Peptide-Mediated Deposition of Nanostructured TiO 2 into the Periodic Structure of Diatom Biosilica and its Integration
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Peptide-Mediated Deposition of Nanostructured TiO2 into the Periodic Structure of Diatom Biosilica and its Integration into the Fabrication of a Dye-Sensitized Solar Cell Device Haiyan Li2, Clayton Jeffyres1, Tim Gutu2, Jun Jiao2, and Gregory L. Rorrer1 1
Department of Chemical Engineering, Oregon State University, Corvallis, Oregon 97331
2
Department of Physics, Portland State University, Portland, Oregon 97207
ABSTRACT Biological fabrication approaches were used to enhance the performance of a dye-sensitized solar cell (DSSC) device stack for the conversion of light to electricity. Diatoms are singlecelled algae that make silica shells called frustules that possess periodic structures ordered at the micro- and nanoscale. Nanostructured TiO2 was deposited onto the frustule biosilica of the diatom Pinnularia sp. Poly-L-lysine (PLL) conformally adsorbed onto surface of the frustule biosilica. The hydrolysis and condensation of soluble Ti-BALDH to TiO2 by PLL-adsorbed diatom biosilica deposited 0.77 ± 0.05 g TiO2/g SiO2 onto the diatom biosilica. The periodic pore array of the diatom frustule served as a template for the deposition of ~20 nm TiO2 nanoparticles, which completely filled the 200 nm frustule pores and also coated the frustule outer surface. This material was then integrated into the DSSC device stack. Specifically, a single layer of diatom-TiO2 frustules was deposited to surface coverage 100μg/cm2 on top of the 25 nm anatase TiO2 nanocrystal layer (2.5 mg/cm2) that was doctor-bladed onto conductive FTO glass. The composite structure was thermally annealed in air at 400 oC, followed by addition of N719 dye, I3-/3I- liquid electrolyte, and semi-transparent Pt back electrode sputter coated on FTO glass. The solar cell efficiency increased from 0.20% to 0.70% when the diatom-TiO2 layer was added to anatase TiO2 base layer of the semi-transparent device. The increase in efficiency cannot be attributed solely to the added TiO2, because the amount of TiO2 in the diatom-TiO2 layer contributed to only 3% of the total TiO2 in the device. Instead, it is proposed that the diatom-TiO2 layer may have helped to improve photon capture within the DSSC because of its periodic structure and high dielectric contrast.
INTRODUCTION Photonic crystals have significant potential to increase the efficiency of photovoltaic (PV) solar energy conversion to electricity. Photonic crystals are an emerging class of periodic, dielectric materials with submicron-scale features that allow for precise control of all electromagnetic wave properties. When integrated into a PV device stack, photonic crystal thin films can trap and localize photons within the device [1,2]. However, fabrication of the submicron periodic structures is typically accomplished by top-down lithographic processing techniques that are difficult to scale up [3]. Etching and templating techniques using inverse opals offer scale up potential but limit the range of photonic crystal structures that can be fabricated.
Many photosynthetic marine microorgan
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