X-ray multilayer enables an efficient reflection of X-rays in specific wavelength, serving as an important optics for obtaining monochromatic X-ray. The period thickness of multilayers typically falls within a nano-scale, and it is generally composed of two kinds of thin films alternately due to the short wavelength of X-ray. The multilayer can realize a high reflection of specific wavelength X-ray based on the Bragg diffraction, yielding a pure monochromatic X-ray. Compared to crystal monochromators, the period of multilayer can be adjusted readily, and the multilayer can be suitable for X-rays with different energies. The energy bandwidth of reflected X-ray obtained by the multilayer is 1-2 orders of magnitude broader than that of the crystals, thus providing a higher photon flux. At present, X-ray multilayer is widely used in synchrotron radiation for applications such as X-ray imaging, and X-ray small-angle scattering. According to the working principle of X-ray mutlilayer, the period of multilayer is only a few nanometers for the efficient X-ray reflection at a larger grazing angle due to the short wavelength of X-ray. Therefore, the coating method with a high precision thickness control is essential to prepare X-ray multilayer. Magnetron sputtering is the primary preparation method for X-ray multilayers, although achieving a high precision thickness control remains a challenge. Atomic layer deposition (ALD) method can realize uniform growth of single atomic layer thickness film on substrate and the film thickness control is extremely accurate because of the special film growth process. The ALD method has unique advantages in the preparation of small-period multilayer. It is identified that HfO₂/Al₂O₃ is an effective material pair for X-ray multilayer at a wavelength of 0.154 nm and the X-ray reflectivity is acceptable.

To further investigate the properties of HfO₂/Al₂O₃ X-ray multilayer prepared by the ALD and explore its application, HfO₂/Al₂O₃ X-ray multilayer with a period of 3.8 nm and a period number of 60 was prepared by the ALD method. The surface 3D profile of the multilayer was obtained by a model ICON2-SYS atomic force microscope (AFM, Bruker Co., Germany), and the surface roughness of the multilayer was analyzed by a software named NanoScope Analysis. The microstructure of multilayer was determined by a model Talos F200s G2 transmission electron microscope (TEM, Thermo Fisher Scientific Co., USA) with a software named Digital Micrograph. The X-ray reflectivity of the multilayer was measured by a model D8 Discover X-ray diffractometer (XRD, Bruker Co., Germany) at X-ray wavelength of 0.154 nm. A software named IMD was used to fit the measured reflectance data. The fitting was based on a two-layer model, and the structure parameters of multilayer was obtained, including period and duty cycle. The multilayer was also analyzed by a modle AL-Y3500 diffractometer (Dandong Aolong Ray Instrument Group Co., Ltd., China). Before the installation of multilayer, the X-rays emitted from the source were directly illuminated on the sample by a collimator. After the installation of multilayer, the X-rays emitted from the ray source were firstly reflected by the multilayer and then irradiated on the sample. The diffraction patterns before and after installing multilayer were analyzed. This work consisted of three main parts. Firstly, a software named Fluent was used to simulate the gas flow distribution according to the structure of ALD equipment chamber. The results show that the gas flow rate is uniform, indicating that the chamber is suitable for preparing a film with uniform thickness. Secondly, HfO₂/Al₂O₃ multilayer is prepared by the ALD method, and the surface roughness, period thickness uniformity and X-ray reflectivity are characterized. Finally, the multilayer is installed on the X-ray diffractometer to test the diffraction patterns of a silicon sample. The results show that the quality of the diffraction patterns is improved after the installation of the multilayer.

The characterization results show that the surface root-mean-square roughness of the multilayer is 0.77 nm, the maximum deviation of the period is 0.11 nm and the maximum X-ray (i.e., 0.154 nm) reflectivity of the multilayer is approximately 45%. The multilayer is in an amorphous state, and the interface between two layers is clear and sharp. The XRD pattern of Si powder sample is obtained without and with the HfO₂/Al₂O₃ multilayer in X-ray diffractometer. The results indicate that the background intensity of the pattern with multilayer reduces, and no diffraction peaks of other X-ray appear. The reason is that the X-rays irradiated on the sample are composed of high-intensity Cu characteristic X-rays, other stray energy X-rays and low-intensity bremsstrahring radiation when the multilayer is not installed. After the multilayer is installed, the pure Cu kα characteristic X-rays are irradiated on the sample and thus there is basically no interference peak.

