Electrochromics is a key “green” technology for massive energy savings in the built environment jointly with indoor comfort. This paper surveys basic electrochromic (EC) device designs, useful oxide materials and their nanostructures, and elements of a theoretical description of the EC phenomenon. It also outlines critical manufacturing technologies and their pros and cons. Focus is on EC foil technology, which is shown capable of mass fabrication via roll-to-roll web coating and continuous lamination.

Thermochromic materials have temperature-dependent optical properties. This paper discusses the limitations of thermochromic VO2 films for energy efficient fenestration and shows from calculations that nanocomposites containing VO2 can have superior properties and display high luminous transmittance and large temperature-dependent solar transmittance modulation. Even better results may be found for nanoparticles of VO2:Mg.

Be and Mg co-doped ZnO films Zn1-x-yBexMgyO (0 ≤ x ≤ 0.10, 0 ≤y ≤ 0.20) have been deposited for the first time by novel chemical deposition or spin coating method. From the x-ray diffraction patterns it is noticed that the pristine ZnO film exhibits wurtzite polycrystalline structure, however, co-doped films are (0002) preferentially oriented. The (0002) peak intensity also increases with the corresponding increase in dopants concentrations. The systematic decrease in the c-axis lattice parameter value in the co-doped films as compared to pure ZnO film suggests the incorporation of smaller ions Be+2/Mg+2 at Zn+2 site. From the optical transmittance measurement it is noticed that all the films exhibited almost 80% transmittance in the visible region with sharp and single absorption edges in the UV region. The cut-off wavelength shifts from 375nm for the ZnO film to 330nm with 10 Be and 20% Mg co-doped film. The bandgap calculations revealed an increase in bandgap from 3.26eV (ZnO) to 3.60eV (Zn0.7Be0.1Mg0.2O) film. Such an increase in the co-doped films fabricated by a much simpler and cheaper process is very useful in the realization of UV radiation detection without having little interference from the visible light.

A new chemical vapor deposition method for the growth of ZnO films using the reaction between dimethylzinc (DMZn) and thermally excited H2O produced by a Pt-catalyzed H2–O2 reaction was investigated. The thermally excited H2O molecules formed by the exothermic reaction of H2 and O2 on the catalyst were ejected from a fine nozzle into the reaction zone and allowed to collide with DMZn ejected from another fine nozzle. The ZnO films were grown directly on a-plane (11-20) sapphire substrates at substrate temperatures of 773-873 K with no buffer layer. X-ray diffraction patterns exhibited intense (0002) and (0004) peaks from the ZnO(0001) index plane. The smallest full width at half maximum (FWHM) value of the ω- rocking curve of ZnO(0002) was less than 0.1º. The largest Hall mobility and the smallest residual carrier concentration of the ZnO films were 169 cm2V−1s−1 and 1.7×1017 cm−3, respectively. Photoluminescence (PL) spectra at room temperature exhibited a band edge emission at 3.29 eV, with a FWHM of 104 meV. Green luminescence from deeper levels was generally about 1.5% of the band edge emission intensity. PL spectra at 5 K showed a strong emission peak at 3.3603 eV, attributed to the neutral donor-bound exciton Dºx. The FWHM was as low as 1.0 meV. Free exciton emissions also appeared at 3.3757 eV (FXA, n=1) and 3.4221 eV (FXA, n=2).

Market demand for touch panel/lens has been exceptionally high for the recent years due to smartphones, tablet PCs, etc. Among the available technologies to envision touch functionality, capacitive touch screen has received the great attention due to the various superiorities over the competing ones. Capacitive touch screen features two transparent conductive electrodes, such as ITO (indium tin oxide). However, the difference in refractive indices of ITO, substrate, and air, ITO pattern is clearly visible if there is no proper countermeasure. Most of touch screen makers and ITO substrate supplier utilize “index-matching technology” to prevent this phenomenon.

Even though of the attempts to minimize visible ITO pattern in final product, there are many technical and process challenges. In this study, the causes around visible ITO pattern were investigated to understand and provide the proper countermeasures.

