Doped oxide semiconductors,which are widely used as transparent heat-reflectors, have a wider energy gap than the undoped material. This bandgap widening was investigated in 1n203 and 1n203:Sn. Empirical data were extracted for coatings with electron density 1021 cm-3. They are interpreted within an effective-mass-model for n-doped semiconductors well above the Mott critical density. The impurities are ionized and the associated elect-rons occupy the bottom of the conduction band in the form of an electron gas. The model accounts for a Burstein-Moss shift as well as electron-electron and electron-impurity scattering treated in the Random Phase Approximation. Experiments and theory were recon-ciled by assuming a parabolic valence band with an effective mass ti 0.6 m. Earlier work on doped oxide semiconductors are assessed and criticized in the light of the present results.

Optimal properties of a low emissivity coating are quantified in terms of optical, thermal and aesthetic parameters. Large scale production of a Zinc Oxide/Silver/Zinc Oxide coating deposited on glass by reactive D.C. magnetron sputtering was sampled over a six-month period. The distributions of performance parameters describing the visible and solar transmission and reflection, emissivity and film color were analyzed and related to production process variations.

A new method is introduced to calculate radiative heat transfer between two grey end plates with an arbitrary number of thin grey films in between. With this method it is also possible to do an almost exact analysis for coupled radiative and conductive heat transfer through one film between two grey end plates. It is almost exact for an arbitrary position of the film because the maximum deviation from the true heat flux can be evaluated exactly. There is one position of the film between the plates where the new method for coupled heat transfer is absolutely exact. This is where the heat flux is a minimum. This is a most interesting result for all heat insulating applications. The position for the minimum heat flow through more than one film can be determined exactly as well as the value of the heat flow itself. It has been shown by experiment that the method for radiative heat transfer can be applied not only to multifilm layers but also to PMMA foam or capillary structures. First experiments were in excellent agreement with theory.

Low emissivity coatings for commercial and residential construction uses are being produced every day on large scale, in-line sputter deposition systems. Under full production conditions, this equipment is capable of producing millions of square feet per year, of quality coatings, on glass sheets as large as 100" x 144". Heat mirror coatings of the dielectric sandwich type, with silver as the metal layer, present a special challenge in process control. To maintain emissivities below 0.15 requires delicate control of deposition conditions. Small variations in layer thicknesses can have dramatic effects on overall coating performance and characteristics. Film and glass side reflective color are especially sensitive to layer thickness variation. An indication of the effects of varying layer thicknesses on reflective color is included.

We introduce electrochromic coatings for use on "smart windows" with dynamic control of radiant energy. Applications, operating principles, materials options, and device configuration are briefly reviewed. We then focus on electrochromic WO3 and investigate crystalline films by computations aimed at assessing performance limits, and amorphous films with regard to practrical performance in contact with liquid or solid electrolytes. It appears that there are several approaches to achieving a gradual and reversible modulation of the radiative performance in a manner consistent with uses on "smart windows".

The application of electrochromic materials to the control of radiant solar energy transfer into building interiors is potentially useful for reducing energy consumption. Electrochromic materials would be used as multilayer window glazings that act as variable absorptance or variable reflectance light apertures. In this article a variety of electrochromic window structures, which demonstrate variable aperture operation in both the absorptance and reflectance mode, are presented. The electrochromic and optical properties of several mate-rials, including Mo03 and Ir02, have been investigated. A high near infrared reflectance, >55%, has been measured in crystalline W03 after Li insertion. The performance of a variable aperture W03 electrochromic window has been demonstrated by calculating the spectral solar throughput in various stages of operation.

Multilayer, solid state electrochromic coatings based on a-WO3 (amorphous W0.3) have been tested. A typical coating on glass consists of indium-tin oxide(520 nm), WO3 (410 nm), MgF2(170 nm) and gold (15 nm) all deposited by vacuum evaporation. Optical spectra and solar weighted, integrated transmission values are given for the component films and complete multilayer devices. Electrical characteristics and electro-optic responses are reported. Devices with MgF2 layers deposited at low pressures have high internal resistances and exhibit long term optical memories suitable for diurnal switching. The replacement of the gold electrode layer with an indium-tin oxide layer greatly increases the transmittance of the electrochromic coating stack (from solar weighted transmission of 22% up to 53%). Electrochromic coatings have promise for solar gain control windows, but further improvements in optical and electrical efficiencies are needed.