This work investigated the characteristics of HfO₂/Al₂O₃ multilayer prepared by the ALD method and explored its application in X-ray diffractometers. The results showed that HfO₂ and Al₂O₃ layers were amorphous with a maximum X-ray (0.154 nm) reflectivity of approximately 45%. The quality of the diffraction patterns after the installation of the multilayer was improved, demonstrating a potential application of the HfO₂/Al₂O₃ multilayer.

Dye-sensitized solar cells (DSSC), as the third generation of solar cells, have the advantages of low cost, environmental protection, pollution-free, and abundant raw materials. Conventional liquid-state electrolyte of DSSC restricts an absorption capacity of visible light and is corrosive, which is considered as an obstacle to the long-term use of DSSC. Solid-state electrolyte has attracted much attention because it overcomes the shortcomings of liquid-state electrolyte (i.e., volatile organic solvent, poor stability and easy leakage). TiO₂ is often used as a photoanode material for DSSC, and its conduction band can match the energy level of common dyes to accelerate electron transfer. However. TiO₂ has a low electron mobility, a low conductivity, a long-term ultraviolet irradiation and the existence of oxygen vacancy, which hinders the effective current output and reduces the photoelectric conversion efficiency. ZnO material can replace TiO₂ as a photoanode because of its high electron mobility and transparency, and it is also a wide-band gap semiconductor material. To improve the photoelectric conversion efficiency of DSSC and solve the problem of liquid-state electrolyte leakage, ZnO solid-state dye-sensitized solar cells were simulated by a software named SCAPS-1D, and the photoelectric performance of solid-state DSCC was analyzed.

Based on FTO/ZnO/N719/PEDOT: PSS/Au structure modeling by the software SCAPS-1D, a solid-state DSSC model in each layer material interface lose band gap, dielectric constant, mobility and other parameters, and inside layer and layer between the defects was set up under AM1.5G 1 standard solar lighting at an incident light power of 100 mW/cm². The material defect was set as a neutral defect to ensure that the defect could generate SRH recombination without generating space charge because the charge recombination mode of DSSC was mainly SRH. The Poisson equation, carrier continuity equation and carrier drift diffusion equation were numerically solved by the software of SCAPS-1D. The influences of material thickness, operating temperature, series parallel resistance and back contact metal type on the DSSC photoelectric parameters were simulated, and the internal mechanism of the influences of various factors on the DSSC was analyzed.

The open circuit voltage, short circuit current density and photoelectric conversion efficiency increase significantly, and the thickness continues to increase to 1000 nm, as well as the photoelectric parameters increase slowly when the thickness of the dye layer increases from 100 nm to 500 nm. The maximum photoelectric conversion efficiency can be obtained at the thickness of electron transport layer of 20 nm. The photoelectric conversion efficiency increases with the increase of hole transport layer thickness. The efficiency decreases with the increase of operating temperature, and the maximum photoelectric conversion efficiency is 15.17% at 300 K. The open circuit voltage and short circuit current density change little, and the filling factor and photoelectric conversion efficiency decrease when DSSC series resistance increases. The short circuit current density basically unchanges, and other parameters improve when the shunt resistance increases. The effect of changing the type of back contact metal on the photoelectric performance of DSSC is analyzed. The open circuit voltage, short circuit current density and photoelectric conversion efficiency all increase when the back contact metal work function value increases, and the maximum photoelectric conversion efficiency can be obtained when Au is used as the back contact metal.

The optimal thickness of dye layer was 500 nm, and the maximum photoelectric conversion efficiency could be obtained at the thickness of electron transport layer of 20 nm, and the photoelectric conversion efficiency increased with the thickness of hole transport layer. The maximum photoelectric conversion efficiency was 15.17% at the operating temperature of 300 K. The series parallel resistance had an important effect on the photoelectric performance of DSSC. The smaller the series resistance was, the larger the parallel resistance could be, for the improvement of the photoelectric conversion efficiency of DSSC. The electrical conversion efficiency increased when the back contact metal work function value increased, and the maximum photoelectric conversion efficiency could be obtained as Au was used as the back contact metal.

The inverted inorganic perovskite solar cells (IPSCs) with a bandgap of 1.7 eV are prospective candidates for the next generation of photovoltaic cells due to their elemental composition and unparalleled light and thermal stability. However, the higher defect state density and energy level mismatch at the interface result in an inferior photovoltaic performance to that of organic-inorganic hybrid perovskite solar cells (HPSCs) with the same bandgap. In this paper, tetrabutylammonium iodide (TBAI) was used to treat the surface of the optical absorption layer of the inverted device. The interface engineering technique can effectively reduce the density of defect states in the inverted device, suppress non-radiative recombination, and decrease the carrier accumulation at the interface. Finally, the photoelectric conversion efficiency (J) of IPSCs prepared in air is increased from 17.10% to 19.76%, and the PCE is increased by 15.56%. In addition, the stability of the device is also considerably improved.