One of the possible causes for visible ITO pattern was improper annealing process in ITO especially for film substrate. According to XPS (X-ray photoelectron spectroscopy)/ESCA (electron spectroscopy for chemical analysis) and other analysis results, ITO, which is normally deposited through sputtering, is not fully transformed to oxidized state. After aligning and adjusting annealing condition, acknowledged visible ITO pattern was disappeared.

Other causes for visible patterns were also discussed in detail, and the relevant countermeasures were provided.

CuO and CuGaO2 thin films have been grown on Si (100) substrates using a sol-gel spincoating method. CuO films were successfully fabricated by the annealing around 700°C. At higher temperatures (>800°C), pyramidal CuO islands with 1~2μm in width and 0.4~0.8μm in height were observed. They arranged structures as a straight line parallel to the <110> and <010> directions, which suggests the self-organized growth of CuO pyramidal islands. Delafossite CuGaO2 films were fabricated as well, using Cu-Ga-O mixed solutions with Ga/(Cu+Ga) atomic ratio of 0.5. These results indicate that Cu-based compounds were fabricated by the sol-gel spincoating method.

In this paper, we report the characterization of vertically aligned ZnO nanowire (NW) arrays synthesized by metal-catalyzed chemical vapor deposition. The growth mechanism of ZnO NWs may be related to vapor-solid-nucleation. Morphological, structural, optical and field emission characteristics can be modified by varying the growth time. For growth time reaches 120 min, the length and the diameter of ZnO NWs are 1.5 μm and 350 nm, and they also show preferential growth orientation along the c-axis. Moreover, strong alignment and uniform distribution of ZnO NWs can effectively enhance the antireflection to reach the average reflectance of 5.7% in the visible region as well. Field emission measurement indicated that the growth time play an important role in density- and morphology-controlled ZnO NWs, and thus ZnO NWs are expected to be used in versatile optoelectronic devices.

Epitaxial ZnO layers heavily doped with Ga (GZO) were grown at 400 °C under metaland oxygen-rich conditions in terms of metal-to-reactive oxygen ratio by plasma-assisted molecular beam epitaxy (MBE). Several atomic force microscopy (AFM) techniques were used to characterize the surface morphology and electrical properties of these GZO films in ambient conditions. Local I-V spectra indicate that layers grown under both O-rich and metal-rich conditions are highly resistive until a relatively high voltage sweep (±12 V) is used. After removal of an insulating surface layer, conduction is possible at lower voltages, but eventually the film resistivity increases and it again becomes insulating. In addition to local I-V spectra, local charge injection and subsequent surface potential measurements were used to probe surface charging characteristics. For charge injection experiments, a reverse-bias voltage is applied to the sample while scanning in contact mode with a metallized tip. The resultant change in surface potential due to trapped charge is subsequently observed using scanning Kelvin probe microscopy (SKPM). The layers deposited in a metal-rich environment demonstrate the expected behavior, but the O-rich layers show anomalous negative and positive charging. Finally, surface photovoltage (SPV) measurements using above-bandgap UV illumination were performed. The GZO layers produce SPV values of 0.4 to 0.5 eV, where the films deposited in an O-rich environment have slightly higher SPV values and faster restoration.

Single orientation ZnO (00.2) films were deposited by means of high temperature high vacuum reactive magnetron sputtering onto Al2O3 (0001) and GaN (0001) substrates. In order to obtain films of high crystalline quality a novel approach to ZnO sputter deposition was employed, adapting the practice used in MBE technology, of using a MgO buffer layer deposited on sapphire at a high-temperature followed by a ZnO nucleation layer deposited at low temperature. ZnO films were also grown on epitaxial GaN/Al2O3 substrates where the GaN layer was treated as the buffer layer. Following the deposition, all samples were annealed ex-situ in an O2 flow at 800°C. The obtained ZnO films have a lattice constant c equal to 5.2036 Å and 5.214 Å for the films deposited on Al2O3 and GaN substrates, respectively. Secondary ion mass spectroscopy depth profiles, scanning and transmission electron microscopy cross sectional images and atomic force microscope were used to characterize the structural properties of the films. Electrical properties were assessed using Hall effect measurement. Photoluminescence spectra were also taken.

