Thin metal coatings have been used for several years as selective radiation filters in architectural window applications. These coatings are usually produced by vacuum deposition techniques such as evaporation or sputtering, and coatings are deposited either directly onto glass, or onto polyester film which is then laminated to glass. Recently, metal coatings have begun to be used as reflectors in lighting and other applications.

Airco Solar Products began as a business unit of Airco Temescal in the early 1970's. The first large area magnetron sputtering deposition occurred in 1974, and the first large area magnetron sputtering system was built and operated under contract to Guardian Industries in Carleton, Michigan in 1977, and was later sold to Guardian. This system continues in three-shift production today. A smaller development system, designed for use in the architectural glass coating industry, was introduced in parallel with the large area coaters. There are now over seventeen of these systems, called the ILS-1600, in use or on order throughout the world. This is a proven, industrial-style development sputter deposition system and has an excellent field record in the areas of versatility and low maintenance requirements. Airco Solar Products has recently begun to market this system into other applications such as the photovoltaics industry, the flat panel display industry and other specialty industries. The features of this system such as overall design, expandability, process scale-up and available options will be discussed. Expanded versions of this system currently in the field will be reviewed, and future applications will be discussed.

A detailed investigation of a multilayer design for a temperature resistant low emissivity and highly electrical conductive coating is performed. The optical transmittance, reflectance and the color coordinates are discussed. A good agreement with computer simulated spectra and experimental data was achieved. The layer system was prepared by high rate magnetron sputtering on large float glass sheets. By gravity bending in normal atmosphere these coated substrates were formed and then further processed to heated windshields and curved double glazed units. The performance characteristics of these final products are discussed.

ZnO:Al films were produced by dual-target reactive magnetron sputtering. The effects of different deposition conditions were investigated. Under optimized conditions, 0.3-pm-thick films had -1% luminous absorptance, ≈85 % thermal infrared reflectance, and a dc resistivity of ≈5 x 10^-4 Ω cm. Rutherford Backscattering Spectrometry showed that the Al content was ≈2 at.%. Transmission electron microscopy showed that the crystallite size was ≈50 nm for films deposited onto unheated substrates.

Tin oxide (TO) films were coated by spray-deposition technique using monobutyl tin trichloride (MBTC) and dibutyl tin diacetate (DBDA) solutions. Spectrophotometric transmittance characteristics of samples deposited on Corning 7059 glass were used to evaluate refractive index, and extinction coefficient spectra, n -λ and k-λ respectively of TO films. Samples exhibit a V-shaped absorption spectrum with a minimum of ≈/LieV. Absorption minima of TO films were found to be thickness and starting solution dependent. MBTC-TO films exhibit lower absorption than DBDA-TO films with higher absorption for thicker films. Bond properties and structural investigations of spray-deposited TO films were also studied.

The oxidation of silver and zinc films was studied by exposing metallic films to low-power 0₂ plasmas and analyzing the reacted films. This type of oxidation is an important phenomenon near the barrier layer in sputter-deposited metal-oxide/Ag/metal-oxide low-emissivity (low-e) coatings. Barrier layers generally are deposited on the Ag layer to prevent its degradation during subsequent 0₂ reactive sputtering. Both individual layers and complete stacks were studied. In addition, the thermal stability of plasma-oxidized Ag was examined. There are several important findings for the individual layers. Ag oxidizes rapidly in the plasma, forming Ag_≈1.70 after complete reaction. Relative to the original Ag, the 9ide has -l.7 times greater thick-ness, >10 times higher electrical resistiv-ity (p), and increased surface roughness. Zn oxidizes slowly, at only -1% to 0.1% times the rate for Ag, and is thus more difficult to characterize. The results for individual layers are discussed as they relate to practical pro-perties of low-e stacks: the difficulty of obtaining complete barrier layer oxidation without partially degrading the Ag layer as well as the effects of heat treatment and aging.

