Key parameters for enhancing the thermoelectric power factor of PEDOT:PSS/PANI-CSA multilayer thin films

Among the conducting polymers, poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been extensively investigated for organic thermoelectric device applications owing to its high electrical conductivity (σ), flexibility and easy processability. The thermoelectric (TE) power factor – a factor that determines the efficiency of a thermoelectric material, is very critical in developing high-efficiency thermoelectric devices. The TE power factor of PEDOT:PSS requires further enhancement in realizing efficient organic TE devices. Recently, we have reported a layer-by-layer deposition technique to deposit PEDOT:PSS and poly aniline-camphor sulfonic acid (PANI-CSA) forming a PEDOT:PSS/PANI-CSA multilayer (ML) thin film structure with an enhanced thermoelectric power factor up to 49 μW m⁻¹ K⁻¹. However, there exist several ambiguities regarding the parameters that control the TE power factor in (ML) thin films. In order to identify the parameters that control the TE power factor of ML thin films, PEDOT:PSS/PANI-CSA ML thin films have been deposited by varying the deposition conditions such as spin speed, the number of layers, solvent treatment, and thickness of each layer. A thermoelectric power factor up to 325 μW m⁻¹ K⁻¹ is achieved by properly optimizing the spin speed, number of layers, and the thickness of each layer in ML thin films. The enhanced thermoelectric power factor is the result of multiple factors such as stretching of PEDOT chains, structural conformation change from benzoid to quinoid, and excess PSS removal from the top of the PEDOT:PSS layer through solvent treatment and at the PEDOT:PSS/PANI-CSA interface. Our study provides the basis for realizing an enhanced thermoelectric power factor of organic thermoelectric multilayer structures consisting of ultra-thin polymer thin films similar to inorganic superlattices having 2D confinement.

The key factors that control the thermoelectric (TE) properties of PEDOT:PSS/PANI-CSA multilayer thin films to enhance the TE power factor.     

The effect of post-deposition annealing conditions on structural and thermoelectric properties of sputtered copper oxide films

The development of thin-film thermoelectric applications in sensing and energy harvesting can benefit largely from suitable deposition methods for earth-abundant materials. In this study, p-type copper oxide thin films have been prepared on soda lime silicate glass by direct current (DC) magnetron sputtering at room temperature from a pure copper metallic target in an argon atmosphere, followed by subsequent annealing steps at 300 °C under various atmospheres, namely air (CuO:air), nitrogen (CuO:N) and oxygen (CuO:O). The resultant films have been studied to understand the influence of various annealing atmospheres on the structural, spectroscopic and thermoelectric properties. X-ray diffraction (XRD) patterns of the films showed reflexes that could be assigned to those of crystalline CuO with a thin mixed Cu^(I)Cu^(II) oxide, which was also observed by near edge X-ray absorption fine structure spectroscopy (NEXAFS). The positive Seebeck coefficient (S) reached values of up to 204 μV K⁻¹, confirming the p-type behavior of the films. Annealing under oxygen provided a significant improvement in the electrical conductivity up to 50 S m⁻¹, resulting in a power factor of 2 μW m⁻¹ K⁻². The results reveal the interplay between the intrinsic composition and the thermoelectric performance of mixed copper oxide thin films, which can be finely adjusted by simply varying the annealing atmosphere.

This study reveals the interplay between the composition and thermoelectric performance of mixed copper oxide thin films, which can be finely adjusted by varying the annealing atmosphere.     

Fabrication of chemically stable hydrogen- and niobium-codoped ZnO transparent conductive films

H- and Nb-doped ZnO (HNZO) thin films were fabricated on glass substrates with radio frequency magnetron sputtering. The effect of the flow rate of H₂ has been investigated by analyzing the structural, optical, and electrical properties. The incorporation of H during the deposition of Nb-incorporated ZnO films significantly improved their crystallinity, conductivity, and transmittance. The crystallites of the HNZO films were preferentially oriented in the c-axis direction; the films possess high transmittance (approximately 85%) in the visible and near-infrared regions (400 to 1400 nm). The lowest room-temperature resistivity of the HNZO films was measured as 1.28 × 10⁻³ Ω cm. Such optical and electrical properties along with the remarkable chemical stability of the HNZO films make them a promising candidate for applications in solar cells.

