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A vital objective in the wetting of Au deposited on chemically heterogeneous oxides is to synthesize a completely continuous, highly crystalline, ultrathin-layered geometry with minimized electrical and optical losses. However, no effective solution has been proposed for synthesizing an ideal Au-layered structure. This study presents evidence for the effectiveness of atomic oxygen-mediated growth of such an ideal Au layer by improving Au wetting on ZnO substrates with a substantial reduction in free energy. The unexpected outcome of the atomic oxygen-mediated Au growth can be attributed to the unconventional segregation and incorporation of atomic oxygen along the outermost boundaries of Au nanostructures evolving in the clustering and layering stages. Moreover, the experimental and numerical investigations revealed the spontaneous migration of atomic oxygen from an interstitial oxygen surplus ZnO bulk to the Au-ZnO interface, as well as the segregation (float-out) of the atomic oxygen toward the top Au surfaces. Thus, the implementation of a 4-nm-thick, two-dimensional, quasi-single-crystalline Au layer with a nearly complete crystalline realignment at a mild temperature (570 K) enabled exceptional optoelectrical performance with record-low resistivity (7.5 × 10

Structure engineering is essential for manipulating the chemical, electrical, and optical properties of Au. However, it is challenging to design nanoscopic structures because no effective method is available to deviate from the intrinsic evolution behavior during and after synthesis via vapor deposition. Here, we propose an approach that utilizes the oxidation-induced clustering and layering of Au due to the strong O interference at the outmost surfaces of nanoscopic Au geometries. This promotes the evolution of Au clusters and layers that are highly wetted on their oxide supports. A 4-nm-thick epitaxial Au layer eventually evolved from the proposed growth mode, simultaneously exhibiting higher optical transparency than Ag, a near-bulk resistivity of 8 × 10−8 Ω m, and extreme resilience to chemical corrosion and mechanical deformation. This result provides a definite solution to transparent metal electrodes that are highly vulnerable to degradation in ambient and working environments.

Perovskite solar cells (PSCs) fabricated on transparent polymer substrates are considered a promising candidate as flexible solar cells that can emulate the advantages of organic solar cells, which exhibit considerable freedom in their device design thanks to their light weight and mechanically flexibility while achieving high photocurrent conversion efficiency, comparable to that of their conventional counterparts fabricated on rigid glasses. However, the full realization of highly efficient, flexible PSCs is largely prevented by technical difficulties in simultaneously attaining a transparent electrode with efficient charge transport to meet the specifications of PSCs. In this study, an effective strategy for resolving this technical issue has been devised by proposing a simple but highly effective technique to fabricate an efficient, multilayer TiO2/Ag(O)/ZnO (TAOZ) configuration. This configuration displays low losses in optical transmittance and electrical conductivity owing to its completely continuous, ultrathin metallic Ag(O) transparent electrode, and any notable current leakage is suppressed by its pinhole-free TiO2 electron transport layer. These features are a direct consequence of the rapid evolution of Ag(O) and TiO2 into ultrathin, completely continuous, pinhole-free layers owing to the dramatically improved wetting of metallic Ag(O) with a minimal dose of oxygen (ca. 3 at%) during sputtering. The TAOZ configuration exhibits an average transmittance of 88.5% in the spectral range of 400–800 nm and a sheet resistance of 8.4 Ω sq−1 while demonstrating superior mechanical flexibility to that of the conventional TiO2 on ITO configuration. The photocurrent conversion efficiency of flexible PSCs is significantly improved by up to 11.2% thanks to an optimum combination of optoelectrical performance and pinhole-free morphologies in the TAOZ configuration.

Fabricating polymer solar cells (PSCs) on flexible polymer substrates, instead of on hard glass, is attractive for implementing the advantage and uniqueness of the PSCs represented by mechanically rollable and light-weight natures. However, simultaneously achieving reliable robustness and high-power conversion efficiency (PCE) in such flexible PSCs is still technically challenging due to poor light harvesting of thin photoactive polymers. In this work, we report a facile, effective strategy for improving the light-harvesting performance of flexible PSCs without sacrificing rollability. Very high transparent (93.67% in 400&ndash, 800 nm) and low sheet resistance (~10 &Omega, sq&minus, 1) ZnO/Ag(O)/ZnO electrodes were implemented as the flexible substrates. In systematically comparison with ZnO/Ag/ZnO electrodes, small amount of oxygen induced continuous metallic films with lower thickness, which resulted in higher transmittance and lower sheet resistance. To increase the light absorption of thin active layer (maintain the high rollability of active layer), a unique platform simultaneously utilizing both a transparent electrode configuration based on an ultrathin oxygen-doped Ag, Ag(O), and film and plasmonic Ag@SiO2 nanoparticles were designed for fully leveraging the advantages of duel microresonant cavity and plasmonic effects to enhance light absorbance in photoactive polymers. A combination of the ZnO/Ag(O)/ZnO electrode and Ag@SiO2 nanoparticles significantly increased the short-current density of PSCs to 17.98 mA cm&minus, 2 with enhancing the photoluminescence of PTB7-Th film. The flexible PSC using the optimized configuration provided an average PCE of 8.04% for flexible PSCs, which was increased by 36.27% compared to that of the PSC merely using a conventional transparent indium tin oxide electrode.

