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Organic light-emitting diodes (OLEDs) with both high transparency and stretchability are of importance for next-generation wearable and deformable displays, which have not been studied in depth. In this work, highly flexible and transparent OLEDs (TrOLEDs) are achieved by using ultrathin metal films as both anode and cathode to fabricate stretchable TrOLEDs (S-TrOLEDs) based on a wrinkling strategy. The TrOLEDs show a transmittance value of 73% at 550 nm and a negligible micro-cavity effect with near Lambertian emission characteristics at a wide angle of view. Furthermore, almost symmetric electroluminescent properties are obtained from the anode and cathode, which is important for dual-side display. Two-dimensional S-TrOLEDs with random wrinkles show 50% stretchability and retain 80% of their initial luminance after 200 cycles of stretching. The effect of random wrinkles on the transmittance of S-TrOLEDs is researched and the transparency losses of the device are analyzed deeply. We hope that this work is meaningful for promoting the development of S-TrOLEDs in the display industries.

Organic single crystals are highly promising for applications in optoelectronic devices because of their higher mobility and thermal stability than amorphous thin films. Although white organic single crystals have been fabricated by the double-doped method and applied to realize white organic light‐emitting devices (WOLEDs), the unbalanced carrier transport properties of the unipolar crystals severely limit the device performance. Here, ambipolar white organic single crystals are obtained by using mixed p- and n-type molecules as an ambipolar host for the red and green dopants. The white crystal with balanced carrier transport and balanced blue, green, and red emission intensity was applied to the single-crystal WOLEDs. The highest brightness of 1956 cd m−2 and the current efficiency of 1.31 cd A−1 are achieved, which are the best performance of the single-crystal WOLEDs reported to date. A high color rendering index is obtained, which varies between 82 and 87 with increasing driving current. It is expectable that this strategy would support the practical applications of organic single crystal-based OLEDs.

Effective governance of thermal conductivity and other properties is of significant interest for science, including the fields of thermal barrier coatings, thermoelectric materials, and limit alloys. In this study, we investigated the impact of entropy engineering on properties of fluorite RE3NbO7, and limit thermal conductivity and strengthened mechanical properties are achieved. The solution strengthening mechanism leads to an 80% increase in toughness when the intrinsic stiffness and Young's modulus of the fabricated samples are identified via nanoindentation. Thermal conductivity is as low as 1.03–1.17 W m−1 K−1 at 25–900 °C, drastically reducing the gap between experimental results and theoretical limit values of fluorite RE3NbO7. The limit thermal conductivity as well as enhanced thermal expansion coefficients (11.2 × 10−6 K−1) and mechanical properties imply that the working performance of RE3NbO7 is evidently promoted by entropy engineering.

The effect of uniaxial compressive stress on the crystal structure of a 6 mol. % Li-doped (K,Na)NbO3 (LKNN6a) ceramic was investigated using in situ synchrotron X-ray diffraction, revealing the stress-induced relative change in monoclinic Pm and tetragonal P4mm phases. As such, stress-induced phase transformations, in addition to the lattice deformation and domain switching, are the contributing factors for the observed macroscopic mechanical behavior of LKNN6a. The in situ stress-dependent diffraction data also demonstrates a method to mechanically modulate the polymorphic phase transition temperature (TPPT) to a higher temperature, as observed by the temperature-dependent permittivity measurements under a constant bias stress. The external uniaxial compressive stress increases the stability of the lower symmetry monoclinic phase, shifting TPPT to a higher temperature by 60 °C for the maximum uniaxial compressive stress of 300 MPa in the studied composition. Importantly, the stress-induced stabilization of the room-temperature ferroelectric phase can be useful to optimize the phase transition region, as well as increase the temperature stability of lead-free KNN.