H- and Nb-doped ZnO (HNZO) thin films were fabricated on glass substrates with radio frequency magnetron sputtering.     

Rapid synthesis of thermoelectric SnSe thin films by MPCVD

Microwave plasma chemical vapor deposition (MPCVD) has been traditionally used to synthesize carbon-based materials such as diamonds, carbon nanotubes and graphene. Here we report that a rapid and catalyst-free growth of SnSe thin films can be achieved by using single-mode MPCVD with appropriate source materials. The analysis combining microscope images, X-ray diffraction patterns and lattice vibration modes shows that the grown thin films were composed of orthorhombic structured SnSe polycrystals. Further thermoelectric (TE) characterization of the SnSe films reveals the high-performance power factor of 3.98 μW cm⁻¹ K⁻² at 600 K. Our results may open an avenue for rapid synthesis of new types of materials such as IV–VI compounds and be useful for TE application of these materials.

Here we report that a rapid and catalyst-free growth of high quality SnSe thin films can be achieved by using single-mode MPCVD with appropriate source materials, the SnSe films exhibit high TE performance.     

Approaching subthreshold-swing limit for thin-film transistors by using a giant-dielectric-constant gate dielectric

Low-temperature giant-dielectric-constant thin films (In_0.0025Nb_0.0025Ti_0.995O₂) fabricated with simple radio frequency (RF) sputtering on glass substrates are employed as the gate dielectrics for thin-film transistors (TFTs) for the first time. The 380 nm-thick In_0.0025Nb_0.0025Ti_0.995O₂ film exhibited a quasi-static capacitance of as high as 36 156 nF cm⁻² with a quasi-static permittivity of 15 525 (and 7607 nF cm⁻² at 1 kHz). Indium zinc oxide (IZO) TFTs with In_0.0025Nb_0.0025Ti_0.995O₂ gate dielectrics exhibited high output current at low operation voltage and little hysteresis in the transfer curves between forward and reverse sweeps. The subthreshold swing (SS) of the IZO TFTs is 0.068 V dec⁻¹, very close to the lowest limit of the SS of the field-effect transistors (0.06 V dec⁻¹). The results also proves that the lowest limit of the SS (0.06 V dec⁻¹) cannot be broken no matter how high the gate dielectric capacitance is (except for negative capacitors). The TFTs demonstrate the potential for the applications in low-power circuits or flat-panel displays.

Low-temperature giant-dielectric-constant thin films (In_0.0025Nb_0.0025Ti_0.995O₂) fabricated with RF sputtering are employed as the dielectrics for IZO-TFTs.     

Theoretical investigations of thermoelectric phenomena in binary semiconducting skutterudites

In this study, we explored the thermoelectric properties of the host thermoelectric materials (TM), namely, binary skutterudites, using a combination of simulations based on density functional theory and post-DFT Boltzmann''s semiclassical theory. The calculations were performed close to the Fermi surface for the Seebeck coefficient and other thermoelectric parameters. Our results demonstrated that CoSb₃ exhibited the highest Seebeck value at room temperature among all the compounds (CoP₃, CoAs₃, CoSb₃, IrP₃, IrAs₃, IrSb₃, RhAs₃, and RhSb₃), which confirmed that this compound is an ideal host material for thermoelectric applications. Furthermore, the calculated electrical conductivity values show that RhAs₃ has the largest value of 3.736 × 10⁵ Ω⁻¹ m⁻¹. However, at high temperatures, the Seebeck values for all of these compounds are almost constant due to the activation of the minority charge carriers.