Artificially designing the crystal orientation and facets of noble metal nanoparticles is important to realize unique chemical and physical features that are very different from those of noble metals in bulk geometries. However, relative to their counterparts synthesized in wet-chemical processes, vapor-depositing noble metal nanoparticles with the desired crystallographic features while avoiding any notable impurities is quite challenging because this task requires breaking away from the thermodynamically favorable geometry of nanoparticles. We used plasma-generated N atoms as a surface-active agent, a so-called surfactant, to control the structural development of Ag nanoparticles supported on a chemically heterogeneous ZnO substrate. The N-surfactant-facilitated sputter deposition provided strong selectivity for crystalline orientation and facets, leading to a highly flattened nanoparticle shape that clearly deviated from the energetically favorable spherical polyhedra, due to the drastic decreases in the surface free energies of Ag nanoparticles in the presence of the N surfactant. The Ag nanoparticles successively developed a nearly unidirectional (111) orientation aligned by stimulating the crystalline coupling of Ag along the orientation of the ZnO substrate. The experimental and simulation results not only offer new insights into the advantages of N as a surfactant for the orientation and shape-controlled synthesis of Ag nanoparticles via sputter deposition but also provide the first solid evidence validating that immiscible, nonresidual gaseous surfactants can be used in the vapor deposition processes of noble metal nanoparticles to manipulate their surface free energies.

An ultrathin, highly crystalline, two-dimensional Cu layer is necessary for simultaneously achieving ultralow electrical and optical losses in transparent electrodes. However, perfect Cu wetting on heterogeneous oxide substrates has not yet been achieved. Herein, we report the Ge-mediated fabrication of an ultrathin, highly crystalline, complexly continuous Cu layer. The unique surfactant-like segregation of atomic Ge towards the outermost boundaries of the Cu geometries remarkably enhanced Cu wetting on the ZnO substrate. Numerical simulation indicated that the enhanced wetting can be attributed to the simultaneous decreases in the thermodynamic cohesive and formation energies at the surface and interface of the Cu nanostructures owing to Ge segregation. This enabled the fabrication of an ultrathin (∼3 nm), highly crystalline, two-dimensional Cu layer in a ZnO/Cu/ZnO configuration, which exhibited a record-low average optical loss at a near-bulk resistivity (8 × 10−8 Ω m) comparable to those of conventional Ag electrodes; it also showed exceptional durability in water, ozone, and high-temperature (up to 400 °C) environments. These unique features would ensure the development of highly reliable optoelectrical devices employing Cu superstructure-based transparent electrodes as inexpensive alternatives to Ag-based transparent electrodes.

Controlling the shape and crystallography of nanocrystals during the early growth stages of a noble metal layer is important because of its correlation with the final layer morphology and optoelectrical features, but this task is unattainable in vapor deposition processes dominated by artificially uncontrollable thermodynamic free energies. We report on experimental evidence for the controllable evolution of Ag nanocrystals as induced by the addition of nitrogen, presumed to be nonresidual in the Ag lattice given its strong float-out behavior. This atypical formation of energetically stable Ag nanocrystals with significantly improved wetting abilities on a chemically heterogeneous substrate promotes the development of an atomically flat, ultrathin, high-purity Ag layer with a thickness of only 5 nm. This facilitates the fabrication of Ag thin-film electrodes exhibiting highly enhanced optical transparency over a broad spectral range in the visible and near-infrared spectral range. An Ag thin-film electrode with a ZnO/Ag/ZnO configuration exhibits an average transmittance of about 95% in the spectral range of 400-800 nm with a maximum transmittance of over 98% at 580 nm, which is comparable with the best transparency values so far reported for transparent electrodes. This degree of optical transparency provides an excellent chance to improve the photon absorption of photovoltaic devices employing an Ag thin film as their window electrode. This is clearly confirmed by the superior performance of a flexible organic solar cell with a power conversion efficiency of 8.0%, which is far superior to that of the same solar cell using a conventional amorphous indium tin oxide electrode (6.4%).

Improving the wetting ability of Ag on chemically heterogeneous oxides is technically important to fabricate ultrathin, continuous films that would facilitate the minimization of optical and electrical losses to develop qualified transparent Ag film electrodes in the state-of-the-art optoelectronic devices. This goal has yet to be attained, however, because conventional techniques to improve wetting of Ag based on heterogeneous metallic wetting layers are restricted by serious optical losses from wetting layers. Herein, we report on a simple and effective technique based on the partial oxidation of Ag nanoclusters in the early stages of Ag growth. This promotes the rapid evolution of the subsequently deposited pure Ag into a completely continuous layer on the ZnO substrate, as verified by experimental and numerical evidence. The improvement in the Ag wetting ability allows the development of a highly transparent, ultrathin (6 nm) Ag continuous film, exhibiting an average optical transmittance of 94% in the spectral range 400-800 nm and a sheet resistance of 12.5 Ω sq-1, which would be well-suited for application to an efficient front window electrode for flexible solar cell devices fabricated on polymer substrates.

Organic solar cells (OSCs) supported on mechanically flexible and optically transparent polymer substrates have been receiving increased attention owing to their noticeable merits of low cost, light weight, and flexible design that are unattainable by their existing counterparts supported on rigid glass substrates. However, technical issues such as relatively low photon-to-electron conversion efficiencies and long-term stabilities of OSCs on polymer substrates require the enhancement and maintenance of the efficiency of OSCs. In this study, a simple, direct vacuum deposition strategy was used to fabricate a multifunctional silica nanoparticle array (SNA) layer on polymer substrates for improving and maintaining the light harvesting efficiencies of OSCs; this induces simultaneous and significant enhancements in the light-scattering and contaminant-repelling (or self-cleaning) properties of the substrate. The SNA layer led to improved light scattering features, representing haze transmittances ranging from 3.4% to 80.4% in the visible spectral range with strong influences of its geometrical features on the hydrophobic/oleophobic characteristics of the substrate. Any contaminant-induced reduction in the performance of OSCs could be successfully prevented by the strong contaminant-repelling feature, characterized by high contact angles (>150°) and low sliding angles (

