Ultra-thin lamellar gratings represent a new kind of transparent heat mirror based on the principle of waveguides. Wavelengths shorter than double the waveguide diameter are propagated, while longer wavelengths are reflected at the opening of the waveguide. Parallel metal strips mounted perpendicular to a transparent surface exhibit equivalent behaviour for waves polarized perpendicular to the strips. For unpolarized radiation, two of these lamellar gratings have to be crossed. These gratings are manufactured by embossing a profile of right-angle triangles onto a transparent substrate. They have a period and depth of approximately 0.8 m. The vertical faces of the profile are then covered with a thin conducting metal layer by oblique evaporation. According to theoretical calculations, the JR-reflectance of the optimized grating is as high as the reflectance of a coherent metal coating, whereas the solar transmittance is very high even for diffuse radiation. The grating has a very sharp cut-off wavelength which can be adjusted depending on the application. A nickel master profile for embossing has been manufactured by photolithographic techniques. The structure has been replicated on transparent PVC. First measurements of evaporated gratings show the expected characteristics.

Snox films were made by reactive ifmagnetron sputtering of Sn in Ar + onto unheated glass. Electrical dc resistivity (Pdc) and spectral optical properties were measured as a function of sputtering parameters. A sharp minimum in Pdc was found at a well-defined gas mixture. Optimized deposition parameters gave films with Pdc 3 x iO c2 cmat low sputter rate (r) and Pdc 102 ç cm at r -3 nm/s. The luminous transmittance was -75 %. The optical and electrical properties could be quantitatively reconciled with a theoretical model for wide-bandgap semiconductors, heavily n-doped by doubly ionized oxygen vacancies, that accounted for ionized impurity scattering of the free electrons.

Transparent and durable thin films of NiSiO were prepared by reactive d.c. magnetron sputtering at room temperature. The target materials used were Si, Ni, NiSi2 and NiSi alloys with 20/80 and 40/60 wt % for nickel and silicon, respectively. With a suitable composition of Ar, N2 and 02 we were able to obtain a stable sputtering process for NiSiO-films without any arcing and flickering. The stable sputtering process formed non-absorbing layers with a deposition rate of 20 A/sec. This is approximately 2 to 3 times higher than the deposition rate for Si02 at the same deposition parameters. The optical transmission and reflection were measured in the wavelength region from 0.28 itm to 2.5 rim. The index of refraction n and the extinction coefficient k were calculated in the same range. The "theoretical" index of refraction was determined by Effective Medium Approximation (ENA).

A new layer system based on the interference filter of Fabry Perot type was investigated both by computer simulations and experimentally. The aim was to prepare by magnetron sputtering a Solar-control coating of the type TiN/Sn02/TiN for architectural applications on large glass sheets with improved optical and thermal performance. For this reason the sputtering process of TiN was investigated to find the optimum conditions resulting in uniform film appearance across the glass pane. It turned out that the best results in the optical uniformity were obtamed with an excessive amount of the nitrogen in the sputtering chamber. To obtain good mechanical durability an additional layer was sputtered between the second TiN and the top Sn02 film. The light and solar energy transmission and reflection of the final product were measured in the wave range from 0.28 to 2.5 jim. It turned out that at a given light transmission the direct solar energy transmission for the prepared coating was much lower than that for the conventional layer system of oxide/nitride/oxide. The measured shading coefficients for the glass with 35% light transmission were 0.55 and 0.46 for conventional and the new coating, respectively. Furthermore, the possible colour co-ordinates, the mechanical and chemical durability of the final coating have been measured.

The application of submicron grating structure for light trapping in thin silicon solar cells has been investigated theoretically and experimentally. A gain in absorption corresponding to an increase in thickness of more than a factor of 4 for polarized light and about 3 for unpolarized light has been demonstrated.

Pyrite (Fe52) has been investigated as a promising new absorber material for thin film solar cell applications because of its high optical absorption coefficient of 1OL cm1, and its bandgap of 0.9 to 1.0 eV. Thin layers have been prepared by Metal Organic Chemical Vapor Deposition, MOCVD, Chemical Spray Pyrolysis, CSP, Chemical Vapor Transport, CVT, and Sulfurization of Iron Oxide films, 510. It is postulated that for the material FeS2, if x is not zero, a high point defect concentration results from replacing 2 dipoles by single S atoms. This causes the observed photovoltages and solar conversion efficiencies to be lower than expected. Using the Fe-O-S ternary phase diagram and the related activity plots, a thermodynamic understanding is formulated for the resulting composition of each of these types of films. It is found that by operating in the oxide portion of the phase diagram, the resulting oxidation state favors pyrite formation over FeS. By proper orientation of the grains relative to the film surface, and by control of pinholes and stoichiometry, an efficient thin film photovolatic solar cell material could be achieved.