In this study, we explored the thermoelectric properties of the host thermoelectric materials (TM), namely, binary skutterudites, using a combination of simulations based on density functional theory and post-DFT Boltzmann''s semiclassical theory.     

Optimization of the thermoelectric performance of layer-by-layer structured copper-phthalocyanine (CuPc) thin films doped with hexacyano-trimethylene-cyclopropane (CN6-CP)

Copper-phthalocyanine (CuPc), as a classical small molecular organic semiconductor, has been applied in many fields. However, the low intrinsic conductivity limits its application in thermoelectricity. Here, hexacyano-trimethylene-cyclopropane (CN6-CP), a strong electron acceptor, is synthesized as dopant for CuPc thin films to improve their conductivities. Multilayer thin films constructed from alternate thermally evaporated CuPc and CN6-CP thin layers are investigated. Under the optimized condition, the doped CuPc film with a conductivity of 0.76 S cm⁻¹ and a Seebeck coefficient of 130 μV K⁻¹, shows a high power factor of 1.3 μW m⁻¹ K⁻² and the carrier concentration is estimated to be 2.8 × 10²⁰ cm⁻³. Considering the relatively superior performance, the CN6-CP doped CuPc film is a promising small molecular organic thermoelectric (OTE) material. In addition, for those highly crystalline materials with poor solubility, the layer-by-layer structure offers a general strategy for investigation and optimization of their TE performance.

The alternately deposited multilayer structure of a small molecular semiconductor and dopant molecules offers a general strategy for investigating their TE performance.     

Effect of oxygen vacancy concentration on indium tungsten oxide UV-A photodetector

An indium tungsten oxide (IWO) ultraviolet (UV) photodetector was fabricated with radio frequency magnetron sputtering. IWO thin films were deposited on devices under various oxygen partial pressure ambiences. With higher oxygen flow ratio, the oxygen vacancies were filled up, reducing the carrier concentration. Lowering the number of defects, such as oxygen vacancies, was effective for optimizing device performance. The on–off current ratio of an IWO UV-A photodetector at 10% oxygen partial pressure could reach 4.56 × 10⁴, with a photoresponsivity of 1.9 × 10⁻² A W⁻¹, as well as a rejection ratio of 2.68 × 10⁴ at a voltage bias of 10 V.

An indium tungsten oxide (IWO) ultraviolet (UV) photodetector was fabricated with radio frequency magnetron sputtering.     

Enhanced thermoelectric performance of CNT/P3HT composites with low CNT content

Carbon nanotubes (CNTs) have emerged as one of the leading additives for improving the thermoelectric properties of organic materials due to their unique structure and excellent electronic transport properties. However, since as-grown CNTs generally possess different diameters, it is of high interest to determine the influence of the diameter of carbon nanotubes on the thermoelectric properties of CNT/poly(3-hexylthiophene) (P3HT) composite films. Herein, we prepared CNT/P3HT composite films with diameters of <8 nm, 8–15 nm, 20–30 nm, 30–50 nm and >50 nm and studied their thermoelectric properties. It was found that the diameter of CNTs had an important influence on the TE performance of the composite films. The P3HT-d_CNT (<8 nm) and P3HT-d_CNT (8–15 nm) composite films exhibited almost the same thermoelectric performance and almost more than double that of the other three composite films with increased CNT diameter. The different mass fractions of CNT/P3HT composite films have also been investigated. The maximum TE power factor of CNT (d < 8 nm)/P3HT composite films reached 49.0 μW mK⁻² at the mass fraction of 95 wt% P3HT, that is, 5 wt% CNTs. This superior TE power factor of CNT (d < 8 nm)/P3HT composite films can be ascribed to the fully connected interlayer of the P3HT polymer and also the heterogeneous dispersion of short-length CNTs.

The maximum TE power factor of CNT (d < 8 nm)/P3HT composite films reached 49.0 μW mK⁻² at the mass fraction of 5 wt% CNTs.     

