Improved and intelligent windows are an important component to minimize the energy consumption of houses. On the one hand highly insulating windows with low U-values (high R-value) are necessary to reduce the heat transmission losses during the cold season, but on the other hand, components with high solar transmittance are desirable to get solar gains in the same period of the year. In addition, overheating problems might occur during summer, so smart windows with variable characteristics might be useful. These demands are just conflicting. Recent developments to overcome this problem are summarized. The combination of new technologies like antireflection layers, low emission coatings and switchable films may give a chance to produce smart windows with a wide dynamic range in solar transmittance.

This paper reviews some of the electrochromic device development carried out in our laboratories over the last few years. An initial discussion of the device material properties required and achieved, in particular some considerations concerning WO₃, is given. This highlights the use of systematically optimized thin films produced by sputtering in a variety of different ways. It is found that the thin films produced for large area depositions are often not the 'best' electrochromically, but may have to be this way because of a number of deposition and production constraints. The production of a large area electrochromic device is ultimately an exercise in compromises. Consideration of the WO₃ layer alone shows this to be true. Compromises must be made to determine the thin film properties, as they are all related to one another through the deposition conditions, but economic considerations must also be taken into account.

The optical performance of an electrochromic window is found to deviate with window color state and with sky condition from clear to cloudy. A new spectral cloud model ALLSKY1 (Soule) is developed and applied to an electrochromic window recently developed at NREL (Zhang and Benson). A comparison in spectral selectivity also is made between the electrochromic window and spectrally selective standard windows. Two series of double- glazed window sections, including the electrochromic window with color state and a series of standard windows with spectral selectivity, were measured for transmittance and reflectance (300 - 2500 nm). A new near-infrared blocking factor, that depends strongly on sky conditions, is developed for warm-climate window applications with cooling load reduction. The color shifts of both the incident daylight spectra from clear to cloudy and the electrochromic window with color state are studied with a chromaticity analysis (CIE 1931 2 degrees). Computed daylight correlated color temperatures show a wide range, with values of 5660 K for clear global irradiation, 6210 K for clouds, and 13,250 K for a zenith blue sky. Chromatic trajectories with color state for transmitted radiation extend further toward the blue to 8180 K for the global and 28,990 K for the zenith sky irradiation.

Wide-gap, transparent amorphous silicon based photovoltaics can be integrated with electrochromic materials to produce a self-powered 'smart' window coating. Existing electrochromic window designs require an external electrical connection, which may be economically unfeasible. This problem is solved by the tandem photovoltaic-electrochromic (PV/EC) device, in which a wide-gap amorphous silicon-based alloy (a-SiC:H) photovoltaic device is deposited together with an electrochromic optical transmittance modulator in a monolithic device on a single substrate. In this paper, we discuss our proposed monolithic photovoltaic-electrochromic device. We also present studies of transparent, wide-gap (Tauc gap of 1.8 to 2.2 eV) amorphous silicon-carbon thin films and p-i-n devices designed for use in the photovoltaic-electrochromic device. The photovoltaic cells in the PV-EC can operate at low current (< 1 mA/cm²) because a total injected charge of only 60 (mu) C/cm² will darken the EC layer to a visible transmission of 5%, but they will need a high open-circuit voltage (> 1.0 V) and high transparency (approximately equals 70%). We describe our progress toward these design targets.

This paper concerns the autonomous responsive type light adjustment window (intelligent windows) among smart windows which adjust the light upon receiving environmental energy. More specifically, this is a thermotropic window panel that laminates and seals a new type of highly viscous polymer aqueous solution gel. A conventional thermotropic window panel has never been put to practical use since the reversible change between the colorless, transparent state (water-clear) and translucent scattered state (paper-white) with uniformity was not possible. The change involved phase separation and generated non-uniformity. The author, after fundamental studies of hydrophobic bonding, successfully solved the problem by developing a polymer aqueous solution gel with amphiphatic molecule as the third component in addition to water and water-soluble polymer with hydrophobic radical, based on the molecular spacer concept. In addition, the author established peripheral technologies and succeeded in experimentally fabricating a panel type 'Affinity's Intelligent Window (AIW)' that has attained the level of practical use.

