Thin film passive solar windows produced by reactive evaporation of In-Sn

The semiconductor indium tin oxide (ITO) when present as a thin film has been shown to be transparent to visible radiation while opaque to IR radiation. Sputtering, chemical vapor deposition and other coating methodologies have been used to prepare ITO thin films. Reactive evaporation is an alternative coating technique, which has as its major advantage technical simplicity. Our prepation of ITO thin films (30–90 nm) for passive solar windows included the reactive evaporation of In-Sn alloys (In-5wt.%Sn, In-10wt.%Sn and In-20wt.%Sn) onto commercial soda-lime glass held between 25 and 300 °C. The reactive evaporation atmosphere consisted of oxygen at partial pressures from 1 × 10^-4 to 1 × 10^-3 Torr in residual nitrogen. In selected instances ultrathin palladium nucleating layers were evaporated onto the glass substrates prior to the deposition of the ITO. This was done in order to minimize initial alloy-glass agglomeration effects, thus decreasing the final overall ITO film thickness while increasing the visible transmission properties. The film's visible and IR spectral transmission properties were examined using ratio recording spectrophotometry. The agglomeration, nucleation and growth phenomena of the films were extensively investigated by transmission electron microscopy. The agglomeration was found to be a function of the film thickness, with increasing agglomeration for thinner films. Surface analysis by scanning Auger microscopy (SAM), electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy and energy-dispersive analysis of X-rays was also extensively carried out to determine our particular film properties. SAM indicated that only indium, tin and oxygen were present. No tungsten from the evaporation filament or elements from the glass were found. ESCA indicated that ITO was indeed present on the surface. Such work definitely indicated that ITO can be prepared by reactive physical vapor deposition and that the resultant films have the properties commonly found in sputtered ITO films.     

Transparente Barriereschichten auf flexiblen Polymersubstraten

Transparent permeation barrier layers on flexible polymer substrates This paper reviews different vacuum based technologies for manufacturing transparent permeation barrier layers and layer stacks on flexible polymer substrates. With plasma assisted reactive evaporation, a cost‐efficient, highly productive process for food packaging applications is presented. Reactive dual magnetron sputtering is a technology for the deposition of oxide layers with a very low water vapor and oxygen transmission rate at a reasonable deposition rate. Many groups suggest multilayer stacks for the encapsulation of flexible electronic devices. In this paper, an all‐in‐vacuum inline concept for manufacturing such multilayers is presented. It is based on the combination of reactively sputtered barrier layers with interlayers grown by using a magnetron based PECVD process (Magnetron‐PECVD). Both, process parameters, such as deposition rate and process pressure, and important layer properties, such as morphology and the water vapor and oxygen transmission rate are compared for the different single and multi layer technologies.     

High-rate reactive deposition of transparent SiO2 films containing low amount of Zr from molten magnetron target

The paper reports on a reactive deposition of transparent SiO₂ films with a low amount (≤ 3 at.%) of Zr prepared from the molten target using the AC pulsed dual magnetron. It is shown that the deposition rate a_D of the transparent oxide film strongly increases at the critical target power density (W_t)_cr when the solid target starts to melt and the magnetron operates with a molten target. In this case, the evaporation of target material plays a dominant role in the reactive deposition of thin films. This process is called the ionized magnetron evaporation. Oxide films reactively deposited from the molten target are well transparent and highly elastic. The maximum deposition rate of the transparent oxide film achieved in our experiments is 814 nm/min.     

Low-temperature crystallization of oriented ZnO film using seed layers prepared by sol–gel method

Transparent zinc oxide (ZnO) films were coated on seed layers prepared by the sol–gel method by chemical solution deposition method. Firstly, seed layers were prepared from zinc acetate and monoethanolamine, 2-methoxyethanol by the sol–gel method on a silicon substrate or a slide glass. Next, the substrate coated with a seed layer was immersed in zinc nitride solution with hexamethylenetetramine, and ZnO films were obtained. The transmittance of the ZnO films depended on the morphology and crystallinity of the seed layers. When the seed layer were dried on a hot plate, the seed layer had flat surface and transparent ZnO film could be obtained on the seed layers dried at temperatures above 200 °C. When the seed layer was prepared from zinc acetate dihydrate dried in a petri dish, the seed layer were smooth without cracks and the transparent ZnO films were obtained at temperature below 100 °C.     

