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Trunov M.L.,Uzhgorod National University | Lytvyn P.M.,Institute of Semiconductor Physics of Ukraine | Yannopoulos S.N.,FORTH ICE HT | Szabo I.A.,Debrecen University | Kokenyesi S.,Debrecen University
Applied Physics Letters | Year: 2011

Surface relief gratings formation in amorphous selenium thin films in two recording configurations with light intensity modulation were studied in situ by real-time atomic force microscopy and diffraction efficiency measurements. We report observation of mass transport effect in films induced by band-gap irradiation when the light polarization of the recording beams has a component along the light intensity gradient (p-p scheme of recording) that allows obtaining giant stable gratings in this versatile chalcogenide material. On the contrary, only a pure scalar weak grating caused by photoinduced volume shrinkage is obtained in the s-s recording configuration, even for long-term irradiation. © 2011 American Institute of Physics.

Pop L.-C.,University of Patras | Dracopoulos V.,FORTH ICE HT | Lianos P.,University of Patras
Applied Surface Science | Year: 2015

Photoelectrocatalytic hydrogen production was realized my means of a double electrode carrying photocatalyst and electrocatalyst, deposited side by side on an FTO electrode, acting as a "Photoelectrocatalytic Leaf". As photocatalyst we used plain commercial nanoparticulate titania and as electrocatalyst a conductive carbon film made by a commercial carbon paste enriched with a small quantity of Pt nanoparticles (0.0134 mg/cm2). This quantity of Pt is much smaller than used in other applications and it may be further optimized. Hydrogen was produced in an alkaline environment in the presence of ethanol acting as sacrificial agent. A few variants of electrode geometry were studied in order to set the basic terms for efficient hydrogen production. It was found that optimal electrode geometry necessitates a much larger area for photocatalyst coverage than electrocatalyst and that it is preferable to divide photocatalyst and electrocatalyst areas in alternating zones. © 2015 Elsevier B.V. All rights reserved.

Balis N.,University of Patras | Dracopoulos V.,FORTH ICE HT | Bourikas K.,Hellenic Open University | Lianos P.,University of Patras
Electrochimica Acta | Year: 2013

Quantum dot sensitized solar cells have been constructed using photoanodes made of nanocrystalline titania and an optimized combination of ZnS, CdS and CdSe nanoparticles. Pt, CoS and CuS have been used as electrocatalysts on counter electrodes. Attachment of quantum dot sensitizers on mesoporous titania was made by successive ionic layer adsorption and reaction and by chemical bath deposition obeying a certain order, where the first layer was crucial in defining the quality and the quantity of the subsequent layers as well as of the ensuing solar conversion efficiency. Thus the first quantum dot layer consisted of 75% CdS and 25% ZnS and it was followed by a CdSe layer and by an additional ZnS layer on the top. The quantity of material deposition seems to be affected not only by the employed deposition method but also and mainly by the nature of the underlying layer. Optimized anode electrodes led to solar cells producing high current densities but did not much affect open-circuit voltage. The maximum solar conversion efficiency reached in this work was 2.7% and was obtained by using CuS electrocatalyst. Both CoS and CuS gave high currents and this was in line with the low charge transfer resistances recorded in their case. © 2013 Elsevier Ltd. All rights reserved.

Pop L.-C.,University of Patras | Sfaelou S.,FORTH ICE HT | Lianos P.,University of Patras
Electrochimica Acta | Year: 2015

Current-voltage curves recorded during the study of photoelectrochemical cells functioning in the presence of aqueous electrolytes contain a characteristic anodic current feature, which may interfere in the interpretation of the results. This anodic current is observed at negative potentials and it derives from the adsorption of cations into the mesoporous structure of nanoparticulate titania photoanodes. The shape and the height of the peak depends on the size of the cation, its concentration, the thickness of the titania film and the nature of the counter ion and the corresponding pH. This anodic current is similar to the one observed in other works during ion storage and electrochromism studies with mesoporous titania. In the presence of an organic sacrificial agent, like ethanol, adsorption of cationic species is still strong but it decreases at higher organic content. © 2015 Elsevier Ltd. All rights reserved.

Syrrokostas G.,University of Patras | Siokou A.,FORTH ICE HT | Leftheriotis G.,University of Patras | Yianoulis P.,University of Patras
Solar Energy Materials and Solar Cells | Year: 2012

This work investigates the stability of platinum (Pt) electrodes prepared by electrodeposition and thermal decomposition of hexachloroplatinic acid (H 2PtCl 6) solutions. To this aim, the electrodes were stored in an electrolyte solution (0.5 M KI, 0.05 M I 2 in 90%/10% PC/EG) or in air, within a closed vessel, for up to 70 days. A drop of up to 40% in the current density for triiodide reduction was caused by storage in the electrolyte solution and of about 15%-20% when the electrodes were stored in air. Electrolyte storage was found to cause a 40% increase in the activation energy of both kinds of electrodes. XPS measurements have shown that the main degradation mechanism in the case of electrolyte storage is the dissolution of Pt from the substrate. Regeneration of the electrodes by heat or acid treatment was not possible. The observed electrode degradation is expected to appear in dye sensitized solar cells using this kind of counter electrodes and thus affect their long term stability. © 2012 Elsevier B.V. All rights reserved.

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