An all-solid-state electrochromic device based on NiO/WO3 complementary structure and solid hybrid polyelectrolyte

An all-solid-state electrochromic (EC) device based on NiO/WO₃ complementary structure and solid polyelectrolyte was manufactured for modulating the optical transmittance. The device consists of WO₃ film as the main electrochromic layer, single-phase hybrid polyelectrolyte as the Li⁺ ion conductor layer, and NiO film as the counter electrochromic layer. Indium tin oxide- (ITO) coated glass was used as substrate and ITO films act as the transparent conductive electrodes. The effective area of the device is 5×5 cm². The device showed an optical modulation of 55% at 550 nm and achieved a coloration efficiency of 87 cm² C⁻¹. The response time of the device is found to be about 10 s for coloring step and 20 s for bleaching step. The electrochromic mechanism in the NiO/WO₃ complementary structure with Li⁺ ion insertion and extraction was investigated by means of cyclic voltammograms (CV) and X-ray photoelectron spectroscopy (XPS).     

Characterization and electrochromic properties of CuxNi1−xO films prepared by sol–gel dip-coating

Cu_xNi_1−xO electrochromic thin films were prepared by sol–gel dip coating and characterized by XRD, UV–vis absorption and electrochromic test. XRD results show that the structure of the Cu_x Ni_1−xO thin films is still in cubic NiO structure. UV–vis absorption spectra show that the absorption edges of the Cu_xNi_1−xO films can be tuned from 335 nm (x = 0) to 550 nm (x = 0.3), and the transmittance of the colored films decrease as the content of Cu increases. Cu_xNi_1−xO films show good electrochromic behavior, both the coloring and bleaching time for a Cu_0.2Ni_0.8O film were less than 1 s, with a variation of transmittance up to 75% at the wavelength of 632.8 nm.     

Influence of coloring voltage on the optical performance and cycling stability of a polyaniline–indium hexacyanoferrate electrochromic system

An electrochromic system based on the multielectrochromic polyaniline (PANI) and pseudo-transparent indium hexacyanoferrate (InHCF) thin-film electrodes was studied in this work. In combination with a hybrid H⁺/K⁺-conducting solid polymer electrolyte—KCl-doped poly(2-acrylamido-2-methylpropanesulfonic acid) (K-PAMPS), a precoloring-free PANI–InHCF electrochromic device (ECD) with an active area of 3×3 cm² was fabricated and exhibited yellowish-green-blue multicolor electrochromism. From in situ spectroelectrochemical experiments, we found that the performance of a PANI/K-PAMPS/InHCF ECD was significantly affected by the operating voltages, especially by the coloring voltage. Both the bleached and yellowish state of the ECD could be attained reversibly by applying a voltage ranging from +1.5 to +1.7 V (InHCF vs. PANI). Different coloring voltages resulted in different optical properties and cycling stabilities, however. For instance, the device biased at −1.6 V (InHCF vs. PANI) showed a deep blue color, but the optical activity decayed quickly (less than 50 cycles) when the device was switched between +1.6 and −1.6 V. Nevertheless, the device could be reversibly operated between +1.6 and 0 V for several hundred cycles, although a narrower electrochromic extent (yellowish-to-green) was observed correspondingly. The optimization of the coloring voltage is therefore of paramount importance to the PANI/K-PAMPS/InHCF ECD.     

A complementary electrochromic device based on polyaniline and poly(3,4-ethylenedioxythiophene)

In this study, two conducting polymers, polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT), were used to construct an electrochromic device (ECD). PANI was employed as the anodic coloring polymer while PEDOT was used as the cathodic coloring polymer. The electrochemical and optical properties of PANI, which has a coloration efficiency of 25 cm²/C at 570 nm, were coupled with the complementary coloring material, PEDOT, which has a coloration efficiency of 206 cm²/C at 570 nm. A suitable operating potential window was switched between −0.6 and 1.0 V to explore the cycle life of the ECD. We tested the PANI–PEDOT ECD, which consisted of PANI, PEDOT, and an organic electrolyte containing 0.1 M LiClO₄ in propylene carbonate and 1 mM HClO₄. The transmittance of the ECD at 570 nm changed from 58% (−0.6 V) to 14% (1.0 V) with a coloration efficiency of 285 cm²/C. Within the selected operating voltage range, the PANI–PEDOT ECD could be cycled for up to 2×10⁴ cycles.     