The transition temperature (tau) _c of the V_1-xW_xO₂ films deposited by dual-target sputtering was precisely determined from the changes both in IR transmittance and in electrical resistivity against temperature. The relationship between x (0-0.026) in V_1-xW_xO₂ and (tau) _c(0-67 degree(s)C) in the most applicable range for window coatings was clarified and a confirmed. The V_1-xW_xO₂ films containing the desired tungsten doping amount were fabricated with reproducibility by sputtering of a V-W(1.6at.%) alloy target under optimal conditions. The (tau) _c reduction efficiency for the films deposited using alloy target is almost identical of that for the films deposited by dual-target sputtering. The V_1-xW_xO₂ films deposited using alloy target showed thermochroism comparative to those previously prepared by dual-target sputtering.

Viologen derivatives adsorbed on TiO₂ surfaces in nanocrystalline-nanoporous electrodes have been studied with respect to electrochromic phenomena. The transparent nature and the high internal surface area of these electrodes are very beneficial for this purpose. Two different viologens were studied giving rise to blue, green, and violet coloration. For one of the viologens we show the possibility to vary the color for the same viologen/TiO₂ electrode from transparent to green or violet depending on the applied potential. Depending on the applied potential different optical densities were obtained. Optical density changes from 0.1 up to 1 and coloration efficiencies above 100 cm²C^-1, with a maximum value of 440 cm²C^-1, were obtained. The switching times for these electrodes for both coloration and bleaching were faster than 1s for a transmittance change larger than 60%, using 0.5M LiClO₄ in acetonitrile as electrolyte. Preliminary stability tests were performed. One electrode has been cycled 654 times without substantial decline in coloration efficiency.

The adsorption on a titanium dioxide substrate of organic monolayers used in the nanocrystalline dye sensitized solar cells was investigated by Raman spectroscopy, owing to the high resonance effect in these molecules. During the polarization of TiO₂ modified by Ru-bi or ter pyridinium compounds in a photoelectrochemical cell, an enhancement affect appeared, allowing us to scrutinize the part of the complex which is in contact with the substrate. This affect remains to a large extent unexplained; it could be attributed to SERRS (surface enhanced Raman resonance). Noticeable differences appeared in the function of the nature of the pyridil ligands. In the case of bipy, in addition to the `normal' (ground state) Raman bands, a new series of bands appeared which correspond to the particular ligand exchanging electrons with the substrate titanium atoms. The Raman intensity of these new peaks is directly related to the electric field (i.e., to the potential magnitude independently of its cathodic or anodic nature). In the case of terpy, the enhancement mechanism seems different. The similarity of the molecular configuration created by the adsorption with the radical anion formed by the excitation of the metal ligand charge transfer complex has to be emphasized. Very interesting prospects for the understanding of the adsorption mechanisms are therefore opened.

We survey some recent work related to electrochromic W-oxide-based thin films. The electronic structure of cubic (perovskite) WO₃ and HWO₃ was calculated from first principles. It was found, among other things, that hydroxide formation was energetically favored. Experimental studies were made on films prepared by reactive magnetron sputtering in Ar + O₂ with and without CF₄ addition and substrate bias. Structural studies by atomic force microscopy, x-ray diffraction, infrared reflectance spectroscopy, and Raman spectroscopy indicated that the electron bombardment associated with a positive substrate bias led to grain growth and partial crystallization while maintaining a high density of W equals O double bonds presumably on internal surfaces. Electrochemical and spectrophotometric measurements demonstrated, in particular, that tandem films -- with a thin protective layer of electron bombarded oxide covering a thicker oxyfluoride layer -- were able to combine rapid dynamics of the electrochromism with good durability. Oblique angle sputtering in Ar + O₂ gave films whose microstructure comprised inclined columns, as seen from scanning electron microscopy. Pronounced angular selective transmittance was found to coexist with electrochromism.

Two sets of WO₃ thin films were prepared by rf sputtering from tungsten oxide and tungsten metal targets, respectively. Lithium insertion studies were carried out in these two types of films. It has been found that the films sputtered from the metal targets showed an irreversible uptake of lithium without any coloration. The aim of the present work is to study this specific behavior of such films in comparison to those deposited from tungsten oxide targets. These films have been studied by thermogravimetry, UV-Vis spectroscopy, electron probe, ellipsometry, and ATR-FTIR spectroscopy. The stoichiometry of both types of films is found to be identical. The ATR-FTIR spectra show a difference in the W-O stretching vibration pattern of the two types of films, clearly indicating structural differences in the as- deposited WO₃ films. However, both types of films show the presence of little or no water in the as-deposited state. Upon the insertion of lithium it is found that the films deposited from the oxide target show the formation of 'bronze' right from the very early stage of insertion as indicated by the blue coloration. This formation is reflected in the ATR-FTIR spectra by the increasing slope of the absorption in the mid-infrared range. Contrary to this behavior, the films deposited from the metal target do not show any coloration in the initial stages of lithium insertion. The infrared spectra corresponding to this behavior show little change in the mid-infrared range. However, a widening of the W-O stretching band is observed in these spectra reflecting a structural reorganization in the films. With continued lithium insertion, however, the behavior in the two types of films becomes similar. Hence, in the initial stages of coloration the quantity of lithium participating in the electrochromic coloration of the films deposited from metal target seems to be lower than in the other types of film. The optical constants of these films have also been determined using reflection- transmission ellipsometry showing important differences in the films. Hence, the electrochromic behavior of sputtered tungsten oxide films depends strongly on the type of deposition.

