Preparation Of TiO₂Photoanode And Mechanism Of Solid State Dye-Sensitized Solar Cells

Dye-Sensitized Solar Cell (DSSC) was firstly invented by Prof. M. Gratzel’s group atEcole polytechnique federale de Lausanne (EPFL) in1991. Compared with expensive traditional silicon based solar cell, DSSC is a promising alternative to the former because its ease of fabrication, low cost and high power conversion efficiency. A typical DSSC consists of photoanode, electrolyte, dye sensitizer and counter electrode, while photoanode plays an important role in dye absorption and electron transportation, which are responsible for photoelectric conversion. This thesis mainly focuses on TiO2photoanode, aiming at improvement of DSSC’s photovoltaic performance. The main results included in this dissertation are summarized asfollows:(1) TiO2nanoparticles were synthesized by hydrothermal reaction and used as photoanode for DSSCs. By optimizing the amount of TMAH in reactants, the reaction time and the amount of ethyl cellulose, DSSC based on our TiO2nanoparticles (12μm) generates a short-circuit current of16.72mA cm-2and an open-circuit voltage of0.736V, correspondingto a power conversion efficiency of8.25%.(2) In situ grown TiO2nanorod arrays on conductive substrates, on which a layer of TiO2nanoparticles is screen printed, are used as a new type of TiO2nanorod arrays/nanoparticles photoanode for DSSCs. Compared with TiO2nanoparticles based DSSCs, the former have a lower conduction band edge, which is beneficial to electron injection, leading to a higher short-circuitphotocurrent and power conversion efficiency. Furthermore, the TiO2nanorod arrays/nanoparticles photoanode shows a great ability of charge recombination inhibition, which partially compensates the voltage loss caused by the positive movement of conduction band edge.(3)TiO2nanorod arrays have in situ grown onto the conductive glass via a facile one-step low temperature hydrothermal reaction, then combined with graphene, and multi-layer TiO2nanorod arrays can be obtained by repeating the former hydrothermal reaction. When the multi-layer TiO2nanorod arrays get thicker, it can absorb more dye sensitizer, and the corresponding DSSC shows a remarkable enhanced short-circuit current, though the open-circuit voltage decreases slightly. By optimization, DSSC based on two layers of TiO2nanorod arrays (4μm) exhibits the best photovoltaic performance, with a short-circuit current of7.30mA cm-2, an open-circuit voltage of0.702V, a fill factor of0.75, and a power conversion efficiency of3.86%.(4) The synthesizedTiO2nanoparticles were applied for solid-state DSSCs. A solid state ester-functionalizedimidazolium iodide (EMImI) was combined with I2and LiI, and used as solid-state electrolytes, with an alkyl-substituted imidazolium iodide (DMPImI) as contrast. Through the discussion about movement of conduct band edge, charge recombination rate, charge collection efficiency of DSSCs based on the two types of electrolytes, we clarify how the ester group influences the solar cell performance, which is essential for furtherinvestigationof efficient solid state electrolytes.