Synthesis Of "Oriented Attachment" TiO₂Nanorods And Their Applications In Highly Efficient Dye-sensitized Solar Cells

Dye-sensitized solar cell （DSSC） is a new-concept next-generation solar cell which hasattracted extensive attentions due to its low-cost, easily fabricated properties, and acceptablyhigh efficiency. After its fast development during the past20years since the first report of7.12%efficiency by Gr tzel and co-workers in1991, DSSC is now regarded as a technicallyand economically credible alternative to the currently dominating p-n junction photovoltaiccells. Photoanodes made of one-dimension nano-materails than the nanoparticles counterpartgenerally show better electrical transport properties in DSSC system due to less grainboundaries embeded. More and more effort has been dedicated to exploring the possibility ofreplacing TiO₂nanoparticles by nanorods or nanowires.With the goal to further improve the performance of DSSC, this thesis focuses onintroducing a novel oriented attachment TiO₂nanorods as photoanode material in DSSCsystem. The main points of the thesis include:（1） By using titanium isopropoxide as Ti source, ethylene glycol（EG） as structuredirecting reagent and tetramethylammonium hydroxide as alkaline source, a novel,high-yielded and cost-effective hydrothermal method was realized for the preparation ofsingle crystal-like anatase TiO₂nanorods with tunable sizes. The specific nanorods weredemonstrated with {101} exposed crystal planes and preferred [001] growth direction, thesynthesis of which was governed by the “oriented attachment” mechanism.（2） On the basis of systematically comparative experiments, the key factors effect onthe oriented attachment process were elucidated. The synthesis of nanorods/nanoparticles/nanowires with diverse sizes and crystal structures were under control in similarhydrothermal conditions by simply varying the “H2O-ethanol-EG” solvent compositions.（3） Three kinds of oriented attachment TiO₂nanorods with fine tuning diameters （14-25nm） and lengths （50-150nm）, defined as short-thin, long-thin and long-thick nanorods, havebeen critically compared in DSSC system. Cell performance has been correlated to the sizeand shape dependant electron diffusion and recombination kinetics, monitored by thetransient photocurrent/photovoltage techniques.（4） A high efficiency of8.87%has been finally achieved for DSSC based on long-thinnanorods with the Z907dye as sensitizer,. Long-thin nanorods rather than short-thin and long-thick nanorods achieving the best performance is due to the balanced optimization ofcharge collection perperty and light harvesting efficiency of the nanorods based photoanodes.To the best of our knowledge, this is the first time in the world to conduct comparativestudies on finely tuning on the size and shape of TiO₂nanorods with regard to their chargecollection kinetics and cell performances.