Mixed hydroxides films with various Mn/Ni ratio (Ni concentration of 26, 46, 68, 86, and 90%) were obtained by cathodic precipitation starting with a mixture of manganese and nickel nitrates. Their electrochromic properties in 0.1 M KOH solution were studied using in situ Raman spectroscopy (RS) which gives us the chemical identification of the films in their bleached and colored states, UV/visible spectroscopy, and optical multichannel analysis (OMA) which allows us to obtain, besides the optical properties of the material, the kinetics of the color changes. A large difference is observed between the films containing a nickel percentage <EQ 50 or >= 70%. The addition of manganese does not improve the electrochromic properties of nickel oxide, except for the kinetic point of view, since the coloration times are reduced by about one order of magnitude passing from Ni(OH)₂ to Mn(OH)₂.

To investigate the microstructure of nickel oxide electrochromic films, cross-sectional observation of sputtered nickel oxide film was performed using a high resolution electron microscope. Lattice and atomic image could be observed for an as-deposited sample and a bleached sample. These images showed that crystallized NiO exists in both samples. As- deposited film contained a small amount of Ni₂O₃. One of [111] axis shrank about 3% and the lattice was a little bit strained in the bleached state. The fact that no trace of Ni(OH)₂ or other species was observed implies that the boundary and surface of NiO microcrystallites played an important role in the electrochromic reaction.

The electrochromic nickel oxide films were prepared onto transparent conducting film on glass substrate by the sol-gel method using an ethylene glycol solution of nickel nitrate hexahydrate. The films produced by the dip-coating method and calcined at 250, 300, and 350 degree(s)C. The formed films were characterized by their electrochromic behavior in cyclic voltammetry. The formed films showed electrochromic behavior in 1M KOH aqueous solution as electrolytic solution. The cyclic voltammograms were recorded up to 100 cycles for each film. The anodic peak of the coloration reaction appeared at approximately +400 mV, while the cathodic peak of the bleaching reaction occurred at about +200 mV versus Ag/AgCl. Both the anodic peak and the cathodic peak increased with an increase of the cyclic numbers in voltammograms, whereas these peaks at 100 cycles decreased with an increase of the calcination temperature of nickel oxide films. The calcination gave great influence on the other electrochromic behaviors of nickel oxide films.

The optical and electrochemical properties of sol-gel spin coated CeO₂-TiO₂ (50% CeO₂) films were investigated for electrochromic applications. The coating solutions were prepared by using mixed organic-inorganic [Ti(OC₂H₅)₄ and Ce(NH₄)₂ (NO₃)₆] precursors. X-ray diffraction studies showed the sol-gel spin- coated films were composed of an amorphous matrix of titanium oxide containing nanocrystallites of cerium oxide. The coating solar transmission value was T_s equals 0.8 (250 nm thick). The refractive index and the extinction coefficient were derived from transmittance measurements in the UV-VIS-NIR regions. These films had refractive index value of n equals 2.18 and extinction coefficient value of k equals 8 X 10^-4 at (lambda) equals 550 nm. Cyclic voltametric measurements showed reversible electrochemical insertion of lithium ions in a CeO₂-TiO₂/LiClO₄-propylene carbonate electrochemical cell. During cycling the films maintain high optical transmittance. Spectrophotometric and electrochemical investigations performed on CeO₂-TiO₂ films revealed that these films are suitable as an optically passive counter-electrode in lithium electrochromic devices.

Recently, Rauh and Cogan presented a model for the thermodynamic equilibrium optical and electrical properties of electrochromic optical modulation devices. Such an empirically based, predictive model is very useful in the engineering design of practical electrochromic devices. The existing model, however, requires considerable computation to model the effects of changes in important device parameters such as layer thicknesses and total mobile ion charge. We present a simple, graphical technique for evaluating the equilibrium electrochemical interaction of two electrochromic layers at any applied voltage based on independent, empirical, back-EMF measurements of the materials. Our technique allows extremely rapid evaluation of different candidate materials, layer thicknesses, and total ion charges. We present the results of the model for Li-based electrochromic devices employing WO and VO layers with an emphasis on design for low coloration voltage.