Study on the growth of Al-doped ZnO thin films with (112̄0) and (0002) preferential orientations and their thermoelectric characteristics

In this work, using a conventional magnetron sputtering system, Al-doped ZnO (AZO) films with (11$\bar{2}$0) and (0002) preferential orientations were grown on r-sapphire and a-sapphire substrates, respectively. The effect of substrate and deposition temperature on the growth of AZO films and their preferential orientations were investigated. The crystallographic characteristics of AZO films were characterized by X-ray diffraction (XRD). The surface morphology of AZO films was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It is found that the lattice mismatch between AZO and substrate determines the growth of AZO films and their preferential orientations. The thermoelectric properties are strongly dependent on the crystal grain shape and the grain boundaries induced by the preferred orientation. The highly connected and elongated grains lead to high thermoelectric properties. The in-plane anisotropy performances of thermoelectric characteristics were found in the (11$\bar{2}$0) preferential oriented ZnO films. The in-plane power factor of the (11$\bar{2}$0) preferential oriented ZnO films in the [0001] direction was more than 1.5 × 10⁻³ W m⁻¹ K⁻² at 573 K, which is larger than that of the (0002) preferential oriented ZnO films.

In this work, using a conventional magnetron sputtering system, Al-doped ZnO (AZO) films with (11$\bar{2}$0) and (0002) preferential orientations were grown on r-sapphire and a-sapphire substrates, respectively.     

The deposition and wet etching of Mg-doped ZnO films and their applications for solidly mounted resonators

In this report, a solidly mounted resonator (SMR), consisting of an Au electrode, Mg-doped ZnO (Mg_XZn_1−XO) piezoelectric film and Bragg acoustic reflector, was fabricated on a Si substrate by radio frequency (RF) magnetron sputtering. As a key processing step for the SMR, Mg_XZn_1−XO films with high c-axis orientation were fabricated and the crystalline structure, surface morphology and roughness of the films were investigated. The surface morphology, optical transmittance and shape control of Mg_XZn_1−XO films were investigated by the chemical wet-etching method with various etchants. The profiles and line patterns of Mg_XZn_1−XO films etched with FeCl₃·6H₂O solutions are satisfactory and fully meet the industrial requirements. The Bragg acoustic reflector, made entirely of metal, has small internal stress and good heat conduction. An SMR based on a Mg_XZn_1−XO piezoelectric film shows a resonant frequency of 2.402 GHz, and the k_eff², Q_S and Q_P of the SMR are 3.07%, 415 and 546, respectively.

In this report, a solidly mounted resonator (SMR), consisting of an Au electrode, Mg-doped ZnO (Mg_XZn_1−XO) piezoelectric film and Bragg acoustic reflector, was fabricated on a Si substrate by radio frequency (RF) magnetron sputtering.     

Simultaneous improvement in electrical conductivity and Seebeck coefficient of PEDOT:PSS by N2 pressure-induced nitric acid treatment

As a thermoelectric (TE) material suited to applications for recycling waste-heat into electricity through the Seebeck effect, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) is of great interest. Our research demonstrates a comprehensive study of different post-treatment methods with nitric acid (HNO₃) to enhance the thermoelectric properties of PEDOT:PSS. The optimum conditions are obtained when PEDOT:PSS is treated with HNO₃ for 10 min at room temperature followed by passing nitrogen gas (N₂) with a pressure of 0.2 MPa. Upon this treatment, PEDOT:PSS changes from semiconductor-like behaviour to metal-like behaviour, with a simultaneous enhancement in the electrical conductivity and Seebeck coefficient at elevated temperature, resulting in an increase in the thermoelectric power factor from 0.0818 to 94.3 μW m⁻¹ K⁻² at 150 °C. The improvement in the TE properties is ascribed to the combined effects of phase segregation and conformational change of the PEDOT due to the weakened coulombic attraction between PEDOT and PSS chains by nitric acid as well as the pressure of the N₂ gas as a mechanical means.

As a thermoelectric (TE) material suited to applications for recycling waste-heat into electricity through the Seebeck effect, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) is of great interest.     

