Sabine Heusing

Gravure printing of transparent conducting ITO coatings for display applications

Transparent conducting coatings and patterns of ITO (indium tin oxide) were deposited by a direct gravure printing on PET foils using nanoparticle-based UV-curable inks. Solid areas with thicknesses ranging between 300 and >1000 nm were obtained by varying the ink composition (e.g. ITO content, solvents) and fundamental parameters of the printing plate such as the line density. The best ITO coating patterns showed a sheet resistance of 3 to 10 kΩ□ and a transmission of up to 88 % with a haze of less than 1 %. One of the most crucial steps during film formation is the drying of the wet film as it changes the rheology and polarity of the ink and in consequence decisively influences the film formation. Typical fields of application of the gravure-printed ITO patterned electrodes include smart windows, flexible displays and printed electronics.

Influence of water on the electrochemical properties of CeO 2 TiO 2 sol-gel coatings and electrochromic devices

The paper focuses on a systematic study of the influence of water on the electrochemical and optical properties of CeO2-TiO2 amd WO3 sol-gel coatings as well as devices made with these layers. The coatings were studied electrochemically in 1 M LiC1O4 in propylene carbonate electrolyte with water content up to 3 wt%. The intercalculated and deintercalated charge was measured during Cyclic Voltammetry (CV) and Chronoamperometric (CA) cycles up to 500 cycles (TiO2-CeO2) and 7000 cycles (WO3). For CeO2-TiO2 it was found to increase from 3mC/cm2 (dry electrolyte) up to 11 mC/cm2 (3 wt% water). This increase is important for the coloration of EC-devices because the charge capacity of this counter electrode is known to be a limiting factor for the transmission change of the EC-devices. For WO3 coatings, the transmission change (Tcolored-Tbleached)is higher in wet electrolytes (1 wt% water) than dry electrolyte and above all remains constant (74%). These improvements are essentially due to an increase of the kinetics of the intercalation and deintercalation of Li+ ions. The electro-optical behavior of solid state EC-devices with and without incorporation of water in the solid electrolyte measured up to 500000 CA cycles is also presented and discussed.

Characterization of nonsensitized and Ru(II)-sensitized sol-gel Nb2O5 electrodes by impedance spectroscopy

The impedance spectra of non-sensitized and Ru(II)-sensitized Nb2O5 nanoporous coatings have been measured in the dark and under solar illumination using an electroactive electrolyte. All the Nyquist plots consist of a high and a low frequency depressed semicircle. The results have been modeled and fitted by an equivalent electric circuit consisting of a resistor Rs in the series with two parallel RC circuits containing both a constant phase element (CPE). The resistor Rs describes the total resistance of the electrolyte and conducting electrodes (SnO2:F). The high frequency semicircule (f<1kHz) describes the capacitance and resistance of the semiconducting materials (grain boundaries and interfaces). The low frequency cycle (f < 1 kHz) is related to the formation of a double charge layer capacitance at the nanoparticle/electrolyte interface and a charge transfer resistance. Both values are strongly dependant of the experimental conditions, in particular of the applied potential and the state of illumination. The evolution of the electric elements is presented and discussed. It is shown in particular that the measurements in the dark cannot be directly compared to those under illumination as in teh latter all the Nb2O5-film is accessed.

Stand der Anwendung der Elektrochromie in der Architektur

Vorstellung elektrochromer Systeme Elektrochrome Materialien ändern ihre optischen Eigenschaften (Transmission, Reflexion) reversibel bei Reduktion bzw. Oxidation, was z.B. durch Anlegen einer Spannung und Fließen eines elektrischen Stromes bewirkt werden kann [1, 2]. Großflächige elektrochrome (EC) Verglasungen können als „Smart Windows” und Sonnendächer zur variablen Kontrolle der Energieeinstrahlung in der Gebäudeund Fahrzeugverglasung eingesetzt werden und dadurch zur Energieeinsparung beitragen. Weitere Anwendungen für EC-Systeme sind EC-Displays und selbst abblendbare EC-Automobil-Rückspiegel, die bereits seit mehreren Jahren auf dem Markt verfügbar sind (Gentex, Magna Donnelly). Beispiele für elektrochrome Materialien sind anorganische Komplexe (z.B. Berliner Blau), organische Moleküle (z.B. Viologene => Anwendung in EC-Automobil-Rückspiegeln), organische Polymere (z.B. Polyanilin, PEDOT) und eine große Anzahl von Übergangsmetalloxiden (z.B. Wolframoxid (WO ), Nioboxid (Nb O ), Nickeloxid (NiO)). 3 2 5 Eines der bekanntesten und häufig verwendeten EC-Materialien ist Wolframoxid (WO3). WO3 Schichten ändern ihre Farbe reversibel von transparent nach tiefblau bei Reduktion und gleichzeitigem Einbau („Interkalation“) von kleinen Ionen (z.B. H, Li) aus dem Elektrolyten, während sie bei Oxidation und Ausbau (Deinterkalation) der Ionen entfärben:

Thick CeO2-TiO2 sol-gel coatings for Li-ion storage electrode in electrochromic devices

CeO2-TiO2 sol-gel coatings are well known as Li-ion storage electrode in electrochromic (EC) devices of the form glass/ TE /WO3/ electrolyte/ CeO2-TiO2/ TE/ glass (TE: transparent electrode, e.g. SnO2:F, FTO). The charge capacity of the CeO2-TiO2 coating is a limiting factor to get a high coloration intensity of such devices. In order to improve the charge capacity of these electrodes, new routes for the preparation of thick porous CeO2-TiO2 sol-gel layers were tested. One route was the preparation of thick porous TiO2 coatings on a conducting glass support (FTO) using a solution of colloidal TiO2 particles. After heat treatment at temperatures up to 550°C the coatings were soaked in a solution of a cerium-IV (Ce(NH4)2(NO3)6) or a cerium-III salt (Ce(NO3)3 6H2O) and heat treated again. Another route was the preparation of sols by mixing a solution of the cerium-IV or cerium-III salt or a colloidal CeO2-sol with the colloidal solution of TiO2. After dip coating on FTO-glass the coatings were also heat treated at temperatures up to 500°C. ALl these coatings were studied electrochemically in 1 M LiC1O4 in propylene carbonate electrolyte. Although thick porous single coatings could be obtained, typically 450 nm for TiO2 and 600 nm for cerium-titanium oxide, the intercalated and deintercalcated Li+ charges remain small and lie in the range of 2 mC/cm2 to 3 mC/cm2. The reasons for such low charge capacity is discussed.