Developing a sensor that identifies and quantifies trace amounts of analyte molecules is crucially important for widespread applications, especially in the areas of chemical and biological detection. By non-invasively identifying the vibrational signatures of the target molecules, surface-enhanced Raman scattering (SERS) has been widely employed as a tool for molecular detection. Here, we report on the reproducible fabrication of wafer-scale dense SERS arrays and single-nanogap level near-field imaging of these dense arrays under ambient conditions. Plasmonic nanogaps densely populated the spaces among globular Ag nanoparticles with an areal density of 120 particles per μm2 upon application of a nanolithography-free simple process consisting of the Ar plasma treatment of a polyethylene terephthalate substrate and subsequent Ag sputter deposition. The compact nanogaps produced a high SERS enhancement factor of 3.3 × 107 and homogeneous (coefficient of variation of 8.1%) SERS response. The local near fields at these nanogaps were visualized using photo-induced force microscopy that simultaneously enabled near-field excitation and near-field force detection under ambient conditions. A high spatial resolution of 3.1 nm was achieved. Taken together, the generation of a large-area SERS array with dense plasmonic nanogaps and the subsequent single-nanogap level characterization of the local near field have profound implications in the nanoplasmonic imaging and sensing applications.

The optimization of Ag wetting on oxides is essential to facilitate the synthesis of ultrathin Ag layers with ultralow electrical and optical losses. However, the primary challenge of increasing the Ag wetting on oxides is the strong cohesion and weak adhesion of Ag with chemically heterogeneous oxide substrates. In the present study, it was observed that the dissolution of excess atomic oxygen in ZnO lattices prior to Ag deposition induced the pronounced migration of atomic oxygen across the Ag − ZnO interface and subsequent incorporation into Ag lattices. The substantial intermixing of atomic oxygen in the Ag − ZnO matrices contributed to a decrease in the free energy at the interface, thereby weakening the driving force for the agglomeration of Ag nanoparticles during coalescence. This resulted in an increase in the adhesion and wetting of Ag geometries on the ZnO surfaces. These findings were confirmed based on the results of detailed experimental investigations in conjunction with numerical predictions. These outcomes elucidated the unconventional oxygen spillover dynamics from atomic oxygen-excess oxide surfaces. The findings obtained in the present study refute the existing convictions that the intermixing of oxygen at Ag − oxide interfaces is limited by weak charge transfer.

Ag wetting on oxides is essential for implementing exceptional layered Ag superstructures with simultaneous ultralow losses in electrical conductance and optical transmittance. This goal is difficult to achieve by conventional synthetic techniques involving the incorporation of heterogeneous transition metals or metalloids into Ag as wetting inducers as they cause detrimental optoelectrical changes. This study provides novel insights into the use of homogeneous Ag wetting seeds to improve the wetting of Ag on oxides. We investigated the effect of atomic O incorporation on the improvement of Ag wetting by monitoring its participation in and contribution to the Ag clustering and layering processes. Minimal incorporation of dissolved atomic O as a surfactant into the Ag nanoparticles transposed the nanoparticle evolution path from a complete to incomplete coalescence mode at significantly reduced thicknesses, which was attributed to a reduction in the nanoparticle free energy. The size and shape of the O-incorporated Ag nanoparticles were precisely controlled to accelerate the wetting transition of Ag on ZnO substrates by circumventing the transmutation effect of O. These results demonstrate a notable strategy for accomplishing a rapid Ag wetting transition toward a completely continuous layer with ultralow optoelectrical losses.

Controlling the number and size of nanoparticles on oxides is essential for manipulating the chemical and physical properties of Au to manifest its catalytic and sensing activities. This task requires a drastic deviation from the current understanding of the inherent nucleation behavior of Au nanoparticles weakly adhered on oxides. Herein, we report experimental and computational evidence supporting the effectiveness of incorporating excessive atomic O at ZnO surfaces on enhancing the adhesion of Au − ZnO. This result is highly contrary to current beliefs, emphasizing the advantage of O-deficient oxide surfaces for enhancing the nucleation. The use of atomic O-excessive ZnO surfaces facilitated the implementation of extremely high nucleation densities (>4 × 1012 cm−2) of Au nanoparticles, primarily with reduced diameters of 2–3 nm. These structural features were primarily attributed to the reduction in the free energy at the Au − ZnO interface due to the diffusion and participation of atomic O in Au oxidation. This result offers new insights into the crucial role played by atomic O in enhancing the adhesion of Au with oxides and the development of unique structural features of Au nanoparticles.

The development of highly efficient flexible transparent electrodes (FTEs) supported on polymer substrates is of great importance to the realization of portable and bendable photovoltaic devices. Highly conductive, low-cost Cu has attracted attention as a promising alternative for replacing expensive indium tin oxide (ITO) and Ag. However, highly efficient, Cu-based FTEs are currently unavailable because of the absence of an efficient means of attaining an atomically thin, completely continuous Cu film that simultaneously exhibits enhanced optical transmittance and electrical conductivity. Here, strong two-dimensional (2D) epitaxy of Cu on ZnO is reported by applying an atomically thin (around 1 nm) oxygen-doped Cu wetting layer. Analyses of transmission electron microscopy images and X-ray diffraction patterns, combined with first-principles density functional theory calculations, reveal that the reduction in the surface and interface free energies of the wetting layers with a trace amount (1-2 atom %) of oxygen are largely responsible for the two-dimensional epitaxial growth of the Cu on ZnO. The ultrathin 2D Cu layer, embedded between ZnO films, exhibits a highly desirable optical transmittance of over 85% in a wavelength range of 400-800 nm and a sheet resistance of 11 Ω sq