Variable angle of incidence spectroscopic ellipsometry was used to study the ZnO/Ag/ZnO (dielectric-metal-dielectric) optical coatings. As a result, the three layer thicknesses, the optical constants of the ZnO layers (3000-8000 W), and the optical constants of the Ag layers (3500-8000 Å) measured on three coated glass samples are reported here. The thickness measurements obtained by ellipsometry agreed with those determined from cross sectional TEM photos well within the error margins of the two techniques. In addition, the spectral dependence of the index of refraction of the silver layers were characterized by oscillations absent in the bulk silver optical data, and likely due to the generation of surface and bulk plasmons.

This paper outlines some recent work on electrochromic and thermochromic coatings for smart windows. The purpose is to illustrate materials options and operation principles rather than to present detailed results. Specifically, we discuss electrochromic NiO_xH_y films operated in a KOH electrolyte, electrochromic Li_xWO₃ films operated in conjunction with a novel transparent elastomer electrolyte, thermochromic V0₂ films whose semiconductor-metal transition point was depressed as a result of a dielectric top layer or by applied strain, and a thermochromic material comprising Si0₂ fibres in CC1₄.

Laboratory procedures have been developed for depositing thin films of electrochromic metal oxides by plasma-enhanced chemical vapor deposition (PE-CVD). In this process, vapor phase reactants, such as tungsten hexafluotIde, are mixed with oxygen and excited by RF energy at a frequency of 13.56 MHz and power levels up to≈1W/cm² substrate area. Large rates of oxide deposition have been achieved (> 8 nm/s) making this process a candidate for high-speed coating of large area substrates, such as window glass. Amorphous WO1 films prepared by PE-CVD have been shown to have electrochromic responses virtually identical to films prepared by vacuum evaporation. The lithium ion diffusion rate, for example, is approximately 1.3 x 10^-11 cm² /s at x = 0.03 in Li_xWO₃ prepared by PE-CVD. On the other hand, molybdenum oxide films and mixed molybdenum/tungsten oxide films prepared by PE-CVD from the hexafluorides differ markedly from vacuum evaporated films. Their electrochromic responses are spectrally different and are much slower. Lithium ion diffusion rates in such Mo0₃ films are lower by about three orders of magnitude. These differences are tentatively attributed to a large fraction of fluorine (Mo:F ratios of the order of 2:1) which are incorporated into the molybdenum and mixed oxides, but are not incorporated into the tungsten oxides.

Some of the materials properties required for successful use in electrochromic windows are reviewed. The preparation of thin films of lithium niobate and lithium tantalate by rf sputtering is described. The films are shown to be amorphous to X-rays, and transparent to visible and NIR radiation. The sputtering process on substrates of tungsten trioxide leads to the formation of the lithium tungsten bronze. Estimates of the electronic resistivity and conuctivity are given as 10¹²Ω-cm and 10^-7(Ω-cm)^-1.

In the development and production of transparent multilayer solid-state ionic structures, and in particular, electrochromic Smart Window the measurement of electron and ion transport properties of the layers is essential, since it can determine the feasibility as well as the speed of operation of devices with those layers. We are developing a novel electro-optical technique to measure the ion and electron mobilities of several layers of the electrochromic Smart Window^TM glass essentially in situ. Presented in this paper are the technique, preliminary models, and transport properties of two such films.

The optical transmissivity (and especially the reflectivity) of a ultilayer electrochvomic smart window^TM glass structure can be reversibly modulated by an electrical current pulse; and the modulation is spectrally selective. This is important for building and vehicle windows and for other electro-optical applications. Discussed is the state of development of each of the layers for, and the state of development of, prototype all-solid electrochemically reversible, 5-layer smart window devices. These devices employ: a lithium-insertable rf sputter-deposited polycrystalline WO₃ film that exhibits reflection modulation as the electrochromic layer; a lithium-insertable rf sputter deposited In₂0₃ film or a thermally deposited V₂0₅ film as the counterelectrode layer; an rf sputter deposited LiNbO₃ film as the ion conducting (solid electrolyte) layer; and rf sputter deposited ITO (Sn-doped In₂0₃) or undoped In₂0₃ films as the transparent conducting layers. The devices exhibit useful operating characteristics and indicate that robust and economical practical smart window^TM glass could soon become a commercial reality.

