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Abstract: The amorphous indium tin oxides (ITOs) and the transparent conducting oxides (TCOs) electrode on the flexible polymer substrate, polyvinylidene difluoride (PVDF), and their application to the suggested combinational device system were studied. The lower range ordered crystalline structure of the ITOs enable the reduction of micro-cracks or defect grains under flexible conditions. With the piezoelectric function of substrate polymer, which is added to the display function with OLED (Organic light emitting diodes), the pattern design with the separated electrodes for two devices for emitting light and vibration was considered. From these results, the concept of a combinational flexible electronic device system with a functional polymer substrate could be suggested. [Copyright &y& Elsevier]

Abstract: The interfacial characteristics of high-κ HfO2 on NH3- and N2O-plasma treated p-Si substrates have been investigated using high-resolution transmission electron microscopy (HRTEM), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and auger electron spectroscopy (AES). NH3- and N2O-plasma treated films show the formation of a nitrogen-rich Hf-silicate interfacial layer between the deposited HfO2 and Si substrates. The electrical characteristics have been studied using metal–oxide-semiconductor (MOS) structures. Interfacial nitrogen increases the capacitances by ∼33% for NH3 and ∼47% for N2O-treated Si as compared to the untreated surface. A dielectric constant of ∼26 for HfO2 film, ∼6.0 for Hf-silicate, ∼9.0 for NH3- and ∼11.0 for N2O-treated interfacial layers have been calculated from the accumulation capacitances of the MOS capacitors. The relatively higher dielectric constant, lower capacitance equivalent thickness (CET), lower leakage current and higher breakdown voltage for N2O-plasma treated film makes it attractive for scaled Si MOSFET applications. [Copyright &y& Elsevier]

Abstract: High-quality ZnO thin films were deposited on c-plane sapphire substrates with the low-temperature (LT) ZnO homo-buffer layer by plasma-assisted molecular beam epitaxy. LT ZnO buffer layer with the thickness of 15nm was grown at 500°C. After high-temperature annealing at 800°C for 30min, the growth of ZnO with about 800nm thickness was restarted at different temperatures from 680 to 800°C. Although the surface of the LT-buffer layer was three-dimensional, appropriate subsequent growth temperature facilitated two-dimensional growth. The smallest full-width at half-maximum (FWHM) of X-ray -rocking for ZnO(0002) diffraction was 85arcsec and then slightly increased with the increament of the deposition temperature. The RHEED pattern over the surface of ZnO film grown at 720°C showed very streaky lines, while streaky lines superimposed with spotty patterns were obtained at other temperatures. From the Hall measurement, the mobility values for the ZnO films deposited at 720 and 760°C were 103 and 105cm2/Vs, and the carrier concentration was 2.45×1017 and 2.21×1017/cm3, respectively. In low-temperature photoluminescence measurement at 10K, most of the ZnO thin films showed neutral donor-bound exciton, I4(D0, X) at 3.362eV and acceptor-bound exciton, I10(A0, X) at 3.3497eV were clearly observed with the phonon replica at 3.308eV, and the lowest FWFM of I10 peak was found to be 8.4meV for the ZnO grown at 720°C. [Copyright &y& Elsevier]

ZnO thin films were deposited on c-plane sapphire substrates on the ZnO homo-buffer layer with different thickness and growth temperature by plasma assisted molecular beam epitaxy. The effects of buffer-layer growth variables on the properties of the ZnO films were investigated and discussed on a collective basis compared with other reports. RHEED patterns were taken over different buffer layer surfaces and the initial growth mode of ZnO buffer layer was recognized as Stranski–Krastanov mode by the direct observation of a streaky pattern superimposed with a spotty pattern of thicker than 8 nm. Through examining the XRD θ-rocking curve of ZnO (0 0 0 2) peak, it seems that the crystalline quality of the ZnO thin film grown on the ZnO buffer layer was gradually improved with the increase of the buffer layer thickness. Strong near band-edge emission at 378 nm was well observed without deep-level emission at the ZnO films grown on the 15 nm buffer layer prepared at 500–600°C, and those grown on the thicker buffer layer or prepared at 400°C or 700°C showed deep-level emission around 510 nm. In Hall measurement, the ZnO films showing deep-level emission gave also carrier concentration higher than 1×1019/cm3 and those with better crystalline quality seemed to have high mobility of μ=40–57 cm2/V s. [Copyright &y& Elsevier]