Reaktives Magnetronsputtern von Dünnschichtsolarzellen

Reactive Magnetron Sputtering of Thin Film Solar Cells We show that reactive magnetron sputtering is well suited to deposit CuInS₂‐thin film absorber layers of high electronic quality. Using metallic targets and substrate temperatures below 500 °C, compact films with grain sizes in the micrometer range can be obtained. The structural and electronic properties of these layers are comparable to CuInS₂ thin films prepared by a 2‐step sulfurization process, which is being commercialized at present. In particular, the reactively sputtered films show minority carrier diffusion lengths larger than the layer thickness (≈ 2μm). This results in solar cells with conversion efficiences larger than 10 %, comparable to the best conversion efficiencies for CuInS₂‐solar cells obtained from other deposition processes. These results are promising for the potential application of magnetron sputtering as a large area deposition process for absorber layers in thin film solar cells.     

Surface roughness effects and their influence on the degradation of organic light emitting devices

Organic light emitting devices typically consist of one or several organic layers which are sandwiched between two electrodes, one of which has to be transparent. In most cases indium tin oxide (ITO) is employed as the transparent, hole-injecting anode material. Usually, the functional organic layers possess a thickness of about 100 nm. For such thin films the homogeneity and the surface roughness are especially important factors for the device performance. Therefore, the surface roughness of all those layers which are the basis for subsequent deposition processes were systematically studied by atomic force microscopy (AFM). For these investigations both the ITO substrate and the layers consisting of different organic materials deposited onto the ITO substrate were analyzed. In addition, the two different basic deposition methods for the organic materials, namely the deposition from solution by spin coating and the deposition by thermal evaporation, were compared to one another with respect to their resulting surface roughness. It was found that the large surface roughness of the ITO substrate induces layer inhomogeneities, especially for the vapor deposited organic layers. They can be reduced by the incorporation of a polymeric smoothing layer.     

Layer-by-layer assembled graphene oxide/polydiallydimethylammonium chloride composites for hydrogen gas barrier application

Poly(diallyldimethylammoium chloride) (PDDA)/acid or base modified graphene oxide (MGO) composite (PDDA/MGO)-based gas barrier films were prepared by layer-by-layer (LBL) assembly method on polyethylene terephthalate (PET) substrate using a spray coating assisted deposition. The effect of pH on the hydrogen gas permeability (H₂GP) values of the different MGO-based films was investigated to determine the optimum pH value of the MGO solution for the preparation of PDDA/MGO-based LBL assembly. Accordingly, the different numbers of bilayers based LBL-assembled films were prepared using alternate deposition of PDDA and MGO solutions and the H₂GP values were measured for those assemblies. The films were characterized by XRD, FT-IR, and Raman spectroscopy analyses. The morphology of the LBL-assembled film was observed by cross-sectional field emission scanning electron microscopy which confirms densely packed layered structure. The H₂GP of six bilayers PDDA/MGO composite film is 5.7 cc/m²?d?atm, which is much lower than that of pure PET substrate (170.7 cc/m²?d?atm), indicating 96.7% decrease in H₂GP. This result suggests that the PDDA/MGO composite film could be used as a potential candidate to fabricate hydrogen gas barrier coating material.     

A comparative study of the UV optical and structural properties of SiO2, Al2O3, and HfO2 single layers deposited by reactive evaporation, ion-assisted deposition and plasma ion-assisted deposition

Growing requirements for the optical and environmental stability, as well as the radiation resistance against high-power laser radiation, especially for optical interference coatings used in the ultraviolet spectral range, have to be met by new, optimised, thin-film deposition technologies. For applications in the UV spectral range, the number of useful oxide thin film materials is very limited due to the higher absorption at wavelengths near to the electronic bandgap of the materials. Applying ion-assisted processes offers the ability to grow dense and stable films, but in each case careful optimisation of the deposition process (evaporation rate, substrate temperature, bombarding gas, ion energy and ion current density) has to achieve a balance between densification of the layers and the absorption. High-quality coatings and multilayer interference systems with SiO₂ as the low-index material can be deposited by various physical vapour deposition technologies, including reactive e-beam evaporation, ion-assisted deposition and plasma ion-assisted deposition. In order to improve the degradation stability of dielectric mirrors for use in UV free-electron laser optical cavities, a comparative study of the properties of SiO₂, Al₂O₃ and HfO₂ single layers was performed, and was addressed to grow very dense films with minimum absorption in the spectral range from 200 to 300 nm. The films were deposited by low-loss reactive electron-beam evaporation, by ion-assisted deposition using a ‘Mark II’ ion source, and by plasma ion-assisted deposition using the advanced plasma source. Optical and structural properties of the samples were studied by spectral photometry, infrared spectroscopy, X-ray diffraction and reflectometry, as well as by investigation of the surface morphology. The interaction of UV radiation with photon energy values close to the bandgap was studied. For HfO₂ single layers, laser-induced damage thresholds at 248 nm were determined in the 1-on-1 and 1000-on-1 test modes as a function of the deposition technology and film thickness.     