Electrically variable reflectivity electrochromic windows have the potential to significantly reduce heating and cooling loads in buildings. The importance of reducing the optical frequencies free electron scattering in the variable reflectivity electrochromic layer will be shown. Based on spectroscopic ellipsometry studies and an analysis of the dynamical resistivity of polycrystalline films of colored W03 and of single crystals of NaxW03, it is tentatively concluded that the principal source of free electron scattering in W03 films is structural disorder, and probably crystallographic shear planes which act as monopolar dislocations. This is in contrast to the much higher reflectivity single crystal tungsten bronzes for which the more dominant scattering mechanism appears to be that associated with ionized impurities. We therefore conclude that it should be possible to improve the reflectivity modulation in films of electrochromic TM), and consequently that a practical variable reflectivity electrochromic window should be acriievable.

The degradation mechanism of gradual decrease of the contrast between colored and bleached states of Lix'. WO3 films with switching cycles was investigated. We made electro-chemical and quantitative chemical analyses to clarify this phenomenon. It was found that the decrease in contrast was mostly attributed to the parallel cathodic shift of emf(x), passibly caused by ion exchange reaction expressed by: WOH + Li+ WOLi + H. Fully ion-exchanged WO3 films showed no appreciable change in spite of the presence of a large amount of Li in them. These films were capable of accepting as much Li as the fresh films did on coloration and reached to the same optical densities. It is concluded that there are two kinds of active sites available for accepting lithium ions in the WO3 structure, one for ion exchange and the other for coloration.

A considerable amount of effort has been expended by the Department of Energy (DOE) and by commercial interests to develop solar absorber selective paints; the goal is to develop an inexpensive, durable selective coating that has moderately good optical properties. This report is intended to focus on those research programs monitored by Los Alamos, the research efforts in progress at Los Alamos, durability evaluations, and the progress that has been made toward commercialization.

Theoretical analysis of the interaction between concentrated solar radiation and an honey-comb matrix or a bed of particles cooled by a gas is proposed. The computation and the ex-perimental results show evidence of an overheating of the solid near the irradiated surface. To prevent the upper surface from this phenomenon and to reduce the radiative heat losses, we propose to use selective semi transparent porous absorbers. First results about coatings on silica are presented.

The selectivity of an interference controlled oxide/metal solar absorber is considered. It is argued that for high solar absorption it is important to have a low interference maximum as well as minimum. The reflectance of a double layer is calculated within the conventional interference formalism assuming homogenous layers and sharp boundaries. With the use of some simplifications the value of the interference maximum is derived corresponding to an interference minimum at 0.8 μm. The results are presented as interference maximum iso-reflectance contours in the nk-plane for the oxide. It is found that lower metal reflectance gives lower Rmax-values and that the oxide should have low n-values with an k/n-ratio -0.4. In a few cases the predictions are compared with experiments and the special case of Ir02/steel is commented upon.

A spectral reflectance model for a homogeneous complex index film on a metal substrate is presented which illustrates the importance of interference in producing selective absorption. In this model the real part of the film's index of refraction (n) and the film thickness (d) are chosen to satisfy the normal quarter wave condition at a shoulder wavelength of approximately 1-2 microns, while the imaginary part of the film's index (k) is chosen so as to match amplitudes of a front and back surface reflected wave. In order to isolate the effects of interference, all optical constants are assumed to be independent of wavelength and all surfaces are considered smooth. The conditions under which zeroes in the reflectivity occur are investigated with a vector diagram technique and the effect of varying these conditions on the spectral reflectivity is studied. A tradeoff between the solar absorptance and the width of the visible-infrared transition region is shown to be a natural consequence of the conditions placed on (n,k) of the interference film. The effect of grading the film's index on this tradeoff can be treated analytically without approximating the film as a stack of homogeneous layers. This analytical approach is outlined and preliminary results are presented.

