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An alternative oxide anode material to surpass Ni electrode in the solid oxide fuel cell (SOFC) technology, used at high temperature range (500–1000 °C), is needed for the SOFC industry. We investigated an advanced perovskite oxide electrode, CaVxO3-δ system, for the alternative oxide anode material. The CaVxO3-δ powder and bulk were fabricated by using an atmosphere controlled solid-state reaction method and spark plasma sintering (SPS), respectively. The bulk specimen showed 3-3 type nonstoichiometric composite structure, and the electrical conductivity and Seebeck coefficient measurements revealed metallic n-type conductivity. Surprisingly, the high electrical conductivity (> 12,000 S/cm at room temperature; >1000 S/cm at 1000 K) was stable at different atmospheres between air and reduction atmospheres, attributing to a non-redoxable electron-cloud-channel phase protected by a redoxable protection phase. It is believed that the CaVxO3-δ system can be used as a promising and atmosphere stable oxide electrode in the fuel cell technology and other applications.

We report on the facile synthesis of alloyed CdS x Se1−x quantum dots (QDs) via a one-pot method using the simultaneous injection of Se and S source into a solution of the Cd precursor dissolved in a coordinating mixture of hexadecylamine and trioctylphosphine, during which the formation of CdS x Se1−x nanocrystals was controlled by growth time at a temperature of 260 °C. In particular, the emission peak and full width at half maximum of the photoluminescence (PL) of alloyed CdS x Se1−x QDs were tunable in the range of 588–604 nm and 36–38 nm, respectively, with a PL quantum yield of up to 55% by a reaction time of 60 min. Importantly, the structural advantage of alloyed CdS x Se1−x QDs-based light emitting devices have been fabricated and their electroluminescence properties characterized. A good performance device with a maximum luminance and luminous efficiency of 761 cd m−2 and 0.82 cd A−1, respectively, was obtained.

In the present work, composition dependent crystal structure, ferroelectric, piezoelectric, and temperature dependent dielectric properties of the BiGaO3-modified (1–x)(0.65Bi1.05FeO3–0.35BaTiO3) (BFBT35–xBG, where x = 0.00–0.03) lead-free ceramics were systematically investigated by solid-state reaction method, followed by water quenching process. The substitution of BG successfully diffuses into the lattice of the BFBT ceramics, without changing the pseudo-cubic structure of the samples. The scanning electron microscopy (SEM) results revealed that the average grain size was increased with BG-content in BFBT system. The BFBT–xBG ceramics showed a maximum in permittivity (ɛmax) at temperatures (Tmax) above 500 °C in the compositional range of 0.00 ≤ x ≤ 0.03. The electro-strain is measured to be 0.125% (d*33 ~ 250 pm/V) under unipolar fields (5 kV/mm) for BFBT–0.01BG ceramics. The same composition (x = 0.01), large static piezoelectric constant (d33 ~ 165 pC/N) and electromechanical coupling factor (kp ~ 25%) were obtained. The above investigated characterizations suggests that BFBT–BG material is favorable for piezoelectric and high temperature applications.

Bi-Te based materials have been used for near-room-temperature thermoelectric applications. However, their properties dramatically decrease at high temperatures (over 100 °C), limiting their use in power generation. In this study, we investigated the enhanced thermoelectric properties of Bi-Te based materials by Cu doping and employing the melt-spinning (MS) process that can be utilized especially at elevated temperatures. By changing the doping amount, we could modulate the temperature dependence of thermoelectric properties, where the maximum ZT temperature could be shifted from room temperature to 450 K. The highest ZT value, 1.34, was achieved at 400 K for 2% Cu-doped Bi0.5Sb1.5Te3, which is due to the enhancement in power factor and reduction in lattice thermal conductivity. The average ZT value between room temperature and 530 K was 1.17 for 2% Cu-doped Bi0.5Sb1.5Te3, which is 46% higher than that of pristine Bi0.5Sb1.5Te3. Consequently, the synergetic effect of MS process and Cu incorporation can be a promising method to widen the application of Bi-Te based thermoelectric materials for mid-temperature power generation.

We demonstrate subcycle electron pulse generation in a nanogap of graphene when irradiated by a femtosecond laser pulse in the near-infrared region (800 nm). A strong photoinduced emission was prod...