Polycrystalline W03 films have been prepared which exhibit high near infrared reflectance (≈69% at 2.5μm wavelength) when lithiated. This is a significant increase in near infrared reflectance over what has been previously reported for lithiated W0₃. The films also exhibit a decrease in the Drude scattering parameter and a reversible structure change to higher symmetry (monoclinic to cubic) with increased lithiation. The results are consistent with models previously reported; and both the possibility of further imprvement and its significance for smart window^TM glass glass will be discussed.

The fabrication and design of electrochromic windows based on cathodically coloring amorphous tungsten trioxide (a-W0₃) and anodically coloring iridium oxide (a-Ir02) are described. Using electrochemical data obtained from slow-sweep-rate cyclic voltammetry and coloration efficiency measurements of the individual a-W0₃ and Ir0₂ films, the optical switching characteristics of an a-W0₃/a-Ir0₂ electrochromic window may be predicted. The evolution of the optical absorbance spectra of a-W0₃/a-Ir0₂ windows are presented and used to determine the solar (350-1300 nm) and visible (400-700 nm) transmittance. The effect of multicycle switching and temperature (-20 to 60°C) on the performance of the electrochromic windows are also discussed.

In this investigation, in-situ spectroscopic studies of anodically deposited electrochromic hydrated nickel oxide electrodes were performed by visible/near-infrared spectroscopy and Fourier-Transform Infrared (FTIR) spectroscopy. All measurements were taken while the nickel oxide thin films were switching between the bleached and colored states, where the electrodes were not removed from the electrochemical cell. Optical transmittance measurements of the nickel oxide film relative to tin oxide coated glass varied during coloring from the integrated solar spectral transmittance, T_p=101%-54%, and average near-infrared transmittance, T_nir 101%-83%. The photopic transmission was Tp = 101 - 31%. Transmittance measurements versus time were also performed at selected wavelength values, ranging from 375 to 1100 nm. Also different scan rates (10-100 mV/s) were investigated at each of these wavelengths, where optimum switching rates could be determined. All changes in optical density were achieved by continuously cycling between a potential range of -500 to +800 mV. Coloration occurs at a faster rate than bleaching of the films at every switching rate selected. Also, maximum and minimum transmission meas-urements at 420 nm do not to correspond to the cathodic and anodic peak current densities. Instead these transmission measurements correspond to the regions past the peak current densities. From these optical experiments, plots of transmis-sion (%) versus voltage (mV) and transmission (%) versus total extracted charge (mC) were obtained. For FTIR spectros-copic experiments, chemical identification of the 10-20 nm thick films showed that the films exhibit different bonding environ-ments for both the colored and bleached states. There exist surface hydroxyl groups associated with nickel oxide in the region of 3600-3800 cm" wave numbers. Fundamental water vibrations are also found at 3200-3500 cm^-1 and at 1600-1700 cm^-1 wave numbers. The nickel oxygen vibration region is at 400-525 cm^-1 for both states. The comparison of bleached and colored states exhibits distinctive molecular vibrational states, which correspond to Ni(OH)₂ and Ni0OH respectively.

Electrochromic film has been prepared through liquid phase deposition (LPD) process with an aqueous solution containing an oxalatotungstate (V) complex, and its chemical and electrochromic properties have been investigated. Results showed that two redox couples exist on a cyclic voltammogram and that oxalate ligands would be present in the film coordinating to the tungsten atoms. The redox couple at positive potential is considered due to movement of the cation getting into and out of the sites like crown ether formed by oxlato ligands. The film has fairly good electrochromism exhibiting reversibility as much as 10⁵colourbleach cycles or more in response to an applied potential.