An all-thiophene electrochromic device fabricated with poly(3-methylthiophene) and poly(3,4-ethylenedioxythiophene)

A novel all-organic electrochromic device (ECD) is presented. By electrodepositing poly(3-methylthiophene) (PMeT) in boron fluoride ethyl ether (BFEE), a strong Lewis acid, a good-quality PMeT film was obtained. On the basis of studies of PMeT, it can be regarded as a pseudo-anodic coloring material for ECDs. On the other hand, poly(3,4-ethylenedioxythiophene) (PEDOT) is an ideal cathodic coloring electrochromic material known for its high optical contrast, long-term stability, and high coloration efficiency. By combining these two thiophene derivatives, the application potential of this device was determined. The color of the ECD switches between deep blue at −1.4 V (PEDOT vs. PMeT) and light red at 0.6 V. The device exhibits stable electrochromic performance, with a maximum optical attenuation (ΔT_max) at 655 nm reaching 46% (from 9% to 55%), and achieves a high coloration efficiency of 336 cm²/C. After 100 repeated cycles, the cell still retained at 91.3% of its ΔT_max at 655 nm.     

Electronic and photovoltaic properties of Al/p-Si/copper phthalocyanine photodiode junction barrier

Al/p-Si/copper phthalocyanine photovoltaic device has been fabricated and characterised by current–voltage and capacitance–voltage measurements. Electrical properties of the device were determined by current–voltage characterizations under dark and illumination conditions. The density distribution of the interface states of the photodiode was found to vary from 8.88×10¹² eV⁻¹ cm⁻² in E_ss-0.54 eV to 4.51×10¹² eV⁻¹ cm⁻² in E_ss-0.61 eV. The device shows a photovoltaic behaviour with a maximum open circuit voltage Voc of 0.16 V and short-circuits current I_sc of 0.45 μA under 3500 lux light intensity.     

An electrochromic device working in absence of ion storage counterelectrode

The fabrication and the characterization of a full solid state electrochromic device are discussed. The peculiarity of the realized device is the absence of a specific ion storage counterelectrode, in fact a film of an electrochromic material (EC) is interfaced and coupled with a particular ion conducting solid polymer and a second conducting layer. This kind of structure greatly simplifies the procedure of fabrication. The EC is Tungsten trioxide doped with Molybdenum oxide, electrochemically deposited on ITO coated glass. The electrolyte is a polymer film of Nafion-H^™ (Trade Mark of E.I. Du Pont de Nemours). The presence of Nafion-H (hydrogenated form of Nafion), which has a very high proton concentration, totally avoids the necessity of presence of another component. Moreover, in the assembling procedure of the device, it is not necessary to charge preventively the electrochromic and/or the ion storage counterelectrode. The second electrode is constituted by another ITO coated glass.The realized device switches between the dark blue and transparent state with a low value of applied potential ranging from −4 upto 2 V. Different waveform potentials have been tested in the past in order to find the optimum bias conditions to operate between stable phases. Previous experimental results indicate the trapezoidal waveform potential as the most convenient one. The visible optical transmittance in the bleached and coloured state has been measured and has given the following values: T_v(blached) = 57.7% and T_v(coloured) = 8.4%. Taking also into account the magnitude of the exchanged charge ( 12.8 mC/cm²), these values of transmission give a very good coloration efficiency. Dynamical measurements evidence an acceptable switching rate, in fact the typical switching time for the bleaching process is about 20 s, while a somewhat longer time is necessary for coloration. The device exhibits quite good long memory properties and chemical stability.     

WO3−x nanowires based electrochromic devices

A simple method was developed to fabricate tungsten oxide (WO_3−x) nanowires based electrochromic devices. The WO_3−x nanowires are grown directly from tungsten oxide powders in a tube furnace. The WO_3−x nanowires have diameters ranging from 30 to 70 nm and lengths up to several micrometers. The WO_3−x nanowires based device has short bleach-coloration transition time and can be grown on a large scale directly onto an ITO-coated glass that makes it potential in many electrochromic applications. The structure, morphology, and composition of the WO_3−x nanowires were characterized using the scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy-dispersive spectrometer. The optical and electrochromic performance of the nanowires layer under lithium intercalation was studied in detail by UV–VIS–NIR spectroscope and cyclic voltameter.     