We demonstrate highly efficient multi-colored semitransparent perovskite solar cells that can create high angular tolerant controllable transmissive colors up to 60°, based on phase-compensated microcavities. The efficiency of the semitransparent colors was improved by impedance matching, which was enabled by placing a dielectric functional layer on top of traditional optical microcavities, with negligible influence on color pureness. The vast majority of the visible part of solar radiation is efficiently utilized for solar energy harvesting, achieving 10.47%, 10.66%, and 11.18% of efficiency for red, green, and blue (RGB) colored solar cells, respectively, while a very small proportion of the visible solar spectrum is used for structural coloration that can be readily tuned by altering the cavity medium thickness. The approach described herein can be suitable for a variety of applications such as display systems with ultra-low power consumption, highly efficient colorful solar panels, low-power wearable electronics, and energy-efficient optoelectronics.

Electrical characteristics of ion gels prepared by loading different amounts of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) in Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) are investigated and compared with those of ion liquid, [EMIM][TFSI] for possible application as a gate stack for flexible electronic devices. Capacitance and impedance as a function of frequency are measured, which can be well accounted for by a simple circuit model identifying the local device components. The operation of a flexible field effect transistor based on graphene and the ion gel as a top gate stack is also demonstrated.

Finding alternatives for Bi2Te3, the only thermoelectric material for near-room-temperature (RT) applications, is of great importance in thermoelectrics. Here, we report a very promising near-RT th...

This paper reports a novel synthesis of iron (Fe) powders in which high-purity and controlled primary and secondary assembled particles can be produced at low cost with safe process. Iron hydroxide powder precursors with fine-sized and acicular morphology were prepared and then reduced at an optimum temperature under reducing atmosphere by using single-step and two-step reduction. In the case of two-step reduction, the precursor powders were reduced by using a hydrogen/argon mixed gas for 1.5 h with a subsequent second reduction using higher hydrogen/argon mixed gas for 2 h. The morphology of the Fe powders strongly depends on the reduction conditions and precursor's morphology. The two-step reduced powders had pure iron powders with large elongated shape and porous sponge-like interlocking structure. The synthesized Fe powders were mixed with KClO4 and the pyrotechnic performance was examined. It is found that metal powder prepared by using two-step reduction is very suitable for producing porous sponge-like microstructure and for pyrotechnic applications.

We demonstrated imaging of the depletion layer in a MoS2/graphene heterojunction fabricated by chemical vapor deposition and obtained their transport parameters such as diffusion length, lifetime, and mobility by using scanning photocurrent microscopy (SPCM). The device exhibited a n-type operation, which was determined by the MoS2 layer with a lower mobility. The SPCM revealed the presence of the depletion layer at the heterojunction, whereas graphene provided an excellent electrical contact for the MoS2 layer without resulting in a rectifying behavior, even if they were anchored within a very short range. The polarity of the photocurrent signal switched when we applied a drain–source bias voltage, from which we extracted the potential barrier at the junction. More importantly, a bias-dependent SPCM allowed us to simultaneously record the diffusion lengths of both majority and minority carriers for the respective MoS2 and graphene layers. By combining the diffusion lengths with the lifetimes measured by ...

It has been a difficulty to form well-distributed nano- and mesosized inclusions in a Bi2Te3-based matrix and thereby realizing no degradation of carrier mobility at interfaces between matrix and inclusions for high thermoelectric performances. Herein, we successfully synthesize multistructured thermoelectric Bi0.4Sb1.6Te3 materials with Fe-rich nanoprecipitates and sub-micron FeTe2 inclusions by a conventional solid-state reaction followed by melt-spinning and spark plasma sintering that could be a facile preparation method for scale-up production. This study presents a bismuth antimony telluride based thermoelectric material with a multiscale structure whose lattice thermal conductivity is drastically reduced with minimal degradation on its carrier mobility. This is possible because a carefully chosen FeTe2 incorporated in the matrix allows its interfacial valence band with the matrix to be aligned, leading to a significantly improved p-type thermoelectric power factor. Consequently, an impressively hig...

•High capacitance on In0.53Ga0.47As epitaxial layers grown on Si substrates•Achievement of capacitance equivalent thickness lower than 1.5nm with low leakage current•Enhancement of electrical performances by a surface treatment using trimethylaluminum.