TiNx and TiNx0y films are deposited by DC reactive bias sputtering in an argon atmosphere with nitrogen and oxygen added as reactive gases. The DC resistivity and deposition rate of biased and non-biased layers have been determined.X-ry and eil,,ctron diffractim are used to investigate the structure of the films. Their composition was investigated using X-ray Facto-electron Spectroscopy (XPS) and Rutherford Back Scattering (RBS) combined with Nuclear Reac-tion Analysis (NRA). The optical properties are investigated in the spectral region 0.4-25 μm. Bias sputtered TiNx films show a low resistivity and a solar absorptance which is too low for practical use as a spectrally selective absorbing layer in a solar collector. Non-biased films, sputtered in an argon/nitrogen atmosphere, and TiNx0y films, bias sputtered with oxygen added to the glow discharge, show a much higher resistivity and a higher solar absorptance. The solar absorptance of spectrally selective TiNxOy/copper tandems is moderate (0.80-0.85) but their thermal emittance is low (0.05 at 1500C). Heat treatment for 12 h at 4000C in vacuum hardly affects the optical properties.

A composite system for solar energy conversion has been developed and tested. It comprises a mixture of some of the halogens and inter-halogen compounds. The system proves to be energetically viable for solar energy conversion. A temperature rise above an identical assembly containing air alone of 160C has been attained. With the aid of a plane mirror reflector this temperature increment reached 20°C.

During the past several years, DSET Laboratories, Inc. has been involved in developing information for a solar materials design handbook.' The scope of this program is to subject materials to both real-time and accelerated exposure tests, measure optical and physical properties at periodic intervals, and report the retention (or loss) of properties as a function of exposure. The primary objectives of this program are to develop new materials information for a current data base and to validate the existing data base. There are several features that distinguish this program from previous materials testing programs: (1) All materials are commercially available and were purchased from distributors or manufacturers without their knowledge of the purpose; (2) Exposure intervals are based on the total ultraviolet radiation received; (3) Most of the test methods employed simulate actual end-use conditions of solar device materials by utilizing special fixtures designed for that purpose. This paper will emphasize two facets of the above referenced program: (A) test methods employed in the weathering of solar device materials, and (B) the use of a multiple-integrating sphere spectrophotometer for determining the optical properties of solar materials.

There is a dramatic need in solar energy collection systems for lightweight, inexpensive polymeric materials that exhibit improved performance and durability. One approach to altering the properties of polymeric materials, surface fluorination, is appealing because of its potential for low cost. The literature indicates that such properties as permeability, wettability, bondability, thermal stability, weatherability, and optical transmittance can be improved by treating the surface with gaseous fluorine. A gas phase fluorination reactor system (GPFRS) was designed, built, and used. The initial emphasis was on improving optical transmittance by having an effective antireflection coating form on the surface of a wide variety of commercially available transparent polymeric films. These included such materials as polypropylene, acrylic, polyacrylonitrile, highly cross-linked polyethylene, polyester, polycarbonate and polymethylpentene. Two techniques were used to quantify the effect of exposing the surface of the polymers to gaseous fluorine. Transparent films were characterized before and after fluorine exposure by specular transmittance measurements. Surface analysis of selected treated and untreated samples was accomplished by x-ray photoelectron spectroscopy and depth profiling. Surface analysis confirmed the deposit of fluorine at the surface and into the bulk of all specimens examined after treatment in the GPFRS. Optical measurements revealed substantial improvement in specular transmittance following surface fluorination of almost all materials considered. Increases in solar weighted specular transmittance as high as 4.6% were measured.

The structure of silica aerogel was studied by transmission electron microscopy. The aerogel network consists of particles about 10.0 nm in diameter. The chemical composition of these aggregates was found to be a pure stoichiometric Si0; by both ESCA and Auger spectroscopy. These SiO2 groups appear to form a random network within each particle. The details of this arrangement have yet to be determined, because in this preliminary study, silica aerogel was found to transform after exposure to the intense electron beam.

Hydrogenated amorphous silicon-tin alloy (a-Si1_xSnx:H) films were prepared by simultaneous rf sputtering of polycrystalline silicon and tin in a H2- Ar gas mixture. The optical gap E0 of the films depends on alloy composition x and preparation conditions. As tin content increases, the optical gap of the films becomes narrower linearly, but the dark conductivity increases exponentially. For films at lower substrate temperature and target power density, the optical gap becomes wider.

The photoelectrochemical responses of ternary, chalcogenide glasses of the form: V-VI-M have been surveyed where M=metal or chalcogen. Of those examined, the As-Se-Cu composition appeared most promising for solar energy conversion. In particular, glassy compositions at or near the AsSe2Cu stoichiometry exhibited apparent bandgaps near 1.0 eV, open circuit photopotentials as high as 600 mV under white light, and, conversion efficiencies (at 500 nm) of 0.01-0.5% for a range of oxidants. In all cases p-type semiconduction dominates. Attempts to synthesize and then compare polycrystalline AsSe2Cu's photoelectrochemical response to the glass are described. The latter so far appears to have generally superior properties for solar energy conversion.