Photovoltaic cells based on cadmium sulphide–phthalocyanine heterojunction

Hybrid photovoltaic (PV) cells based on cadmium sulphide (CdS) single crystal and phthalocyanine (Pc) films have been developed and their PV performance was measured. Five different Pcs have been selected as candidates for the PV cell, PcCu, PcMn, PcZn, PcMg, and PcVO. It was found that all the chosen Pcs are capable of forming a hybrid heterojunction with the CdS surface, and that illumination results in charge separation at the interface. However, the performance of the In/CdS/Pc/Au device was dependent on the Pc used. PV cells with PcMg and PcZn showed the best results. An unoptimized cell with the PcZn film showed an open-circuit voltage V_oc=0.595 V, a short-circuit current density J_sc=1.88 μA/cm², a fill factor FF=0.265, and a power conversion efficiency PCE=3.0×10⁻⁴% under the AM1.5 conditions.     

Solid hybrid polyelectrolyte with high performance in electrochromic devices: Electrochemical stability and optical study

This paper presents a high-stability, single-phase hybrid polyelectrolyte (SPHP) applied in a large EC device (5×10 cm²) using WO₃ (electrochromic) and CeO₂–TiO₂ (counter-electrode–ion storage) electrodes, both produced by Leibniz—Institut of New Materials (Leibniz—INM, Germany). The electrochromic device exhibited excellent color and bleach reversibility, high coloration efficiency (>35 cm²/C) from the first cycle up to more than 60,000 CA cycles, and a maximum constant rate of deintercalation/intercalation (O_out/Q_in=1). Its remarkable behavior and high stability render this material an excellent candidate for application in electrochromic devices.     

Characterization of Pr1−xSrxCo0.8Fe0.2O3−δ (0.2 ≤ x ≤ 0.6) cathode materials for intermediate-temperature solid oxide fuel cells

Cathode materials consisting of Pr_1−xSr_xCo_0.8Fe_0.2O_3−δ (x = 0.2–0.6) were prepared by the sol–gel process for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The samples had an orthorhombic perovskite structure. The electrical conductivities were all higher than 279 S cm⁻¹. The highest conductivity, 1040 S cm⁻¹, was found at 300 °C for the composition x = 0.4. Symmetrical cathodes made of Pr_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (PSCF)–Ce_0.85Gd_0.15O_1.925 (50:50 by weight) composite powders were screen-printed on GDC electrolyte pellets. The area specific resistance value for the PSCF–GDC cathode was as low as 0.046 Ω cm² at 800 °C. The maximum power densities of a cell using the PSCF–GDC cathode were 520 mW cm⁻², 435 mW cm⁻² and 303 mW cm⁻² at 800 °C, 750 °C and 700 °C, respectively.     

Investigation of non-aqueous electrodeposited CdS/Cd1−xZnxTe heterojunction solar cells

Polycrystalline Cd_1−xZn_xTe solar cells with efficiency of 8.3% were grown by cathodic electrodeposition on glass/ITO/CdS substrates using non-aqueous ethylene glycol bath. The deposit is characterised versus the process conditions by XRD and found to possess a preferred (1 1 1) orientation on Sb doping in the electroplating bath. The surface morphology of the deposit is studied using atomic force microscope. The average RMS roughness for the ternary film was higher than that for the binary CdTe. Optical properties of the films were carried out to study the band gap and calculation of molar concentration ‘x’. The effects of Sb doping in CdS/Cd_1−xZn_xTe heterojunctions have been studied. The short circuit current density (c) was found to improve and series resistance (R_s) reduced drastically upon Sb doping. This improvement in J_sc is attributed to an increase in quantum efficiency. The evaluation of solar cell parameters was also carried out using the current–voltage characteristics in dark and illumination. The best results were obtained when 2×10⁻³ M ZnCl₂ along with antimony were present in the deposition bath. Under AM 1.5 conditions the open circuit voltage, short circuit current density, and fill factor of our best cell were V_oc=600 mV, J_sc=26.66 mA/cm², FF=0.42 and efficiency, η=8.3%. The carrier concentration and built-in potential of Cd_1−xZn_xTe calculated from Mott–Schottky plot was 2.72×10¹⁷ cm⁻³ and 1.02 eV.     