Thin transparent conducting oxide (TCO) films of gallium-doped zinc oxide have been deposited on glass substrates by atomic layer deposition (ALD) using diethyl zinc, triethyl gallium and water vapour as precursors. The gallium-doped zinc oxide films were deposited over the temperature range 100-350°C. Transmission electron microscopy reveals that the as-deposited films are polycrystalline in character. The electrical resistivity of the gallium-doped zinc oxide films was evaluated using four-point probe and contactless measurement methods as a function of film thickness. The lowest sheet resistance of 16 Ω/☐ was measured from a film thickness of 400nm and a gallium content of 5 atomic percent. The electron Hall mobility of this film was 12.3 cm2/Vs. The visible transmittance of the films was 78% with a haze of 0.2%.

Magnesium and titanium doped indium oxide (IMTO) thin films were grown using pulsed laser deposition technique. Magnesium was added to enhance the bandgap, whereas titanium was added to improve carrier concentrations and mobility of indium oxide films. The effect of growth temperature on structural, optical, and electrical properties were studied. It was observed that the optical transparency of the films strongly depends on growth temperature and increases with increase in growth temperature. The films grown at 600 °C showed optical transparency > 85%. We observed widening in bandgap of indium oxide by doping with magnesium and titanium. The bandgap of IMTO films increases with increase in growth temperature. The maximum bandgap of 3.9 eV was observed for film grown at 600 °C. It was observed that growth temperature strongly affects the electrical properties such as resistivity, carrier concentration, and mobility. The electrical resistivity and mobility of the films increases with increase in growth temperature. On the other hand, carrier concentration decreases with increase in growth temperature. Temperature dependence electrical resistivity measurements showed that films grown at low temperatures are semiconducting in nature, while films grown at high temperature showed transition from semiconducting to metallic behavior. These wide bandgap, highly transparent, and high mobility films could be used for photovoltaic applications.

Transparent conducting oxides have been previously investigated for both bulk and thin film thermoelectric applications, and have shown promising results due to their thermal stability and electrical conductivity. Alloys of two or more transparent conducting oxides have been deposited using pulsed laser deposition (PLD) and combinatorial sputtering, and the resulting films were optimized for optical applications. In this study, thermoelectric materials were prepared by co-sputtering techniques, whereby a chemical gradient was formed across an alumina substrate that was patterned using photolithography to form hundreds of micro-thermocouples. The systems indium tin oxide (ITO), indium zinc oxide (IZO), and zinc tin oxide (ZTO) were investigated for this purpose and the resulting combinatorial libraries were rapidly screened to establish room temperature resistivity, Seebeck coefficient, and power factor as functions of both composition and heat treatment, in nitrogen and air ambients. Due to their chemical stability, oxidation resistance, and large Seebeck coefficients relative to metal thermocouples, these materials are ideal for temperature measurement or energy harvesting in harsh environments such as gas turbine engines.

A novel fabrication method of ZnO films utilizing solid-phase crystallized seed layers has been developed. In this method, solid phase crystallization (SPC) is performed by annealing amorphous ZnON films, which are prepared by sputtering of ZnO targets in Ar/N2 mixed gases, in an oxidization atmosphere. The grain size of ZnO films deposited on the seed layers is significant larger than that of ZnO films directly deposited on glass substrates, which is considered to be due to the low grain density of seed layers. By utilizing this technique, the resistivity of ZnO:Al (AZO) films is decreased from 20 × 10-4 Ωcm to 5 × 10-4 Ωcm at the film thickness of 30nm. Furthermore, we observed that SPC seed layers are in-plane aligned when Al2O3 substrates are used, which suggests that the fabrication method proposed here is also promising for synthesizing epitaxial ZnO films.

The purpose of this paper is to accelerate the pace of material discovery processes by systematically visualizing the huge search space that conventionally needs to be explored. To this end, we demonstrate not only the use of empirical- or crystal chemistry-based physical intuition for decision-making, but also to utilize knowledge-based data mining methodologies in the context of finding p-type delafossite transparent conducting oxides (TCOs). We report on examples using high-dimensional visualizations such as radial visualization combined with machine learning algorithms such as k-nearest neighbor algorithm (k-NN) to better define and visualize the search space (i.e. structure maps) of functional materials design. The vital role of search space generated from these approaches is discussed in the context of crystal chemistry of delafossite crystal structure.