Deposition of electrochromic metal oxide thin films by dip coating has received scant attention in the literature. This paper describes the applicability of the dip coating technique to the process and performance needs of electrochromic devices, particularly electrochromic windows. Coloring efficiencies at 550nm of 49 to 38 cm² /C are reported for tungsten oxide dip coatings that have been fired over a 25°C to 300°C range. Rutherford back scattering spectroscopy was used to verify that the mole ratio in a mixed oxide electrochromic coating matches the mole ratio in the dip solution from which it was deposited.

Both photochromic and thermochromic compounds were synthesized and physical measurements were made to determine coefficients of relectance, absorbance and emission. The most interesting group of thermochromic compounds are related to silver tctraiodomercurate and the most interesting photochromic compounds are substituted benzoindolinopyrospirans. The synthesis and optical reflectance and absorbance properties of other classes of compounds are also reported.

A new, advanced liquid crystal technology has made economical, large area, electrically-controlled windows a commercial reality. The new technology, Nematic Curvilinear Aligned Phase (NCAP), is based on a polymeric material containing small droplets of nematic liquid crystal which is coated and laminated between transparent electrodes and fabricated into large area field effect devices. NCAP windows feature variable solar transmission and reflection through a voltage-controlled scattering mechanism. Laminated window constructions provide the excellent transmission and visibility of glass in the powered condition. In the unpowered condition, the windows are highly translucent, and provide 1) blocked vision for privacy, security, and obscuration of information, and 2) glare control and solar shading. The stability is excellent during accelerated aging tests. Degradation mechanisms which can limit performance and lifetime are discussed. Maximum long term stability is achieved by product designs that incorporate the appropriate window materials to provide environmental protection.

We present the results of experimental and theoretical studies of the photochromic properties of electrons trapped in clusters of polar molecules. We examined the UV fluence dependent visible absorbance of a pyrene/methanol solution with attention given to the kinetic properties of the system, its transient response and fade times, and long term photochemical properties. Preliminary data on dimethyl sulfoxide are also discussed.

Two amorphous films, Cu_xO-W0₃ and V₂0₅-W0₃, are investgated Co determine electrochromism and their optical properties. The color and transmittance of the films can change continuously and reversibly. This multi-colored effect is due to sequential transfer of Cu²-Cu^l+ and W⁶⁺=== W⁵⁺ in Cu_x0W0₃ films and V⁴⁺ reversible processes occurring in V20₅-W0₃ films. Because of these optical properties, this type of films may be used for selectively transmitting windows or information display devices.

In this report we present the up-to-date knowledge acquired in the design and manufacturing of optimized holographic solar concentrators. The optimization procedure is based on ray-tracing analysis and generates information necessary for the manufacturing of a focus-correcting diffraction grating. The solar concentrator and the correction grating are pasted together and form an integrated optical element whose "blue-to-red" foci are located on the geometrical axis of the holographic solar concentrator.

In this report we present the experience gained in the controlled manipulation of dichromated gelatin layers used in holographic solar concentrators. The experimental investigation is aimed at the development of procedures leading to the improvement of their diffraction efficiency and bandwidth. Emphasis is placed on the un-derstanding of the phenomena controlling the spacing of the lamellar structure throughout the thickness of the gelatin layer. Controlling the spacing of the lamellae through the depth of the gelatin layer facilitates the enhancement of the bandwidth.

Degradation of the optical performance by ultraviolet (UV) light is currently one of the principal barriers in the development of silver/polymer films for solar thermal applications. We have conclusively shown that stabilizers added to polymer films do improve the weatherability of mirrors, and we have identified a series of representative examples within the most commonly used groups of UV stabilizers and incorporated them into polymethylmethacrylate (PMMA) to enhance its effectiveness. We have found that the permanence of the stabilizers may limit mirror durability and that the stabilizer performance slowly diminishes because of photolysis and/or leaching and removal from the host polymer. Polymeric stabilizers are of interest on the basis that they will not leach from the host. Various polymeric UV-absorbing stabilizers have been synthesized from derivatives of 2-hydroxybenzophenone and 2-hydroxyphenylbenzotriazole. The relative effectiveness of the stabilizers in acrylic films will be discussed in terms of the weathering modes and retention of optical properties.

