KEYWORDS: Particles, Dye sensitized solar cells, Aerosols, Solar cells, Temperature metrology, Solar energy, Crystals, Nanoparticles, Transmission electron microscopy, Titanium dioxide
Titanium dioxide films are a critical component of many next-generation low cost solar cells. Film morphology has been
identified as an efficiency-limiting property. A gas phase, single-step, rapid, atmospheric-pressure process to synthesize
TiO2 films with controlled morphology is reported. The process is based on a flame aerosol reactor (FLAR). Two
different morphologies were synthesized for this report, granular and columnar. The granular morphology consists of
nanoparticles aggregated into fractal structures on the substrate, and is characterized by high surface area and poor
electronic properties. The columnar morphology is highly crystalline; composed of 1D structures oriented normal to the
substrate, characterized by lower surface area and superior electronic properties. Films with both morphologies are
applied to a hydrogen-producing photo-watersplitting cell and a photovoltaic dye-sensitized solar cell. For watersplitting,
the columnar morphology outperforms the granular by almost 2 orders of magnitude, achieving a uv-light to hydrogen
conversion efficiency of about 11%. In contrast, for the dye-sensitized solar cell, the granular morphology outperforms
the columnar, due to enhanced dye absorption arising from the larger TiO2 surface area.
The paper describes methodologies for deposition of nanostructured films in single step processes using flame aerosol
reactors. An understanding of the process parameters such as precursor feed rate, temperature histories and residence
times that control resultant film parameters such as thickness, crystallinity and morphology are developed. Control of
temperature profiles allow control of sintering rates to produce desired nanostructured thin films. These films are then
tested for photocurrent generation under uv light illumination - and overall conversion efficiencies of around 5 % are
readily obtained. Results of the study indicate that conditions could be optimized to improve water splitting
efficiencies.
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