Performance of p-type silicon-oxide windows in amorphous silicon solar cell

a-SiO_x films have been prepared using silane and pure oxygen as reactive gases in plasma CVD system. Diborane was introduced as a doping gas to obtain p-type conduction silicon oxide. Infrared absorption spectra show the incorporation of Si–O stretch mode around 1000 cm⁻¹. The optical bandgap increases with the oxygen to silane gas ratio, while the electrical conductivity decreases. Hydrogenated amorphous silicon solar cells have been fabricated using p-type a-SiO_x with around 1.85 eV optical bandgap and conductivity greater than 10⁻⁷ S/cm. The measured current–voltage characteristics of the solar cells under 100 mW/cm² artificial light are V_oc=0.84 V, J_sc=14.7 mA/cm², FF=0.635 with a conversion efficiency of 7.84%.     

A note on fast protonic solid state electrochromic device: NiOx/Ta2O5/WO3−x

In the present investigation, the electrochromic properties of a fast protonic solid state device: NiO_x/Ta₂O₅/WO_3−x prepared at room temperature (300 K) is reported. The non-stoichiometric tungsten oxide thin film is prepared by reactive DC magnetron sputtering technique on ITO coated glass; the oxides of tantalum (300 nm) and nickel (100 nm) are prepared by electron beam evaporation. This proton device has a coloration efficiency of 82.4 cm²/C and coloration and bleaching time of 6 and 5 s, respectively, and a transmittance variation of 60%. The work function of WO_3−x thin films by Kelvin probe in uncolored and colored states are 4.73 and 4.30 eV, respectively.     

Pulsed laser deposition of W–V–O composite films: Preparation, characterization and gasochromic studies

Modified tungsten oxide films by vanadium oxide provide neutrally coloring electrochromic electrodes for smart windows technology. In this study W–V–O mixed oxide films were fabricated by Nd:YAG pulsed laser deposition (PLD), λ=1064 nm, from mixed pressed powders of (WO₃)_1−x(V₂O₅)_x, x=0, 0.09, 0.17, 0.23, 0.29 and 0.33, at 13.3 Pa oxygen partial pressure and 200 °C temperature on glass substrates. X-ray photoelectron spectroscopy (XPS) revealed V⁵⁺, V⁴⁺, W⁶⁺ and W⁵⁺ surface oxide states, where the ratio of W⁵⁺/W⁶⁺ enhances by the amount of vanadium in the films. Surface morphology was studied by scanning electron microscope (SEM) and optical properties by transmission-reflection spectra. Results showed that films with a low amount of vanadium oxide have better porosity and higher optical band gaps. The gasochromic response to hydrogen gas exposure was found better for x=0.09 in the sense of both deeper and faster coloring. Weak responses of samples with more vanadium oxide were attributed to higher amounts of W⁵⁺ in the films and also to lower porosity.     

Properties of CuIn1−xGaxSe2

Polycrystalline bulk samples of CuIn_1−xGa_xSe₂ weregrown with nominal x = 0.15, 0.25 and 0.5. Mobility, conductivity and band gap were measured at room and low temperatures. Mobilities for x = 0.21 were several hundred cm² V⁻¹s⁻¹ at room temperature and for x = 0.15 were 10³ cm² V⁻¹ s⁻¹, all n type. The band gaps were estimated from the spectra of photoelectrochemical cells at room temperature (with 8.5 K photoluminescence estimates shown in brackets), as 1.10 eV (1.14) for x = 0.21, and 1.07 eV (1.093) for x = 0.15. Crystal mechanical properties as regards cracks were not as good as for CuInSe₂, using similar growth techniques.     