Solar cells are, in their simplest form, large area p-n junctions. Light falls upon the upper surface, is absorbed, and generates electron-hole pairs which are separated by the electric field associated with the depletion region. The performance of a solar cell is generally believed to be closely related to the precise nature of the surfaces and interfaces involved. The nature of the surfaces and interfaces is in turn related to the exact conditions under which the cell was fabricated. Traditionally the optimum production conditions have been determined directly and empirically, and the influence of the precise nature of the cell on its performance has not been a matter of major concern. This approach has met with considerable success for several types of cell. However some applications make stringent demands on solar cells. An example of this would be the long operating lifetimes required of solar cells used in space environments where radiation tends to cause degradation. For this type of application more exotic semiconductors are of interest. The high cost of these materials means that empirical methods for optimising fabrication conditions are not viable and models have been developed to predict the optimum cell structure. Most models operate by solution of the transport equations(1 ). The model described here is based on the Transmission Line Matrix (TLM) method which is a technique of transient analysis. An iterative technique has been chosen since it gives the greatest flexibility to incorporate spacial variations in parameters. Of iterative techniques available, TLM has many advantages in terms of implementation as well as being rather more accessible to non-mathematicians In this case the particular cell of interest is the ITO-InP based solar cell. In this structure the rf- sputtered ITO film acts as a transparent conductor and a shallow p-n junction exists within the single crystal InP(2,3).

In the present paper results obtained in photoelectrochemical (PEC) cells are presented. Electrochemically deposited CdSe photoanodes, covered by reduced polypirrole films have been studied. In particular, polypirrole was polymerized through an electrodeposition technique utilizing oxidation and reduction cycles. This procedure allows to obtain conducting polymer films with optical characteristics more suitable to the employement in PEC cells. Both CdSe and polypirrole films have been characterized utilizing several experimental techniques, mainly in order to determine their cristallograpliic properties and their uniformity. The morphology of polycrystalline CdSe films was widely studied with scanning electron microscopy (SEM) and X-ray diffraction. The behavior of current flowing in the cell versus time for CdSe electrodes covered by polymer films was analyzed. A good evidence for a protectioii effect is given.

Nonstoichiometric nickel oxide films were made by reactive dc magnetron sputtering. Subsequent electrochemical treatment in KOH established electrochromism. The material was studied by combined mechanical and optical measurements during electrochemical cycling, spectral infrared reflectance, XPS, and X-ray diffraction. Mechanical stress data showed that electrochromic bleaching was associated with proton insertion. P-polarized infrared reflectance showed OH stretching vibrations representative of "free" OH for the bleached state and OH in the presence of hydrogen bonds for the coloured state. XPS data for 01 s core level electrons indicated one binding state in the bleached material and two binding states in the coloured material. Heat-treated samples had significantly decreased electrochromism.

Different colouration states of W03 and NiO H have been analyzed by optical spectroscopy and characterized with The films were produced by reactive evaporation. Electrochromic (EC) behaviour were investigated in liquid electrolyte experiments and as a part of allsolid -state devices. Changes in optical properties were determined as a function of injected charge. Spectral colouration efficiencies (CE) are presented for both materials. A linear relationship between macroscropic optical behaviour and change in oxidation state is proved for W03 up to a certain amount of injected charge.

Electrochromic all-solid-state devices (ASSD) produced by reactive evaporation have been investigated by iaeans of reflectance measurements in the VIS/NIR range and cyclovoltammetry. Hydrogen depth proil were then by a NRA-technique employing the resonant reaction H( N, ar) C. Two different types of designs have been characterized. The electrochromic behaviour of ASSD's can not be described by models based on H transport for devices containing only W03 layers as active materials. Using NiOXH films as electrochromic substances, the injected/ejected charge corelates with changes in the H content.