The paper outlines several unique properties of C₆₀ (environmental, electronic, and structural), compared to standard semiconductors such as Si and GaAs, that render it a most promising material for the fabrication of high-efficiency photovoltaic cells. Details are presented of an experimental Schottky barrier solar cell we have constructed using a single crystal of C₆₀. Preliminary results of our experimental studies of the optical properties of crystalline and amorphous C₆₀ films are discussed.

Using photoluminescence, photoluminescence excitation, and secondary ion mass spectroscopy (SIMS) investigations we show in this paper that two luminescence objects with different PL excitation spectra exist in PS. Two stages of photoluminescence aging were observed which are connected with desorption and oxidation processes.

In the course of developing amorphous silicon based solar cells, it is very important to know the profile of photo-generation rate in the device. This profile is strongly dependent on the optical properties of all the layers, the interface properties, and the incident light spectrum. In the case of a solar cell with flat interfaces, the interference effect at long wavelengths should be taken into account. The light absorption can be optimized at a certain layer thickness. However, in the case of a solar cell with a textured substrate, the problem becomes more complicated since light will be scattered at several rough interfaces. We have studied the light scattering at the rough interfaces in typical amorphous silicon solar cells, developed a computer model to simulate the optical behavior of a multi-layer system with rough interface and simulated amorphous silicon based solar cells with different structures: glass/TCO/pin(a- Si:H)/Ag, glass/TCO/pin(a-Si:H)/pin(a-Si:H)/Ag, glass/TCO/pin(a-Si:H)/TCO/Ag, and ITO/pin(a-Si:H)/TCO/Ag. In this paper, we present the method and the results of our optical modeling of amorphous silicon based solar cells. This modeling is performed for cells with flat or textured substrates.

Thin-film Cu(In,Ga)Se₂(CIGS) is used as the absorber in an all-thin-film solar cell for both conventional 1-sun and concentrator applications. The absorber fabrication process is represented by time-dependent profiles of elemental Cu, In, Ga, and Se fluxes. The Cu/(In+Ga) ratio determines the phase chemistry during growth whereas the Ga/(Ga+In) ratio determines the CIGS band gap profile. All film-growth processes enter the CIGS:Cu_xSe two-phase field where the Cu_xSe facilitates large grain growth. Characterization of cells under 1-sun illumination reveals world-record total-area performance of 17.1%. Improvements relative to previous cells are linked to decreased inter-diffusion of In and Ga within the absorber. Cell parameters include an open-circuit voltage (V_oc) of 654 mV and short-circuit current (J_sc) of 33.9 mA/cm². A second cell was fabricated for operation under concentration. The 1-sun, direct-spectrum measurement yielded at 15.1%- efficient cell. Under 5- and 22-sun concentration, the cell improved to 16.5% and 17.2%, respectively. This achievement is significant in that it proves a compatibility of polycrystalline thin-film and concentrator technologies. Further optimization could yield 1-sun performance in excess of 18% and concentrator performance in excess of 20%. A path to this goal is outlined.

We report new results on continuous wave Nd:YAG laser deposition of cadmium sulfide thin films. Substrates were soda-lime silicate glass, silica glass, silicon, and copper coated formvar sheets. As deposited films were mixtures of cubic and hexagonal phases, with two different grain sizes. As revealed by SEM micrographs, films had smooth surface morphology. As revealed by TEM analysis, grain sizes were extremely small.

We report on new p-type ternary metal chalcogenide absorber films for possible solar energy applications. The films are formed by interfacial diffusion in chemically deposited multilayer films: CuS films (0.15 - 0.6 micrometer) deposited on ZnS, PbS or Bi₂S₃ films (approximately equal to 0.1 micrometer). The diffusion takes place during annealing at temperatures above 150 degree(s)C and is shown in the XPS depth profile spectra of the annealed samples: metal atoms (Zn, Pb or Bi) of the underlying substrate films are detected at the surface layers after the annealing. The peculiarity of the multilayer films is that they show almost constant sheet resistance upon further annealing until 350 degree(s)C. The sheet resistances are in the range of 20 - 100 (Omega) suggesting conductivities (p-type) of up to 400 (Omega) ^-1cm^-1. In the case of CuS on Bi₂S₃ films, the formation of a compound, Cu₃BiS₃, is clearly detected.