The NiO_x solution was spun on the surface of FTO glass and annealed at 130 ℃ for 20 min. After cooling to room temperature, the P3CT-N solution was spun coated on the surface of the annealed NiO_x and annealed in air at 130 ℃ for 10 min. Afterwards, the prepared perovskite precursor liquid was spun coated on the surface of P3CT-N preheated at 70 ℃, and annealing on a hot plate at 190 ℃ for 5-8 min. The annealed films were transferred to a N₂ atmosphere glove box for dynamic spin coating of TBAI (IPA) solution, and then annealed at 80 ℃ for 5 min. MgF₂ was thermally evaporated on the surface of TBAI by an evaporation equipment. PC₆₁BM (CB) was spun as the electron transport layer, and BCP (IPA) was spun as the hole barrier layer. Finally, the evaporation device vaporized Ag with the thickness of 80.0 nm on the surface of the BCP as a metal electrode.

The SEM images show that the particles of TBAI treated films are fuller and the holes significantly reduce. These holes are the center of non-radiative recombination, seriously restricting the improvement of photovoltaic performance of devices. The results of UV-absorption test indicate that TBAI post-treatment does not change the bandgap of inorganic perovskite CsPbI_2.85Br_0.15. The results of TRPL test show that the TBAI-treated films have a longer carrier lifetime, indicating that the non-radiative recombination is inhibited. Based on the results of the Mott-Schottky test, the TBAI-treated device demonstrates a built-in electric field of 1.196 V, which is much higher than that of the reference group (i.e., 1.038 V), and a larger built-in electric field means a more intense carrier separation drive, corresponding to a higher V_OC. The steady-state power output (SPO) efficiency of the TBAI treated device is tested for 300 s, and the average SPO efficiency of the device is 19.36% for over 400 s. A pure hole device is constructed to analyze the defect state density of the two films. The V_TFL values of the control and TBAI treated devices are 1 V and 0.95 V, respectively, and the corresponding defect state densities are 1.68×10¹⁶ and 1.56×10¹⁶ cm^-3, respectively. The TBAI post-treatment reduces the defect state density of the films, inhibiting non-radiative recombination. The humidity stability of the two films is monitored under specific conditions. The decomposition the films in the control group appears when the films in the control group are in humid air for 72 h, while that in the experimental group almost constancy.

The defect state density at the interface of IPSCs was high, and the non-radiation recombination loss was serious, thus restricting the further improvement of the photovoltaic performance of the device. In this paper, TBAI was used to post-treated the surface of CsPbI_2.85Br_0.15, which improved the crystal quality of the film, effectively reduced the density of defect states, inhibited non-radiative recombination, and reduced unnecessary carrier accumulation at the interface. IPSCs prepared in air treated by this interface engineering achieved a champion PCE of 19.76% with a V_OC of 1.200 V. This work could provide a method for preparing highly efficient and stable IPSCs in air, thus promoting the practical process.

TEC technology offers precise temperature control, addressing challenges like localized hotspots and complex heat flows in high-power-density chips, which is a key technology for sustainable and high-efficiency thermal management. However, the existing researches still face significant challenges in achieving the ultra-thin designs and high-efficiency required for modern chip architectures. The ability to manage transient high heat flux while maintaining scalability and cost-efficiency remains a concern. Future efforts should focus on the balance of cost, durability, and TE properties of materials through nanoengineering, doping, and interface engineering to enhance their performance. In terms of device design, optimizing multi-stage architectures and achieving miniaturization alongside intelligent functionalities will enable more efficient heat dissipation. These improvements are indispensable for catering to the increasing demands of high-power chips. At the system level, the integration of TEC with liquid cooling or heat pipes will enhance overall thermal management efficiently. The incorporation of TE generation provides new opportunities for constructing sustainable and energy-efficient cooling systems. With continued innovation in materials preparation, device design, and system integration, TEC may pave a way for efficient, reliable, and scalable solutions for the next generation of electronic systems.

