Rapid synthesis of nanostructured metal-oxide films for solar energy applications by a flame aerosol reactor (FLAR)

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 ID 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 wv-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.