High performance polypyrrole/SWCNTs composite film as a promising organic thermoelectric material

Conducting polymer thermoelectric (TE) materials have received great attention due to their unique properties. In this work, polypyrrole (PPy)/single-walled carbon nanotubes (SWCNTs) composite films with improved TE performance have been prepared by chemical interfacial polymerization at the cyclohexane/water interface under a controlled temperature. Attributed to the smooth surface, higher conjugation length and more ordered molecular structure of the interfacial polymerized PPy film, the electrical conductivity can be as high as ∼500 S cm⁻¹. To further enhance the TE properties of PPy, SWCNT was added to construct a PPy/SWCNTs composite. Due to the synergistic effect between the two phases and the energy filtering effect at the interfaces between PPy and SWCNTs, the Seebeck coefficient of the composite enhanced significantly with the increase SWCNTs content. The composite shows an optimal power factor of 37.6 ± 2.3 μW mK⁻² when the content of SWCNTs is 0.8 mg. This value is one of the largest values among the reported PPy based composites fabricated by the chemical polymerization method. The results indicate that interfacial polymerization under a controlled temperature is a promising way to improve the TE performance of conducting polymer based composite materials.

PPy/SWCNTs composite films with high thermoelectric performance were prepared by chemical interfacial polymerization under a controlled low temperature.     

3D nanorhombus nickel nitride as stable and cost-effective counter electrodes for dye-sensitized solar cells and supercapacitor applications

Transition metal nitride based materials have attracted significant interest owing to their excellent properties and multiple applications in the field of electrochemical energy conversion and storage devices. Herein we synthesize 3D nanorhombus nickel nitride (Ni₃N) thin films by adopting a reactive radio frequency magnetron sputtering process. The as-deposited 3D nano rhombus Ni₃N thin films were utilized as cost-effective electrodes in the fabrication of supercapacitors (SCs) and dye-sensitized solar cells (DSSCs). The structure, phase formation, surface morphology and elemental composition of the as-deposited Ni₃N thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). The electrochemical supercapacitive performance of the Ni₃N thin films was examined by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) techniques, in 3 M KOH supporting electrolyte. The areal capacitance of the Ni₃N thin film electrode obtained from CV analysis was 319.5 mF cm⁻² at a lower scan rate of 10 mV s⁻¹. Meanwhile, the Ni₃N thin film showed an excellent cyclic stability and retained 93.7% efficiency of its initial capacitance after 2000 cycles at 100 mV s⁻¹. Interestingly, the DSSCs fabricated with a Ni₃N CE showed a notable power energy conversion efficiency of 2.88% and remarkable stability. The prominent performance of the Ni₃N thin film was ascribed mainly due to good conductivity, high electrochemically active sites with excellent 3D nano rhombus structures and high electrocatalytic activity. Overall, these results demonstrate that the Ni₃N electrode is capable of being considered for efficient SCs and DSSCs. This investigation also offers an essential directive for the advancement of energy storage and conversion devices.

Self-supported 3D nano-rhombus (nano-diamond) shaped Ni₃N coated on FTO glass which serves as a CE in DSSCs and supercapacitors. .     

Pseudo in situ construction of high-performance thermoelectric composites with a dioxothiopyrone-based D–A polymer coating on SWCNTs