The initial optical performance of silvered polymer mirrors exceeds the long-range goals for heliostat applications. Durability studies of silvered polymer mirrors use accelerated weathering devices and outdoor exposures. Continuing tests of outdoor exposures show that silvered polymer mirrors can maintain specular reflectances greater than 90% into an acceptance angle of 4 mrad for over 1 year. Materials placed in tests earlier, while the initial optical performance was still being improved, show that silver corrosion is resisted for at least 3 years and that the reflectance can be maintained at a specularity of at least 12 mrad. The polymer films do not resist abrasion as well as glass; however, hard-coats applied as a top-coat to the polymer significantly improve abrasion resistance. Ongoing durability studies of the hard-coated mirrors show that optical performance is maintained outdoors for at least 13 months.

The effect of several metal substrates (A], Cu, Ag and Au) on the photodegradation of polyethylene terephthalate (PET) and polyvinylfluoride (PVF) films has been examined. The effect of M on M/PET systems under both oxidative and non-oxidative conditions shows that the orders of photodegradation are: Cu/PET»Al/PET>PET>Au/PET>Ag/PET (Non-oxidative) and Cu/PET>>>PET>Al/PET>Au/PET>Ag/PET (Oxidative) The effect of M on M/PVF films when irradiated under non-oxidative conditions shows that all metals have an adverse effect on the photodegradation of these films. Under oxidative conditions, Cu/PVF shows extreme photodegradation while the other M/PVF films show far less photodegradation than under the non-oxidative conditions. The trends in photodeg-radation are as follows: Al/PVF>>Cu/PVF>Au/PVF>Ag/PVF>PVF (Non-oxidative) and Cu/PVF»PVF>A1/PVF>Au/PVF>Ag/PVF (Oxidative)

A Large Aperture, Near-Specular Imaging Reflectometer (LANSIR) was designed and built for performing optical surface quality tests on laminate mirror specimens. LANSIR can quantify the extent of reflective light-scattering from the surface of layered mirrors. It allows real-time examination of scatter from sample areas ranging up to 14 in. in diameter. An illuminated round pinhole as the source, and a video camera with image digitization as the sensor, allows easy detection of directionality (anisotrophy) in the scatter. LANSIR can detect and distinguish the light-scattering con-tributions from surface features which are both directional and widely spaced. These light-scattering contributions can include non-uniform thickness of individual layers, "print-through" texture from reinforcing fibers in composite materials, of and various fabrication flaws such as that caused by extrusion and rol-ling. LANSIR can also control and measure tension in the laminate membrane mirror specimens. Metalized polymer film reflective surfaces laminated to structural metal, or composite material substrates such as those used in stretched membrane heliostats and dishes were investigated. Initial results are encouraging. Mirror samples from most of the recent DOE "membrane mirror" projects have exhibited scatter within the acceptable limits for moderate temperature applications. Even the relatively thick fiber-reinforced polyester structures which are now under initial development come close to passing the test. Nevertheless, our tests have pointed out the need for continued attention, especially of new materials, and of new forming and joining processes.

Performance of 3M's Total Internal Reflection Film (TIRF) is reported. Results include the total reflectance at various incident angles, transmission, angular distribution of reflected energy and TIRF light pipe efficiency.

The optical properties of electrolytic black cobalt coatings with different film thickness are reviewed. Although the intrinsic selectivity of black cobalt is only moderate, efficient selective surfaces can be prepared on highly infrared reflecting metals like smooth copper. The optical and structural investigations show that the porous material consists of a granular distribution of a cobalt-rich phase, which causes a significant infrared absorption. Due to this, the angular dependence of the thermal emission is strongly dependent on film thickness. The influence of different annealing steps on the film properties is discussed. It is shown that black cobalt can be used in high-temperature designs of flat plate evacuated tubular collectors, provided the annealing process is performed under inert conditions. If the coating is used in air, degradation may occur due to oxidation of cobalt metal above 200°C.