Low‐Temperature Soft‐Cover Deposition of Uniform Large‐Scale Perovskite Films for High‐Performance Solar Cells

Large‐scale high‐quality perovskite thin films are crucial to produce high‐performance perovskite solar cells. However, for perovskite films fabricated by solvent‐rich processes, film uniformity can be prevented by convection during thermal evaporation of the solvent. Here, a scalable low‐temperature soft‐cover deposition (LT‐SCD) method is presented, where the thermal convection‐induced defects in perovskite films are eliminated through a strategy of surface tension relaxation. Compact, homogeneous, and convection‐induced‐defects‐free perovskite films are obtained on an area of 12 cm², which enables a power conversion efficiency (PCE) of 15.5% on a solar cell with an area of 5 cm². This is the highest efficiency at this large cell area. A PCE of 15.3% is also obtained on a flexible perovskite solar cell deposited on the polyethylene terephthalate substrate owing to the advantage of presented low‐temperature processing. Hence, the present LT‐SCD technology provides a new non‐spin‐coating route to the deposition of large‐area uniform perovskite films for both rigid and flexible perovskite devices.     

Exceptional Flame Resistance and Gas Barrier with Thick Multilayer Nanobrick Wall Thin Films

Layer‐by‐layer (LbL) assembly is a powerful and versatile technique to deposit functional thin films, but often requires a large number of deposition steps to achieve a film thick enough to provide a desired property. By incorporating amine salts into the cationic polyelectrolyte and its associated rinse, LbL clay‐containing nanocomposite films can achieve much greater thickness (>1 μm) with relatively few deposition cycles (≤6 bilayers). Amine salts interact with nanoclays, causing nanoplatelets to deposit in stacks rather than as individual platelets. This technique appears to be universal, exhibiting thick growth with multiple types of nanoclay, including montmorillonite and vermiculite (VMT), and a variety of amine salts (e.g., hexylamine and diethanolamine). The characteristic order found in LbL‐assembled films is maintained despite the incredible thickness. Films assembled in this manner achieve oxygen transmission rates below 0.009 cc m⁻² d⁻¹ atm⁻¹ with just 6 bilayers (BLs) of chitosan/VMT deposited. These thick clay‐based thin films also impart exceptional flame resistance. A 2‐BL film renders a 3.2 mm polystyrene plate self‐extinguishing, while an 8‐BL film (3.9 μm thick) prevents ignition entirely. This ability to generate much thicker clay‐based multilayers with amine salts opens up tremendous potential for these nanocoatings in real world applications.     

Uniformity of gallium doped zinc oxide thin film prepared by pulsed laser deposition

Recently, transparent conducting oxide thin films have attracted attention for the application to transparent conducting electrodes. In this work, we evaluated the uniformity of electrical, optical and structural properties for gallium doped zinc oxide thin films prepared on the 10 × 10 cm² silica glass substrate by pulsed laser deposition. The resistivity, carrier concentration, mobility, bonding state and atomic composition of the film were uniform along in-plane and depth direction over the 10 × 10 cm² area of the substrate. The film showed the average transmittance of 81-87%, resistivity of 1.4 × 10^− 3 Ω cm, carrier concentration of 9.7 × 10²⁰/cm³ and mobility of 5 cm²/Vs in spite of the amorphous X-ray diffraction pattern. The gradual thickness distribution was found, however, the potential for large-area and low temperature deposition of transparent conducting oxide thin film using pulsed laser deposition method was confirmed.     