A facile thin film encapsulation (TFE) method having a triple-layered structure of a-SiN x :H/SiO x N y /hybrid SiO x (ASH) on QD-LEDs was performed utilizing both reproducible plasma-enhanced chemical vapor deposition (PECVD) and simple dip-coating processes without adopting atomic layer deposition (ALD). The ASH films fabricated on a polyethylene terephthalate (PET) substrate show a high average transmittance of 88.80% in the spectral range of 400-700 nm and a water vapor transmission rate (WVTR) value of 7.3 × 10 -4 g per m 2 per day. The measured time to reach 50% of the initial luminance (T 50 ) at initial luminance values of 500, 1000, and 2000 cd m -2 was 711.6, 287.7, and 78.6 h, respectively, and the extrapolated T 50 at 100 cd m -2 is estimated to be approximately 9804 h, which is comparable to that of the 12 112 h for glass lid-encapsulated QD-LEDs. This result demonstrates that TFE with the ASH films has the potential to overcome the conventional drawbacks of glass lid encapsulation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Zn-doped SnO x /Ag/Zn-doped SnO x (ZTO/Ag/ZTO) multilayer thin films fabricated on a polyethylene terephthalate (PET) substrate using an optimized N 2 -to-(Ar + O 2 ) gas ratio are used for transparent thin-film heaters with high performance and chemical stability. The ZTO/Ag/ZTO-based multilayer thin film exhibits enhanced durability at high temperatures and humid environments by incorporating nitrogen. The bending test results-there was no significant change in the sheet resistance even after 10,000 bending cycles-highlight the mechanical flexibility of the ZTO/Ag/ZTO multilayer thin film. The ZTO/Ag/ZTO-based thin-film heater on PET, fabricated under optimized deposition gas conditions, exhibits a fast thermal response time of 30 s and a low driving voltage of 6 V to attain 100 °C. It also exhibits uniform heat distribution at saturated temperature and chemical stability after 100 heating-cooling cycles. Hence, the proposed ZTO/Ag/ZTO-based thin-film heater is applicable for use in front and rear window automobile and building applications.

Organic electronic devices such as organic light-emitting diodes (OLEDs), quantum dot LEDs, and organic photovoltaics are promising technologies for future electronics. However, achieving long-term stability of organic-based optoelectronic devices has been regarded as a crucial problem to be solved. In this work, a simple and reproducible fabrication method for ultralow water permeation barrier films having a triple-layered (triad) hydrogenated silicon nitride (a-SiN x :H)/nanosilicon oxynitride (n-SiO x N y )/hybrid silicon oxide (h-SiO x ) multistructure is presented. Two triad (a-SiN x :H/n-SiO x N y /h-SiO x ) n =2 multistructure barrier films are deposited on both sides of a poly(ethylene terephthalate) substrate using a combination of low-pressure plasma-enhanced chemical vapor deposition and dip coating. The deposited films show a high average transmittance (400-700 nm) of 84% and an ultralow water vapor transmission rate of 2 × 10 -6 g/m 2 /day. In the electroluminescence characteristics of OLEDs encapsulated with two triad barrier films, the operational lifetime ( T 50 ) of OLEDs is 1584 h, which is almost similar to that (1416 h) of OLEDs encapsulated with a glass lid.

In modern society, advanced technology has facilitated the emergence of multifunctional appliances, particularly, portable electronic devices, which have been growing rapidly. Therefore, flexible thermally conductive materials with the combination of properties like outstanding thermal conductivity, excellent electrical insulation, mechanical flexibility, and strong flame retardancy, which could be used to efficiently dissipate heat generated from electronic components, are the demand of the day. In this study, graphite fluoride, a derivative of graphene, was exfoliated into graphene fluoride sheets (GFS) via the ball-milling process. Then, a suspension of graphene oxide (GO) and GFSs was vacuum-filtrated to obtain a mixed mass, and subsequently, the mixed mass was subjected to reduction under the action hydrogen iodide at low temperature to transform the GO to reduced graphene oxide (rGO). Finally, a highly flexible and thermally conductive 30-μm thick GFS@rGO hybrid film was prepared, which showed an exceptional in-plane thermal conductivity (212 W·m -1 ·K -1 ) and an excellent electrical insulating property (a volume resistivity of 1.1 × 10 11 Ω·cm). The extraordinary in-plane thermal conductivity of the GFS@rGO hybrid films was attributed to the high intrinsic thermal conductivity of the filler components and the highly ordered filler alignment. Additionally, the GFS@rGO films showed a tolerance to bending cycles and high-temperature flame. The tensile strength and Young's modulus of the GFS@rGO films increased with increasing the rGO content and reached a tensile strength of 69.3 MPa and a Young's modulus of 10.2 GPa at 20 wt % rGO. An experiment of exposing the films to high-temperature flame demonstrated that the GFS@rGO films could efficiently prevent fire spreading. The microcombustion calorimetry results indicated that the GFS@rGO had significantly lower heat release rate (HRR) compared to the GO film. The peak HRR of GFS@rGO10 was only 21 W·g -1 at 323 °C, while that of GO was 198 W·g -1 at 159 °C.

