The electrochromic properties of hydrated nickel oxide films formed by colloidal and anodic deposition

Hydrated nickel oxide NiO_xH_y films were deposited onto indium tin oxide (ITO) coated glass by two methods (i) colloidal precipitation and (ii) anodic electrodeposition. The electrochromic properties of hydrated nickel oxide films were studied by transmittance measurements (UV/VIS/NIR), and Fourier transform infrared reflectance spectroscopy as a function of the key deposition parameters. The solar transmittance was calculated for films switched in both bleached and coloured states. The best results were achieved for films produced by anodic electrodeposition from stable solutions with solar transmittance T_s(bleached) = 0.82 and T_s(coloured) = 0.22. Corresponding optimum values for the films produced by colloidal precipitation were solar transmittance T_s(bleached = 0.82 and T_s(coloured) = 0.47. Fourier transform spectrophotometry was used for elucidating changes in hydration, hydroxylation and for the characterization of structural characteristics in the bleached and coloured states. It was found that free OH stretching vibration at 3647 cm⁻¹ corresponds to Ni(OH)₂ for both anodic and colloidal deposited films in the reduced (bleached) state. In the oxidised state hydrogen bonded OH at 3360 cm⁻¹ is observed.     

Synthesis and characterization of rough electrochromic phosphotungstic acid films obtained by spray-gel process

Rough electrochromic phosphotungstic acid (PWA) films were fabricated by spraying a gel of phosphotungstate anions with a molar ratio of P:W=1:12 onto glass substrates. The substrates were coated with transparent and electrically conducting SnO₂:F at 300°C. Analysis by X-ray photoelectron spectroscopy determined that the P:W molar ratio in the films was approximately 1:14. Infrared spectroscopy and X-ray diffraction showed that the film is a form of polycrystalline phosphotungstic acid. SEM micrographs showed that the films have a rough morphology based on fiber-shape bridges. Optoelectrochemical measurements demonstrated pronounced electrochromism in the PWA films upon H⁺ intercalation/deintercalation with a high diffuse reflectance (R_d) and transmittance (T_d). We found for as-deposited films that R_d/total reflectance (R_t) and T_d/total transmittance (T_t) at 550 nm was around 0.83 and 0.68, respectively. This ratio decreases at bleached state to 0.74 and 0.41 for R_d/R_t and T_d/T_t, respectively.     

Brown coloring electrochromic devices based on NiO–TiO2 layers

Brown coloring electrochromic 5×10 cm² windows with the configuration K-glass/NiO–TiO₂/electrolyte/CeO₂–TiO₂/K-glass have been prepared and characterized by optoelectrochemical techniques (cyclic voltammetry, chronoamperometry and galvanostatic measurements). The electrochromic layers have been prepared by the sol–gel technique. As electrolyte either a 1 M aqueous KOH solution or a newly developed starch-based gel impregnated with KOH have been used. The CeO₂–TiO₂ sol–gel layers sintered at 550 °C have been previously characterized in 1 M aqueous KOH electrolyte as a function of the thickness up to 2000 cycles and showed a highly reversible behavior without any corrosion effect. The NiO–TiO₂ sol–gel layers sintered at 300 °C have been extensively characterized in the same electrolyte up to about 7000 cycles. All windows present a deep brown color characteristic of the presence of Ni³⁺ (NiOOH) species, that is fully reversible for several thousands of cycles with a rather-fast kinetics (<30 s). The transmittance of the bleached state however slowly decreases with cycling (permanent coloration). The full-bleached condition can be nevertheless recovered by applying a negative potential for a long duration. Deeper coloration is usually obtained by cycling the windows galvanostatically with a current density of 20 μA/cm². The lifetime of the windows is however limited because of the degradation of the NiO-based layers due to the not fully reversible exchange of OH⁻ that turns the layers mechanically fragile and leads eventually to their complete removal from the substrate. Windows working satisfactorily up to 7000 and 17 000 cycles have been obtained using aqueous KOH electrolyte and starch KOH gel electrolyte, respectively. Memory tests showed that the devices bleach at the open circuit potential from T=39% (colored state) to about T=50% in 60 min.     

