Functional Nanostructures

Dye Sensitized Solar Cells (DSSC’s): Photo-electro-chemical cell, works on the principle of photosynthesis. Q:- How can a device mimic photosynthesis? A:- In plants chlorophyll (dye) absorbs light, the light is converted to electrons, in the proceeding reactions the electron is consumed by metabolic redox reaction. Efficiency of photosynthesis is 33%. Similarly, DSSC’s use a dye to harvests the light into electrons and these electrons are collected to be used for useful work!. The best efficiency of DSSC’s as of today is 11.5% and can be improved to over 23%. I ncreasing concentration of 1, 3, 5 Tri-Methyl Benzene Atomic Force Microscopy images confirm the increase in the pore size ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Ordered Mesoporous TiO 2 : Conclusion: The ability of tuning the morphology of the TiO 2 electrodes by controlling the pore size has been demonstrated, it has been shown that the films have high surface area and good interconnectivity for better electron transport and higher dye adsorption. Future Works: Determination of charge collection efficiency and light harvesting efficiency of the DSSC’s fabricated using ordered mesoporous TiO 2 electrodes. Acknowledgements: USD-DOE subcontracted grant to catalysis group at SDSM&T, Dr, Jan A. Puszynski and Dr. Rajesh V. Shende References: [1] Adv. Funct. Mater. 2006, 16, 1731–1738 [2] Nano Lett., 2006, 6 (2), 215-218 • DOI: 10.1021/nl052099j [3] Nano Lett., 2007, 7 (1), 69-74 • DOI: 10.1021/nl062000o [4] Macromolecules, 1994, 27 (9), 2414-2425• DOI: 10.1021/ma00087a009 [5] J. Am. Ceram. Soc., 2009, 92 [2] 289–301 Photovoltaic (phos) meaning "light", and "voltaic“ meaning electric: a device that on exposure to light generates electricity (solar cell). Solar Spectrum Spectral Irradiance Energy = 1240/Wavelength( λ ) Energy per second: 1000 W/m 2 Q:- How can we harvest light? A:- A light absorber (Si, GaAs etc.), absorbs energy in a range characteristic of the material. A barrier or junction to selectively direct charge to external circuit. P in : Power in, P MAX : Maximum power out Controlling Pore Size and Surface Area: Ability to tune the pore size and the surface area of these materials is very crucial, as it enables us to alter the transport kinetics of the ionic redox species in the porous films. Another important parameter is the surface area, the higher the surface area means more amount of dye can be absorbed in the films, thus higher charge injection or photocurrent. We used a chemical modifier to swell the pores for synthesizing materials with larger pores, the figure shown below describes the effect of the pore swelling agent on the surface area and pore size. Abstract The present studies are focused on two major areas a) synthesis of ordered mesoporous TiO 2 thin film electrodes and tuning pore size of the mesoporous thin film electrodes using chemical modification techniques for DSSC applications, and b) IV evaluation of these novel electrodes. Currently, DSSC’s utilizes 5-20 μm size films of TiO 2 nanocrystals, which provides sufficient anchoring sites for dye sensitizers and yields reasonably well energy conversion. The current state of the art DSSC is reported to have an overall efficiency of 11% and there is a big thrust towards increasing the overall efficiency of these photo-electrochemical devices in DSSC community. In this direction, one goal has been to tune the porosity in the acceptor layer (TiO 2 electrode). The nature of charge transport in these electrolyte permeated porous acceptor electrodes is ambipolar, mass transport limitation due to irregular morphology of TiO 2 nanocrystalytes and distribution of pore size in the film. In this work, we present the synthesis of ordered mesoporous electrodes using two distinct approaches. The prevailing processes will be further modified to tune the pore diameter in the range of 6-50 nm in the ordered electrode film by using suitable chemical modifying agents. The Figure-1a shows the order porosity in TiO2 thin films on silicon substrate synthesized using surfactant template assisted sol-gel technique, whereas Figure-1b & 1c show the thin films synthesized using the supercritical CO 2 assisted infusion of Ti – alkoxide precursor into 100 nm thick solid block co-polymer template containing acid catalyst. The SEM micrographs in figure-1b show uniform size TiO 2 particles arranged in a partially ordered manner. In Figure-1c, it can be observed that the TiO 2 particles are porous having interparticle pore size of approx 2 ~ 4 nm. We anticipate that by using certain non-polar organic modifiers pore swelling can be achieved. We will present synthesis of ordered TiO 2 electrodes and their characterization, fabrication of DSSC devices and evaluation of their IV characteristics. Synthesis of Ordered Mesoporous TiO 2 Thin Film as Back Electrodes For Dye Sensitized Solar Cells Alok Vats, Dr. Jan A. Puszynski, and Dr. Rajesh V. Shende Nanoscience and Nanoengineering Program, South Dakota School of Mines and Technology, Rapid City- SD-57701 Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City- SD-57701 9~11nm 15~17nm 19~23nm Effect of chemical modification on a) surface area, b) & c) Nitrogen adsorption/desorption isotherms Pore size distribution of the ordered mesoporous TiO 2 UV-Vis absorption spectra of dye in solution and dye in ordered mesoporous TiO 2 thin film(Yellow) Ordered mesoporous TIO 2 film synthesized using method A Ordered mesoporous TIO 2 film synthesized using method B I 3 - Craig A. Grimes et al. AJ Frank et al 1D 3I - - 2e -  I 3 - Redox ,[object Object],[object Object],40nm Spin coated TiO 2 on glass substrate fired at 300 o C 40nm 100nm

Functional Nanostructures

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