Molybdenum disulfide with atomic-scale flatness has application potential in high-speed and low-power logic devices owing to its scalability and intrinsic high mobility. However, to realize viable technologies based on two-dimensional materials, techniques that enable their large-area growth with high quality and uniformity on wafer cale is a prerequisite. Here, we provide a route toward highly uniform growth of a wafer-scale, four-layered MoS2 film on a 2 in. substrate via a sequential process consisting of the deposition of a molybdenum trioxide precursor film by sputtering followed by postsulfurization using a chemical vapor deposition process. Spatial spectroscopic analyses by Raman and PL mapping validated that the as-synthesized MoS2 thin films exhibit high uniformity on a 2 in. sapphire substrate. The highly uniform MoS2 layers allow a successful integration of devices based on ∼1200 MoS2 transistor arrays with a yield of 95% because of their extreme homogeneity on Si wafers. Moreover, a pulse elec...

Enhancing light–matter interactions is essential to improving nanophotonic and optoelectronic device performance. In the present work, we developed a new design for 3D plasmonic nanostructures with enhanced near-field interactions among the plasmonic nanomaterials. The 3D plasmonic nanostructures consisted of multilayered bottom Ag/polydimethylsiloxane (PDMS) nanostructures, an alumina middle layer, and top Ag nanoparticles (NPs). High areal density PDMS nanoprotrusions were self-organized by a simple maskless plasma etching process. The conformal deposition of alumina using atomic layer deposition and Ag deposition produced 3D plasmonic nanostructures. These structures induced multiple near-field interactions between the ultrahigh-areal-density (1400 μm−2) top Ag NPs and the underlying Ag nanostructures, and among the top Ag NPs themselves. The high density of hot spots across the 3D space yielded highly efficient and widely tunable plasmonic responses across the entire visible range. The SERS signal enhancement measured at the 3D plasmonic nanostructures was 3.9 times the signal measured at the 2D multilayered structures and 48.0 times the signal measured at a Ag NP layer deposited onto a Si substrate. Finally, the 3D plasmonic nanostructures exhibited excellent uniformity with a variation of 6.8%, based on a microscale Raman mapping analysis. The excellent Raman signal uniformity can be attributed to the ultrahigh areal density of the Ag NPs and the uniform thickness of the alumina spacing layer.

Perovskite solar cells (PSCs) fabricated on transparent polymer substrates are considered a promising candidate as flexible solar cells that can emulate the advantages of organic solar cells, which exhibit considerable freedom in their device design thanks to their light weight and mechanically flexibility while achieving high photocurrent conversion efficiency, comparable to that of their conventional counterparts fabricated on rigid glasses. However, the full realization of highly efficient, flexible PSCs is largely prevented by technical difficulties in simultaneously attaining a transparent electrode with efficient charge transport to meet the specifications of PSCs. In this study, an effective strategy for resolving this technical issue has been devised by proposing a simple but highly effective technique to fabricate an efficient, multilayer TiO

Copper has attracted significant interests as an abundant and low-cost alternative material for flexible transparent conducting electrodes (FTCEs). However, Cu-based FTCEs still present unsolved technical issues, such as their inferior light transmittance and oxidation durability compared to conventional indium tin oxide (ITO) and silver metal electrodes. This study reports a novel technique for fabricating highly efficient FTCEs composed of a copper ultrathin film sandwiched between zinc oxides, with enhanced transparency and antioxidation performances. A completely continuous and smooth copper ultrathin film is fabricated by a simple room-temperature reactive sputtering process involving controlled nitrogen doping (

The wettability of Ag deposited on oxide substrates is generally improved by adding a Ge seed layer. However, the realization of optically transparent Ag electrodes is still a crucial challenge owing to the lack of an effective method for circumventing the catastrophic optical losses caused by the Ge layer. Herein, a strategy is proposed to minimize the optical losses in the Ag-on-Ge configuration grown on ZnO substrates; this provides new insights into the utilization of Ge as a wetting inducer. The evolution of ultrathin films from Ag nanoparticles provided clear evidence for the strong out-diffusion of a substantial amount of Ge atoms toward the top surface of evolving Ag nanostructures. The effective improvement in Ag wetting, even with minimal concentrations of Ge, could be explained by the ability of Ge to reduce the thermodynamic free energy at both the top and bottom boundaries of evolving Ag regions. It was also observed that immiscible and mostly removable Ge atoms from Ag lattices were subsequently oxidized at the boundaries contacting oxides. These unique features of Ge allowed for the fabrication of an extremely smooth, ultrathin (4.5 nm) Ag film on an atomically thin (0.3 nm) Ge layer, with successful circumvention of optical losses.

Wetting of noble metals on oxide structures becomes problematic when attempting to grow two-dimensional, atomically smooth and continuous thin film structures because of a strong tendency for three-dimensional growth. This study redefines the crucial factor that controls the wetting of vacuum deposited Ag on SiO2 substrates and refutes the currently accepted assertion that increasing the nucleation density of Ag is responsible for promoting wetting. Ultrahigh-resolution electron microscopy, supported by X-ray spectroscopic techniques, was used to observe how fast Ag nanoparticles evolve to a continuous film by manipulating the contribution of the crucial factor on Ag wetting, and the results were numerically interpreted using first-principles density functional theory calculations to reveal the relevant dynamics. The experimental and numerical results confirmed that the earliest transition of the coalescence dynamics of Ag nanoparticles from full to partial coalescence is the dominating factor in improving Ag wetting. Surprisingly, Ag wetting is independent of the initial nucleation density of Ag nanoparticles. Favorable partial coalescence with more irregularities in the shapes was readily attainable by artificially reducing the thermodynamic surface and interfacial free energies of the evolving Ag nanoparticles through the addition of a small concentration of Al or O as a wetting agent.

