Mesoporous semiconducting oxide thin films with nanocrystalline walls: Synthesis, characterization, and applications

Mesoporous titania thin films were synthesized using a novel modified sol-gel method, which involves the inhibition of rapid condensative polymerization of hydrolyzed titanium alkoxide using concentrated acid solutions. Lamellar, 2D-hexagonal, and cubic mesostructures were created by varying the volume fraction of the structure-directing block copolymer in the precursor solution. A mesostructured cubic semiconducting framework made up of three-dimensionally arranged anatase nanocrystallites embedded in an amorphous titania matrix was obtained by heat treating the films. Interesting absorbance and photoluminescence properties were observed including a blue shifted band gap and well-defined photoluminescence peaks owing to the high surface area and unusual surface environment of the nanocrystallites present in the framework.;Selected rare earth ions were included into the walls of the mesoporous titania thin films and excitation of the mesoporous titania in its band gap resulted in sensitized photoluminescence in the visible and near infrared regions of the spectrum. The energy transfer mechanism was determined in part by evaluating which rare earth ions exhibited photoluminescence via energy transfer.;Mesoporous titania thin films were incorporated into several devices including a dye sensitized solar cell. The photocurrent, photovoltage and power conversion efficiency of several iterations of solar cell devices were tested. Electrochromic devices were also fabricated and tested using pure mesoporous titania films and those doped with cerium ions. Contrary to the behavior of non-porous Ce-TiO2 thin films, the addition of cerium to mesoporous titania films caused an increased electrochromic effect.;The calcination temperature was varied to correlate the evolution of the structure of the titania thin films with optical and electrochemical properties. Electron microscopy, optical absorbance, photoluminescence, lithium insertion, chronoamperometry, and photoelectrochemical response were used in this study to establish criteria for optimization of the mesoporous titania films for photovoltaic cells, battery electrodes, photocatalysis, and sensors.;Finally, several future directions were proposed based on extensions to the synthesis and applications detailed in this dissertation. These include the synthesis of mesoporous molybdenum oxide thin films and a new design for a photoelectrochemical biosensor.