Organic polymer/inorganic particle composites with thermoelectric (TE) properties have witnessed rapid progress in recent years. Nevertheless, both development of novel polymers and optimization of compositing methods remain highly desirable. In this study, we first demonstrated a simulated in situ coagulation strategy for construction of high-performance thermoelectric materials by utilizing single-walled carbon nanotubes (SWCNTs) and a new D–A polymer TPO-TTP12 that was synthesized via incorporating dioxothiopyrone subunit into a polymeric chain. It was proven that the preparation methods have a significant influence on thermoelectric properties of the TPO-TTP12/SWCNT composites. The in situ prepared composite films tend to achieve much better thermoelectric performances than those prepared by simply mixing the corresponding polymer with SWCNTs. As a result, the in situ compositing obtains the highest Seebeck coefficient of 66.10 ± 0.05 μV K⁻¹ at the TPO-TTP12-to-SWCNT mass ratio of 1/2, and the best electrical conductivity of up to 500.5 ± 53.3 S cm⁻¹ at the polymer/SWCNT mass ratio of 1/20, respectively; moreover, the power factor for the in situ prepared composites reaches a maximum value of 141.94 ± 1.47 μW m⁻¹ K⁻², far higher than that of 104.68 ± 0.86 μW m⁻¹ K⁻² for the by-mixing produced composites. This indicates that the dioxothiopyrone moiety is a promising building block for constructing thermoelectric polymers, and the simulated in situ compositing strategy is a promising way to improve TE properties of composite materials.

High-performance thermoelectric composites with a dioxothiopyrone unit have been constructed utilizing SWCNTs and polymer TPO-TTP12via a simulated in situ compositing strategy based on the coagulation method.     

Enhancement of thermoelectric performance of PEDOT:PSS films by post-treatment with a superacid

Several methods such as the addition of a polar solvent, an acid as well as various post-treatments have been used to improve the thermoelectric performance of conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films. This paper reports a method using a superacid, trifluoromethanesulfonic acid, in methanol to treat PEDO:PSS films to improve their thermoelectric performance. Treatment of PEDOT:PSS films with this superacid in methanol leads to a significant increase in electrical conductivity from 0.7 to 2980 S cm⁻¹ together with a moderate increase in Seebeck coefficient from 17.6 to 21.9 μV K⁻¹, giving a power factor of 142 μW m⁻¹ K⁻², one of the highest values reported in the literature for conductive polymers. The figure of merit (ZT) value is estimated to be 0.19 under optimized conditions. The enhancement of thermoelectric performance, particularly the increase in both electrical conductivity and Seebeck coefficient, is due to the removal of the insulating component and polymer chain realignment giving in turn a denser packing of the conductive PEDOT polymer chains. This post-treatment method would offer an alternative way to improve the thermoelectric performance.

Treatment of PEDOT:PSS films with a superacid results in remarkable improvement of thermoelectric performance with a power factor of 142 μW m⁻¹ K⁻².     

Properties of PEDOT nanowire/Te nanowire nanocomposites and fabrication of a flexible thermoelectric generator

Light-weight, mechanically flexible, transparent thermoelectric devices are promising as portable, and easy-to-integrate energy sources. Poly(3,4-ethylenedioxythiophene) nanowires (PEDOT NWs) possessing high electrical conductivity were synthesized by a facile self-assembled micellar soft-template method. And then, Te nanowires (Te NWs) with high Seebeck coefficient were easily synthesized by the solution process and then added as an inorganic filler to form the PEDOT NW/Te NW nanocomposite films via a simple and convenient vacuum filtration method. The thermoelectric (TE) properties of the nanocomposites were characterized in this research. A maximum power factor of 58.03 μW m⁻¹ K⁻² is obtained from the film containing 90 wt% Te NWs at room temperature, which is dozens of times that of the pure PEDOT NW film. This work uses the as-prepared PEDOT NWs/Te NW (90 wt%) nanocomposite film to fabricate a flexible thermoelectric generator and an output voltage of 2.8 mV was generated at a temperature difference of 13.5 K between the environment and human body.

Light-weight, mechanically flexible, transparent thermoelectric devices are promising as portable, and easy-to-integrate energy sources.     