Here, we study the plasmonic metal-enhanced fluorescence properties of blue-emitting graphene quantum dots (GQDs) and green-emitting graphene oxide quantum dots (GOQDs) using fluorescence lifetime imaging microscopy. Reactive ion sputtered silver (Ag) on zinc oxide (ZnO) thin films deposited on silicon (Si) wafers are used as the substrates. The morphology of the sputtered Ag gradually changes from nanoislands, via and elongated network and a continuous film with nanoholes, to a continuous film with increasing sputtering time. The fluorescence properties of GQD and GOQD on the Ag are modulated in terms of the intensities and lifetimes as the morphology of the Ag layers changes. Although both GQD and GOQD show similar fluorescence modulation on the Ag nanofilms, the fluorescence of GQD is enhanced, whereas that of GOQD is quenched due to the charge transfer process from GOQD to ZnO. Moreover, the GQD and GOQD exhibit different fluorescence lifetimes due to the effect of their electronic configurations. The theoretical calculation explains that the fluorescence amplification on the Ag nanofilms can largely be attributed to the enhanced absorption mechanism arising from accumulated optical fields around nanogaps and nanovoids in the Ag nanofilms.

A highly efficient light-scattering layer, composed of quasi-periodic discrete silica nanoparticles directly deposited onto polymer substrates to produce bendable organic solar cells (OSCs) with enhanced light absorption, is reported. A silica nanoparticle layer (SNL) underwent self-assembly on a highly flexible and heat-sensitive polymer at room temperature during fabrication, which employed a unique plasma-enhanced chemical vapour deposition technique. Such efficient light-scattering SNLs have not been realizable by conventional solution-based coating techniques. SNLs were optimized by precisely controlling dimensional parameters, specifically, the nanoparticle layer thickness and interparticle distance. The optimized SNL exhibited an improved transmission haze of 16.8% in the spectral range of 350–700 nm, where reduction of the total transmission was suppressed to 2%. Coating light-scattering SNLs onto polymer substrates is a promising method for improving the light harvesting abilities of OSCs by enhancing the light absorption of photoactive polymer layers. This SNL-based flexible OSC exhibited a record power conversion efficiency (PCE) of 7.4%, representing a 13% improvement, while reducing the thickness of the photoactive polymer layer by 30%.

Molybdenum disulfide with atomic-scale flatness has application potential in high-speed and low-power logic devices owing to its scalability and intrinsic high mobility. However, to realize viable technologies based on two-dimensional materials, techniques that enable their large-area growth with high quality and uniformity on wafer cale is a prerequisite. Here, we provide a route toward highly uniform growth of a wafer-scale, four-layered MoS

A new way was meticulously designed to utilize the localized surface plasmon resonance (LSPR) effect and the light scattering effect of silver nanoplate (Ag-nPl) and core–shell Ag@SiO2 nanoparticles (Ag@SiO2-NPs) to enhance the photovoltaic performances of polymer solar cells (PSCs). To prevent direct contact between silver nanoparticles (Ag-NPs) and photoactive materials which will cause electrons quenching, bare Ag-nPl were spin-coated on indium tin oxide and silica capsulated Ag-NPs were incorporated to a PBDTTT-C-T:PC71BM active layer. As a result, the devices incorporated with Ag-nPl and Ag@SiO2-NPs showed great enhancements. With the dual effects of Ag-nPl and Ag@SiO2-NPs in devices, all wavelength sensitization in the visible range was realized; therefore, the power conversion efficiency (PCE) of PSCs showed a great enhancement of 14.0% to 8.46%, with an increased short-circuit current density of 17.23 mA·cm–2. The improved photovoltaic performances of the devices were ascribed to the LSPR effect a...

An effective method for depositing highly transparent and conductive ultrathin silver (Ag) electrodes using minimal oxidation is reported. The minimal oxidation of Ag layers signifi cantly improves the intrinsic optical and structural properties of Ag without any degradation of its electrical conductivity. Oxygen-doped Ag (AgO x ) layers of thicknesses as low as 6 nm exhibit completely 2D and continuous morphologies on ZnO fi lms, smaller optical refl ections and absorbances, and smaller sheet resistances compared with those of discontinuous and granular-type Ag layers of the same thickness. A ZnO/AgO x /ZnO (ZAOZ) electrode using an AgO x (O/Ag = 3.4 at%) layer deposited on polyethylene terephthalate substrates at room temperature shows an average transmittance of 91%, with a maximum transmittance of 95%, over spectral range 4001000 nm and a sheet resistance of 20 Ω sq 1 . The average transmittance value is increased by about 18% on replacing a conventional ZnO/Ag/ZnO (ZAZ) electrode with the ZAOZ electrode. The ZAOZ electrode is a promising bottom transparent conducting electrode for highly fl exible inverted organic solar cells (IOSCs), and it achieves a power conversion effi ciency (PCE) of 6.34%, whereas an IOSC using the ZAZ electrode exhibits a much lower PCE of 5.65%.

Semi-transparent organic–inorganic hybrid photo-detector cells were fabricated on glass substrate, composed of pentacene/ZnO photodiodes and pentacene thin-film transistors (TFTs). Semi-transparent NiOx window with a large band gap of ∼4 eV was used as an ohmic electrode on 50 nm-thin pentacene channel in the TFT and simultaneously on the 150 nm-thick pentacene layer, which is deposited on ZnO for p–n diode, to absorb visible and ultraviolet photons from pentacene and ZnO, respectively. Our photo-detector exhibited a minimum temporal response of ∼300 ms for photo-induced output voltage at −1 V input and −3 V supply voltage.