Thermoelectric materials have a promising prospect as they can directly convert thermal energy into electrical energy. Some thermoelectric materials are discovered in recent years, especially bismuth telluride (Bi₂Te₃)-based materials that are capable of large-scale commercialization. At present, the average zT value and conversion efficiency of Bi₂Te₃-based materials can be further enhaced. The low-valent cation doping is achieved via doping to optimize the electrical conductivity, while introducing defects as phonon scattering centers to effectively reduce the lattice thermal conductivity. This strategy is verified to be the most effective optimization method. In this paper, Na₂S was selected as a p-type dopant to dope Bi_0.42Sb_1.58Te₃ (BST) alloys, the conductivity was optimized via replacing the cation position of the BST matrix, and improving the solid solubility of Na and strengthening its mechanical properties by element S. The lattice distortion caused by Na₂S doping in the BST alloys and the nanopore structure generated by the volatile element Te in the matrix were investigated.

The original high-purity Bi powder (99.99%, in mass, the same below), Te powder (99.99%), Sb (99.99%), and Na₂S powder (Aladdin Co., China) were precisely weighed in an Ar atmosphere glove box based on their nominal composition (Bi_0.42Sb_1.58Te₃ + x% Na₂S, where x = 0, 0.2, 0.5, and 1.0). The weighed mixed powder was then placed in a quartz tube, evacuated to a vacuum degree of 10^-4 Pa, and sealed. The quartz tubes were pre-plated with carbon to avoid the possibility of Na corrosion. The mixed powder in the sealed quartz tube was heated in a vertical resistance furnace for melting at 1125 K for 12 h and kept for 16 h. The ingots obtained after melting were ground by a model QM-3SP2 planetary ball mill at 425 r/min for 6 h. Finally, the powder was sintered at 698 K and 50 MPa by spark plasma sintering to prepare the bulk samples.

The phase structure of the samples was analyzed by X-ray diffraction (XRD, Rigaku Co., Japan) with Cu K_α radiation (λ = 1.540 6 Å) in a diffraction angle range of 20°-60° with a step size of 0.02° (5 (°)/min). The microstructure of the samples was examined by scanning electron microscopy (SEM, ZEISS Co., Germany). The thermoelectric performance of the samples was analyzed via measuring their Seebeck coefficient, electrical conductivity, and power factor in a model ZEM-3M10 Seebeck coefficient/electric resistivity measuring system (Ulvac-Riko Co., Japan) under a thin helium atmosphere. The thermal diffusivity of the samples was measured by a model LFA457 laser flash instrument (NETZSCH Co., Germany), and the thermal conductivity was calculated based on κ_tot = DρC_p, where D is the thermal diffusivity, C_p is the specific heat capacity deduced via the Dulong-Petit limit, and ρ is the density of samples. The density was determined according to the Archimedes principle. The carrier concentration and mobility of the samples were measured at 295 K under an applied magnetic field of 1.5 T and an electrical current of 30 mA in a model PPMS-9T physical properties measurement system (Quantum Design Inc., Japan).

When Na₂S is used as a dopant, the electrical conductivity of 0.5% Na₂S-doped BST sample increases from 598 S/cm of the pure sample to 749 S/cm at 300 K, and the lattice thermal conductivity of the sample decreases to 0.55 W/(m·K) at 300 K. The peak zT of 0.5% Na₂S-doped BST sample reaches 1.3 at 300 K due to the increase of power factor and the decrease of thermal conductivity, which is 49.4% higher than that of the undoped sample. The thermoelectric conversion efficiency of the single-arm device reaches 3% as ΔT=275 K due to its excellent thermoelectric figure of merit. In addition, the average hardness of the doped samples also increases to 1.09 GPa.

In this work, p-type BST thermoelectric materials were prepared by a solid-state method and a spark plasma sintering technology. Utilizing Na₂S as a dopant achieved a low-valent substitution at cation sites, and introduced holes, thus enhancing the carrier concentration and optimizing the electrical conductivity of BST matrix thermoelectric materials. The peak zT of 0.5% Na₂S-doped BST sample reached 1.3 at 300 K, which was 49.4% higher than that of the undoped sample. Furthermore, a large number of point defects enhanced phonon scattering and reduced the thermal conductivity of the material. In addition, element S could also enhance the solid solubility of Na in the BST matrix and the solid solution strengthening. The average hardness of the doped samples increased to 1.09 GPa.

Cement industry continues to face significant environmental challenges due to its substantial CO₂ emissions, primarily stemming from carbonate decomposition in raw materials and fossil fuel combustion during production. Carbonatable binders and carbonation curing technologies have a promising potential for CO₂ reduction in cement production, and the existing methods involve the calcination of calcareous and siliceous raw materials to produce low-lime silicates for their emission reduction limits. Natural wollastonite, primarily composed of calcium silicate (CS), has an attractive alternative due to its abundant reserves and ease of extraction. Utilizing natural wollastonite as a carbonatable binder can eliminate both fossil fuel combustion and the need for calcareous raw materials, thereby avoiding the carbonate decomposition entirely. However, its application is currently limited due to its low carbonation reactivity. This study was to investigate the enhancement of carbonation reactivity of natural wollastonite via optimizing calcination activation to develop a high-performance carbonatable binder.