The effects of microstructure,Nb content and secondary Ruddlesden–Popper phase on thermoelectric properties in perovskite CaMn1−xNbxO3 (x = 0–0.10) thin films

CaMn_1−xNb_xO₃ (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn_1−x,Nb_x)O thin films were deposited on 1$\bar{1}$00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn_1−xNb_xO₃ films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn_1−xNb_x)O to orthorhombic during post-deposition annealing at 700 °C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO₃ showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden–Popper (R–P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn_1−xNb_xO₃. The electrical resistivity and Seebeck coefficient of the pure CaMnO₃ film were measured to 2.7 Ω cm and −270 μV K⁻¹ at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 Ω cm and −145 μV K⁻¹ for x = 0.05. Yielding a power factor of 21.5 μW K⁻² m⁻¹ near room temperature, nearly eight times higher than for pure CaMnO₃ (2.8 μW K⁻² m⁻¹). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R–P phase. The thermal conductivity of the CaMn_1−xNb_xO₃ films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m⁻¹ K⁻¹. The low thermal conductivity is attributed to grain boundary scattering and the secondary R–P phase.

Reduction of thermal conductivity of sputtered CaMn_1−xNb_xO₃ thin films by secondary Ruddlesden–Popper phase and grain size optimization.     

Flexible PANI/SWCNT thermoelectric films with ultrahigh electrical conductivity

The effects of polyaniline (PANI) with different polymerization times on the film-forming and thermoelectric properties as well as on the performance of SWCNTs/PANI composites were systematically investigated in this study. It was found that the film-forming and flexibility of PANI films improved with the increase in polymerization time. We showed that a super high conductivity of ∼4000 S cm⁻¹ can be achieved for the SWCNTs/PANI composite film, which is the highest value for the SWCNTs/PANI system at present. Both the electrical conductivity and power factor increase by an order of magnitude than that of pure PANI films and far exceed the theoretical value of the mixture model. These results suggest that the sufficiently continuous and ordered regions on the interlayer between the filler and matrix are key to improve the electrical conductivity of composites. Finally, the maximum PF reaches 100 μW m⁻¹ K⁻² at 410 K for the 0.6CNT/PANI5h. Furthermore, it is found that the composite films have excellent environmental and structural stability. Our results can deepen the understanding of organic–inorganic thermoelectric composite systems and facilitate the practical application of flexible and wearable thermoelectric materials.

Flexible PANI/SWCNT thermoelectric films with ultrahigh electrical conductivity of ~4000 S cm⁻¹. The maximum PF reaches 100 μW m⁻¹ K⁻² at 410 K for the 0.6CNT/PANI.     

Fabrication of Ag2O/WO3 p–n heterojunction composite thin films by magnetron sputtering for visible light photocatalysis

Semiconductor-based nanostructures which are photo-catalytically active upon solar light irradiation were extensively used for environmental remediation due to the potential decomposition of various kinds of pollutants. In this work, we report the preparation of a sustainable thin film composite, i.e. Ag₂O/WO₃ p–n heterojunction, and investigation of its photocatalytic activity. To achieve the composite structure, WO₃/Ag–WO₃ layers were deposited over a quartz substrate by magnetron sputtering at room temperature and subsequently annealed at 823 to 923 K. The thin film structure, morphology, and chemical states were thoroughly characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron spectroscopy, and X-ray photoelectron spectroscopy. The obtained results revealed that the amorphous Ag-doped WO₃ was crystallized into monoclinic WO₃ and Ag₂O, in which nanocrystalline Ag₂O was diffused towards the surface of WO₃. Optical transmittance spectra recorded by UV-vis-NIR spectroscopy revealed that the WO₃/Ag–WO₃ films became transparant in the visible region after annealing at high temperature (873 K and 923 K). The Ag₂O/WO₃ p–n heterojunction composite thin films showed high photocatalytic activity (0.915 × 10⁻³ min⁻¹) under visible light irradiation, which is attributed to the efficiency of effective photogenerated charge-carrier formation and the reduced recombination rate of photogenerated electron–hole pairs. Unlike the powder-based photocatalysts, the reported thin film-based heterojunction photocatalyst could be very sustainable, and cost-effective.

Semiconductor-based nanostructures which are photo-catalytically active upon solar light irradiation were extensively used for environmental remediation due to the potential decomposition of various kinds of pollutants.