Accelerated life testing of solar energy materials has been one of the main topics within the former Task X 'Solar Materials Research and Development' of the International Energy Agency (IEA) Solar Heating and Cooling Programme. In the case study of some selective solar absorber coating materials for domestic hot water systems procedures are presented for service time assessment, applicable for example to absorber coating materials. As a continuation of the finalized Task X a working group, 'Materials in Solar Thermal Systems' also in the framework of the International Energy Agency (IEA) 'Solar Heating and Cooling Programme' was initiated. One of the first projects is described here. Its aim is to investigate the conformity of the durability assessment, applied on solar absorber coatings tested by different laboratories. Each lab is working independently, this means there is no information exchange between the labs until the results are on paper. Test samples are delivered by the participants. Four different absorber coatings are identified to be useful for the project. The coating materials as well as the production procedures of the coatings are not relevant for the study, therefore no information is given. The experimental procedures as well as the judgement over the different absorber coatings are described in detail. Some comparisons between individual results of the different labs indicates possible weaknesses and further necessary refinements. Finally, expected costs for the whole procedure are presented.

Sputtering is a well established coating technology for glass panes. This technology is also interesting for the production of selective solar absorber coatings because the environmental impact is much less than for electroplating. There are already several sputtered absorber coatings for evacuated tubular collectors existing on the market. The application in ventilated collectors requires better durability of the absorbers and a technology which can be applied to planar substrates. The coatings presented here are produced by dc-magnetron sputtering. The maximum sample size was 2 m multiplied by 3 m. A thermal emittance (at 373 K) below 5% was achieved together with a solar absorptance (AM 1.5) above 90%. The coating is deposited directly onto copper sheets without the commonly used anti-corrosion nickel coating in between. The durability of the absorbers was found to be sufficient for the application in ventilated flat-plate collectors containing moisture according to the tests and requirements proposed by Task X of the Solar Heating and Cooling Programme of the International Energy Agency.

An apparatus was built to measure the spectral hemispherical reflectance and transmittance at variable angles of incidence. The apparatus consists of a Fourier-transform spectrometer, polarizers, and two integrating spheres. With one of the spheres, transmittance measurements can be performed, with the other, reflectance or absorptance measurements depending on the transmittance of the samples. The measurement range for transmittance measurements is from 400 nm to 2500 nm and for reflectance or absorptance measurements from 400 nm to 1900 nm. The design of the spheres and the optical set-up is described. The measurement accuracy was determined by measuring well-defined samples. Examples of measurements of different solar selective absorber coatings and anti-reflection layers are shown.

The issue of low emittance in angular selective window systems is discussed in the context of the overall aims of controlling glare and lowering solar gains while maintaining a clear view. Low e adds considerably to the overall performance of the window. The spectral dependence of both angular selectivity and overall transmittance in single layer anisotropic metal-insulator films needed to be improved. While these have excellent visible properties, they have high infrared transmittance and hence the window has high emittance. Results on coatings and systems set up to give the glazing a low e are examined. It is found that the visible performance is not impaired but the solar and thermal performance are improved substantially. Two methods of achieving a low emittance are discussed.

Tungsten doped vanadium oxide (V_1-xW_xO₂) films are known to be reliable thermochromic materials for their semiconductor/metal transition temperature which can be controlled by the doping level x. In this paper, firstly, the optical constants of V_1-xW_xO₂ films on glass substrate were determined from the reflectance spectra and the transmittance spectra measured at 25 degree(s)C and 80 degree(s)C in the wavelength region from 300 to 2500 nm. In the determination we used Drude model in the high temperature metallic-phase and the least square method in the low temperature semiconductor-phase. The calculated reflectance spectra and the transmittance spectra using the Drude model with adequate values of the parameters are consistent with the measured ones in whole spectral region in the high temperature phase. Secondarily, we carried out a simulation of radiative cooling power of some selective radiating materials whose substrates were V_1-xW_xO₂ films, using the optical constants in IR region obtained by the extrapolation of the obtained ones in visible and near IR region. As the high temperature phase of V_1-xW_xO₂ has high reflectivity, we can use this thermochromic film as a substrate of the selective radiating material which consists of an adequate film on a high reflective substrate. The simulation shows the capability of automatic temperature control of the radiative cooling system tandemed by SiO film, V_1-xW_xO₂ film, and the black substrate by different doping level x.