An oxide multilayer structure—consisting of an indium zinc oxide (IZO) conductive layer, a silicon oxide (SiOx, x = 1.8) water vapor permeation barrier, and an aluminum oxide (Al2O3) interlayer—coated on polyethylene terephthalate (PET) is proposed as a transparent flexible substrate for display and photovoltaic applications. Vital properties of the multilayer, such as the low water vapor impermeability of the SiOx barrier and the high conductance of the IZO film, degraded considerably because of the crack formation in bend geometries, attributed to the large difference between elastic properties of the oxide films and polymers. In order to suppress the crack formation, a 10-nm-thick Al2O3 interlayer was sputtered on Ar ion-beam treated PET surfaces prior to a SiOx plasma-enhanced chemical vapor deposition (PECVD) process. Changes in the conductance and water vapor impermeability were investigated at different bending radii and bending cycles. It was found that the increases in resistance and water vapor transmission rate (WVTR) were significantly suppressed by the ion-beam PET pretreatment and by the sputtered Al2O3 interlayer. The resistance and WVTR of IZO/SiOx/Al2O3/PET systems could be kept low and invariable even in severely bent states by choosing the SiOx thickness properly. The IZO (135 nm)/SiOx (90 nm)/Al2O3 (10 nm)/PET system maintained a resistance of 3.2 × 10− 4 Ω cm and a WVTR of

The crystallinity and morphology of single-crystal 3C-SiC homoepilayers grown on heteroepilayer (0 0 1) substrates by low-pressure chemical vapor deposition were investigated. The crystalline qualities of homoepilayers were critically dependent upon the defects of heteroepilayer substrates because planar defects, predominantly stacking faults and twins, and protrusions existing on the heteroepilayer surface propagated into the homoepilayers. A surface etching process using reactive ion etching (RIE) of the backside of free-standing heteroepilayers, the interface with Si substrates, was proposed to minimize the defect densities on the heteroepilayer surface. Analyses of high resolution X-ray diffraction (HRXRD) and atomic force microscope (AFM) reveal that simultaneous reductions of both surface roughness and defect densities on the heteroepilayer surface are achieved by an etching depth of 4 μm. Cross-sectional scanning electron microscopy (SEM) observation clearly shows that protrusions on the RIE-treated heteroepilayer surface are readily buried by growing homoepilayers. Furthermore, the results of cross-sectional transmission electron microscopy (XTEM) indicate that (i) significant amounts of planar defects are removed by the RIE process of the backside of heteroepilayers and (ii) most of planar defects propagating into the homoepilayers are terminated by coalescences between one another during early homoepitaxial growth stages.

Advances in flexible optoelectronic devices have led to an increasing need for developing highly efficient, low-cost, flexible transparent conducting electrodes. Copper-based electrodes have been unattainable due to the relatively low optical transmission and poor oxidation resistance of copper. Here, we report the synthesis of a completely continuous, smooth copper ultra-thin film via limited copper oxidation with a trace amount of oxygen. The weakly oxidized copper thin film sandwiched between zinc oxide films exhibits good optoelectrical performance (an average transmittance of 83% over the visible spectral range of 400–800 nm and a sheet resistance of 9 Ω sq−1) and strong oxidation resistance. These values surpass those previously reported for copper-based electrodes; further, the record power conversion efficiency of 7.5% makes it clear that the use of an oxidized copper-based transparent electrode on a polymer substrate can provide an effective solution for the fabrication of flexible organic solar cells., Light enters and exits optoelectronic devices through transparent conductive electrodes, which are one of their most expensive components. Here, the authors develop stable transparent conductive electrodes based on copper and oxide layers that lead to efficient flexible organic solar cells.

Single-crystal 3C-SiC epilayers were grown on on-axis Si(0 0 1) substrates by low-pressure chemical vapor deposition. The dependence of the densities of stacking faults and twins on epilayer thicknesses and growth conditions—including the reactor pressure, the substrate temperature, and the inlet gaseous composition—were investigated by a series of experiments and simulations. Simple indexes were developed to predict the planar defect densities in terms of the flux ratio of adatoms on the deposition surface. The planar defect densities were significantly reduced with increasing the epilayer thickness until continuous surfaces with {1 0 0} planes were formed at 0.7 μm. The stacking fault density was a function of the surface flux ratio of carbon adatom to atomic hydrogen, while the twin density was a function of that of silicon adatom to atomic hydrogen. Those densities were decreased almost linearly with increases in the surface flux of atomic hydrogen at fixed flux values of carbon and silicon adatoms. The surface flux of atomic hydrogen was increased as either the reactor pressure was decreased or the substrate temperature was increased.

A series of low-pressure chemical vapor deposition experiments and gas-surface chemical kinetic simulations have been carried out to achieve significant reductions of twin and protrusion in 3C-SiC heteroepitaxial growth on Si(1 0 0) substrates. A two-step epitaxial process, consisting of a nucleation stage and a subsequent epitaxial stage, was newly proposed by comparisons between experimental results and numerical predictions. The twin formation was successfully suppressed under the growth conditions of the nucleation stage leading to a relative flux ratio of C to Si larger than 56 on the deposition surface. The surface protrusion density was decreased from 7.5×10 6 to 6.5×10 4 cm −2 when the conventional carbonization process was replaced with the proposed nucleation stage.

