Study On The Triphenylamine-Based Dyes For Dye-Sensitized Solar Cells

Dye-sensitized solar cells(DSCs),which have been emerged as cheap, high-efficiency and environmental friendly solar cells,have attracted significant attention since 1990s.The heart of DSCs system is a mesoporous oxide layer composed of nanometer-sized particle anchored by a monolayer of the charge transfer dye.Sunlight is harvested by a dye sensitizer,and then photo-excitation of the dye results in the injection of electrons into the conduction band of the oxide.Dye is one of the most important parts for DSCs to ontain high efficiency and long lifetime.Up to now,the noble-metal ruthenium polypyridyl dyes have proved to be the best dyes in DSCs,but the cost is relatively high.Metal-free organic sensitizers have been developed due to their advantages such as diversity of molecule structures, simple synthesis,high molar extinction coefficients as well as their low cost. Therefore,design and synthesis of organic dyes with high efficiency to replace Ru-based dyes have become an important work.Based on this,our work focuses on the engineering of the metal-free organic dyes.Triphenylamine(TPA) and their derivatives are excellent optical materials,and TPA is chosen as the basic framework for the design and synthesis of a series of TPA-based dyes.Photophysical and electrochemical properties of these dyes as well as their applications in DSCs were investigated.The main contents of this work are listed as follows:1.Six TPA-based orgnic dyes,which contain the typical electron donor-Ï€conjugation-electron acceptor(D-Ï€-A) structure,were designed and synthesized. Furthermore,seven other organic intermediates were obtained in the experiments. The structures of these componds were characterized by Nuclear Magnetic Resonance Spectrum(NMR) and Mass Spectrum(MS).2.Photophysical properties of the as-prepared dyes in solution and adsorbed on TiO₂ film were investigated.The results show that the as-synthesized dyes have relatively high molar extinction coefficients,and the dye-coated TiO₂ films can capture light efficiently. 3.Electrochemical properties of the dyes in solution were investigated.The results show that the position of the ground-state oxidation potential and the excited-state oxidation potential are suitable for electrons transfer in the DSCs.The influence of molecular structures on the electrochemical properties was also discussed.4.Density functional theory(DFT) calculations were performed at B3LYP/6-31+G(d) level for TPA-based dyes.The populations of the frontier molecular orbitals in dyes' molecular indicated that efficient intramolecular charge transfer occurred.The calculated results validate the rationality of molecular structure design for TPA-based organic dyes.5.Effects on DSCs performance by dye bath solvents were investigated,and dichloromethane(DCM) is chosen for sensitizers' comparison.6.The Incident Photon-to-Ccurrent Conversion Efficiency(IPCE)and Current-Voltage(I-V) curves of the DSCs based on the as-prepared dyes were measured.The relationship between dye structures and photovoltaic performance of the DSCs were studied.The DSCs based on TC16 showed higher short current density (J_sc) and open-circuit voltage(V_oc),thus the best performance with the conversion efficiency of 5.70%was obtained.7.The factors such as the concentration of Li⁺,the additives,the light irradiation, and co-sensitization of dyes,which can affect the performance of the DSCs,were discussed.The results show that increasing Li⁺ could enhance the performance of TI-based cells.The addition of guanidinium thiocyanate(GT),the low light irradiation and co-sensitization of dyes improve the conversion efficiency of the DSCs.8.The thermal stabilities of the TPA-based dyes were investigated.The results show that the as-synthesized dyes have good thermal stability.The long-term stability of a sealed DSC based on TC16 stored in sunlight was investigated.No sign of dye degradation was observed during the test,and the efficiency is steady-going on the whole.