Recently, several creative processing techniques yielded thermoelectrics with reduced thermal conductivity and, thereby, an enhanced figure or merit. These were based on engineered complex microstructures with attendant dislocation structures. In this study, we implement highly controlled mesoscopic dislocation structures into the model thermoelectric SrTiO3 in order to quantify phonon scattering at dislocations. Both single crystals and polycrystalline material have been furnished with enhanced dislocation densities increased by a factor of 150–300 by plastic deformation. Thermal conductivity was measured using laser flash analysis between room temperature and 325 °C. Etch pit techniques and ultra-high voltage electron microscopy afford quantification of dislocation density. Experimental results were compared to predictions by the Debye-Callaway model. The latter revealed that dislocation densities of 1015 m−2 would be necessary for the reduction of thermal conductivity of SrTiO3 in the investigated temperature range, which could not be realized using the plastic deformation mechanism applied.

Antiferroelectric materials are a kind of functional material, which are widely used in electrostatic energy storage, energy conversion devices, and magnetoelectric coupling devices. As a typical lead-free antiferroelectric material, silver niobate has attracted much attention in recent years due to its excellent performance in energy storage. In this work, using the spherical aberration corrected electron microscopy technique, atomic-resolution images of pure silver niobate were obtained, which revealed typical microscopic physical characteristics of such complex antiferroelectric oxides: in such materials, all cations deviate from the average positions of the main lattice, and the displacement of each kind of cation varies periodically in two opposite directions, resulting in periodic wavy (1–10)c atomic planes, and the period of cation displacement is 15.6 A. At the same time, the 90° antiferroelectric domain boundary and the antiphase domain wall defects are further revealed and analyzed.

Using the solid-state reaction method, the (ZrO2)x-(Dy3TaO7)1−x (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) ceramics are synthesized in this work. The identification of the crystal structures indicates that the (ZrO2)x-(Dy3TaO7)1−x ceramics belong to the orthorhombic system, and the space group is C2221 in spite of the value of x increasing to 0.1. The thermal conductivities of the (ZrO2)x-(Dy3TaO7)1−x ceramics range from 1.3 W/(m K) to 1.8 W/(m K), and this value is much lower than that of 7-8 YSZ (yttria-stabilized zirconia). Besides, the (ZrO2)x-(Dy3TaO7)1−x ceramics possess the glass-like thermal conductivity caused by intrinsic oxygen vacancies existing in the lattice of Dy3TaO7. Moreover, the results of thermal expansion rates demonstrate that the (ZrO2)x-(Dy3TaO7)1−x ceramics possess excellent high temperature phase stability, and the thermal expansion coefficients [(9.7–11) × 10−6 K−1] are comparable to that of 7-8 YSZ.

Locally persistent tetragonal distortion in NaNbO3-BaTiO3 relaxor ferroelectrics was identified at multiple length scales by means of in-situ synchrotron x-ray diffraction, absorption fine structure, and Raman spectra although their average symmetry seemingly evolved from a tetragonal to a cubic-like phase with the increasing BaTiO3 content. Theoretical calculations of Nb-O peaks in the R range of 1–2 A provided a clear evidence that Nb5+ in an NbO6 octahedron should be spontaneously shifted along [001]. The competition between B-site Nb5+ ([001]) and Ti4+ ([111]) spontaneous off-center displacement directions would contribute to the disruption of long-range polar ordering. Raman spectra suggested that A-site Ba2+ and Na+ cations should be located at the center of the cubes in the absence of the polar contribution unlike Pb2+/Bi3+ with lone-pairs. A relatively low field-induced strain in NN-BT relaxors was thus ascribed to the small spontaneous polarization magnitude and the absence of structural phase tr...

An insulated poly(sodium 4-styrenseulfonate) (PSS) was used to modify monolayer graphene for anode applications of organic photovoltaics (OPVs). With this PSS interfacial modification layer, the OPVs showed a significant increase of 56.4% in efficiency due to an improved work function and hydrophilic feature of graphene and an enlarged recombination resistance of carriers/excitons. Doping a highly contorted 1,2,5-thiadiazole-fused 12-ring polyaromatic hydrocarbon into the active layer to form ternary blended OPVs further enlarged the recombination resistance of carriers/excitons and improved light absorption of the active layer, with which a high power conversion efficiency of 6.29% was acquired.