The thermal conductivity of amorphous indium zinc oxide (IZO) thin films was measured by the 3ω method. Three IZO films were prepared by dc magnetron sputtering method on Si substrate under different O2 flow ratios (O2 / [Ar+O2]) of 0%, 1%, and 5%. The thermal conductivity of IZO films decreases with an increase in O2 flow ratio, the values of the thermal conductivity were 3.4, 3.1 and 1.2 W m-1 K-1 for O2 flow ratios of 0%, 1%, and 5%, respectively. To investigate relationships among the thermal conductivity, the structure and other physical properties, we were carried out nanoindentation, Rutherford back scattering (RBS), electron spin resonance (ESR). The result of ESR measurements indicated that the amount of conduction electron in the IZO film decreases with increasing O2 flow ratio. Increase of O2 flow ratio reduces the amount of oxygen vacancies for providing free electrons. Therefore, decreasing thermal conductivity with an increase in O2 flow ratio is attributed to decreasing conduction electrons as thermal carrier. On the other hand, the chemical composition of IZO films is independent of O2 flow ratio. Furthermore, density, Young’s modulus and hardness also show little changes with increasing O2 flow ratio. Density, Young’s modulus and hardness are strongly associated with the internal structure. It is probable that influence of oxygen vacancies on the internal structure of IZO film is negligibly small.

Solar cells based on Cu(In, Ga)Se2 (CIGS) have made significant strides in the past decades with a record efficiency of over 20% [1]. A problem with CIGS modules is the high resistive losses along the transparent top contact. One solution is to deposit highly-conductive metal grids to collect the current. We use finite-element analysis to determine the effectiveness of the metal grid under a variety of parameters. We identify the resistance of the top contact and the width of the scribes as the most important factors in determining whether a metal grid would present a significant efficiency gain. Using the same model, we also investigate methods to optimize the design of the grid.

In order to investigate the performance of ZnO-based thin film transistors (ZnO-TFTs), we fabricate devices using amorphous hafnium dioxide (HfO2) high-k dielectrics. Sputtered ZnO was used as the active channel layer, and aluminium source/drain electrodes were deposited by thermal evaporation, and the HfO2 high-k dielectrics are deposited by metal-organic chemical vapour deposition (MOCVD). The ZnO-TFTs with high-k HfO2 gate insulators exhibit good performance metrics and effective channel mobility which is appreciably higher in comparison to SiO2-based ZnO TFTs fabricated under similar conditions. The average channel mobility, turn-on voltage, on-off current ratio and subthreshold swing of the high-k TFTs are 31.2 cm2V-1s-1, -4.7 V, ~103, and 2.4 V/dec respectively. We compared the characteristics of a typical device consisting of HfO2 to those of a device consisting of thermally grown SiO2 to examine their potential for use as high-k dielectrics in future TFT devices.

CZTS (Copper zinc tin sulfide) thin films have been synthesized on transparent conducting oxide (TCO) back contacts on a glass substrate, allowing sun light to pass through the entire solar cell. Aqueous solution based co-electrodeposition followed by elevated temperature sulfurization, was used to grow CZTS on transparent fluorinated tin oxide. Loss in conductivity of FTO is observed after sulfurization, causing reduced device efficiency. Increased resistivity of the FTO is likely due to outdiffusion process. A systematic study of resistivity of back contact at various sulfurization temperatures and times is discussed. Various remedial measures for improved conductivity of back contact were proposed and conducted.

High quality ZnO:Al (AZO) thin films were prepared on glass substrates by direct current filtered cathodic arc deposition. Substrate temperature was varied from room temperature to 425°C, and samples were grown with and without the assistance of low power oxygen plasma (75W). For each growth condition, at least 3 samples were grown to give a statistical look at the effect of the growth environment on the film properties and to explore the reproducibility of the technique. Growth rate was in the 100-400 nm/min range but was apparently random and could not be easily traced to the growth conditions explored. For optimized growth conditions, 300-600 nm AZO films had resistivities of 3-6 x 10-4 Ωcm, carrier concentrations in the range of 2-4 x 1020 cm3, Hall mobility as high as 55 cm2/Vs, and optical transmittance greater than 90%. These films are also highly oriented with the c-axis perpendicular to the substrate and a surface roughness of 2-4 nm.