The chemical vapor deposition of polycrystalline carbon nitride in stagnation flow reactors is simulated. A model is used to predict the gas phase chemistry, temperature and velocity profiles, potential gaseous film growth precursors, and to evaluate the likelihood of bond rearrangement occurring in the bulk phase or on the deposition surface once the gaseous precursors are adsorbed. Numerical studies are carried out to predict the effects of inlet and substrate temperatures, reactor pressure, and inlet gas composition on the gas phase chemistry. Potential gaseous film growth precursors of carbon nitride are determined by quantitatively comparing the calculated results against existing experimental data. Results of the model indicate that the gas phase chemistry, including the gas composition at the deposition surface, is strongly affected by reactor pressure and inlet gas composition. However, the gas composition at the deposition surface does not depend strongly on the inlet temperature, while it is found to be strongly dependent on the substrate temperature. Since no correlation is found between the predicted near-surface concentrations of potential film growth precursors and experimentally measured bond types in the carbon nitride films, the experimentally measured bond types in the films must therefore result from chemical bond rearrangement occurring on the deposition surface or in the bulk phase once the gaseous precursors are adsorbed. Comparison between the calculated film growth rate using potential growth precursors and experimental data indicates that the CHx (x = 0,2,3), C2H2, NHx (x = 0,1,2), and HxCN (x = 1,2) species are the most probable crystalline carbon nitride growth species. Among these, C and CH3 dominate the carbon contribution to the film growth, and N is the primary nitrogen bearing species responsible for the film growth. The sum of predicted film growth rates for carbon bearing species is comparable to the experimentally determined film growth rate.

The presence of thin silicon carbide intermediate layers on silicon substrates during nucleation and the early stages of diamond deposition have been frequently reported. It is generally accepted that the intermediate layer is formed by the bulk diffusion of carbon atoms into the silicon carbide layer and the morphology and orientation of the diamond film subsequently grown on the intermediate layer are strongly affected by that layer. While there have been considerable attempts to explain the mechanism for intermediate layer formation, limited quantitative data are available for the layer formation under the operating conditions conducive to diamond nucleation. This study employs a kinetic model to predict the time evolution of a b-SiC intermediate layer under the operating conditions typical of diamond nucleation in hot filament chemical vapor deposition reactors. The evolution of the layer is calculated by accounting for gasphase and surface reactions, surface and bulk diffusions, the mechanism for intermediate layer formation, and heterogeneous diamond nucleation kinetics and of its dependence on the operating conditions such as substrate temperature and inlet gas composition. A comparison between the time scales for intermediate layer growth and diamond nuclei growth is also performed. Discrepancies in published adsorption energies of gaseous hydrocarbon precursors on the intermediate layer—ranging from 1.43 to 4.61 eV—are examined to determine the most reasonable value of the adsorption energy consistent with observed saturated thicknesses, 1–10 nm, of the intermediate layer reported in the literature. The operating conditions that lead to intermediate layer growth followed by diamond deposition vs. those that yield heteroepitaxial diamond nucleation without intermediate layer formation are discerned quantitatively. The calculations show that higher adsorption energies, 3.45 and 4.61 eV, lead to larger surface number densities of carbon atoms, lower saturated nucleation densities, and larger intermediate layer thicknesses. The observed saturated thicknesses of the intermediate layer may be reproduced if the true adsorption energy is in the range of 3.7–4.5 eV. The intermediate layer thickness increases by increasing substrate temperature and inlet hydrocarbon concentration and the dependence of the thickness on substrate temperature is especially significant. Heteroepitaxial diamond nucleation without intermediate layer formation reported in experimental results can be readily explained by the significant decrease of the intermediate layer thickness at lower substrate temperatures and at higher diamond nucleation densities. Further, the present model results indicate that the intermediate layer thickness becomes saturated when growing diamond nuclei cover a very small surface area of that layer. D 2005 Elsevier B.V. All rights reserved.

The need for the development of transparent conductive electrodes (TCEs) supported on flexible polymer substrates has explosively increased in response to flexible polymer-based photovoltaic and display technologies; these TCEs replace conventional indium tin oxide (ITO) that exhibits poor performance on heat-sensitive polymers. An efficient, flexible TCE is required to exhibit high electrical conductance and high optical transmittance, as well as excellent mechanical flexibility and long-term stability, simultaneously. Recent advances in technologies utilizing an ultrathin noble-metal film in a dielectric/metal/dielectric structure, or its derivatives, have attracted attention as promising alternatives that can satisfy the requirements of flexible TCEs. This review will survey the background knowledge and recent updates of synthetic strategies and design rules toward highly efficient, flexible TCEs based on ultrathin metal films, with a special focus on the principal features and available methodologies involved in the fabrication of highly transparent, conductive, ultrathin noble-metal films. This survey will also cover the practical applications of TCEs to flexible organic solar cells and light-emitting diodes.

A three-dimensional (3D) transparent conducting electrode, consisting of a quasi-periodic array of discrete indium-tin-oxide (ITO) nanoparticles superimposed on a highly conducting oxide–metal–oxide multilayer using ITO and silver oxide (AgOx) as oxide and metal layers, respectively, is synthesized on a polymer substrate and used as an anode in highly flexible organic solar cells (OSCs). The 3D electrode is fabricated using vacuum sputtering sequences to achieve self-assembly of distinct ITO nanoparticles on a continuous ITO–AgOx–ITO multilayer at room-temperature without applying conventional high-temperature vapour–liquid–solid growth, solution-based nanoparticle coating, or complicated nanopatterning techniques. Since the 3D electrode enhances the hole-extraction rate in OSCs owing to its high surface area and low effective series resistance for hole transport, OSCs based on this 3D electrode exhibit a power conversion efficiency that is 11–22% higher than that achievable in OSCs by means of conventional planar ITO film-type electrodes. A record high efficiency of 6.74% can be achieved in a bendable OSC fabricated on a poly(ethylene terephthalate) substrate.

