High-Efficiency Dye-Sensitized Solar Cells Based on Ordered TiO2 Nanotube Arrays

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0967722GaoDye-sensitized solar cells (DSCs) have potential for low-cost solar electricity production. Anodes of current DSCs use sintered mesoporous films of TiO2 nanoparticles. Although the disordered pore structure of such films provides a high surface area for dye adsorption, the short electron lifetime and long pathway electron transport in these materials have limited the improvement of the solar energy conversion efficiency of DSCs. Anodes based on ordered ZnO nanowires have shown promise to overcome these constraints. However, ZnO material properties are not as good as TiO2 for DSC photoanodes. Previous attempts at fabricating TiO2 nanotube photoanodes by anodizing bulk titanium produced opaque films, which required a backside illumination configuration and resulted in nearly 20% of incident photon loss. Intellectual MeritThe proposed research will use a facile method for synthesis of vertically-aligned TiO2 nanotube arrays directly on transparent conductive oxide (TCO) surfaces. DSCs fabricated with these TiO2 nanotubes have to potential to significantly outperform ZnO nanowire-based devices, because the electron lifetime in TiO2 nanotubes is more than ten times longer than that either in ZnO nanowires or in sintered TiO2 nanoparticles. The proposed research will take advantage of the significantly extended electron lifetime and improved accessibility of ordered TiO2 nanotube array photoanodes to develop high efficiency DSCs. This configuration will also facilitate the use of a solid-state electrolyte to overcome the packaging challenges with liquid electrolyte based DSCs. The proposed research has five objectives. The first objective is to synthesize ultra-long ordered TiO2 nanotube arrays directly on TCO. The second objective is to fabricate DSCs with thickened sensitized films enabled by the ultra-long ordered TiO2 nanotube arrays. The remaining objectives are to explore alternative redox mediators in DSCs, fabricate TiO2 nanotube DSCs with a solid-state electrolyte, and sensitize DSCs with quantum dots. The research is potentially transformative because it provides a new approach to make the fundamental improvements in charge transport needed to break through the efficiency barriers of DSC devices. Broader ImpactsThree education and outreach activities are proposed. The first activity is the training graduate and undergraduate students through hands-on research. The second activity focuses on the development of an international field study module for undergraduate students that provides an international perspective to sustainable engineering through a collaboration with Tsinghua University in China. The third activity focuses on outreach to minority pre-college students through 1) development of high-school course unit on "Sustainability and Innovation", and 2) hands-on science workshops in collaboration with Baldwin High School and Westinghouse High School in Pittsburgh, PA.