We have studied the optical properties, as well as the dielectric permittivity in the frequency range 1O-1O' Hz, for electrochromic hydrated nickel oxide films. The films were produced by dc sputtering and were subsequently elecirochemically treated in order to achieve different visible absorption. Dielectric and optical measurements were carried out on clear and dark films as well as films of intermediate absorption. The dielectric spectra showed a dc conductivity at low frequencies crossing over to a percolation behaviour at higher frequencies. For films in the clear state we also observed a broad relaxation peak, superimposed on a background similar to the percolation behaviour. The optical spectra were dominated by a broad absorption in the visible region, peaked at about 2.3 eV with a shoulder around 1 .5eV. We believe that these peaks are due to charge transfer excitations. No evidence of polaron effects was found.

Nickel oxide films, formed by reactive sputtering from a metallic nickel target in argonoxygen atmospheres using an rf diode configuration, show good electrochromic properties when produced at low power densities and high pressures. These results contrast with poorer electrochromic properties observed for films produced under conditions of higher power densities and lower pressures. The optimum conditions result in neutral, grey nickel oxide films which are readily bleached and completely reversible. When deposited on Sn02:F coated glass these films can have a solar transmittance of 0.70 in the bleached state and 0.30 in the coloured state. TEM studies have identified the films to be composed of cubic NiO with grain sizes in the range 2-5 nm.

Two different types of electrochromic nickel oxide films are studied : nickel hydroxide films prepared by cathodic precipitation from a Ni2 containing solution and nickel oxide films formed by anodic oxidation of a nickel substrate in very concentrated sulfuric acid. Chemical and crystallographic nature is analysed by in-situ Raman spectroscopy and the charge insertion mechanisms are studied by A.C. electrochemical impedance technique. The optical transfer function is also determined by means of 1254 Solartron frequency response analyzer. The complex capacitance C*(w), the differential coloration R/(RAE) and the differential coloration efficiency R/(RQ) are calculated.

Raman spectroscopy has been used to study the chemical modifications in polyaniline thin films, when the polymers are equilibrated in solutions of different pH (0-3), in a large range of potentials. The role played by the nature of anion is also investigated.

Electrochromic device testing and durability is discussed in this study. This work begins with a discussion of performance criteria for switchable glazings used in building applications. This is followed by device design of several common electrochromic device types. The types are distinguished by structure and electrolyte type. A number of test methods are used for the analysis of electrochromic devices. Device lifetime and degradation covers considerable work on amorphous tungsten oxide. Some degradation and ageing modes are identified for electrochromic devices during static and cyclic testing. The degradation modes are film dissolution, transparent conductor etching, gas generation, humidity dependence, secondary reactions and photoreactions. Many of these mechanisms are specific to the materials, device design, and the operating conditions used. Overall, future of electrochromic devices looks very promising, but there are many issues in this study that designers need to take into consideration for electrochromic glazings.

Thin vanadium oxide coatings were made by vacuum evaporation followed by annealing posttreatment in the presence of air. The thickness increased by a factor as large as 2.3 upon oxidation. Temperaturedependent electrical conductivity as well as spectral transmittance were measured vs. annealing time; it took a few hours to establish V02 with well-defined semiconductor-metal transition at 57°C. Electron diffractograms indicated a bcc monoclinic transformation upon annealing, and electron micrographs showed pronounced grain growth. Initial XPS core level spectra gave evidence for vanadium in different oxidation states.

WO polycrystalline thin films were prepared by annealing, at 500 or 600°C in air, o black tungsten layers produced by chemical vapour deposition (CVD) of W(CO)6 on fused quartz or Sn02-coated pyrex substrates. The optical and electrical properties were investigated when the electrochromic samples were in the coloured and bleached states. A passage from a semiconductor to metallic behaviour appears during the colouration. This transition is discussed using the Hubbard-Mott and free electron scattering models.

