Study On The Aromatic Amine Dyes For Dye-Sensitized Solar Cells

Photosensitizer is the one of the most important parts for dye sensitized solar cells(DSC) getting higher efficiency,which harvestes the sunlight to form excited state and achieves the process of electrons injection into the conduction band of the oxide.Then,the dye is regenerated by the electrolyte,such as an ionic liquid containing most frequently the iodide/triiodide couple as a redox system.To decrease the cost of DSC,the organic photosensitizers as the alternate to noble metal complex sensitizers have developed rapidly in recent years.In this thesis,twenty-nine novel aromatic organic dyes containing fourteen triphenylamine dyes and fifiteen heteroanthracene(phenothizaine and phenoxazine) derivatives have been engineered and synthesized as sensitizers for the application in DSC.The structures of the dyes have been characterized by mass spectra(MS) and proton nuclear magnetic resonance (¹H NMR) technology.The photophysical and electrochemical properties of the dyes were studied.DSCs based on these dyes were constructed and detailed relationship between dye structures and solar cell performances has been investigated.At the same time,the model compounds were introduced to study the intromolecular energy transfer(E_nT) and charge transfer(ICT) processes.The significant differences in the photophysical and electrochemical properties of the sensitizers can be influenced by small structure changes.For triphenylamine dyes,the introduction of electron-withdrawing units can achieve bathochromic shift of absorption spectra.Also,the absorption band of dye can be red-shifted and broadened by the introduction of largeÏ€-conjugation spacer.For heteroanthracene,with the similar structure,phenoxazine dyes show more perfect absorption spectra than phenothizaine dyes.HOMO and LUMO level of the dyes match well with that of I₃^-/I^- and TiO₂ conduction band,respectively.Introduction of largeÏ€-conjugation spacer moieties(such as,thienyl and DTT unit) will shift HOMO level of dye negatively,and results in a reduced gap between that and redox potential of I₃^-/I^-.This might reduce the efficiency of regeneration of the oxidized dye by I^-.Compared to cyanoacrylic acid group,the(co) rhodanine acetic can also shift LUMO of dye positively and reduce the force of electron injection into conduction band of TiO₂.The different dye-baths for semiconductor sensitization have a crucial effect on the performance of the DSC due to the different absorption spectra,different absorbed amount and different binding modes of anchored dyes on TiO₂ surface in various solvents.The result suggestes that CH₂Cl₂ as dye-bath solvent can obtain the prominent solar-to-electricity conversion efficiency of DSC based on our dyes.Also,due to the differences of photophysical and electrochemical properties,different dyes show different photovoltaic properties.For triphenylamine dyes,the electron-withdrawing groups on phenylene units asÏ€-spacers show the negative effect on the performance of DSC.For heteroanthracen dyes,the different substituted alkyl length in electron-donating groups has significant effect on DSC performance.Based on the optimized dye structure and measurement method,TH208 and TH302 dyes achieve the solar-to-electricity conversion efficiency 6.4%and 6.3%.The study of the effect of different electron donating groups on DSC performance demonstrates that organic sensitizer with non-planar electron donating group could be further designed to complete the monomolecular adsorption and obtain the prominent efficiency without H-aggregation depressor(for example,CDCA).Intramolecular energy transfer and charge transfer processes show positive effect on the performance of DSC.Based on the theory,the phenoxazine dye TH305 shows prominent efficiency,7.7%.Under similar test conditions,the reference dye N719 shows 8.0% efficiency.