Single-crystal SnSe has been found to exhibit exceptional thermoelectric performance, but the efficiency of polycrystalline samples is still far from satisfactory. In this work, with an intention to effectively suppress heat conduction and minimally affect hole transport, we alloyed p-type polycrystalline SnSe with PbSe. Single-phase Sn1−xPbxSe solid solutions were formed up to x ≈ 0.12. The lattice thermal conductivity was reduced from 1.4 to 0.85 W m−1 K−1 by 12 at. % PbSe alloying due to strain and mass fluctuations. Interestingly, the Seebeck coefficient and carrier concentration were nearly unchanged by Pb substitution, indicating a constant effective mass and an undisrupted valence band maximum. A peak figure of merit (ZT) of 0.85 at 800 K was obtained in the x = 0 sample, and relatively high performance was also achieved in solid solutions. A concise model was developed involving multiple carrier scattering mechanisms, capturing the dependence of the mobility on composition and temperature.

An enhanced efficiency organic light-emitting device (OLED) with corrugated nanostructures on a small-molecule organic film has been demonstrated. By patterning the hole transport layer via soft nano-imprinting lithography and coating with Ag, a nanostructured cathode is introduced to enhance the light extraction of the OLED without affecting the flatness and conductivity of the indium-tin-oxide film. Both luminance and current efficiency are improved compared with those of conventional planar devices. The observable improvement in luminance and current efficiency can be ascribed to the surface plasmonic and scattering effects caused by the Ag nanostructures. Moreover, theoretical simulations also demonstrate that the power loss to surface plasmon-polariton modes has been recovered.

Single-crystal Nb-doped Pb(Zr,Ti)O3 (PNZT) films were grown on electric conducting single-crystal Nb-doped SrTiO3 (Nb:STO) wafers by a sol-gel method. Although the films were of the same composition and prepared under the same condition, different crystal phases with corresponding preferential film orientations were formed when the substrate orientation was changed. [001]-oriented tetragonal PNZT film was formed on the {100} surface of the Nb:STO substrate, whereas [111]-oriented rhombohedral PNZT film on the {111} surface. The PNZT films on SrTiO3 substrates showed considerably high remnant polarization and low coercive field, as compared with conventional PZT films on Si wafers. In particular, high d33 value was obtained in the [001]-oriented PNZT films.

Highly efficient electrophosphorescence from light-emitting devices based on two types of rhenium(I) diimine complexes, (1,10-phenanthroline)Re(CO)3Cl (phen-Re) and (2,9-dimethyl-1,10-phenanthroline)Re(CO)3Cl (dmphen-Re), is reported. N, N′-di-1-naphthyl-N, N′-diphenylbenzidine is used as the hole-transporting layer. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used to confine excitons within the luminescence zone. phen-Re and dmphen-Re are doped into the host material (4,4′-N-N′-dicarbazole)biphenyl with mass ratios of 2–20% as the light-emitting layer, respectively. The maximum efficiency and brightness achieved from the devices based on phen-Re and dmphen-Re are 6.67 cd/A and 2769 cd/m2, and 7.15 cd/A and 3686 cd/m2, respectively.

Efficient white emission from the mixing of yellow emission from the Re-complexes, (4,4′-dimethyl-2,2′-bipyridine)Re(CO)3Cl (Dmbpy-Re), and blue emission from the N,N′-di-1-naphthyl-N, N′-diphenylbenzidine (NPB) is reported. NPB is used as the hole-transporting layer. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used as the exciton-blocking as well as electron-transporting layer. Dmbpy-Re is doped into the host material (4,4′-N-N′-dicarbazole)biphenyl (CBP). The chromaticity of the white emission can be tuned by adjusting the thickness of Dmbpy-Re:CBP layer or the concentration of Dmbpy-Re in CBP. The maximum luminance, efficiency, and Commission Internationale De L’Eclairage coordinates at 9 V of the devices with 20-nm-thick and 30-nm-thick Dmbpy-Re:CBP layer at a fixed Dmbpy-Re doping concentration of 2 wt % in CBP are 1332 cd/m2, 2.9 cd/A, and (0.30,0.37), and 2410 cd/m2, 5.1 cd/A, and (0.36,0.43), respectively. The turn-on voltage of these devices is ∼4 V.