Strontium titanium oxide co-doped with yttrium and nickel (SrxY1-xTiyNi1-yO3-δ; hereafter, SYTN), was investigated as an alternative anode material for solid oxide fuel cells. To improve the ionic conductivity of the Sr0.92Y0.08TiO3-δ (SYT) anode, Ni2+ was substituted into the B-site (initially occupied by Ti4+), thereby forming oxygen vacancies. To analyze the effects of Ni-doping in the SYT anode, the electrochemical properties of the SYTN anode were compared with those of the Ni-infiltrated SYT(Ni@SYT) using H2 and CH4 as fuels. The electrochemical reactions at the SYTN anode in the presence of both H2 and CH4 were limited by relatively slow reactions, such as non-charged processes including oxygen surface exchange and solid surface diffusion. The high electrical conductivity and excellent catalytic activity of the Ni nanoparticles in the Ni@SYT anode led to improved cell performance. CH4 decomposition at the Ni@SYT anode occurred via thermal pyrolysis of CH4 rather than by steam methane reforming, resulting in carbon deposition. In comparison, the poor inherent catalytic activity for CH4 oxidation exhibited by the SYTN anode minimized carbon deposition on the anode surface.

Hf-free n-type half-Heusler with a nominal composition of Ti0.5Zr0.5NiSn0.98Sb0.02 has been reported to have a high ZT value of almost 1.2. However, the synthesis process requires a long annealing time to achieve single-phase structure, which contributes to high product costs due to energy and time consumption. Here we introduce a new route to prepare (Ti0.5Zr0.5)1−xNbxNiSn (x = 0, 0.0050, 0.0075, 0.0100, 0.0125, 0.0150, 0.0175 and 0.0200) compounds for high thermoelectric (TE) performance along with shortening time for sample preparation. The samples were prepared by a combination of arc-melting (AM) and melt-spinning (MS) followed by spark plasma sintering process (SPS). The combination of these synthetic methods produced (Ti0.5Zr0.5)1−xNbxNiSn samples with high chemical homogeneity, single-phase structure, and fine grain about 300 nm in size, which are preferred for both charge and phonon transport properties. As a result, a maximum power factor of 44.5 µW cm−1 K−2 at 817 K and a maximum ZT of 1.19 at 874 K were achieved for the sample with x = 0.015, which are comparable to the highest ZT value reported so far for the Hf-free n-type MNiSn (M = Ti, Zr) compounds. The calculated output power density Pd and efficiency η based on a single-leg device showed an excellent performance, which yields the maximum Pd of 16.2 W cm−2 and η of 12.08% at the cold side temperature TC ≈ 305 K and the hot side temperature TH ≈ 875 K for the optimized composition with x = 0.0125. Furthermore, it is noted that the synthetic process here does not require a long-annealing time and it can be easily applied to mass production.

SrTiO3 (STO) is one of the most promising oxide thermoelectric (TE) materials with high thermopower, but the low electrical conductivity and high thermal conductivity are still issues to be solved. Recently, grain boundary engineering using reduced graphene oxide (RGO) has been demonstrated to have capable of simultaneously improving both the electrical and thermal properties of STO. In this study, we investigated the combined effect of La/Nb doping and RGO coating in STO to improve further the electrical conductivity and the TE efficiency of STO materials. Two series of La- and Nb-doped Sr1-xLaxTi1-yNbyO3 (x, y = 0–0.02) samples incorporated with RGO were prepared by a combinatorial procedure of solid-state reaction, RGO coating, and the spark plasma sintering (SPS) process. The structural, morphological and temperature-dependent thermoelectric properties of the Sr1-xLaxTi1-yNbyO3/RGO were studied and as a result, the figure of merit was enhanced ∼6.5 times by the combined effect of donor doping and lowering the double Schottky barrier height due to RGO at grain boundaries.

An approach of composition modification in (Bi,Na,Ba,Sr)(Ti,Nb,Zr)O3 (BNSTNZ)–modified 0.65Bi1.05FeO3–0.35BaTiO3 (BF35BT) piezoelectric materials was investigated. Introducing BNSTNZ into BF35BT ceramics led from the normal-ferroelectric to relaxor-ferroelectric- phase. At the optimum composition, large dynamic piezoelectric coefficient (d33*) of 583 pm/V under the applied field of 5 kV/mm and relatively high static piezoelectric coefficient (d33) of 135 pC/N with high maximum temperature (Tm ≤ 400 °C) were obtained. The unipolar strain and d33* of BNSTNZ into BF35BT ceramics with x = 0.005 increased up to 0.251% and 718 pm/V at 90 °C. The remarkably enhanced field-induced strain response of BF35BT-based compositions is believed to be attributed to the optimum grain size, high tetragonality and the ferroelectric-relaxor phase coexistence. It is noted that this composition can be a favorable lead-free candidate for high-temperature piezoelectric applications.

