Titanium Oxo Clusters Modified With Triphenylamine-Carboxylate Dyes And Their Photoelectric Properties

The energy crisis has prompted people to continuously research and develop new energy sources.Dye-sensitized solar cells?DSSCs?have attracted increasing attention because of their various advantages like designability,low cost and high efficiency.Both the molecular structures of the dyes and the anchoring methods on the TiO₂ electrode will affect the photoelectric conversion efficiency of the cells.Triphenylamine dyes are one of the most widely studied photosensitizers due to their strong electron-donating capability.The TiO₂ electrode was usually sensitized by soaking method for the adsorption of sensitizers.However,the adsorbed dyes in this physical way have poor anchoring ability,and the mixed chemical and physical anchoring mode limit the applications in high performance devices and theoretical calculations.Titanium oxo cluster?TOCs?is a molecular compound similar to nano TiO₂ but with a precise structure.Its well-defined structure can be studied as a structural model of TiO₂.Our work is preparation of TOCs modified covalently with the triphenylamine dyes,and use them as the theoretical structural model of DSSCs to study the effect of charge transfer on photoelectric conversion.At the same time,using these sensitizing dyes with TOC cores that act as anchoring groups to modify TiO₂ electrodes and investigate their special photoelectric conversion properties.The thesis mainly includes the following contents:?1?In chapter 1,a brief introduction of the principle of DSSCs and the researches of sensitizers was made.Then we summarized the latest research progress of titanium oxo clusters,especially the TOCs which were modified with dyes;the idea and significance of the topic were expounded.?2?In chapter 2.1,4-diphenylaminobenzaldehyde?4-diethylaminobenzaldehyde?.malonic acid and Ti?O1Pr?₄ were mixed and then reacted to obtain two TOC compounds of[Ti₆O₃?L1?₂?O1Pr?₁₄]·HO1Pr?1?and[Ti₆O₃?L2?₂?O1Pr?₁₄]?2?,respectively,by one step in situ solvothermal synthesis.The ligands L1 and L2 were formed by Knoevenagel condensation from the aldehydes and malonic acid in the reaction.Another Ti6 oxo cluster modified with TPA derivative L1' and BDC?o-benzene dicarboxylate?was also isolated for contrast,[Ti₆O₄?L1'?2?BDC?₂?OiPr?₁₀]?3?.The compounds were characterized by cyclic voltammetry,UV-vis and 1H NMR spectra.Subsequently,these clusters were used as novel sensitizing dyes to sensitize the TiO₂ electrodes,which were characterized by SEM,Raman spectra and XPS spectra.The experimental results indicated that the main structure of the compounds can still remain stably during the sensitization process,but the isopropyl groups are condensed partially when the cluster was modified onto the surface of TiO₂.The photocurrent response of the sensitized electrodes in a two-electrodes system?I2/I3-electrolyte?were tested.The photocurrent density of the 1 and 2 modified electrodes were superior to the classical triphenylamine-cyanoacrylic photosensitizer LO,since the TOC core can be a more effective anchoring group.The study combined triphenylamine dyes with TOCs for the first time,and the results verified the anchoring effect of TOCs on the electrodes?3?In chapter 3,a reported triphenylamine-cyanoacrylic dye LTPA and its diethylamino derivative LDEPA were mixed with to synthesize two Ti₃ oxo clusters,[Ti₃O?LTPA?₂?O1Pr?₈]?4?,[Ti₃O?LDEPA?₂?O1Pr?g]?5?,by solvothermal method.On the basis of this,phenylphosphoric acid was added to obtain two Ti₆ oxo clusters[Ti₆O₄?LTPA?₂?O3PPh?₂?OiPr?₁₀]?7?,[Ti₆O₄?LDEPA?₂?O3PPh?₂?OiPr?₁₀]?8?.Another Ti6 oxo cluster modified with cyanoacetic acid[Ti₆O₄?CA_?2?O3PPh?₂?OiPr?₁₀]?6?was also crystallized for contrast.Using these crystals as the models with accurate structural information,charge transfer properties of the sensitizers in DSSCs were studied by spectral analysis and DFT calculations.It was found that the intramolecular charge transfer?ICT?of the dye and the charge transfer of the dye ligand to Ti???metal?LMCT?play an important role in reducing the band gap energy.The TiO₂ electrodes were sensitized by these compounds and were used in preparation of the DSSC devices.The photoelectrochemical behaviors of the cells showed that increasing the ICT contribution in LUMO can increase the power conversion effect.Because the TOC core can act as an efficient anchoring moiety,the photocurrent properties then can be improved by the dye-TiO pre-anchored structure.This work successfully prepared TOCs anchored with the practical applied triphenylamine-cyanoacrylic dye and discussed the effects of ICT and LMCT on the photoelectric properties based on the model compounds.