The efficiency of white organic light-emitting devices has been improved dramatically by the introduction of a phosphorescent material, fac tris (2-phenylpyridine) iridium [Ir(ppy)3] as a sensitizer. Ir(ppy)3 and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) are codoped into 4,4′-N,N′-dicarbazole-biphenyl (CBP) host. The chromaticity of white emission can be tuned by adjusting the thickness of the codoped CBP layer or the concentration of Ir(ppy)3. The luminance efficiency of these devices is affected at the same time due to the severe difference in efficiency between the two primary emission peaks.

We present organic red light-emitting devices with improved optical and electrical characteristics utilizing the two-step energy transfer. N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine and tris-(8-hydroxyquinoline) aluminum (Alq) are used as hole and electron-transporting layers, respectively. Quinacridone (QAD) and 4-(dicyanomethylene)-2-t- butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) are codoped into the Alq emitting layer. Compared with devices where the emitting layer is only composed of Alq and DCJTB, the emitting characteristics such as emission efficiency and purity of emission color are greatly improved, and the turn-on voltage is decreased as much as 4 V. We attribute these improvements to the assistant dopant (QAD), which leads to the more efficient energy transfer from Alq to DCJTB.

The effect of film thickness on the NiSi-to-NiSi2 transition temperature in the Ni/Pt/Si(100) system has been studied. Three sets of Ni/Pt/Si(100) bilayered samples with the same Ni:Pt ratios but with different film thicknesses were annealed by rapid thermal annealing at 750–900 °C. Both the x-ray diffraction analysis and the sheet resistance measurement show that the thermal stability of Ni(Pt)Si films improves with a decrease in film thickness. This property of Ni(Pt)Si films reveals the good potential for its applications in ultrashallow junctions. The experimental results are explained in terms of classical nucleation theory.

As a model for composite materials of piezoelectric ceramic and metal, lead zirconate titanate (PZT) and platinum (Pt) particulate composites were fabricated by power processing. The electrical and mechanical properties of the PZT–Pt composites were measured as a function of the Pt volume fraction. The relative dielectric constants of the PZT–Pt composites increased markedly, while the piezoelectric constants and electromechanical coupling coefficients decreased with increasing Pt content. When the Pt volume fraction exceeded 30%, the PZT–Pt composite became electrically conductive because of percolation of the Pt particles. The Pt-dispersed PZT composites enhanced the mechanical properties, particularly the high fracture resistance, compared to the monolithic PZT ceramics.

We demonstrate efficient organic white light-emitting devices (LEDs), using N,N′-diphenyl-N,N′-bis(1-naphthyl)–(1,1′-biphenyl)-4,4′-diamine (NPB) as the hole-transporting layer, 1,6-bis(2-hydroxyphenyl)pyridine boron complex [(dppy)BF)] as the emitting layer, tris-(8-hydroxyquinoline)aluminum (Alq) as the electron-transporting and chromaticity-tuning layer. The white light comes from exciplex emission at the solid-state interface between (dppy)BF and NPB in addition to the exciton emission from NPB and (dppy)BF, respectively. The chromaticity of white emission can be tuned by adjusting the thickness of the Alq layer. The white LEDs with an Alq thickness of 15 nm exhibit a maximum luminescence of 2000 cd/m2 and efficiency of 0.58 lm/W, and the Commission Internationale De l’Eclairage coordinates of resulting emission vary from (0.29,0.33) to (0.31,0.35) with increasing forward bias from 10 to 25 V. The region is very close to the equienergy white point (0.33,0.33).