Studies on membrane viscosity stabilized solar pond

In this nonsalt type of solar pond, the nonconvecting layer is composed of a viscous polymer solution partitioned by a number of transparent films. An advantage of partitioning is that a thinner polymer solution can be used and that the light transmittance increases. Results of experimental and theoretical investigations on the performance of this solar pond are summarized as follows:

1. 1. Ionized polyacrylamide solution was chosen as the thickener based on tests about solubility, viscosity, light transmittance and stability.

2. 2. The critical temperature difference for the onset of convection in the polymer layer (ΔT/L)_cr [°C/m] was given by the following formula based on the measurements in various thicknesses of the polymer layers (L) [m] and various concentrations (ζ) [%],

(ΔT/l)_cr=(55−185lnL)exp(4.66L^0.505lnζ

3. 3. An outdoor model pond, 200 × 150 cm surface and 100 cm depth, was constructed in Osaka. Four types of model ponds were tested, and the availability of membrane type with partition films was confirmed.

4. 4. The theoretical temperature rise of the pond using a one-dimensional model was calculated by solving the equations of the heat balance in the pond. As a result, the optimum values of thickness of polymer layer and number of films was determined

     

Chemical vapour deposited SnO2:Sb heat mirror coatings for cylindrical solar collectors

A chemical vapour deposition technique for growth of SnO₂:Sb heat mirror coatings on the inner walls of long cover glass tubes for cylidrical solar collectors is reported. The best performance of the tin-oxide film is obtained for those films grown from a source of SnCl₂ + 1 mol% Sb on Corning glass tubes at 520°C. These films, supported on 2 mm glass substrates, have a solar transmittance of 0.85 and an infrared reflectance of 0.8. The heat mirror coatings are observed to increase the stagnation temperature of the absorber in anevacuated tubular collector from 142 to 161°C under incident optical flux of 1150 W/m²     

上转换材料TiO2∶Er3+/Yb3+/Li+的制备及其在玻璃盖板中的应用

采用溶胶凝胶法和旋转镀膜法制备Er³⁺/Yb³⁺/Li⁺掺杂TiO₂胶体和薄膜,确定上转换材料最优制备方案为n(乙酰丙酮)∶n(C₁₆H₃₆O₄Ti∶H₂O)∶n(异丙醇)∶n(Er(NO₃)₃·5H₂O)∶n(Yb(NO₃)₃·5H₂O)∶n(LiNO₃)=1∶3∶9∶70∶0.12∶0.60∶0.15(物质的量之比),水的滴加速率为10 s/滴,溶液pH值为2～3,溶胶呈透明均匀淡黄色。吸收光谱在近红外区峰值明显。可见光透光率最高可达94.42%,较普通玻璃提高1%～2%。光伏组件通过光电转换效率测量系统进行检测,玻璃盖板镀膜后光伏组件的光电转换效率从16.5%升至17.2%,增加约0.7%。研究结果表明,该薄膜可提高玻璃盖板透光率,扩大光伏组件光谱吸收范围...     

Optical and electrochemical characteristics of niobium oxide films prepared by sol-gel process and magnetron sputtering A comparison

Electrochromic niobia (Nb₂0₅) coatings were prepared by the sot-gel spin-coating and d.c. magnetron sputtering techniques. Parameters were investigated for the process fabrication of sol-gel spin coated Nb₂0₅ films exhibiting high coloration efficiency comparable with that d.c. magnetron sputtered niobia films. X-ray diffraction studies (XRD) showed that the sot-gel deposited and magnetron sputtered films heat treated at temperatures below 450°C, were amorphous, whereas those heat treated at higher temperatures were slightly crystalline. X-ray photoelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was Nb₂0₅. The refractive index and electrochromic coloration were found to depend on the preparation technique. Both films showed low absorption and high transparency in the visible range. We found that the n, k values of the sot-gel deposited films to be lower than for the sputtered films. The n and k values were n = 1.82 and k = 3 × 10⁻³, and n = 2.28 and K = 4 × 10⁻³ at 530 urn for sot-gel deposited and sputtered films, respectively. The electrochemical behavior and structural changes were investigated in 1 M LiC10₄/propylene carbonate solution. Using the electrochemical measurements and X-ray photoelectron spectroscopy, the probable electrode reaction with the lithiation and delithiation is Nb₂O₅ + x Li⁺ + x e⁻ ↔ Li_xNb₂0₅. Cyclic voltametric (CV) measurements showed that both Nb₂0₅ films exhibits electrochemical reversibility beyond 1200 cycles without change in performance. “In situ” optical measurement revealed that those films exhibit an electrochromic effect in the spectral range 300 < λ < 2100 nm but remain unchanged in the infrared spectral range. The change in visible transmittance was 40% for 250 nm thick electrodes. Spectroelectrochemical measurements showed that spin coated films were essentially electrochemically equivalent to those prepared by d.c. magnetron sputter deposition.     