Natural wollastonite was calcinated under various calcination activation condictions (i.e., temperature, time, and cooling regimes). The activated wollastonite powder was mixed with water and compressed at 4 MPa to form the samples with different two dimensions (i.e., 20 mm × 20 mm × 20 mm and 20 mm × 80 mm × 20 mm). These samples underwent carbonation curing for 24 h before characterization. The mechanical properties were evaluated through compressive and flexural strength tests. The phase composition was characterized by X-ray diffraction (XRD) on both the wollastonite powder and carbonated samples before and after calcination activation. The structure of the samples was determined by Fourier-transform infrared spectroscopy (FT-IR) to analyze both the calcination activation effects and the resulting carbonation products. The microstructural evolution was determined by scanning electron microscopy (SEM). CO₂ uptakes were analyzed by thermogravimetric analysis (TGA).

This study reveals that calcination activation significantly enhances the carbonation hardening performance of natural wollastonite via increasing carbonation reactivity. Optimal conditions are identified at a calcination temperature of 1200 ℃, effectively transforming Para-CS and β-CS into metastable α-CS. The effective calcination time for the complete transformation is 60 min, while preserving the material valuable fibrous structure. Water quenching is found to be the most effective cooling method, retaining higher concentrations of crystal defects in the metastable α-CS. The transformation from a chain structure to a ternary ring structure at 1200 ℃ results in an increased structural distortion, thus leading to an enhanced carbonation reactivity of α-CS. The carbonation analysis reveals the extensive formation of carbonation products, primarily calcium carbonate and highly polymerized silica gel, resulting in a dense microstructure. Note that the preservation of the fibrous structure through calcination activation allows unreacted wollastonite to serve as a fibrous reinforcement within the carbonation hardening system, contributing to enhanced mechanical properties.

The results showed that calcination temperature exhibited a dominant effect, followed by calcination time and cooling regime. The optimal calcination temperature of 1200 ℃ led to the improvements in compressive strength, flexural strength, and CO₂ uptakes of the carbonated samples. The calcination time was critical in ensuring a complete phase transformation, while maintaining structural integrity, and a rapid cooling could preserve crystal defects that enhanced carbonation reactivity. The resulting carbonatable binder developed a carbonation hardening system comprising calcium carbonate, highly polymerized silica gel, and unreacted wollastonite fibers that could serve as an effective reinforcement within the carbonation hardening system. These findings could provide a promising pathway for the large-scale utilization of natural wollastonite in sustainable construction materials, having a potential for reducing the environmental impact of cement industry.

Composite solid electrolytes (CSE), which consist of a polymer matrix combined with inorganic fillers, leverage the advantages of both solid polymer electrolytes (SPE) and inorganic solid electrolytes, offering promising prospects for practical applications. However, the development and implementation of CSE are still in their early stages, revealing a significant gap between their existing performance and application requirements, necessitating further enhancements. To address this, CSE with specific morphologies and microstructures must be designed to improve the connectivity of ion migration channels, facilitating efficient ion transport. An effective interfacial conductive network can be established via carefully controlling the ratio, size, dispersion, and other characteristics of the inorganic fillers, significantly enhancing ionic conductivity. The strategic application of simulation and characterization techniques to elucidate the ion transport mechanisms within CSE is crucial for advancing the performance of these materials. Lastly, to lower the costs associated with ASSB, the fabrication process of CSE should be streamlined to be simple, time-efficient, and material-saving, while also being compatible with the existing battery production lines to enhance the practicality.

Although flexible thermoelectric technology has made remarkable progress in waste heat power generation, wearable devices and smart textiles, having a great application potential, there are still a series of problems in practical application. Therefore, a more systematic and comprehensive study is needed. The output of flexible substrate thermoelectric devices depends on the heat harvesting area and temperature gradient, and can produce power densities ranging from a few microwatts per square centimeter to a few milliwatts per square centimeter. However, the interface thermal resistance of low-dimensional flexible devices will lead to a low conversion efficiency, and its preparation technology is still limited to a large-scale application. Major challenges for fiber thermoelectric devices include building larger temperature gradients in the direction of heat flow, designing scalable architectures, improving mechanical stability, and enhancing comfort. In addition, the development of advanced preparation technologies such as magnetron sputtering and pulsed laser deposition will also achieve a large-scale production. Also, the combination of boost and energy storage technologies, such as efficient DC-DC converters and new energy storage systems, will effectively solve the problem of low output voltage of thermoelectric devices, so that they can directly drive low-power sensors or communication modules. Finally, with the further development of interface stability and flexible design of flexible substrate thermoelectric devices, flexible thermoelectric devices will be more widely used in wearable technology, smart textiles and some related fields.