The growth of b-SiC films via chemical vapor deposition (CVD) has been under intensive investigation because this is viewed to be an enabling material for a variety of new semiconductor devices in areas where silicon cannot eVectively compete. However, the diYculty in achieving single-crystal or highly textured surface morphology in films with low bulk defect density has limited the use of b-SiC films in electronic devices. Although several researchers have reported results relating the morphology of b-SiC films to deposition parameters, including substrate temperature and gas composition, detailed knowledge of the eVects of deposition parameters on film morphology and crystallographic texture is still lacking. If these relationships between deposition parameters and film morphology can be quantified, then it may be possible to obtain optimal b-SiC film morphologies via CVD for specific applications such as high-power electronic devices. The purpose of this study is to predict the dependence of the surface morphology of b-SiC films grown by CVD on substrate temperature and inlet atom ratio of Si:C, and to model the morphological evolution of the growing polycrystalline film. The Si:C ratio is determined by the composition of the reactant gases, propane (C 3 H 8 ) and silane (SiH 4 ). A two-dimensional numerical model based on growth rate parameters has been developed to predict the evolution of the surface morphology. The model calculates the texture, surface roughness, and grain size of continuous polycrystalline b-SiC films resulting from growth competition between nucleated seed crystals of known orientation. Crystals with the fastest growth direction perpendicular to the substrate surface are allowed to overgrow all other crystal orientations. When a continuous polycrystalline film is formed, the facet orientations of crystals are represented on the surface. In the model, the growth parameter a 2D , the ratio of the growth rates of the {10} and {11} faces, determines the crystal shapes and, thus, the facet orientations of crystals. The growth rate parameter a 2D used in the model has been derived empirically from the textures of continuous b-SiC films reported in the literature. © 2000 Elsevier Science S.A. All rights reserved.

Explicit expressions have been derived for momentum and thermal boundary-layer thickness of the laminar, uniform stagnation flows characteristic of highly convective chemical vapor deposition pedestal reactors. Expressions for the velocity and temperature profiles within the boundary layers have also been obtained. The results indicate that, to leading order, the momentum boundary-layer thickness is inversely proportional to the square root of the Reynolds number, while the thermal boundary-layer thickness is inversely proportional to the square root of the Peclet number. Values computed using the approximate expressions are compared directly with numerical solutions of the equations of motion and thermal energy equation, for a specific set of conditions typical of diamond chemical vapor deposition. Because values of the Lewis number do not vary significantly from unity for many different chemical vapor deposition systems, the expression derived here for thermal boundary-layer thickness may be used directly as an approximate concentration boundary-layer thickness.

We report that significantly more transparent yet comparably conductive AgOx films, when compared to Ag films, are synthesized by the inclusion of a remarkably small amount of oxygen (i.e., 2 or 3 atom %) in thin Ag films. An 8 nm thick AgOx (O/Ag=2.4 atom %) film embedded between 30 nm thick ITO films (ITO/AgOx/ITO) achieves a transmittance improvement of 30% when compared to a conventional ITO/Ag/ITO electrode with the same configuration by retaining the sheet resistance in the range of 10-20 Ω sq(-1). The high transmittance provides an excellent opportunity to improve the power-conversion efficiency of organic solar cells (OSCs) by successfully matching the transmittance spectral range of the electrode to the optimal absorption region of low band gap photoactive polymers, which is highly limited in OSCs utilizing conventional ITO/Ag/ITO electrodes. An improvement of the power-conversion efficiency from 4.72 to 5.88% is achieved from highly flexible organic solar cells (OSCs) fabricated on poly(ethylene terephthalate) polymer substrates by replacing the conventional ITO/Ag/ITO electrode with the ITO/AgOx/ITO electrode. This novel transparent electrode can facilitate a cost-effective, high-throughput, room-temperature fabrication solution for producing large-area flexible OSCs on heat-sensitive polymer substrates with excellent power-conversion efficiencies.

We report the fabrication of a highly flexible indium tin oxide (ITO) electrode that is completely transparent to light in the visible spectrum. The electrode was fabricated via the formation of a novel ITO nanoarray structure, consisting of discrete globular ITO nanoparticles superimposed on an agglomerated ITO layer, on a heat-sensitive polymer substrate. The ITO nanoarray spontaneously assembled on the surface of the polymer substrate by a simple sputter coating at room temperature, without nanolithographic or solution-based assembly processes being required. The ITO nanoarray exhibited a resistivity of approximately 2.3 × 10(-3) Ω cm and a specular transmission of about 99% at 550 nm, surpassing all previously reported values of these parameters in the case of transparent porous ITO electrodes synthesized via solution-based processes at elevated temperatures. This novel nanoarray structure and its fabrication methodology can be used for coating large-area transparent electrodes on heat-sensitive polymer substrates, a goal unrealizable through currently available solution-based fabrication methods.

We report the direct coating of a novel antireflective (AR) nanoarray structure of silica nanoparticles on highly flexible polymer substrates by a conventional vacuum coating method using plasma-enhanced chemical vapor deposition. Globular-shaped silica nanoparticles are found to be self-arranged in a periodic pattern on subwavelength scales without the use of artificial assemblies that typically require complicated nanolithography or solution-based nanoparticle fabrication approaches. Highly efficient AR characteristics in the visible spectral range are obtained at optimized refractive indices by controlling the dimensions and average distances of the silica nanoparticle arrays in a level accuracy of tens of nanometers. The AR nanoarrays exhibit sufficient structural durability against the very high strain levels that arise from the flexibility of polymer substrates. This simple coating process provides a cost-effective, high-throughput, room-temperature fabrication solution for producing large-area polymer substrates with AR characteristics.