磁控溅射电致变色非晶态氧化钨薄膜

利用平面磁控反应溅射在具有透明导电膜的玻璃基片上沉积氧化钨膜层。Ｘ射线衍射分析结果表明，基片在室温状态下得到的膜呈非晶态。以０．２Ｎ浓度的ＨＣｌ为电解液，用电化学方法研究了Ｈ＋注入及抽出后氧化钨膜光学性能的变化及这种变化与膜的制备参数之间的关系。获得了沉积氧化钨膜近于最佳的工艺条件。在纯氧气氛下，溅射功率密度１．２Ｗ／ｃｍ２，溅射气体压强１．３Ｐａ时，制备的非晶态氧化钨膜，在５０次电化学循环后，漂白态与着色态的可见光透射率之差约为０．５７，其电化学循环的变色寿命也长。光电子能谱（ＸＰＳ）分析表明，Ｈ＋注入后着色态膜内出现了Ｗ５＋、Ｗ４＋。对电致变色机理也作了讨论。     

Properties, performance and current status of the laminated electrochromic glass of Gesimat

In the last 10 years Gesimat has developed a large-area electrochromic glazing with an advanced polymer electrolyte and tungsten oxide and Prussian Blue as complementary electrochromic layers. This electrochromic glass has a switching range between 75% and 8% visible transmittance and between 56% and 6% solar transmittance. The polymer electrolyte is based on polyvinyl butyral (PVB), a polymer in use as an interlayer for laminated safety glass since more than 60 years. The electrochromic films are deposited by a new large-area electrodeposition process. For lamination the standard methods of laminated safety glass production can be used.     

Large-area electrochromic glazing with ion-conducting PVB interlayer and two complementary electrodeposited electrochromic layers

A new laminated large-area electrochromic glass consisting of two FTO-coated glass panes coated with complementary electrochromic thin films by electrodeposition and laminated together by the use of an ion-conducting PVB sheet is presented. The visible light transmittance can be changed between 77% and 8% and the solar transmittance between 56% and 6%.     

Preparation and properties of sprayed CuGa0.5In0.5Se2 thin films

CuGa_0.5In_0.5Se₂ thin films were prepared by spray pyrolysis technique at substrate temperatures (T_s) in the range 100–400°C. The films prepared at T_s = 300–350°C were nearly stoichiometric, polycrystalline with a strong preferred (112) orientation. The resistivity of the films varied in the range, 50–1000 Ω cm and the evaluated optical band gap was 1.35 eV.     

Electrochromic properties of lithiated Co-oxide (LixCoO2) and Ni-oxide (LixNiO2) thin films prepared by the sol–gel route

Layered Li_xCoO₂ and Li_xNiO₂ thin films (x1) were prepared by a peroxo wet chemistry route from Li(I), Co(II) and Ni(II) acetate precursors and the addition of H₂O₂. Structural changes during the processing of xerogel to final oxide were followed by X-ray diffraction and infrared spectroscopy. Electrochromic properties were determined with in-situ potentiodynamic, potentiostatic and galvanostatic spectroelectrochemical measurements. Single dipped films with composition Li_0.99Co_1.01O₂ or Li_0.94Ni_1.06O₂ exhibited stable voltammetric response in 1 M LiClO₄/propylene carbonate electrolyte after about 60 cycles. The total charge exchanged in a reversible charging/discharging cycle was about ±30 mC cm⁻² for Li_0.99Co_1.01O₂ and ±20 mC cm⁻² for Li_0.94Ni_1.06O₂ oxide films. Galvanostatic measurements showed that about 1/2 (x0.5) and 2/3 (x0.3) of Li⁺ ions could be reversibly removed from the structure of Li_0.99Co_1.01O₂ and Li_0.94Ni_1.06O₂ films, respectively. Practical applicability of Li_0.99Co_1.01O₂ and Li_0.94Ni_1.06O₂ oxide films was studied in electrochromic devices with WO₃(H⁺)Li⁺ormolyteLi_0.99Co_1.01O₂ and WO₃(H⁺)Li⁺ormolyteLi_0.94Ni_1.06O₂ configuration. The monochromatic transmittance T_s (λ=633 nm) of dark blue coloured devices was extremely low (T_s3%), whereas in bleached state the value reached around T_s70%.     