Indium tin oxide (ITO) thin films on soda-lime-silicate (SLS) and silica glasses were fabricated using an rf plasma mist deposition process. SEM analysis showed that the ITO films consisted of uniform particle size with a size ranging from 50 to 200 nm. XRD revealed that In₂O₃ phase is present in the film when In:Sn ratio is 5:5 and higher. The resistivity of the ITO films was between 1 - 10 ohm-cm. The structural change near the surface of the glass was investigated by DRIFT (diffuse reflectance infrared Fourier transform) spectroscopy. The infrared results indicated that the structure near the surface was significantly changed with higher indium concentration. The coating materials create non-bridging oxygen near the surfaces. The effects of deposition time and substrate temperature were also studied.

The aim of this work was to investigate the thermodynamic properties of nitrate tris(4-amino- 1,2,4-triazole) iron(II) for which a thermochromic effect takes place at T equals 342 K on heating and at 310 K on cooling. For the measurement of the isobaric heat capacity in the 5 - 355 K range, a vacuum adiabatic calorimeter was used. Below 300 K, the C_p,m(T) curve has no anomalies; the average deviation of the experimental heat-capacity values from the smoothed C_p,m(T) curve was 0.1 percent. Above 300 K, the C_p,m(T) curve shows a complicated behavior. The abnormal part of the heat capacity first increases smoothly, then from 330 K a sharp rise begins. There is a peak on the C_p,m-curve at T equals 343.0 K. This fact is in a good agreement with the magnetic measurement data. The transition enthalpy was determined to be 22.8 kJ(DOT)mol^-1 (M equals 432.10 g(DOT)mol^-1). Further increase of the heat capacity suggests the existence of a new phase transition above 350 K. This suggestion was confirmed qualitatively by the measurements on a differential scanning calorimeter. It should be noted that on the low- temperature slope of the anomaly, at 320 < T < 330 K, there is a small anomaly with the maximum deviation of 5 - 10% from the regular part. To compare the phonon characteristics, the heat capacity of nitrate tris(4-amino-1,2,4-triazole) copper(II) was studied.

The fabrication of such an all-solid-state EC device using the combination of amorphous WO₃ film as the electrochromic layer and VO₂ as the counter electrode is studied. Lithiation studies of two transition metal oxides (WO₃ and VO₂) were done for their use as base electrochromic layer and counter electrode layer in the solid device. A dry method of lithiation of the device is proposed and characterized completely for it use in the fabrication of EC device. The properties of thermally evaporated LiAlF₄ were also studied for its use as the ion conducting layer. Using these three materials an all-solid-state electrochromic device has been fabricated and studied for its use as a `smart window.'

In past years much interest developed in lanthanides and uranyl doped glasses. The energy transfer phenomenon in these glasses produced interest for preparation of highly efficient laser materials and optical transformators. We present some experimental results about mechanism of donor-acceptor interaction and energy transfer in highly activated by uranyl and three-valent rare earths ions cesium-phosphate glasses and luminescent converters and concentrators, using these glasses and films. Our investigation shows that donor-acceptor interaction proceeds by exchange mechanism. Efficiency of energy transfer is about 0.9 for optimal composition of glasses. The quantum yield of luminescence of some lanthanides, in particular Nd³⁺, is more than 0.8. The reactive ions sputtering and following thermal treatment allows us to receive optical quality thin films of the discussed materials. Efficiency of transfer and quantum yield of luminescence in films reaches more than 0.8 and 0.7 accordingly. Preliminary experiments of using the glasses as transforming filters in lasers showed their prospectives for the overall laser's efficiency increasing. Collectors made on the base of UO₂²⁺ - Nd³⁺ glasses allows them to increase on about 40% effectiveness of solar light energy in electric energy transformations by some cells.

The formation mechanism of anodically grown porous silicon is experimentally shown to be controlled by two electrochemical reactions: the silicon dissolution reaction occurring at fluorine-covered sites on the surface and the oxidation of molecular hydrogen that takes place at hydrogen-covered sites. The latter reaction injects electrons in the silicon surface and produces an increase in dissolution rate at fluorine-covered sits. The dissolution rate increase in the presence of excess charge at the fluorine-covered sites is investigated theoretically by semi-empirical Hartree-Fock calculations that show that this spatially variable dissolution generates the porous silicon structure.

Electrical, photoelectrical, and impurity-structural properties of the Si-SiO₂ structures formed under the same technological conditions at flat type (FS) and textured (TS) surface regions of silicon wafers were investigated. Enhanced in comparison with FS surface generation velocity, S_g, increased built-in oxide charge density, N_sO, and comparatively high differential concentration of interface states, N_ss, were obtained with TS. Typical for P_b-centers maximums in N_ss(E) spectra at energy position E equals E_c-0.25 eV were observed both for FS and TS samples indicating the participation of silicon atoms with dandling bonds in formation of the Si-SiO₂ interface states. Accordingly to SIMS data, the oxide layer at TS was highly contaminated by alkali metals (Na, K) the microstructure of the Si-SiO₂ interface being more disordered and 'friable' than in the FS case.