A photocatalytic material of Ag₁₀Si₄O₁₃ is widely concerned due to its band structure suitable for visible light response and built-in electric field promoting photogenerated carrier separation. However, in the photocatalysis process, Ag₊ in Ag₁₀Si₄O₁₃ is easily reduced by photoelectrons and accumulates Ag elements, affecting the cycle stability of the photocatalytic system. Graphene oxide can effectively transfer photogenerated electrons, and amorphous SiO₂ can inhibit ion diffusion leaching, which are expected to slow down the photoreduction of Ag₁₀Si₄O₁₃. In this paper, x% SiO₂/Ag₁₀Si₄O₁₃/GO (SAG) composites with different amounts of amorphous SiO₂ were prepared via adding graphene oxide (GO) and silica sol in the process of Ag₁₀Si₄O₁₃ preparation by a sol-gel method. The effect of amorphous SiO₂ addition on the crystal structure, morphology and photoelectrochemical properties was investigated. Methylene blue (MB) was used as a target. The results show that a small amount of amorphous SiO₂ can greatly improve the photoreduction resistance of Ag₁₀Si₄O₁₃ photocatalysts, and broaden the photoresponse range and increase the adsorption capacity of the material for MB. However, the addition of amorphous SiO₂ can simultaneously reduce the migration rate of photogenerated carriers and accelerate the recombination of photogenerated electron-hole pairs. Therefore, the photocatalytic degradation efficiency of the composite system firstly increases and then decreases with the increase of SiO₂ addition. The degradation rate of SiO₂/Ag₁₀Si₄O₁₃/GO (SAG-1) samples can reach 99% under visible light for 40 min, showing a good cyclic stability. After 5 cycles, the crystal structure of the materials becomes stable and the degradation rate can still reach 97%.

In pre-hydrolysis of ethyl orthosilicate: 0.47 g of citric acid was added to 26 mL of anhydrous ethanol under magnetic stirring until complete dissolution, and then 5 mL of ethyl orthosilicate and 1.65 mL of distilled water were added in dropwise to the solution and the solution was stirred for 1 h and sealed for 1 week aging to obtain the silica sol. In preparation of Ag₁₀Si₄O₁₃/GO, 2.1 mL of silica sol and GO sol containing 1%(in mass) Ag₁₀Si₄O₁₃ were added to 10 mL of distilled water under ultrasound and magnetic stirring. 1.6 mL of 0.38 g/mL AgNO₃ solution was added in dropwise to the mixed solution above under stirring for 1 h and aging for 24 h to obtain the precursor sol. The precursor sol was dried, ground and heat-treated at 400 ℃ for 5 h to obtain a brick-red Ag₁₀Si₄O₁₃/GO powder=(i.e., AG). In preparation of SiO₂/Ag₁₀Si₄O₁₃/GO, x%(in mass) Ag₁₀Si₄O₁₃ (x=1, 2, 3, 4) of silica sol was added, stirred continuously for 1 h and aged for 24 h to obtain x% SiO₂/Ag₁₀Si₄O₁₃/GO precursor sol. The subsequent steps were the same as for AG to obtain x% SiO₂/Ag₁₀Si₄O₁₃/GO powders (i.e., SAG-1, SAG-2, SAG-3, and SAG-4), respectively.

The crystal structure of the materials was characterized by a model D8/axs X-ray diffractometer (XRD, Bruker Co., Germany). The microscopic morphology of the materials was observed by a model JSM-6701F transmission electron microscope (TEM, Electro-Optics Co., Japan). The chemical state was analyzed by a model PHI5702 X-ray photoelectron spectrometer (XPS, Physical Electronics Inc., USA). The photoresponsive properties were determined by a model U-3900H diffuse reflectance spectrometer (UV-Vis, Hitachi High-Technologies Co., Japan). The fluorescence emission spectra of the materials were determined by a model F97 fluorescence spectrophotometer (FSP, Shanghai Prismatic Technology Co., Ltd., China). The impedance, transient photocurrent, and Mott-Schottky curves were determined by a model CHI660D electrochemical workstation (Shanghai Tatsuwa Instrumentation Co., Ltd., China).