阻隔薄膜在复合软包装材料中的应用与发展动向

按阻隔性的赋予方法对复合软包装材料进行了分类,对阻隔薄膜在复合软包装材料中的应用与开发历程进行了综述。通过对铝箔类、树脂类、透明蒸镀陶瓷类阻隔薄膜的市场动向与发展趋势进行分析,指出透明蒸镀陶瓷阻隔薄膜及其复合软包装材料将是今后环境适应型软包装材料开发的重要方向。     

Diagnostic in TCOs CVD processes by IR pyrometry

Infra red pyrometry is a sensitive, simple and low-cost technique commonly used for the measurement of the deposition temperature in CVD processes. We demonstrate in this work that this optical technique can be used as diagnostic tool to provide fruitful informations during the growth under atmospheric pressure of TiO₂ films on various substrates chosen as an example of transparent oxide. Significant variations of the pyrometric signal were observed during the deposition of TiO₂ thin films due to interferences in the growing film resulting from multi-reflections at the interfaces and scattering induced by the surface roughness. Modeling of the time dependence of the IR pyrometric signal allows simultaneously the determination of the layer thickness, the growth rate, surface roughness and refractive index of the thin films under the growth conditions. This diagnostic technique can be used for various transparent thin films grown on opaque substrates and is well adapted to control CVD processes operating either under atmospheric or low pressure and more generally any thermal treatment processes.     

柔性高阻隔薄膜材料的研究现状

目的为柔性高阻隔薄膜的应用提供理论指导。方法综述柔性高阻隔膜的应用现状及存在问题,总结热蒸发、化学气相沉积、原子层沉积等制备柔性高阻隔薄膜的方法、原理、特点及应用,展望高阻隔膜包装材料的发展前景。结果高阻隔薄膜制备工艺趋向于单次制备,采用等离子体辅助原子层沉积技术是制备超高阻隔薄膜的首选,原子层沉积(ALD)和分子层沉积(MLD)结合也是获得超高阻隔薄膜的未来发展方向。结论快速、高效地制备柔性高阻隔薄膜是包装工业的发展趋势。     

Transparente Elektroden auf Kunststofffolien

Transparent electrodes have gained a considerable importance in various fields, like e.g. touchscreen devices. Future applications will require higher performance with regard to both electrical and optical properties and they will require lower cost. Today most electrodes are made of transparent conducting oxides like indium tin oxide (ITO). These materials can be sputtered from ceramic targets by dc sputtering processes with simple process control setups. Polymer films can be coated with these materials in vacuum roll coaters. These systems allow the sputtering processes to be run during an unwind‐rewind‐cycle of the roll. Sheet resistance values as low as 20 Ω_squ can be achieved by this technology. Lower resistance values require different approaches. A new and very effective solution is the superposition of the transparent oxide with a metal network. However, also approaches which completely base on organic materials are under investigation. These solutions benefit from the progress in organic conductors. They can be made without any vacuum coating technology. Besides the low sheet resistance also the mechanical robustness against bending is an important advantage of full‐organic approaches.     

Development of new transparent conductors and device applications utilizing a multidisciplinary approach

Transparent and conductive films are key components for optoelectronic devices. They are applied as n-type transparent electrical contacts for inorganic and organic light emitting diodes, solar cells and flat panel displays as well as p- and n-type active semiconductive oxides to setup wide band gap p-n junctions and devices for the emerging field of transparent and radiation hard electronics.The demand for these films is strongly increasing due to the extensive market growth in these areas but the solutions available today only partially fulfill the requirements on low resistivity, high transmittance, large area deposition, low cost manufacturing, and ability for fine patterning, light scattering and precise alignment of the electronic structure to surrounding semiconductors.The cooperation of five Fraunhofer Institutes within the “Fraunhofer Project MAVO METCO” aims towards establishing fundamental knowledge and control about the defect chemistry, structure and morphology of the transparent semiconductive oxides. The goal is to achieve materials with outstanding properties such as n-type transparent conductive oxides with tailored work function and excellent durability, novel delafossite based p-type materials allowing cost effective large area deposition, oxide based p-n heterojunctions and Ag based electrodes to be used for thin film photovoltaics and organic light emitting diodes.Starting from first-principle modelling of the electronic structure, we address the development of new transparent conductive layers by PVD and Sol-Gel ending up with device implementation for OLEDs and organic as well as Si based a-Si:H/µc-Si:H and HIT solar cells.     

Low temperature (< 100 °C) deposited P-type cuprous oxide thin films: Importance of controlled oxygen and deposition energy