Blue light organic electroluminescent (EL) devices with high-performance were fabricated by using a highly fluorescent material, bis[2-(2-hydroxyphenyl)-pyridine]beryllium (Bepp2). The double layer devices with a structure of [indium tin oxide/N, N′-di(α-naphthyl)-N-N′-diphenyl(1, 1′-biphenyl)-4, 4′-diamine (600 A)/Bepp2 (500 A)/LiF (10 A)/Al (2000 A)] exhibited a maximum luminance of 15 000 cd/m2 and a maximum electroluminescent efficiency of 3.43 lm/w (3.8 cd/A).

The effect of a thin interlayer of Pt on the stability of NiSi films on Si(111) substrates has been investigated. Both x-ray diffraction (XRD) data and sheet resistance measurements show a remarkable improvement in the thermal stability of NiSi due to the Pt interlayer. Detailed study on the XRD data shows PtSi and NiSi form a solid solution following a Vegard’s law. It was found in Ni/Pt/Si samples that a transition in NiSi texture from (200)NiSi‖(111)Si to (002)NiSi‖(111)Si took place before the nucleation of NiSi2, which may contribute to the enhanced stability of NiSi films.

We demonstrated a strategy to realize broadband enhanced absorption in the top-incident inverted organic solar cells (OSCs) by employing an external antenna layer on top of the periodic corrugated metallic anode. Surface-plasmon polaritons (SPPs) are excited on the opposite interfaces of the periodic corrugated metallic anode, which mediate the energy transfer from the antenna layer to the active layer through the anode. The absorption of the OSCs is significantly broadened and enhanced by tuning the SPP resonance to coincide with both the emission of the antenna and the absorption of the active material. The power conversion efficiency exhibits an enhancement of 16% compared to that of the OSCs without the antenna layer.

A multi-functional gold nanorods-mesoporous silica Janus nanoparticles (NPs) were fabricated by a facile and mild strategy. These Janus NPs not only exhibit small shift of the local surface plasmon resonance wavelength but also have high potential for drug loading and low cytotoxicity. More importantly, the Janus nano-composites could efficiently deliver the imaging agents or drugs into liver cancer cells, at the same time the Janus NPs have good effect on photothermal, which indicate that the unique Janus NPs could be a promising candidate of theranostic system for combined photothermo-/chemo-cancer therapy.

Lead-free (Na0.52K0.48)(Nb1−ySby)O3 (NKNSy) ferroelectric ceramics were reported to exhibit an ultrahigh electrostrain (dynamic d33* (=S/E) of 800–1100 pm/V) in a relatively low driving electric field range (1–4 kV/mm). As evidenced by in-situ synchrotron x-ray diffraction and dielectric measurements, the mechanism of generating large strains was ascribed to both the low-field induced reversible rhombohedral-monoclinic phase transition (1–2 kV/mm) and the enhanced domain switching (2–4 kV/mm) owing to the normal to relaxor phase transformation, which contribute to ∼62% and ∼38% of the total strain, respectively. The results indicate that the NKNSy compositions would have excellent potentials for applications of lead-free actuator ceramics.

Effective and tunable light trapping in organic solar cells (OSCs) has been demonstrated by employing Au-Ag alloy nanoparticles (NPs). A simple vacuum thermal annealing method has been employed to fabricate the Au-Ag alloy NPs with tunable molar ratio, and thereafter tunable localized surface plasmon resonance (LSPR). The incorporation of the alloy NPs with an appropriate molar ratio into the OSCs structures supports amplification of the electric field near the particles surface through LSPR and results in an enhanced light absorption at the absorption wavelength region of the absorber owing to the near field coupling. The short-circuit photocurrent density of the alloy NPs-based OSCs is improved from 7.37 to 8.74 mA/cm2 compared to that of control OSCs, and the efficiency of 3.03% is obtained, which corresponds to an enhancement factor of 19%.