Owing to the growth of demand for highly integrated electronic devices, high heat dissipation of thermal management materials is essential. Epoxy composites have been prepared with vertically aligned (VA) three-dimensional (3D)-structured SiC sheet scaffolds. The required VA-SiC sheet scaffolds were prepared by a novel approach starting with a graphene oxide (GO) scaffold. The VA-GO scaffolds were reduced to VA-graphene scaffolds in an argon environment, and the latter were subsequently transformed into VA-SiC sheet scaffolds by a template-assisted chemical vapor deposition method. Epoxy resin was filled in the empty spaces of the 3D scaffold of SiC sheets to prepare the composite mass. The material so prepared shows anisotropic thermal property with ultrahigh through-plane conductivity of 14.32 W·m -1 ·K -1 at a SiC sheet content of 3.71 vol %. A thermal percolation is observed at 1.78 vol % SiC filler. The SiC sheet scaffold of covalently interconnected SiC nanoparticles plays a vital role in the formation of the thermal conductive network to significantly enhance the thermal conductivity of epoxy composites. The application of the VA-SiC/epoxy composite as an efficient thermal dissipating material has also been presented. The VA-SiC/epoxy composites have a strong potential for preparing heat-dissipating components in integrated microelectronics.

All-solid-state thin-film batteries have been actively investigated as a power source for various microdevices. However, insufficient research has been conducted on thin-film encapsulation, which is an essential element of these batteries as solid electrolytes and Li anodes are vulnerable to moisture in the atmosphere. In this study, a hybrid thin-film encapsulation structure of hybrid SiO y /SiN x O y / a -SiN x :H/Parylene is suggested and investigated. The water-vapor transmission rate of hybrid thin-film encapsulation is estimated to be 4.9 × 10 -3 g m -2 ·day -1 , a value that is applicable to batteries as well as flexible solar cells, thin-film transistor liquid-crystal display, and E-papers. As a result of hybrid thin-film encapsulation, it is confirmed that the all-solid-state thin-film batteries are stable even after 100 charge/discharge cycles in the air atmosphere for 30 days and present a Coulombic efficiency of 99.8% even after 100 cycles in the air atmosphere. These results demonstrate that the thin-film encapsulation structure of hybrid SiO y /SiN x O y / a -SiN x :H/Parylene can be employed in thin-film batteries while retaining long-term stability.

Despite the great interest in inorganic halide perovskites (IHPs) for a variety of photoelectronic applications, environmentally robust nanopatterns of IHPs have hardly been developed mainly owing to the uncontrollable rapid crystallization or temperature and humidity sensitive polymorphs. Herein, we present a facile route for fabricating environment- and phase-stable IHP nanopatterns over large areas. Our method is based on nanoimprinting of a soft and moldable IHP adduct. A small amount of poly(ethylene oxide) was added to an IHP precursor solution to fabricate a spin-coated film that is soft and moldable in an amorphous adduct state. Subsequently, a topographically prepatterned elastomeric mold was used to nanoimprint the film to develop well-defined IHP nanopatterns of CsPbBr 3 and CsPbI 3 of 200 nm in width over a large area. To ensure environment- and phase-stable black CsPbI 3 nanopatterns, a polymer backfilling process was employed on a nanopatterned CsPbI 3 . The CsPbI 3 nanopatterns were overcoated with a thin poly(vinylidene fluoride- co -trifluoroethylene) (PVDF-TrFE) film, followed by thermal melting of PVDF-TrFE, which formed the air-exposed CsPbI 3 nanopatterns laterally confined with PVDF-TrFE. Our polymer backfilled CsPbI 3 nanopatterns exhibited excellent environmental stability over one year at ambient conditions and for 10 h at 85 °C, allowing the development of arrays of two-terminal, parallel-type photodetectors with nanopatterned photoactive CsPbI 3 channels. Our polymer-assisted nanoimprinting offers a fast, low-pressure/temperature patterning method for high-quality nanopatterns on various substrates over a large area, overcoming conventional costly time-consuming lithographic techniques.

