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4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 243 C109 - Electrochemical deposition of ZnO nanorods for application in light harvesting solar cells Kamila Zarebska, Magdalena Skompska Laboratory of Electrochemistry, Faculty of Chemistry, University of Warsaw, Pasteura 1, Warsaw, 02093, PL The use of fossil fuels (oil, coal, gas) has led to adverse impacts on environment. It is necessary to make us independent on conventional energy sources - one of way is the sun energy. For many decades the solar cell industry has been dominated by inorganic solid state devices, mainly based on silicon. Manufacturing of this type large area devices is very expensive. One of possible alternatives are semiconductor-sensitized solar cells (SSSC), consisting of metal oxide (MeO) deposited on the light transparent conducting oxide (in this case indium tin oxide - ITO). MeO nanostructures are covered with semiconductor quantum dots (CdS, PbS) and layer of hole acceptor (conducting polymer). The MeO is a wide bandgap semiconductor, playing the role of an electron transporting material and support for organic or inorganic sensitizer. It should provide a large surface area for deposition of the light absorber and high electron mobility. These requirements are well fulfilled by mesoporous and nanotubular TiO2, which is the most-widely used material in the typical SSSC. A ZnO has been emerged as promising alternative due to its high electron mobility (10-100 times higher than that in TiO2) which may result in the decrease of the charge carriers recombination. Other advantage of this compound is easy way of its synthesis. Figure 1 SEM image of ZnO nanorods deposited from solution containing Zn(NO3)2 and NH3 at 80oC at potential - 0,9V for 2,5h on ITO surface seeded from Zn(NO3)2. In this work the ZnO nanorods were prepared on ITO substrate by potentiostatic method. The growth was performed from the solution containing Zn(NO3)2 and NH3 at 80 o C. Before deposition the ITO surface was seeded in zinc nitrate or zinc acetate solution by potentiostatic method. The main aim of these studies was to examine the influence of seeding layer and applied potential on morphology of ZnO nanostructures and determine the mechanism of seeding and growing processes. The samples were examined by SEM, X-ray diffraction and electrochemical methods and compared with the results obtained by means of hydrothermal method. Acknowledgment:This work was partially supported by Polish Ministry of Science and Higher Education (grant NN 204117039). © SEFIN 2012
4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 244 C110 - Low cost counter electrodes for dye-sensitized solar cells based on graphenelike MoS2 Flavio S. Freitas, Agnaldo S. Gonçalves, Andréia de Morais, João E. Benedetti, Luiz C. P. Almeida, Ana F. Nogueira University of Campinas - UNICAMP, Cidade Universitária Zeferino Vaz, Campinas, 13083, Brazil Molybdenum carbide, nitride, and oxide have demonstrated good catalytic properties in dye-sensitized solar cells (DSSC). Similarly, their sulfides are expected to have the same function due to their high catalytic activity, thermal and chemical stability as reported recently for MoS2 bulk material. Rao and co-workers have reported that typical layered transition metal sulfides have an analogous structure to graphite, which are composed of three atomic layers. These characteristics provide a good combination for applications as counter electrodes for DSSC, where graphene-like MoS2 provides a high interfacial area for triiodide reduction as alternative to high cost platinum counter electrodes. The graphene-like MoS2 was obtained as described elsewhere and applied directly using a doctor blading technique on the conducting glass without any thermal treatment. This is an advantage compared to platinum and decreases significantly the process cost. The layered structure can be viewed in FEG-SEM and TEM images, as showed in the inset of Fig.1. Cyclic voltammetry for iodide/triiodide redox pair demonstrated resolved peaks for anodic and cathodic reactions, indicating a good activity and a catalytic mechanism for the tri-iodide reduction. The linearity of the peak current densities vs. the square root of the scan rate, indicates that mass transport is controlled by diffusion. The application in DSSC presented a promising effect to substitute high cost counter electrodes, reaching to 2.5% in efficiency, as showed in Fig. 1. Figure 1 J-V curves measured under illumination of 100 mW cm-2 (AM1.5). Geometrical cell area of 0.16 cm2. In the inset FEG-SEM and HR-TEM images of as-prepared MoS2. The graphene-like MoS2 provided CE for DSCs with 86% of the performance compared to analogue devices based on Pt CEs. Poor FF values for MoS2 in this work might be associated to a relatively high series resistance of the corresponding DSCs, probably due to the electrical conductivity of the CE layers. FF can be enhanced by preparing composite CE layers with the © SEFIN 2012
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