We report an in situ characterization of transition-metal dichalcogenide (TMD) monolayers and twisted bilayers using a high-speed second-harmonic generation (SHG) imaging technique. High-frequency laser modulation and galvano scanning in the SHG imaging enabled a rapid identification of the crystallinity in the TMD, including the orientation and homogeneity with a speed of 1 frame/s. For a twisted bilayer MoS2, we studied the SHG peak intensity and angles as a function of the twist angle under a strong interlayer coupling. In addition, rapid SHG imaging can be used to visualize laser-induced ablation of monolayer and bilayer MoS2 in situ under illumination by a strong femtosecond laser. Importantly, we observed a characteristic threshold behavior, the ablation process occurred for a very short time duration once the preheating condition was reached. We investigated the laser thinning of the bilayer MoS2 with different twist angles. When the twist angle was 0°, the SHG decreased by approximately one-fourth of the initial intensity when one layer was removed. Conversely, when the twist angle was approximately 60° (the SHG intensity was suppressed), the SHG increased abruptly close to that of the nearby monolayer when one layer was removed. Precise layer-by-layer control was possible because of the unique threshold behavior of the laser-induced ablation.

This article reports structural evolution and electromechanical properties of lead-free (1-x)(0.965Bi0.5Na0.5TiO3-0.035BaTiO3)-xSrTiO3 (BNTBT-100xST with x = 0.00–0.30) ceramics synthesized by sol-gel and hydrothermal methods. The crystal structure investigation shows a compositionally-driven phase transition from the dominant rhombohedral (R) phase to the tetragonal (T) phase. However, the physical properties revealed that BNTBT converts from normal ferroelectric to relaxor ferroelectric due to the disruption of long-range ferroelectric order with ST modifications. Highest electric field-induced strain coefficient (d33* = 320 pm/V) for the optimum composition was attributed to the crystal structure morphotropic phase boundary of the R and T phases. A phenomenological explanation from the ferroelectric properties strongly supports the argument of the high piezoelectric strain response. A phase diagram was developed based on the crystal structure, dielectric, ferroelectric and piezoelectric properties that provide a systemic correlation and better elucidation of the BNTBT-100xST ceramic system.

We investigate the interaction of carbon nanotubes (CNTs) embedded in a polymer matrix [poly(methyl methacrylate) (PMMA)] with Ar plasma, which results in the formation of PMMA nanostructures, as CNTs act as an etching mask. Because of the large differences in the Ar ion sputtering yields between CNTs and PMMA, PMMA lines with the width comparable to that of CNTs and as high as 20 nm (for single-walled CNTs) or 80 nm (for multiwalled CNTs) can be obtained after repeated exposure of CNT/PMMA films to Ar plasma. We also follow the etching process by investigating changes in the IV characteristics and Raman spectra of CNTs after each exposure to Ar plasma, which shows progressive defect generations in CNTs while they maintain structural integrity long enough to act as the etching mask for PMMA underneath. We demonstrate that the PMMA nanostructure patterns can be transferred to a different polymer substrate using nanoimprinting.

In this work we improved the thermoelectric figure of merit ZT in a LaxCoFe3Sb12 (x = 0.80, 0.85, 0.90) skutterudite system by applying a conductivity ratio (electrical to thermal) control method based on the phonon-glass electron-crystal (PGEC) approach. Polycrystalline bulks of LaxCoFe3Sb12 were prepared by melt-spinning and subsequent spark plasma sintering. Based on the thermoelectric transport properties and microstructural analysis, we found that large amount of La-filler (x ≥ 0.9) in the LaxCoFe3Sb12 system is necessary to increase the conductivity ratio required to improve the thermoelectric properties in the LaxCoFe3Sb12 system. Resultantly, the maximum ZT value of 0.87 was obtained at 723 K in the heavily filled La0.9CoFe3Sb12. We discuss our results on the basis of the filling level dependence of the rattling effect and on the formation of the skutterudite single phase. We also confirm that a large amount of La-filling level is necessary to meet the electrical neutrality condition of the p-type LaxCoFe3Sb12 skutterudite system.