With the emergence of transparent electronics, there has been considerable advancement in n-type transparent semiconducting oxide (TSO) materials, such as ZnO, InGaZnO, and InSnO. Comparatively, the availability of p-type TSO materials is more scarce and the available materials are less mature. The development of p-type semiconductors is one of the key technologies needed to push transparent electronics and systems to the next frontier, particularly for implementing p-n junctions for solar cells and p-type transistors for complementary logic/circuits applications. Cuprous oxide (Cu₂O) is one of the most promising candidates for p-type TSO materials. This paper reports the deposition of Cu₂O thin films without substrate heating using a high deposition rate reactive sputtering technique, called high target utilisation sputtering (HiTUS). This technique allows independent control of the remote plasma density and the ion energy, thus providing finer control of the film properties and microstructure as well as reducing film stress. The effect of deposition parameters, including oxygen flow rate, plasma power and target power, on the properties of Cu₂O films are reported. It is known from previously published work that the formation of pure Cu₂O film is often difficult, due to the more ready formation or co-formation of cupric oxide (CuO). From our investigation, we established two key concurrent criteria needed for attaining Cu₂O thin films (as opposed to CuO or mixed phase CuO/Cu₂O films). First, the oxygen flow rate must be kept low to avoid over-oxidation of Cu₂O to CuO and to ensure a non-oxidised/non-poisoned metallic copper target in the reactive sputtering environment. Secondly, the energy of the sputtered copper species must be kept low as higher reaction energy tends to favour the formation of CuO. The unique design of the HiTUS system enables the provision of a high density of low energy sputtered copper radicals/ions, and when combined with a controlled amount of oxygen, can produce good quality p-type transparent Cu₂O films with electrical resistivity ranging from 10² to 10⁴ Ω-cm, hole mobility of 1-10 cm²/V-s, and optical band-gap of 2.0-2.6 eV. These material properties make this low temperature deposited HiTUS Cu₂O film suitable for fabrication of p-type metal oxide thin film transistors. Furthermore, the capability to deposit Cu₂O films with low film stress at low temperatures on plastic substrates renders this approach favourable for fabrication of flexible p-n junction solar cells.     

Transition Metal Oxides for Organic Electronics: Energetics,Device Physics and Applications

During the last few years, transition metal oxides (TMO) such as molybdenum tri‐oxide (MoO₃), vanadium pent‐oxide (V₂O₅) or tungsten tri‐oxide (WO₃) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long‐term stable p‐type doping of wide band gap organic materials, charge‐generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi‐transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO‐based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution‐based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed.     

Characterization of silicon oxide gas barrier films with controlling to the ion current density (ion flux) by plasma enhanced chemical vapor deposition

Silicon oxide gas barrier films were deposited on polyethylene terephthalate (PET) substrates by plasma enhanced chemical vapor deposition (PE-CVD) for applications to transparent barrier packaging. The barrier properties of the silicon oxide coated film were optimized by varying the bias conditions and input power in the radio frequency plasma. The plasma diagnostics, ion current density and substrate temperature were characterized by optical emission spectrometry (OES), an oscilloscope and thermometer, respectively. The coating properties were examined by Fourier transform infrared (FT-IR) spectroscopy and the water vapor transmission rate (WVTR). A high intensity of O and H ions and a high ion current density (ion flux) with a low temperature plasma process were found to be suitable for improving the barrier properties of the silicon oxide film coatings. The Si-O cage-like structure adversely affected the gas barrier properties of the deposited coating. The energy provided by ion bombardment (ion flux) can induce changes in the film density and composition similar to those that may occur by the increase in deposition temperature through rf bias. In addition, the film properties depend not only on a high ion current density (ion flux) and input power, but are also related to a silicon oxide film with a widely distributed planar ring size.     

Growing Oxide Nanowires and Nanowire Networks by Solid State Contact Diffusion into Solution‐Processed Thin Films

New techniques to directly grow metal oxide nanowire networks without the need for initial nanoparticle seed deposition or postsynthesis nanowire casting will bridge the gap between bottom‐up formation and top‐down processing for many electronic, photonic, energy storage, and conversion technologies. Whether etched top‐down, or grown from catalyst nanoparticles bottom‐up, nanowire growth relies on heterogeneous material seeds. Converting surface oxide films, ubiquitous in the microelectronics industry, to nanowires and nanowire networks by the incorporation of extra species through interdiffusion can provide an alternative deposition method. It is shown that solution‐processed thin films of oxides can be converted and recrystallized into nanowires and networks of nanowires by solid‐state interdiffusion of ionic species from a mechanically contacted donor substrate. NaVO₃ nanowire networks on smooth Si/SiO₂ and granular fluorine‐doped tin oxide surfaces can be formed by low‐temperature annealing of a Na diffusion species‐containing donor glass to a solution‐processed V₂O₅ thin film, where recrystallization drives nanowire growth according to the crystal habit of the new oxide phase. This technique illustrates a new method for the direct formation of complex metal oxide nanowires on technologically relevant substrates, from smooth semiconductors, to transparent conducting materials and interdigitated device structures.