Electrical Conducting Diamond Thin-Films: An Alternative Counter Electrode Material for Dye Sensitized Solar Cells
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Electrical Conducting Diamond Thin-Films: An Alternative Counter Electrode Material for Dye Sensitized Solar Cells R.D. Vispute1, Alok Vats, Vinod Venkatesan, Andrew Seiser, Jaurette Dozier, Jeremy Feldman and Lance Robinson. Blue Wave Semiconductors Inc. 1450, UMBC Technology Center, Baltimore, MD-21227, USA 1. Contact author e-mail: [email protected] ABSTRACT Carbon is a favorable alternative as counter electrode material for dye sensitized solar cells (DSSC) as compared to Pt. Various carbon materials such as carbon nanotubes (CNT), activated carbon (AC) and carbon nanofibers have been investigated as counter electrodes for DSSC applications, based on their high electrochemical activity, high specific surface area, chemical inertness and high electrical conductivity. Among various phases of carbon, diamond is the most robust and chemical inert material that can be used for electrode application. It has band gap of 5.5 eV, high thermal conductivity. its electrical resistivity can be tuned by doping such as boron. In this work, we investigate boron doped diamond thin film electrode for DSSCs. The conductive diamond thin electrode films were grown using Blue Wave hot wire chemical vapor deposition (HWCVD) system. The electrical resistance in diamond thin films was tuned by controlling grow temperature, filament power, dopant concentration and sp3/sp2 ratio in the film, it thickness, and initial seeding process. Scanning electron microscopy, Raman spectroscopy and electrical resistivity measurement were used to characterize morphology, diamond quality and electrode conductivity, respectively. Diamond film electrodes with optimized surface morphology and electrical characteristics were used for DSSC fabrication. We used nanocrystalline TiO2 paste (P25 Degussa) with average particle size of 25nm as an active layer, the electrolyte comprised of a LiI/I2 electrolyte in acetonitrile (CH3CN), a Ru based metal complex dye [cis-diisothiocyanato-bis(2,2’-bipyridyl-4,4’-dicarboxylato) ruthenium(II) bis(tetrabutylammonium)] OR N719 was used as sensitizer. The photovoltaic performance was determined using J-V characteristics under standard illumination conditions and was compared to a reference DSSC with Pt counter electrode. Results are discussed in the context of diamond electrical and durability and chemical stability of diamond films against most commonly used family of iodine based electrolytes. INTRODUCTION Third generation photovoltaics technologies such as dye sensitized solar cells are very lucrative for their low cost and high light harvesting efficiencies up to 11 % for single junction DSSC 1,2. The current best DSSC comprises of a thin Pt layer coated on Indium doped SnO2 substrate acting as counter electrode 3,4. In order to achieve lower cost/Watt from solar dye cells, use of Pt for counter electrodes poses a limitation towards commercializing DSSC technology. As a result, research efforts are aimed at developing alternative materials, which can replace use of Pt and ITO for counter electrode.
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