping with In, which induces the distortion of the density of states near the Fermi level. Moreover, Sb and In codoping reduces the phase-transition temperature to extend the better thermoelectric behavior of cubic GeTe to low temperature. Additionally, electronic microscopy characterization demonstrates grain boundaries, a high-density of stacking faults, and nanoscale precipitates, which together with the inevitable point defects result in a dramatically decreased thermal conductivity. The fundamental investigation and experimental demonstration provide an important direction for the development of high-performance Pb-free thermoelectric materials.

Precursors for PbTe, PbSe, SnTe, and SnSe synthesized using diphenyl dichalcogenides

Alternative metal chalcogenide precursor syntheses (instead of hydrazine or thiol–amine approaches) along with corresponding thermoelectric properties of PbSe_xTe_1−x films.

One-pot solution synthesis of shape-controlled copper selenide nanostructures and their potential applications in photocatalysis and photothermal therapy

Developing a facile and reliable method for the fabrication of transition metal chalcogenides is a vital and endless pursuit of scientific and technological disciplines. In this work, we develop a one-pot solution approach to obtain copper selenide nanostructures with different morphologies and crystal structures (Cu₂Se nanoparticles, CuSe nanoplates and CuSe₂ nanosheets). In comparison to previously reported methods, our method did not use expensive and very toxic raw materials. After detailed studies of reaction conditions, including temperature, reaction time, and feeding amount of surfactants and precursors, we found that the feeding ratio of precursors played a key role in the crystal structures and morphologies of the final products. Moreover, as a proof-of-concept study, the potential applications of the as-prepared copper selenide nanostructures in the photocatalytic discoloration of aqueous methylene blue (MB) under visible light irradiation and near-infrared (NIR) light induced photothermal therapy for cancer treatment were investigated. Encouraged by their strong photocatalytic activities and high photothermal conversion efficiencies (calculated to be 51.0%, 49.5% and 48.9% for Cu₂Se nanoparticles, CuSe nanoplates and CuSe₂ nanosheets, respectively), we believe that copper selenide nanostructures fabricated from the one-pot solution approach developed in this work would be promising candidates for a wide variety of emerging applications.