The sample of 0.1 g was weighed and stirred in 100 mL of 20 mg/L MB solution, which was protected from light. For every 10 min, 3 mL of the sample was removed and the supernatant was centrifuged to determine the concentration of MB by a UV spectrophotometer. The adsorption performance was evaluated by a ratio of the concentration of the solution after adsorption, c_t, to the initial concentration of MB, c₀, at time t (c_t/c₀). After dark adsorption equilibrium, a 300 W xenon lamp was used as a light source, a filter (λ>420 nm) was added to simulate visible light, the distance from the light source to the liquid surface was fixed at 15 cm, the sample of 3 mL was taken for every 5 min, and the supernatant was centrifuged to determine the concentration of MB by a UV spectrophotometer. The photocatalytic performance was evaluated by a ratio of the concentration of the degraded solution to the initial concentration of MB, c₀, at the time of t′ (c_t/c₀).

Five cycling experiments were performed on AG and SAG-1 to evaluate the stability of the photocatalytic properties of the materials. The stability of the crystal structure of the materials was evaluated based on the XRD patterns after each cycle.

The XRD patterns show that the introduction of SiO₂ has no effect on the crystal structure of Ag₁₀Si₄O₁₃. The TEM images of SAG-1 indicate the presence of graphene oxide, Ag₁₀Si₄O₁₃ and SiO₂. The UV-Vis diffuse reflectance spectra show that the edge of the absorption band of SAG-1 extended to 660 nm, which can be caused by the defects formed during the preparation of the material, but the forbidden bandwidth changes slightly, indicating that the protective layer of SiO₂ does not cause any significant changes in the band gap. The PL spectra show that the fluorescence intensity of the material increases gradually with the increase in the content of amorphous SiO₂, showing that the photogenerated carrier complexation rate increases with the increase of SiO₂ incorporation. The photocatalytic performance of Ag₁₀Si₄O₁₃ decreases significantly from 99% to about 90% after 5 cycles, while the photocatalytic performance of SAG-1 does not change after 5 cycles and still reaches 97%. The results show that the introduction of a small amount of SiO₂ can slow down the reduction production of Ag⁺ during the photocatalytic degradation of Ag₁₀Si₄O₁₃, and the crystal structure remains stable after some cycles, which greatly improves the stability of the material structure.

SiO₂/Ag₁₀Si₄O₁₃/GO ternary composites with different SiO₂ composite amounts were synthesized by a sol-gel method with GO and excess silica sol in an one-pot method. The complexing agent citric acid was used as a "bridge" to allow Ag₁₀Si₄O₁₃ nanoparticles to grow uniformly on GO, and the excess silica sol was attached to the precursor surface, forming an amorphous SiO₂ protective layer after heat treatment. The introduction of the amorphous SiO₂ protective layer did not affect the crystal structure of Ag₁₀Si₄O₁₃, which could extend the visible-light response range of the composite photocatalyst and significantly improve the adsorption performance for cationic dyes. However, SiO₂ could reduce the migration rate of photogenerated carriers and accelerate the assembly of photogenerated electron-hole pairs, affecting the photocatalytic performance of the material. An appropriate amount of amorphous SiO₂ protective layer could improve the photoreduction resistance and cycling stability of Ag₁₀Si₄O₁₃ photocatalysts, while maintaining the original photocatalytic activity. The degradation rate of the SAG-1 sample was still 97% after 5 cycles, and the crystal structure remained stable after 5 cycles (I₍₁₃₂₎/I₍₁₁₁₎ =1.16). This work could provide an reference for solving the problem that the materials of Ag-based efficient photocatalysts could be susceptible to photocorrosion during the photocatalytic process.

With the rapid development of portable and wearable microelectronics, flexible thermoelectric materials have attracted much attention due to their ability to enable self-powered devices via utilizing the temperature difference between the skin and the environment. However, the scarcity of tellurium resources and its high toxicity pose some challenges to the commercial application of tellurium-based thermoelectric materials. It is thus critical to develop high-performance, low-cost, and non-toxic alternatives for flexible thermoelectric films. Copper(I) selenide (i.e., Cu₂Se), as a representative liquid-like thermoelectric material, has attracted recent attention. Cu₂Se is an intrinsic p-type semiconductor composed of abundant, low-cost, and non-toxic elements, thus offering significant advantages in the field of sustainable energy. The existing studies report the fabrication of high-performance Cu₂Se thin films using conventional preparation techniques. However, these processes face significant limitations in pattern refinement and miniaturization, hindering their application in the fabrication of micro-thermoelectric devices. Inkjet printing technology, as a low-cost, efficient, and high-precision digital printing process, offers a promising solution to these challenges. This technique enables the preparation of complex patterns without masks or templates and is suitable for a variety of substrate materials. Therefore, this study was to prepare Cu₂Se nanopowders and explore their dispersion properties in different solvents to develop Cu₂Se inks suitable for inkjet printing technology, thereby offering insights into the preparation of flexible thermoelectric films and their application in next-generation wearable devices.