Electrical and optical properties of F-doped textured SnO2 films deposited by APCVD

This paper presents the structural, electrical and optical properties of transparent conducting F-doped textured SnO₂ films prepared by atmosphere pressure chemical vapour deposition (APCVD). Polycrystalline SnO₂:F films having a variable preferred orientation have been obtained with resistivity as low as 5 × 10⁻⁴ Ωcm, with carrier concentrations between 3.5 × 10²⁰ and 7 × 10²⁰ cm⁻³, and Hall mobilities from 15.7 to 20.1 cm²/V/s. The average transmittance (including diffusion transmittance) is as high as 94% in the wavelength range of the visible spectrum and the maximum infrared reflectance reaches 92% for a film 655 nm thick. The figure of merit ƒ_TC = T10/_sh, (7.12 × 10⁻² S) of these films is the highest amongst the results reported on doped SnO₂ films.     

The temperature behavior of smart windows under direct solar radiation

The purpose of this paper was to investigate the variation in temperature of electrochromic devices under direct solar radiation and to compare the results with double-glazed glass. The devices consisted of a V₂O₅ layer as an ion storage film and a WO₃ layer as an electrochromic layer. The V₂O₅ and WO₃ films were prepared by thermal and electron beam evaporation, respectively. The optical properties and structures of these films were investigated. Both the ion storage film and the electrochromic layer were amorphous. The optical absorption was caused by a direct-forbidden transition in V₂O₅ and by an indirect-allowed transition in WO₃. The maximum temperatures under solar radiation were measured for colored and bleached devices, double glass and air, they were found to be approximately 63, 63, 53 and 36 °C, respectively. The rates of increasing temperature to the incident power density for colored, bleached devices and double glass were 0.051, 0.049 and 0.041 °C/(W/m²), respectively.     

Visual and energy performance of switchable windows with antireflection coatings

The aim of this project was to investigate how the visual appearance and energy performance of switchable or smart windows can be improved by using antireflective coatings. For this study clear float glass, low-e glass and electrochromic glass were treated with antireflection (AR) coatings. Such a coating considerably increases the transmittance of solar radiation in general and the visible transmittance in particular. For switchable glazing based on absorptive electrochromic layers in their dark state it is necessary to use a low-emissivity coating on the inner pane of a double glazed window in order to reject the absorbed heat. In principle all surfaces can be coated with AR coatings, and it was shown that a thin AR coating on the low-e surface neither influences the thermal emissivity nor the U-value of the glazing. The study showed that the use of AR coatings in switchable glazing significantly increases the light transmittance in the transparent state. It is believed that this is important for a high level of user acceptance of such windows.     

The effect of glass coating emittance and frame rebate on heat transfer through vacuum and electrochromic vacuum glazed windows

The thermal performance of an electrochromic vacuum glazing and a vacuum glazing with a range of low-emittance coatings and frame rebate depths were simulated for insolations between 0 and 1000 W m⁻² using a three-dimensional finite volume model. The vacuum glazing simulated comprised two 0.4 m×0.4 m glass panes separated by a 0.12 mm wide evacuated space supported by a 0.32 mm diameter pillar array spaced at 25 mm. The two glass sheets were sealed contiguously by a 6 mm wide metal edge seal and had either one or two low-emittance coatings. For the electrochromic vacuum glazing, a third glass pane on which an electrochromic layer was deposited was assumed to be sealed to an evacuated glass unit, to enable control of visible light transmittance and solar gain and thus improve occupant thermal comfort. It is shown that for both vacuum glazing and electrochromic vacuum glazings, when the coating emittance value is very low (close to 0.02), the use of two low-emittance coatings only gives limited improvement in glazing performance. The use of a single currently expensive low-emittance coating in both systems provided acceptable performance. Deeper frame rebate depths gave significant improvements in thermal performance for both glazing systems.     