Inorganic glasses prepared by the 'cold' chemical sol-gel process can present an alternative host material for organic fluorescent dyes. We report on measurements done on thin Si02 layers prepared as sol-gels and doped with various dyes on a glass substrate. The preparation is done by dip-coating of the substrate in the corresponding alcoxide solutions. Good quality layers without crazing after drying are achieved with a thickness of up to 1-2 microns. The measurements include absorption measurements (UV to IR), fluorescence and excitation measurements (visible to NIR), and measurements of photo-decomposition. The optical properties of the dye molecules in the layer and in the sol-gel solutions are studied as a function of dye concentration and changes in the thermal treatment of the layers. The results are examined for their applicability to FPC's. Further we report on small silver islands (submicron size) brought into the sol-gel solution as stabilized colloids or by chemical reduction of Ag+ salts. According to theoretical predictions, the electromagnetic interaction of silver surface plasmons and dye molecules can result, under certain conditions, in an enhanced fluorescence quantum efficiency and photostability of the dye.

Results are presented of a round-robin programme of optical properties measurements carried out on a commercial chemically oxidised stainless steel spectrally selective solar absorber surface and two commonly employed reference calibration standards. Measurements of solar absorptance and thermal emittance were obtained using a number of different spectrophotometric, broad-band and radiometric techniques. The results are analysed for each technique employed and comparisons are also made of results obtained from different methods. The results highlight differences which can occur when supposedly identical methods are employed using different commercially available instruments and reflectance attachments. The importance of understanding calibration techniques, the use of diffuse and specular reference standards, calculation methods for optical properties determinations and sample dependent observable effects are clearly demonstrated. Lessons have been learned regarding 'routine' measurements which will assist in developing better practices and refining recommended procedures for commonly quoted surface optical properties.

Spectrally selective absorber coatings, deposited on engineering material substrates such as stainless steel, have been developed for service as efficient solar photothermal energy converters. The selective solar absorber is based on a multilayer of thin films, produced by sputtering. The main solar absorber is a metal/ceramic (cermet) composite, such as, Mo/Al2th or Mo/Si02, with a graded metal concentration. Such a cermet layer, strongly absorbs radiation over most of the range of the solar spectrum but is transparent to longer wavelength radiation. The cermet layer is deposited on a highly reflecting infrared metal layer. Two more layers were added: An AhO diffusion barrier layer which is deposited first on the substrate and an AI2O or a Si02 antireflection layer which is deposited on the top of the cermet film. In order to better understand the spectral reflectivity of the multilayered selective coating, a procedure for the calculation of the optical properties was developed. After the R&D development phase was successfully completed, a full scale production coating machine was constructed. The production machine is a linear in line coater. The selective coating is deposited on stainless steel tubes, translating in the coating machine while rotating about their axes, along their axial direction. Measurements of reflectance, solar absorptivity, a, thermal emissivity, C, and high temperature durability, are all parts of the quality control routine. The results show values of a in the range 0.96 - 0.98. The thermal emissivity at 350CC is in the range 0.16 - 0.18. Thermal durability tests, show no degradation of the coating when subjected to up to 65O in vacuum for one month and when passed through a temperature cycling test which includes 1200 cycles between temperatures of 150CC and 450CCfor a period of two months.

We introduce a model of the optical properties of nickel pigmented aluminium oxide selective solar absorbers that can explain the degradation at elevated temperatures. The properties of the Ni-A1203 cermet layer are described by the Bruggeman effective medium theory. On top of this layer we assume one homogeneous and one graded aluminium oxide layer. Our optical model can qualitatively explain the change in opticai properties of the coatings upon heat treatments in air. The degradation mechanism appears to be oxidation of the nickel particles throughout the cermet layer. We also propose a novel theoretical model that can be used to account for optical degradation of solar collector coatings. The degradation is described in terms of an activation energy and a kinetic exponent. These quantities are determined for the Ni-A1203 coatings and are compared to data on the oxidation kinetics of nickel.

Transparent or translucent insulation materials (TIM's) represent a new class of materials with a high potential for increasing the efficiency of solar thermal systems. A large number of materials and material combinations have been subjected to theoretical and experimental investigation. An overview of generic TIM's and existing materials available on the market, characterisation methods and the future potential of transparently insulated systems follows.