Various systems that offer potential solutions to the problem of interior daylighting have been discussed in the literature. Virtually all of these systems rely on some method of tracking the sun along its azimuth and elevation, i.e., direct imaging of the solar disk. A simpler approach, however, involves a nontracking nonimaging device that effectively eliminates moving parts and accepts both the diffuse and direct components of solar radiation. Such an approach is based on a system that combines in a common luminaire the light emitted by luminescent solar concentrators (LSC), of the three primary colors, with a highly efficient artificial point source (HID metal halide) that automatically compensates for fluctuations in the LSC array via a daylight sensor and dimming ballast. A preliminary analysis suggests that this system could supply 90% of the lighting requirement, over the course of an 8 hour day, strictly from the daylight component under typical insolation con-ditions in the Southwest United States. In office buildings alone, the total aggregate energy savings may approach a half a quad annually. This indicates a very good potential for the realization of substantial savings in building electric energy consumption.

The design and fabrication of a highly insulating, evacuated window glazing have been investigated. A thermal network model has been used to predict the thermal performance of such a window parametrically. Achievable design options are pdicted to provide a glazing with a thermal conductance less than 0.6 W/m2K (R > 100 re F ft hr/Btu) which is compact, light weight and durable. A CO2 laser has been used to produce a continuous, leak tight, welded glass perimeter seal around 25 cm x 25 cm square test specimens. Various diameters of regularly spaced spherical support spacers were incorporated in the specimens as well as an integral Sn02:F transparent, low emissivity coating for suppression of radiative heat transfer. Laser sealing rates of .06 cm/s were achieved at a 580°C glass working temperature with 400 W of continuous wave (CW) laser power.

There are many materials or optical systems that are not ideally measured using current ASTM or other test methods. The transmittance or reflectance of various window treatments, patterned or corrugated materials, and full-size tempered glazings are but a few examples of optical systems that are difficult if not impossible to measure using present test methods. In most cases, the problems encountered are: (1) inability to illuminate a representative section of the material, (2) the receptor is not capable of measuring all of the transmitted or reflected flux, or (3) size restrictions associated with conventional measurement techniques. In order to determine the optical properties of large and/or complex systems, a unique 8-foot diameter integrating sphere has been designed and constructed. Designated the LMPI sphere, it has a 12-inch diameter aperture, and is capable of making absolute solar transmittance, reflectance, and absorptance measurements from a 0° to 60° angle of incidence. The sphere uses natural sunlight as its source illuminant, and incorporates a novel solar siderostat to focus sunlight into the sphere. A detailed description of the sphere and its optical system, along with a complete mathematical analysis of the energetics of the sphere, is presented. Solar transmittance, re-flectance, and absorptance measurements of large specimens at various angles of incidence are compared to both the pyranometric method (ASTM Standard E 424, Method B) and the spectrophotometric method (Method A). In general, transmittance and reflectance measurements of isotropic surfaces using the LMPI sphere gave results that agreed to within 0.01 units of the measurements obtained utilizing DSET's multiple-integrating sphere (MIS) spectro-photometer. For nonisotropic, textured, or corrugated specimens, the superiority of the LMPI sphere measurement vs. either Method A or Method B of ASTM Standard E 424 is demonstrated.

Linear Presnel lenses (LPL) manufactured from glass are cheap and durable concentrators of direct solar radiation. Optical properties of LPL manufactured from glass are briefly discussed. Several exmples of LFL applications are described.

During the past two years the National Research Council of Canada's Solar Energy Program has commenced support of research on low emittance coatings, transparent aerogels and phase-change energy storage materials. The work on coatings and aerogels is part of a major activity to develop "super" windows with overall thermal resistance equivalent to or better than RSI 1 (R6).

Materials used in medium to high temperature flat plate, evacuated tube and concentrating tube collectors and the problems associated with them are identified. The material and research needs of solar industry are presented. Polymeric and composite materials for high temperature applications, heat mirror coatings, sealants, gasketing materials, solid to solid phase change materials are some of the areas where development work is necessary.