Effect of temperature on the morphological and photovoltaic stability of bulk heterojunction polymer:fullerene solar cells

In high performance polymer:fullerene bulk heterojunction solar cells the nanoscale morphology of interpenetrating acceptor:donor materials is optimized through appropriate preparation conditions such as annealing and choice of solvent, but this initial state-of-the-art morphology will not remain stable during long-term operation. We report the effects of prolonged storage at elevated temperatures on both the morphology and the photovoltaic performance for the model systems MDMO-PPV:PCBM and P3HT:PCBM as compared to ‘High T_g PPV’:PCBM based solar cells, where the ‘High T_g PPV’ is characterized by its high glass transition temperature (138 °C). In situ monitoring of the photocurrent–voltage characteristics at elevated temperatures, in combination with a systematic transmission electron microscopy (TEM) study and complementary optical spectroscopy, reveals distinct degradation kinetics and morphological changes that indicate the occurrence of different underlying physico-chemical mechanisms.     

Thermodynamic assessment of hydrogen production via solar thermochemical cycle based on MoO2/Mo by methane reduction

Inspired by the promising hydrogen production in the solar thermochemical (STC) cycle based on non-stoichiometric oxides and the operation temperature decreasing effect of methane reduction, a high-fuel-selectivity and CH₄-introduced solar thermochemical cycle based on MoO₂/Mo is studied. By performing HSC simulations, the energy upgradation and energy conversion potential under isothermal and non-isothermal operating conditions are compared. In the reduction step, MoO₂: CH₄ = 2 and 1020 K<T_red<1600 K are found to be most favorable for syngas selectivity and methane conversion. Compared to the STC cycle without CH₄, the introduction of methane yields a much higher hydrogen production, especially at the lower temperature range and atmospheric pressure. In the oxidation step, a moderately excessive water is beneficial for energy conversion whether in isothermal or non-isothermal operations, especially at H₂O: Mo= 4. In the whole STC cycle, the maximum non-isothermal and isothermal efficiency can reach 0.417 and 0.391 respectively. In addition, the predicted efficiency of the second cycle is also as high as 0.454 at T_red = 1200 K and T_oxi = 400 K, indicating that MoO₂ could be a new and potential candidate for obtaining solar fuel by methane reduction.     

Temperature effect on the electrical and optical properties of indium-selenide thin-films

Indium-Selenide thin-films have been prepared by the thermal-evaporation technique at a pressure of 4.5×10⁻⁶ torr and a temperature of 673–873 K. For both the as-deposited and annealed films, (i) the electrical conductivity increased with increasing temperature and (ii) the variation of activation energy follows the island structure theory. The temperature co-efficient of resistance (T.C.R.) and Hall-effect measurements indicate that the sample is a n-type carrier. The optical spectra for both types of films were obtained in the wavelength range 0.3<λ<2.5 μm, and by comparing the magnitude of transmittance spectra, it is found that the annealed films are more transparent than the as-deposited ones in the UV and visible range. The integrated transmittance and reflectance values were obtained: the high values of T_lum and T_sol for the annealed films suggest that indium selenide may be used in selective-surface devices.     

Thermal performance of an electrochromic vacuum glazing

Using a three-dimensional finite volume model, the thermal performance of an electrochromic vacuum glazing was simulated for insolation intensities between 0 and 1200 W m⁻². The electrochromic evacuated glazing simulated consisted of three glass panes 0.5 m by 0.5 m with a 0.12 mm wide evacuated space between two 4 mm thick panes supported by 0.32 mm diameter pillars spaced on a 25 mm square grid contiguously sealed by a 6 mm wide metal edge seal. The third glass pane on which the electrochromic layer was deposited was assumed to be sealed to the evacuated glass unit. The simulations indicate that when facing the indoor environment, the temperature of the glass pane with the electrochromic layer can reach 129.5 °C for an incident insolation of 600 W m⁻². At such temperatures unacceptable occupant comfort would ensue and the durability of the electrochromic glazing would be compromised. The glass pane with the electrochromic layer must therefore face the outdoor environment.