Metallic glass (MG) offers the advantage of outstanding oxidation resistance, since it has disordered atomic-scale structure without grain boundaries. We fabricated Al-based MG ribbons (Al84.5Y10Ni5.5) by a melt spinning process. We evaluated the adhesion strength of interfaces between the Al-based MG and a Ni-coated Cu electrode formed under various conditions at high temperature. In addition, we attempted to optimize the process conditions for pulverizing MG ribbons to

Partially double-filled (Nd1−z Yb z ) y Fe4−x Co x Sb12 (z = 0.25, 0.75, y = 0.8, and x = 0, 0.5, 1.0) skutterudites were prepared by encapsulated melting, annealing, and hot pressing, and the effects of Nd/Yb partial double filling and Co charge compensation on the microstructure, charge transport, and thermoelectric properties were investigated. All the specimens were transformed to the skutterudite phase together with a few secondary phases such as FeSb2, but FeSb2 formation was suppressed on increasing Co content. Nd and Yb were successfully double-filled in the voids of the skutterudite lattice and Co was well substituted at Fe sites, as indicated by changes in the lattice constant with Nd/Yb filling and Fe/Co substitution. All the specimens showed p-type conduction and exhibited degenerate semiconductor characteristics at temperatures from 323 K to 823 K, and the charge transport properties depended on the filling ratio of Nd and Yb because of the difference between the valencies of Nd and Yb. The electrical conductivity decreased and the Seebeck coefficient increased owing to a decrease in the carrier concentration with increasing Co content. The lattice thermal conductivity decreased because phonon scattering was enhanced by Nd and Yb partial double filling, but partially double-filled specimens did not exhibit a further significant reduction in the lattice thermal conductivity compared with the completely double-filled specimens. A maximum ZT of 0.83 was obtained for (Nd0.75Yb0.25)0.8Fe3CoSb12 at 723 K.

We investigate the thermoelectric properties of reduced graphene oxide (RGO) incorporated Bi0.36Sb1.64Te3 composites. A melt spinning process enables RGO to be uniformly distributed with Bi0.36Sb1.64Te3 matrix and the incorporated RGO increases the carrier mobility of Bi0.36Sb1.64Te3 matrix with the enhancement of the power factor by 20%. The grain sizes of the Bi0.36Sb1.64Te3 materials decrease with the RGO amount, leading to the reduction in lattice thermal conductivity by enhancing grain boundary scattering. Owing to the above effects, the thermoelectric figure of merit (ZT) can be enhanced in the measured temperature range, where the optimum ZT value is reached to 1.16 at 393 K, ∼15% higher ZT value than pristine Bi0.36Sb1.64Te3. Consequently, this RGO incorporation method could be widely used to improve thermoelectric performances in other conventional thermoelectric materials.

The effects of Sn-deficiency on the thermoelectric properties of polycrystalline Sn1-xSe (x = 0, 0.01, 0.02, and 0.04) compounds were investigated. The Sn-deficiency caused the formation of the SnSe2 secondary phase in the compounds, and the charge and thermal transport properties were affected significantly by the secondary phase. Although the Sn-deficient compounds exhibited higher thermal conductivities than stoichiometric compound due to its high thermal conductivity of SnSe2, significantly improved power factors led to the enhancement of ZT. The highest ZT of 0.61 at 848 K was achieved in Sn0.98Se compound, and detailed effects of SnSe2 on the enhancement were discussed.

This paper demonstrates a time-of-flight mass spectrometer (TOFMS) fabricated using simple micro electromechanical system technologies. It consists of two components: a triode-type field emitter for electron-impact ionization and ion separator with a repeller, an acceleration electrode, and a flight tube. As a cold-cathode, the field emitter with carbon nanotube is a promising electron source and offers several advantages over conventional thermionic electron sources, such as compact size, low power consumption because of the absence of heating elements, excellent durability, and high electron emission density. Micromachined TOFMS successfully detects signals of Ar and CH3I. This is practically proved with preliminary experiments on ionization and mass spectrum tests with Ar and CH3I, ions, including finite element modeling and theoretical analysis.

We report the effects of Cu incorporation on the thermoelectric transport properties in n-type CuxBi2Te2.7Se0.3 (0 ≤ x ≤ 0.08) compounds. The acceptor roles of Cu in the compounds were elucidated by the charge and thermal transport properties. Considerable change in the density of state (DOS) effective mass depending on the Cu content was evidenced by the cross-over of Seebeck coefficients, and the effects of the DOS effective mass on the thermoelectric transport properties were interpreted by temperature-normalized Pisarenko plot. Significant enhancement of thermoelectric figure of merit and the control of optimum operating temperature could be achieved by the Cu incorporation, and their origins were discussed.