It is well known that the light absorption in an amorphous silicon solar cell can be enhanced by applying textured transparent conductive oxide (TCO) substrates. However, the degree of the enhancement depends on the optical and surface properties of the TCO substrates: the refractive index n((lambda) ), the extinction coefficient k((lambda) ), the thickness d of the layer and the root mean square (rms) roughness (sigma) _r of the rough surface. Because light scattering takes place at the rough surface, the transmittance spectroscopy cannot be directly applied to determine the TCO layer properties. We have studied the light scattering at the rough TCO surfaces. Based on our analysis, the reflected and transmitted light at a rough interface consists of a specular part and a diffused part. The specular reflectance and transmittance depend on the optical and surface properties of the TCO layer. We have developed a procedure to extract the optical and surface properties from the measured specular reflectance and transmittance. This extracting procedure and the results are presented in this paper.

Methods for preparing good quality CdS and CdSe thin films of 0.1 - 0.7 micrometer thickness from solutions at 24 - 50 degree(s)C containing citratocadmium(II) ions and thiourea (for CdS) or N, N-dimethyl selenourea (for CdSe) are presented. The as prepared CdS thin films are photosensitive showing photo- to dark-conductivity ratio (S) of > 10⁶ under AM-2 illumination. Annealing of these films at 400 - 450 degree(s)C for a few minutes converts them to n-type through partial conversion of the films to nonstoichiometric CdO. In the case of CdSe, such annealing improves the photosensitivity of the films from S equals 10 (as prepared) to greater than 10⁷ (after annealing) under AM-2 illumination. Either film can be converted to n-type with dark conductivities of greater than 1 (Omega) ^-1 cm^-1 and S equals 1 to 10 under AM-2 illumination using a post deposition treatment in dilute (0.01 - 0.05 M) HgCl₂ solution followed by heating at 200 degree(s)C.

Indium tin oxide (ITO) film has been prepared by sequential vacuum deposition of indium and tin on plain glass followed by oxidation at temperatures around 400 degrees - 650 degrees Celsius. By a proper control of the time of evaporation and the heating current the concentration of vacuum evaporated indium was maintained constant and tin concentration was varied in the range of 10 - 60% by weight. ITO films with good optical and electrical properties can be obtained by adjusting the ratio of Sn:In in the range of 1:9 to 1:35 after heat- treatment at 400 degrees to 600 degrees Celsius. The films exhibit a sheet resistance of 20 ohms per square with an optical transmission of 60% at 500 nm when the Sn:In ratio was maintained at 1:9. The film was found suitable for ITO/Si solar cells and as substrates for photo anodes in PEC cells.

Described in the work is a two-stage process of the fabrication of indium oxide films, consisting in a preliminary synthesis of indium sulphide and its subsequent oxidation. Films of In₂S₃ were prepared by the method of gas-phase deposition from the volatile complex compound indium(III) isopropylxanthate. The crystal structure and electrical characteristics of the In₂S₃ films were studied when the temperature of the synthesis was varied in the 230 - 450 degree(s)C range. According to the x-ray phase analysis of the indium sulphide films, they were polycrystalline with cubic ((alpha) -phase) or tetragonal ((beta) -phase) structure. They were oriented with the (alpha) [111] direction perpendicular to the glass substrate for the whole interval of the synthesis temperatures. The In₂S₃ films turned into cubic In₂O₃ after annealing in the presence of oxygen. It was shown by auger analysis that annealed samples were indium oxide films with a small admixture of sulphur. The electrical resistance was measured in situ, during the oxidation process. The specific electrical resistance of indium sulphide films varied from 0.1 to 500 Ohm.cm depending on the temperature of the synthesis. The electrical characteristics of the In₂O₃:S films were connected with the properties of the starting In₂S₃ films. The lowest values of specific resistivity ((rho) approximately equals 1.10^-2 Ohm.cm) for In₂O₃:S films were attained by the oxidation of In₂S₃ films synthesized at T >= 370 degree(s)C .