In our study, to optimize the electron-hole balance through controlling the electron transport layer (ETL) in the QD-LEDs, four materials (ZnO, ZnGaO, ZnMgO, and ZnGaMgO NPs) were synthesized and applied to the QD-LEDs as ETLs. By doping ZnO NPs with Ga, the electrons easily inject due to the increased Fermi level of ZnO NPs, and as Mg is further doped, the valence band maximum (VBM) of ZnO NPs deepens and blocks the holes more efficiently. Also, at the interface of QD/ETLs, Mg reduces non-radiative recombination by reducing oxygen vacancy defects on the surface of ZnO NPs. As a result, the maximum luminance ( L max ) and maximum luminance efficiency (LE max ) of QD-LEDs based on ZnGaMgO NPs reached 43 440 cd m -2 and 15.4 cd A -1 . These results increased by 34%, 10% and 27% for the L max and 450%, 88%, and 208% for the LE max when compared with ZnO, ZnGaO, and ZnMgO NPs as ETLs., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

ZnO nanoparticles (NPs) of 4-5 nm, widely adopted as an electron transport layer (ETL) in quantum dot light emitting diodes (QD-LEDs), were synthesized using the solution-precipitation process. It is notable that synthesized ZnO NPs are highly degenerate intrinsic semiconductors and their donor concentration can be increased up to N D  = 6.9 × 10 21 cm -3 by annealing at 140 °C in air. An optical bandgap increase of as large as 0.16-0.33 eV by degeneracy is explained well by the Burstein-Moss shift. In order to investigate the influence of intrinsic defects of ZnO NP ETLs on the performance of QD-LED devices without a combined annealing temperature between ZnO NP ETLs and the emissive QD layer, pre-annealed ZnO NPs at 60 °C, 90 °C, 140 °C, and 180 °C were spin-coated on the annealed QD layer without further post-annealing. As the annealing temperature increases from 60 °C to 180 °C, the defect density related to oxygen vacancy (V O ) in ZnO NPs is reduced from 34.4% to 17.8%, whereas the defect density of interstitial Zn (Zn i ) is increased. Increased Zn i reduces the width (W) of the depletion region from 0.21 to 0.12 nm and lowers the Schottky barrier (Ф B ) between ZnO NPs and the Al electrode from 1.19 to 0.98 eV. We reveal for the first time that carrier conduction between ZnO NP ETLs and the Al electrode is largely affected by the concentration of Zn i above the conduction band minimum, and effectively described by space charge limited current and trap charge limited current models.

We have demonstrated a few-layer black phosphorus (BP) phototransistor of stable operation in ambient air environment and at near-infrared light (λ = 1550 nm). The air-stable electronic and optoelectronic properties of the few-layer BP phototransistor have been achieved by a proper Al 2 O 3 passivation. The optical identification method and qualitative and quantitative electrical characterizations of the few-layer BP phototransistor in dark state confirmed that the device performance was robust in ambient air, to further chemical treatments, and storage of more than six months. In addition, the low-frequency noise characterizations had revealed that the noise spectral density related to the sensitivity of phototransistor was reduced. Owing to the suppression of interaction between few-layer BP and adsorbates arising from the Al 2 O 3 passivation, a fast rise time of the few-layer BP phototransistor, less than 100 μs, had been observed, demonstrating the intrinsic photoresponse properties of few-layer BP. The low dark current of ∼4 nA at the operation bias and the reasonable responsivity of ∼6 mA W -1 were obtained under the condition lacking adsorbates interactions. Internally, the dark current and responsivity level was tunable by changing the operation bias. Our results are close to the intrinsic properties of the few-layer BP phototransistor, implying that it can be a building block of functioned few-layer BP photodetectors.

Transparent conductive electrodes (TCEs) are widely used in a wide range of optical-electronic devices. Recently, metal nanowires (NWs), e.g. Ag and Cu, have drawn attention as promising flexible materials for TCEs. Although the study of core-shell metal NWs, and the encapsulation/overcoating of the surface of single-metal NWs have separately been an object of focus in the literature, herein for the first time we simultaneously applied both strategies in the fabrication of highly stable Ag-Cu NW-based TCEs by the utilization of Ag nanoparticles covered with reduced graphene oxide (rGO). The incorporation of Ag nanoparticles by galvanic displacement reaction was shown to significantly increase the long term stability of the electrode. Upon comparison with a CuNW reference, our novel rGO/Cu-AgNW-based TCEs unveiled remarkable opto-electrical properties, with a 3-fold sheet resistance decrease (from 29.8 Ω sq -1 to 10.0 Ω sq -1 ) and an impressive FOM value (139.4). No detrimental effect was noticed in the relatively high transmittance value (T = 77.6% at 550 nm) characteristic of CuNWs. In addition, our rGO/Cu-AgNW-based TCEs exhibited outstanding thermal stability up to 20 days at 80 °C in air, as well as improved mechanical flexibility. The superior performance herein reported compared with both CuNWs and AgNWs, and with a current conventional ITO reference, is believed to highlight the great potential of these novel materials as promising alternatives in optical-electronic devices.