Optical and electrical studies on molybdenum sulphoselenide [Mo(S1−xSex)2] thin films prepared by arrested precipitation technique (APT)

Nanocrystalline stoichiometric [Mo(S_1−xSe_x)₂] thin films were deposited by using arrested precipitation technique (APT) developed in our laboratory. The precursors used for this are namely, molybdenum triethanolamine complex, thioacetamide and sodium selenosulphite; and various preparative conditions are finalised at the initial stages of deposition. Formation of [Mo(S_1−xSe_x)₂] semiconducting thin films are confirmed by studying growth mechanism, optical and electrical properties. X-ray diffraction analysis showed that the composites are nanocrystalline being mixed ternary chalcogenides of the general formula [Mo(S_1−xSe_x)₂]. The optical studies revealed that the films are highly absorptive (α×10⁴ cm⁻¹) with a band-to-band direct type of transitions and the energy gap decreased typically from 1.86 eV for pure MoS₂ down to 1.42 eV for MoSe₂. The thermoelectrical power measurement shows negative polarity for the generated voltage across the two ends of semiconductor thin films. This indicate that the [Mo(S_1−xSe_x)₂] thin film samples show n-type conduction.     

Electrochromic windows based on viologen-modified nanostructured TiO2 films

The construction of an electrochromic window based on a modified transparent nanostructured metal oxide film (TiO₂ anatase, 4.0 μm thick) supported on conducting glass (F-doped tin oxide, 10 Ω/square, 0.5 μm thick) is described. The nanostructured TiO₂film is modified by adsorption of a monolayer of the redox chromophore bis-(2-phosphonoethyl)-4,4′-bipyridinium dichloride, the electrolyte is 0.05 M LiClO₄ and 0.05 M ferrocene in γ-butyrolactone and the counter electrode is conducting glass. The performance of the above device (colouration efficiency of 170 cm² C⁻¹ at 608 nm, switching time of 1 s and stability over 10 000 standard test cycles) suggests an electrochromic technology with commercial potential.     

Characteristics of laminated electrochromic devices using polyorganodisulfide electrodes

The application of polyorganodisulfides as optically passive counter-electrodes in a variety of electrochromic smart glazing devices are discussed. Characteristic data is presented for electrochromic devices using proton, and lithium coloration ions with modified polyethylene oxide electrolyte and polydimercaptothiadiazole positive electrodes. Solid state devices consisting of molybdenum doped WO₃, amorphous polyethylene oxide electrolyte (a-PEO), and a polyorganodisulfide counter-electrode colored rapidly from a pale yellow to a deep blue-green, upon application of −1.2 V DC. The photopic transmittance (T_p) changes from 61 to 9%, and the solar transmittance (T_s) changes from 45 to 5% during the coloration process. Also, our experiments with polyimidazole are detailed. This family of compounds due to its unique electrical and ion conduction properties allow a single composite ion storage and ion conductor electrode to be made, simplifying the device construction. Devices made from this family of compounds color to deep blue-gray upon application of −1.2–1.5 V DC. Bleaching occurs at −0.4 to −0.5 V DC. The photopic transmittance changed from 55 to 9%, and the solar transmittance from 34 to 4% during coloration. Both coloration and bleaching are quite rapid.     

Theoretical possibilities of InxGa1−xN tandem PV structures

We designed a model of In_xGa_1−xN tandem structure made of N successive p–n junctions going from two junctions for the less sophisticated structure to six junctions for the most sophisticated. We simulated the photocurrent density and the open-circuit voltage of each structure under AM 1.5 illumination in goal to optimize the number of successive junctions forming one structure.For each value of N, we assumed that each junction absorbs the photons that are not absorbed by the preceding one. From the repartition of photons in the solar spectrum and starting from the energy gap of GaN, we fixed the gap of each junction that gives the same amount of photocurrent density in the structure. Then we calculated the current density accurately and optimized the thicknesses of p and n layers of each junction to make it give the same output current density. The evaluation of n_i: the intrinsic concentration permitted to calculate the saturation current density and the open-circuit voltage of each junction. Assuming an overall fill factor of 80%, we divided the output peak power by the incident solar power and obtained the efficiency of each structure.The numerical values for In_xGa_1−xN were taken from the relevant literature. The calculated efficiency goes from 27.49% for the two-junction tandem structure to 40.35% for a six-junction structure. The six-junction In_xGa_1−xN tandem structure has an open-circuit voltage of about 5.34 V and a short circuit current density of 9.1 mA/cm².