Cu₂Se nanoparticles were synthesized by the following methods. In method 1 (i.e., hydrothermal method), 5 mmol copper chloride, 2.5 mmol selenium powder, 0.05 mol sodium hydroxide were mixed with 50 mL deionized water, and continuously stirred at room temperature for 20 min, and then a certain amount of hydrazine hydrate solution was added, and the mixture was transferred to 100 mL PPL-stainless steel autoclave. Subsequently, the sealed autoclave reactor was heated at 180 ℃ for 20 h and then naturally cooled to room temperature. The precipitate at the bottom of the reactor was centrifuged at 10 000 r/min and washed with ethanol and distilled water for several times to obtain Cu₂Se powder. In method 2 (i.e., hydrothermal method), 1 mmol of selenium dioxide and 2 mmol of copper acetate were mixed with 65 mL of deionized water, and then stirred at room temperature until there was no sediment. Afterwards, hydrazine hydrate was slowly added and stirred for 10 min. The mixture was transferred to 100 mL PPL-stainless steel autoclave, and then the sealed autoclave reactor was heated at 180 ℃ for 24 h. After cooling to room temperature, the resulting sediment was collected and centrifugally cleaned. The content of hydrazine hydrate was changed by the control variable method in the synthesis process to investigate its effect on the morphology. In method 3 (i.e., wet synthesis), 1.54 g polyvinylpyrrolidone (PVP) was dispersed in 77 mL deionized water, followed by 1.92 mmol selenium dioxide (9.6 mL) and 11.52 mmol ascorbic acid (28.8 mL) solutions and stirred for 15 min. Afterwards, 3.84 mmol cupric sulfate pentahydrate (9.6 mL) and 15.36 mmol -ascorbic acid (38.4 mL) solution were added successively. The solution was magnetically stirred at room temperature for 16 h. After washing with deionized water for several times, Cu₂Se core-shell nanoparticles were collected by centrifugation at 11 000 r/min.

For Cu₂Se ink configuration, the prepared Cu₂Se powder was dispersed in deionized water and ethanol by an ultrasonic dispersion method. After ultrasonic treatment for 1 h, the dispersion effect was analyzed.

Cu₂Se nanoparticles are prepared by the three methods, and the crystal structure of the synthesized products is verified by the XRD patterns. The morphology and size of Cu₂Se particles prepared by different methods are different. In method 1, Cu₂Se powder prepared under alkaline conditions has a flake structure with a particle size of more than 10 μm, which does not meet the size requirements of inkjet printing. In method 2, under the influence of different contents of hydrazine hydrate, the synthesized powders show a large irregular flake structure (~500 nm) and small granular structure, and the particle size does not decrease significantly. The particle size of the powder is reduced when PVP is introduced into the subsequent synthesis process, indicating that the particles do not continue to grow into sheets during the synthesis process due to the coating of PVP, but remain small and irregular nanoparticles, and the particles are still agglomerated, which can cause a nozzle clogging in the subsequent printing process. In method 3, Cu₂Se particles synthesized by the wet method are spherical with a particle size of approximately 40 nm, and uniform in sizes without particle agglomeration, which can meet the requirements of material size for inkjet printing.

Cu₂Se particles synthesized by the wet method and dispersed under ultrasound in ethanol show a well-dispersion, and the particles in ink do not settle significantly after placing for a period of time, showing a good stability and suitable for inkjet printing.

Cu₂Se particles were prepared by the three methods for Cu₂Se ink suitable for inkjet printing, respectively, and nano-sized particles of Cu₂Se with uniform particle size and non-agglomeration were prepared by the wet method. The effective dispersion and stability of Cu₂Se particles were mainly attributed to the coating of PVP on the surface of the particles, improving the solubility of the particles in ethanol, effectively preventing the particle aggregation. This study could provide a foundation for the subsequent development of high-performance Cu₂Se thermoelectric thin films and their microdevices.