The determination of the hemispherical-hemispherical (or diffuse-diffuse) solar transmittance Tdif of transparent insulation materials like honeycomb structures or of shading devices like venetian blinds is important to estimate the efficiency of passive solar components using these materials. Tdjf may be calculated from the measured angle-dependent hemispherical (or diffuse) transmittance 7çj(). Alternatively one may try to measure the quantity directly by using a large radiation source for isotropic irradiation of the sample. The measuring device in both cases is a large integrating sphere. A calculation of Td.f needs an underlying physical model for the radiation transmittance of the sample. This model might not be availab'e for complicated structures and is idealized for samples in practice. The arising problems for a honeycomb structure will be discussed in detail. The differences of up to 10 percent in Tdjf are not negligible. The main problem is a practical one, not a fundamental one. In order to save measurement time and costs, only two scans along the principal directions of the cell walls are selected, thus essentiallyvarying only the polar incidence angle. These two curves can be fitted with a transmittance model. Then for every arbitrary incidence angle the transmittance can be calculated using the theoretical model, i.e. also Tdjf may be determined. The selection of the right model, however, needs information about the azimuthal dependance. This in principle can be obtained by varying the azimuthal angle systematically in additional scans. Information about this dependance can be obtained also from a scanning radiometer, where both angles for incident and outgoing radiation can be chosen without restrictions. However, this is rather time-consuming and poses new problems as well. Therefore the use of isotropic irradiation of the sample certainly is the fastest way. This approach may be realized in different ways. Two of them are discussed in the article and possible problem areas are identified.

For a composite with spherical inclusions, made of two components, whose composition is close to the perfect index matching composition, it is shown that there are extremely optically inhomogeneous core-shell particle structures with extinction coefficients of one or more orders of magnitude smaller than a structureless inclusion with the same radius and particle composition. The effect on transparency of, the radius, particle composition, shell thickness and wavelength for this structures is discussed. It is found that these optically inhomogeneous inclusions are more wavelength selective than the homogeneous ones with the same global composition.

The relations between the optical, electrical and structural properties of pyrolytically sprayed, Fluorine-doped tinoxide coatings have been examined by analyzing coatings having a different Fluorine doping, different preparation temperature and different coating thickness. The results show that doping tinoxide coatings with fluorine increases the electron density and the mobility ii the coating. The maximum electron density which can be obtained is about 410 6/m . The maximum mobility of about 45 cm /Vs which has been obtained, roughly equals the maximum mobility predicted by the theory for ionized impurity scattering. This leads to a minimum attainable thermal emittance of about 0. 15. When the maximum mobility has not been reached, this can be due to a too weak preferential orientation in the (200) direction or to a small electron density in the coating.

As part of Task X in the Solar Heating and Cooling Programme of the International Energy Agency, methods for the lifetime assessment of solar absorber coatings have been investigated. In a first step, the degradation caused by the individual contributing factors (e.g. temperature, moisture, 502) was tested for each factor separately. The results of the temperature tests in particular could be used for a lifetime estimation with respect to this single degradation factor. The errors in the measured degradation of the coatings, as detected by the changes of the solar absorptance and the thermal emittance, and their influence on the estimated lifetime, were investigated empirically in a Round Robin Test. This was performed on the same black chrome coating by seven different laboratories following the same test procedures. The results agree surprisingly well and are very encouraging for the definition of a recommended standard procedure for the assessment of the thermal stability of solar absorber coatings in the future.

A broad spectrum of metal/dielectric composite materials for solar absorber coatings has been investigated in the past. In order to find a cost-effective coating which is easy to manufacture, the material combination Al/A1203 was investigated. The coatings were produced by simultaneous evaporation of Al and A12O3 from two separate electron gun sources as well as reactively by evaporation of Al in oxygen. The results of both procedures are compared for layers with a homogeneous and a graded filling factor of the metal. A solar absorptance of 0.96 at a thermal emittance (373 K) of 0. 12 was achieved. The thermal stability of the coatings was investigated by annealing in air and under high vacuum conditions. The stability was poor in both cases. The changes of the material composition due to the degradation was investigated by Auger depth profiling.

Various black paints suitable for coil coating application with different PVC ratios (27-39 %) were made from phenoxy resin and FeMnCuO pigment. The influence of the paint formulation on its spectral selectivity, surface properties and thermal responses were established. Optimization (a5 > 0.90, eT < 0.15) of the TSSS paint coating was obtained by addition of fumed silica and silane coupling agent at a PVC ratio of about 30 %. Thermal degradation of the paint coating was investigated by measuring the infrared spectra of coatings for the duration of a 60 hour heat treatment. Comparison of the corresponding FT-IR spectra revealed0 that oxidization of the phenoxy resin took place. The paint is stable up to 135 C, while at 220°C outgassing is already beginning.