The bipolar fatigue behavior of (K,Na)NbO3 (KNN)-based lead-free piezoceramics was investigated. A comparative analysis demonstrated that CaZrO3-modified KNN ceramics exhibited highly enhanced bipolar fatigue resistance due to the reduced lattice distortion (c/a ratio) and coexistence of orthorhombic and tetragonal phases. The hypothesis was verified by systematical studies of cycle-dependent large and small signal parameters and micro-morphologies. It was identified that mechanical stress induced microstructure damage beneath the electrodes renders the KNN ceramics to be vulnerable to bipolar cycling; while the mild fatigue behavior for CaZrO3-modified ones mainly originates from a thermally reversible domain wall pinning.

For further thermoelectric performance enhancement by the nanocomposite effect, a small amount (

Crystallographic structure of sol-gel-processed lead-free (K,Na)NbO3 (KNN) epitaxial films on [100]-cut SrTiO3 single-crystalline substrates was investigated for a deeper understanding of its piezoelectric response. Lattice parameter measurement by high-resolution X-ray diffraction and transmission electron microscopy revealed that the orthorhombic KNN films on SrTiO3 (100) surfaces are [010] oriented (b-axis-oriented) rather than commonly identified c-axis orientation. Based on the crystallographic orientation and corresponding ferroelectric domain structure investigated by piezoresponse force microscopy, the superior piezoelectric property along b-axis of epitaxial KNN films than other orientations can be explained.

For a better understanding of piezoelectricity in epitaxial film systems, epitaxially grown tetragonal Pb(Zr0.3Ti0.7)0.98Nb0.02O3 (PNZT) thin films with three primary crystallographic orientations were studied with a focus on their piezoelectric behaviors and domain configuration. Using piezoresponse force microscopy, the (001)-oriented epitaxial films were found to show superior piezoelectric properties compared with the (110)- and (111)-oriented films. This can be attributed to the structural characteristics of the tetragonal PNZT phase after applying an electrical field. Island-distributed domain shapes were also mapped for all three orientations.

The unipolar fatigue behavior of CaZrO3 and MnO2 co-modified (K,Na,Li)(Nb,Ta)O3 lead-free piezoceramics was investigated systematically. The well-known charge agglomeration model is shown to explain the overall changes observed during unipolar fatigue, such as the development of bias field as well as the anisotropy in bipolar strain hysteresis and field-dependent dielectric permittivity. In addition, it is found that the unipolar strain exhibits only small degradation within 3% at the field amplitude of 2 kV/mm up to 107 cycles. This exceptionally good fatigue resistance is identified due to the presence of additional process, assigned as a “softening” effect that competes against the usual fatigue effect.

Ultrahigh piezoelectric constant (d33 = 683 pC/N) and converse piezoelectric coefficient (dS/dE = 1257 pm/V) were observed in CuO-doped lead-free (Ba,Ca)(Ti,Sn)O3 ceramics at an optimal composition fabricated by a conventional sintering method at a low temperature 1250 °C. Since all samples showed a pure perovskite structure with coexisting multiphases including cubic, tetragonal, orthorhombic, and rhombohedral phases around two converged triple points, a good compositional stability of high piezoelectricity along with a high d33 and dS/dE over 600 pC/N and 1000 pm/V was achieved within a wide compositional region (1.0 ≤ x ≤ 3.0) regardless of the CuO content (x).

The phase structure in the (Ba,Ca)(Ti1−xSnx)O3 lead-free ceramics was evolved from inceptive orthorhombic (O) at 0 ≤ x ≤ 0.04 to a two-phase coexistence of pseudocubic-orthorhombic (PC-O) at 0.06 ≤ x ≤ 0.10 and further to a multiphase coexistence of rhombohedral-pseudocubic-orthorhombic (R-PC-O) at x = 0.11. Due to the multiphase coexistence of R-PC-O at room temperature proved by X-ray diffraction, dielectric constant er and differential scanning calorimetry, an ultrahigh piezoelectric coefficient d33 = 670 pC/N and electrostrain 0.061% were achieved. The high d33 over 520 pC/N was stabilized in a wide compositional range of 0.07 ≤ x ≤ 0.11, suggesting that (Ba,Ca)(Ti,Sn)O3 ceramics are a promising candidate for the lead-free piezoelectric ceramics.