The third-order nonlinear susceptibility, (chi) ⁽³), for a series of complexes of 3,5- ditertbutyl-o-benzoquinone (dbsq), [M(dbsq)₂ where M equals Pd or Pt], o- mercaptophenol (mp), {[TBA][Ni(mp)₂]}, or 1,3-dithiol- 2-thione-4,5-dithiol (dmit), {[TBA][M(dmit)₂] where M equals Ni or Pd}, have been measured in CH₂Cl₂ solution by retroreflection DFWM technique at 1064 nm. The results indicate large (chi) ⁽³) values of the order of 10^-11 esu at concentration levels of 10¹⁸ molecules/cm³. These values are up to two orders higher than those found for other sulphur donor dithiolenes and nitrogen donor ligand systems, although the linear absorption is also higher.

Ellipsometric studies are generally carried out in reflection mode rather than in transmission mode, requiring invariably opaque substrates or substrates in which the back reflection is minimized or suppressed by different methods. In the present work, we have used a transmission and reflection photo-ellipsometry method to study electrochromic materials and their multilayer systems deposited on thick substrates. The role of the substrate is examined carefully and the contributions from multiple reflections in the substrate are taken into account in the theoretical treatment. This procedure not only allows the study of thin films deposited on quasi-transparent substrates but carried out in conjunction with reflection measurements improves greatly the accuracy in the determination of the optical constants. Optical measurements have been carried out on an automatic reflection-transmission spectrophoto- ellipsometer. Solid state ionics materials used in electrochromic systems such as indium-tin oxide, tungsten oxide, and their multilayer structures deposited on glass substrates are used as examples. A software based on the above theory, OPTIKAN, has been developed to model and analyze such systems. It is demonstrated that the photo-ellipsometry method proposed is especially suited to analyze in a non-destructive way electrochromic materials and transmitting devices.

Photoelectrochemical measurements have been performed on film electrodes consisting of linked nano-sized TiO₂ colloids. The film thickness ranged from 1 - 40 micrometers. The film network was attached to a thin transparent conducting layer of SnO₂ allowing for photogenerated electrons to be collected in an outer electrical circuit. By illuminating electrodes of different thicknesses with monochromatic light from either side, it was possible to induce charge separation in different regions of the film network. In this way, it was proved that electrons have different probabilities of reaching the back contact depending on the location in the film where they are created. The results also illustrate the importance of the redox species in the cavities of these porous electrodes. By adding acceptors to the electrolyte it was possible to alter the conditions for charge transfer in the nanocrystalline film. It was shown that electron acceptors such as oxygen or iodine in the solution strongly affects the rate of charge transfer at the particle-electrolyte interface and the transport of electrons throughout the TiO₂ film-network. Modification of the semiconductor-electrolyte interface with surface adsorbed pyridine induced major changes in the charge transfer events at the interface. The photocurrent yields were greatly improved by this surface treatment. The effect of pH in solution was also investigated. The rate of charge transfer at the particle-electrolyte interface was changed at high surface density of OH^--ions. This was explained due to the change of the surface energy causing different driving forces for redox reactions, but also due to the more negatively electrostatic surface potential of the particles preventing the encounter of negatively charged redox species with the colloid surface. Phototransient measurements indicated a depletion of redox species in the pores of the film. Thereby it was pointed out that the dynamics of the redox species in the confined cavities of the film are a limiting factor for the charge separation efficiency in nanocrystalline film. The photovoltage in anaerobic solutions sustained for very long periods, indicating that the linked particles may work as reservoirs for photoexcited electrons if the access to electron acceptors in the solution is choked. It was concluded that surface processes are favored at the small semiconductor particles used in this study.

Spectrally selective paint coatings were prepared from organically modified siloxane in combination with two types of different pigments (organic soot-FW2 or inorganic FeMnCuO_x-P320). To optimize the low-emittance properties, various concentrations of pigments were used for the preparation of paints. From seven prepared paints, different thicknesses were applied on high-reflecting Al foil by draw bar coater. For all paints, optical and thermal properties were determined as well as their adhesion resistance. For higher concentration of used pigment better selectivities were obtained, but at the same time paints exhibited bad adhesion properties. The thickness of paints having different concentration of the added pigment was optimized in correlation with their spectrally selective properties and adhesion resistivities. The results of this study indicate that pigment to volume concentration ratio has to be about 20% for thicknesses of about 1.7 g/m² - 2.0 g/m². Solar absorbance for these samples were a_s equals 0.90 - 0.92 with thermal emittance of e_T equals 0.20 - 0.25. Temperature stability of these samples was followed by FT-IR spectroscopy at 180 degree(s)C and 300 degree(s)C for three weeks and 68 hours, respectively. The obtained results indicate good temperature stability of prepared paints.