A carbonaceous solar selective absorber is formed on a glass substrate by coating the glass with a silver infrared reflecting layer, electroplating a thin nickel catalyst coating on the silver using very special plating conditions, and then exposing the nickel coated, silvered glass substrate to acetylene at a temperature of about 400 - 500°C for about five minutes. A fairly large plater and conveyor oven have been constructed and operated for the formation of these solar selective absorbers in order to study the formation of this absorber by a process which might be used commercially. Samples of this selective absorber on a glass substrate have been formed using the plater and conveyor oven. The samples, which have the best optical properties, have an absorptance of about 0.9 and an emittance of about 0.03. Excessive decomposition of the acetylene by the walls of the oven at higher temperatures with certain wall materials and oven geometries can prevent the formation of good selective absorbers. Procedures for preventing excessive decomposition of the acetylene and the knowledge gained so far by these studies is discussed.

Lead sulfide is a kind of selective surface material with remarkable efficiency but has the defect in durability when it is exposed in air under sunlight. Cobalt oxide is another kind of selective surface material with remarkable efficiency too. Its durability is good but has the defect in its rather high cost. A tandem surface of lead sulfide and cobalt oxides was made by spray pyrolysis method. Its efficiency and durability are similar to that of the cobalt oxides selective surface made by the same method but the production cost is considerably reduced. Its emittance is 0.15-0.32 when its absorptance is raised to 0.90-0.92.

Elastomers employed as gaskets and caulking compounds play an important role in maintaining the energy efficiency of solar collectors by reducing the accumulation of foreign material on the surfaces of the glazing and absorber. Collector efficiencies decrease considerably from the collection of dust and condensed pollutants, and from degradation products evolved from the polymeric components of the solar collector. The proper functioning of the sealants depends upon their resistance to environmental factors that include extremes of temperature, oxygen, ozone, water and ultraviolet radiation. This paper describes several of the methods of evaluation of the elastomeric polymers, and relates the degradation processes to the nature of the polymeric material. In addition to the outgassing studies, data are also presented on the effects on mechanical properties of the various sealants during exposure to thermal and hydrolytic aging conditions.

Collimated transmittance spectra for boroxide alkali-silicate glass wool with different fiber diameter distributions are reported. Three distinct maxima at 1520, 1300 and 600 cm^-1 were observed. Using a normalizing procedure it is demonstrated that the peaks at 1520 and 600 cm^-1 decrease with increasing average fiber diameter. The transmittance maximum at 1300 cm^-1 shows a much weaker fiber size dependence which is explained by the refractive index of the fiber material n=1 at that wavenumber, causing the refraction losses to vanish. Comparison with bulk glass data and model calculations suggest that the collimated trans-mittance at this wavenumber is enhanced by rescattering in the forward direction.

Polycrystalline n-CdSe MIS solar cells have been produced and investigated by I-U measurements and admittance spectroscopy. A high density of interface states (≥ 10¹³ cm^-2(eV)^-1) has been estimated, pos-sibly due to disorder phenomena at the n-CdSe surface.

CdS thin films of high quality with good reproducibility can be prepared on large-area substrates from aqueous baths, icontaining triethanolamine complex of Cd²⁺ ions and thiourea. Depending on the deposition para-meters, a combination of optoelectronic cha-racteristics are obtainable: optical transmi-ssioii, 10.7 q80%; photocnductivity, up to 3 ohm^-1 cm^-1 (at 300 W/m² sim. solar); photo; conductivity to dark conductivity ratio, 10° to 10⁹ and phstocurrent decay time , a few seconds to -10³ s. Absorber layers (p-type) of lower band gap, of the CuxS or CuInS₂ type, with low sheet resistivities have been subsequently chemically deposited on these CdS films. This suggests the possibility of developing 'all-chemically deposited' thin film solar cells.