We report a 47.1% efficiency improvement resulting from the combination of device-architecture modification and inclusion of poly(3-hexylthiophene-2,5-diyl) nanowires (P3HT NWs) in bulk heterojunction (BHJ) active layers (ALs). Modelling of ellipsometry spectra shows substantial changes in inhomogeneity and optical constants of BHJ ALs with P3HT-NW inclusion. Furthermore, finite-difference time-domain simulation results based on actual device structures with inhomogeneous AL models indicate that enhanced light harvesting is a main contributing factor to efficiency improvement. On the contrary, P3HT-NW inclusion has no significant effect on charge carrier collection, other than suppressing occurrence of cul-de-sac in hole-transport pathways and unfavourable indene-C60 bisadduct domains near top anodes.

We investigated the thermoelectric (TE) properties of a p-type oxide material (Li1−x NbO2, with x = 0–0.6). The composition was synthesized via a solid-state reaction method under a reducing atmosphere. The charge transport properties were determined through the electrical conductivity and Seebeck coefficient measurements. The electrical conductivity was non-monotonically varied with x value and showed metallic behavior with increased temperature and above 650 K temperature independent behavior dominated by extrinsic conduction. On the other hand, the Seebeck coefficient was increased with an increase in the temperature, and decreased gradually with an increase in the Li vacancy concentration by both synthesis and gradual phase transition to a Li-rich Li3NbO4 phase with temperature and appeared as an n-type TE at x = 0.6 under high temperatures, which was attributed to an Nb substitution into the Li site. The thermal conductivity was monotonically reduced with the increase in temperature due to the cation disorder defects and second phases. The Li vacancy induced Li1−x NbO2-based compounds under low oxygen partial pressure show promise as a candidate p-type material for thermoelectric applications, particularly for co-processing with n-type oxide thermoelectric materials fabricated under conditions of low oxygen partial pressure.

Biological polymers offer new opportunities for flexible electronics, which are necessary for applications in soft and biological systems, because of their bio- and eco-friendly material traits. However, integrating an arbitrarily patterned electrode, the backbone of electronic devices, is still challenging when transparency of the electrode is required. Here, we report the fabrication of patterned silver nanowire (AgNW) networks buried at the surface of a silk fibroin film, which are suitable for bioelectronic applications that require biocompatibility, flexibility, high conductivity, and optical transparency. The AgNW-buried silk film exhibits excellent low sheet resistance of ∼15 Ω sq.−1 and high optical transparency of over 80%, along with smoothness of the surface. A light-emitting diode (LED) chip is successfully integrated on the patterned electrodes and can be stably turned on and off. Furthermore, we can produce a transparent resistor and a radio-frequency (RF) antenna on the silk film, and use them together as a food sensor that responds to the decreased conductivity caused by rancidity of spoiled food.

We report synergistically enhanced thermoelectric properties through the independently controlled charge and thermal transport properties in a TiO2–reduced graphene oxide (RGO) nanocomposite. By the consolidation of TiO2–RGO hybrid powder using spark plasma sintering, we prepared an interface-controlled TiO2–RGO nanocomposite where its grain boundaries are covered with the RGO network. Both the enhancement in electrical conductivity and the reduction in thermal conductivity were simultaneously achieved thanks to the beneficial effects of the RGO network, and detailed mechanisms are discussed. This led to the gigantic increase in the ratio of electrical to thermal conductivity by six orders of magnitude and also the synergistic enhancement in the thermoelectric figure of merit by two orders. Our results present a strategy for the realization of ‘phonon-glass electron-crystals’ through interface control using graphene in graphene hybrid thermoelectric materials.

We investigated operation of a planar MAPbI3 solar cell with respect to intensity variation ranging from 0.01 to 1 sun. Measured J-V curves consisted of space-charge-limited currents (SCLC) in a drift-dominant range and diode-like currents in a diffusion-dominant range. The variation of power-law exponent of SCLC showed that charge trapping by defects diminished as intensity increased, and that drift currents became eventually almost ohmic. Diode-like currents were analysed using a modified Shockley-equation model, the validity of which was confirmed by comparing measured and estimated open-circuit voltages. Intensity dependence of ideality factor led us to the conclusion that there were two other types of defects that contributed mostly as recombination centers. At low intensities, monomolecular recombination occurred due to one of these defects in addition to bimolecular recombination to result in the ideality factor of ~1.7. However, at high intensities, another type of defect not only took over monomolecular recombination, but also dominated bimolecular recombination to result in the ideality factor of ~2.0. These ideality-factor values were consistent with those representing the intensity dependence of loss-current ratio estimated by using a constant internal-quantum-efficiency approximation. The presence of multiple types of defects was corroborated by findings from equivalent-circuit analysis of impedance spectra.