Colloidal quantum dots (QDs) have been extensively studied for optoelectronic and biological applications due to their unique physical and optical properties. In particular, among the optoelectronics applications, the white light emitting diode (WLED) has great potential in flat panel displays and solid-state lighting. Herein, we demonstrate a novel, facile, and efficient technique for the synthesis of CdTe/ZnO/GO quasi-core-shell-shell hybrid quantum dots containing the CdTe core with multi shells of ZnO and graphene oxide (GO) and fabrication of WQDLEDs. The CdTe/ZnO/GO quasi-core-shell-shell QDs have a unique strong photoluminescence (PL) peak at 624 nm related to the CdTe core and new weak peaks at 382, 404, 422, and 440 nm due to conjugation with ZnO and GO. Also, in the electroluminescence (EL), multiple emission peaks are observed, which can be correlated to the recombination process inside the CdTe core and also recombination of electrons in the lowest unoccupied molecular orbital (LUMO) and LUMO+2 of GO and holes in the valence band (VB) of ZnO. The QDLEDs show clear white color emission with a maximum luminance value of about 480 cd m -2 with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.35, 0.28).

Although various colloidal quantum dot (QD) coating and patterning techniques have been developed to meet the demands in optoelectronic applications over the past years, each of the previously demonstrated methods has one or more limitations and trade-offs in forming multicolor, high-resolution, or large-area patterns of QDs. In this study, we present an alternative QD patterning technique using conventional photolithography combined with charge-assisted layer-by-layer (LbL) assembly to solve the trade-offs of the traditional patterning processes. From our demonstrations, we show repeatable QD patterning process that allows multicolor QD patterns in both large-area and microscale. Also, we show that the QD patterns are robust against additional photolithography processes and that the thickness of the QD patterns can be controlled at each position. To validate that this process can be applied to actual device applications as an active material, we have fabricated inverted, differently colored, active QD light-emitting device (QD-LED) on a pixelated substrate, which achieved maximum electroluminescence intensity of 23 770 cd/m 2 , and discussed the results. From our findings, we believe that our process provides a solution to achieving both high-resolution and large-scale QD pattern applicable to not only display, but also to practical photonic device research and development.

Sub-10 nm In(PO(3))(3) nanocrystals (NCs) were created in an insulating matrix by rapid thermal annealing to form nanocomposite structures. On annealing at a temperature of 400 degrees C, P(2)O(5) NCs were formed by substituting P for Zn atoms in ZnO films via the kickout diffusion mechanism based on the fixed oxygen sublattice. On annealing at a higher temperature of 600 degrees C, however, In(PO(3))(3) NCs were nucleated by diffusion of In atoms from the substrate into the sites of P(2)O(5) NCs that coalesced by moving atoms to neighboring grains in the strain relaxed region. The formation mechanisms of sub-10 nm In(PO(3))(3) NCs in an insulating matrix due to rapid thermal annealing are described on the basis of the experimental results.

The bistable effects of CdSe/ZnS nanoparticles embedded in a conducting poly N-vinylcarbazole (PVK) polymer layer by using flexible poly-vinylidene difluoride (PVDF) and polyethylene terephthalate (PET) substrates were investigated. Transmission electron microscopy (TEM) images revealed that CdSe/ZnS nanoparticles were formed inside the PVK polymer layer. Current-voltage (I-V) measurement on the Al/[CdSe/ZnS nanoparticles+ PVK]/ITO/PVDF and Al/[CdSe/ZnS nanoparticles+ PVK ]/ITO/PET structures at 300 K showed a nonvolatile electrical bistability behavior with a flat-band voltage shift due to the existence of the CdSe/ZnS nanoparticles, indicative of trapping, storing and emission of charges in the electronic states of the CdSe nanoparticles. A bistable behavior for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results. These results indicate that OBDs fabricated by embedding inorganic CdSe/ZnS nanoparticles in a conducting polymer matrix on flexible substrates are prospects for potential applications in flexible nonvolatile flash memory devices.