We report systematic efficiency variations of green-emitting CdSe@ZnS quantum-dot (QD) LEDs (QLEDs) in response to in situ treatments with 1,2-ethanedithiol (EDT) solutions at various concentrations. The main effect of in situ EDT treatment on a QD layer spin-coated onto a ZnO layer was vacuum-level shift due to dipole moments on the surface of the QD layer and at the interface between QD and ZnO layers. Competing contributions of these dipole moments were responsible for changes in energy level configurations and, accordingly, electron and hole barriers that resulted in discrepancies in electron- and hole-current variations. QLED efficiency was best when treated with an EDT solution of 4 mM, attributable to the largest increase in the hole- to electron current ratio. The maximum luminous yield of the 4 mM EDT-treated QLED was 5.43 cd A−1, which is 10 times higher than that of an untreated device. Furthermore, the luminous yield of this treated device remained as high as 2.56 cd A−1 at a luminance of 500 cd m−2.

We report on a substantial increase in luminance and luminous efficiency of green-light emitting devices (LEDs) that use colloidal CdSe@ZnS quantum dots (QDs) as a light-emitting material in response to treatment with 1,2-ethanedithiol (EDT). The maximum luminance increased from 1146 to 8075 cd m-2, and luminous yield from 0.15 to 1.41 cd A-1 as a result of treating an incomplete device with drops of EDT right after spin-coating QDs onto a ZnO-nanoparticle layer. Based on systematic studies on substrate-dependent change in photoluminescence, and current-voltage and luminance-voltage characteristics, we propose that passivation of intra-gap defect states and relative shifts of energy levels relevant to the operation of QD LEDs are two main results of EDT treatment. In particular, we argue that energy-level shift without emission-color change can be attributed to surface-dipole effects.

Effect of Bi non-stoichiometry is one of the big issues in BiFeO3-BaTiO3 (BF-BT) ceramics that have not been resolved clearly. Therefore, 0.65Bi1+xFeO3-0.35BaTiO3 (x = 0–0.06) ceramics were synthesized by a conventional solid-state reaction at different sintering temperatures (TS) to control the Bi non-stoichiometry, which can be varied by the sublimation and/or evaporation of Bi+3 ions during sintering process. The effects of Bi chemical pressure on crystalline phase, microstructure, dielectrics, and piezoelectric properties of BF-BT were evaluated. X-rays diffraction revealed a single perovskite structure with pseudo-cubic symmetry. A prominent enhancement was noticed at x = 0.05 in ferroelectric, dielectric and piezoelectric properties. Typical ferroelectric behaviors were obtained, while unipolar and bipolar strains were enhanced with increasing Bi content. The maximum piezoelectric properties were found at TS = 1000 °C with x = 0.05, having d∗33 = 270 pm/V at 5 kV/mm with Curie Temperature (TC) = 432 °C.

In this paper a comprehensive study that includes structural, magnetic, ferroelectric, dielectric and electrical characterizations of as-prepared and quenched MPB 1-x(BiFeO3)-x(PbTiO3)(BF-xPT) solid solutions prepared by wet chemical method has been presented. Qualitative and quantitively structural analysis revealed coexistence of rhombohedral/monoclinic, tetragonal and orthorhombic phases. Sensitivity to the experimental variables such as composition, synthesis conditions, sintering temperature and particle size, confirms the existence of a complex energy phase diagram where minima associated with various polymorphs lies almost at same level for MPB compositions. Magnetic characterizations reveal the presence of three anomalies, i.e., originating from the Neel transition, iso-structural transition and ferroelectric phase transition. Second anomaly detected to be the most sensitive to the quenching. Enhancement of magnetic moment in quenched compositions is a manifestation of strong interaction between spins of Fe2+ ions with the pinned point defect dipoles. Interestingly, thermal quenching enhanced the ferroelectric properties by removing the domain wall pinning. Saturated ferroelectric loops were observed only for quenched samples which is a consequence of strong domain wall de-pinning. Low temperature dielectric relaxation has been observed while the high temperature dielectric data of as-prepared composition exhibited Maxwell-Wagner and iso-structural phase transition. In contrast, along with these two features, quenched samples showed additional Curie transition. Enhancement in large polaron hoping in the low frequency region for the quenched composition has been confirmed via frequency dependent profile of the ac conductivity. Low value of activation energy of charge carriers for quenched compositions indicates large polaron hoping characteristics in BF-xPT solid solution.

We report a five-fold luminance increase of green-light-emitting CdSe@ZnS quantum-dot LEDs (QLEDs) in response to treatment with a 2-ethoxyethanol solution of cesium carbonate (Cs2CO3). The maximum luminous yield of Cs2CO3-treated QLED is as high as 3.41 cd A−1 at 6.4 V. To elucidate device-performance improvement, we model measured currents as the sum of radiative and non-radiative recombination components, which are respectively represented by modified Shockley equations. Variations in model parameters show that a shift in Fermi level, reduction of barrier heights, and passivation of mid-gap defect states are the main results of Cs2CO3 treatment. In spite of a large luminance difference, light-extraction efficiency remains the same at 9% regardless of Cs2CO3 treatment because of the similarity in optical structures.

We report the operation characteristics of green tris-(8-hydroxyquinoline)aluminium (Alq3) organic light emitting devices (OLEDs) with a N, N′-bis-(1-naphthyl)-N, N′-diphenyl-1, 1′-biphenyl-4, 4′-diamine (NPB) hole transport layer forming by either vacuum evaporation or solution processing. The maximum luminous yield of device having a vacuum-deposited NPB layer was 2.97 cdA-1 while that of device with solution-processed NPB layer was 2.56 cdA-1. To evaluate the operation characteristics of OLED devices, current densities with respect to bias voltages were investigated by using a modified Shockley equation. Similar behavior was obtained for ideality factors n in two types of devices suggesting the equivalent potential barriers and interface states for injection of holes from indium tin oxide anode to Alq3 emission layer. However, a lower parasitic series resistance (RS) and significant larger saturation current density (J0) were observed from the device with vacuum deposition method, which we attributed to a more dense and homogeneous NPB layer that is more favorable for hole current flow.

Metallic glass (MG) can be a candidate for an alternative brazing material of high-temperature thermoelectric modules, since we can expect both a lower brazing temperature and a high operating temperature for the junction from the MG brazers. Another advantage of MG powders is their outstanding oxidation resistance, namely, high-temperature durability in atmosphere. We fabricated three compositions of Al-based MGs—Al-Y-Ni, Al-Y-Ni-Co, and Al-Y-Ni-Co-La—by using the melt spinning process, and their Tgs were 273°C, 264°C, and 249°C, respectively. The electrical resistivity of the Al-Y-Ni MG ribbon dropped significantly after annealing at 300°C. The electrical resistivity of crystallized Al-Y-Ni reduced down to 0.03 mΩ cm, which is an order of magnitude lower than that of the amorphous one. After the MG ribbons were pulverized to sub-100 μm, the average particle size was about 400 μm.

We report the enhanced thermoelectric properties in Cu x Bi 0.38 Sb 1.62 Te 3 compounds through simultaneous achievement of improved charge transport and suppressed thermal transport by Cu incorporation. Incorporated Cu acted as an acceptor rather than donor, resulting in the significant improvement of p -type electric conduction. Density of state effective mass was almost linearly proportional to the Cu content in the compounds, and it led to the enhancement of power factor in Cu-doped compounds regardless of the increase in hole concentration. Furthermore, reduction of bipolar and lattice thermal conductivities could also be achieved by the Cu incorporation, consequently leading to the improved thermoelectric properties of the compounds at relatively high temperatures. Effects of Cu on the thermal and charge transport properties are discussed in detail, and the controllability of the thermoelectric performance for optimum operating temperature is also reported.

Bi2Te3−ySey:Im (y = 0.15–0.6 and m = 0.0025–0.01) solid solutions were prepared by mechanical alloying and hot pressing. The lattice constants that were measured from x-ray diffraction patterns decreased linearly with increasing Se content, but they were not changed remarkably by I doping. The average relative densities of the hot-pressed specimens are higher than 97%. All of the specimens exhibited n-type conductions in the measured temperature range from 323 K to 523 K, and their electrical conductivity decreased slightly with increasing temperature, indicating degenerate semiconductor behaviors. The electrical conductivity decreased with increasing Se content, whereas it was increased by I doping, and this is in contrast with the Seebeck coefficient; this resulted from the changes of the electron concentrations due to the Se substitution and the I doping. The thermal conductivity decreased with increasing Se content, and this is the result of both the decreased electronic thermal conductivity due to the decreased carrier concentration and the decreased lattice thermal conductivity due to the increased alloy scattering. The maximum dimensionless figure of merit for Bi2Te2.4Se0.6, ZTmax = 0.84 at 473 K, is due to its low thermal conductivity and high Seebeck coefficient.