Theoretical Study On Organic Dyes With Different Arylamines Donors For Dye-sensitized Solar Cells

Since1991, Gr tzel group reported a dye-sensitized solar cells(DSSCs) withsimple structure which efficiency was as high as7%, DSSCs has attracted widespreadattention. Compared with traditional silicon-based semiconductor solar cells, DSSCshas many advantages like high energy conversion efficiency and low cost. At present,the highest efficiency of the DSSCs has reached by the one with photosensitizer zincporphyrin dyes, and its efficiency is12.3%.However, he high price of metal haslimited the application of the DSSCs. Recent years, the DSSCs based non-metallicorganic dyes has got more and more attention because of its low cost, easypreparation, environmental friendly while also has the advantages of highphotoelectric conversion efficiency. Photosensitive dye is an important part of theDSSC. Subtle differences of the photosensitive dye can lead to significant differencesof the device performance. However the experiments on the design and synthesis ofefficient dyes are still facing huge challenges. Recent years, quantum chemistrymethod has become a reliable means of study the relationship between structure andperformance of dye molecules.This paper mainly includes two parts of work:In order to discuss the differences in the performance of DSSCs based on twoD-π-A organic dyes, which only differ in the donor part, theoretical parametersclosely related to the short-circuit photocurrent density (Jsc) and the open-circuitvoltage (Voc) were computed with the density functional theory (DFT) andtime-dependent DFT calculations, including absorption spectrum, light harvestingefficiency, injection driving force, vertical dipole moment and number ofphotoinjected electrons and so on. The results reveal that the lower dye regenerationefficiency of2lead to the lower Jscof DSSCs, when the dyes have comparative lightharvesting efficiency and electron injection efficiency. Meanwhile, under thecondition that the dyes have comparative number of photoinjected electrons and theextent of charge recombination, the higher vertical dipole moment of1could be thecrucial factor leading to the higher Voc. The calculated results are in good agreementwith the experimental one. Finally, we hope that our results could provide certainguidance for the future works on the synthesis and design of new efficiency dyes.In order to exploring the relationship between structure of D-D-π-A dyes andperformance of DSSCs, we have analyzed geometrical and electronic structures, absorption spectra, electrochemical properties, charge recombination and conductionband shift for four dyes using DFT and time-dependent DFT. The results show thatcompared with the classical D-π-A dye1, although the introduction of additionaldonors has no significant effect on the conduction band shift, it could changeconjugate degree of molecules and increase their molar absorption coefficient. Dye2with additional phenothiazine donors and dye4with additional diphenylamine donorshave more red-shifted absorption spectra, and this introduction could tune the groundand excited state oxidation potential significantly. Conversely, dye3with additionalcarbazole donors has slightly blue-shifted absorption spectrum as compared to dye1,and it can only fine-tune ground and excited state oxidation potential. Moreover, theintroduction of additional donors could increase the dye cationic hole-surface distanceand make I2locate at the outside of dye, thus reduce the charge recombination. Wehope our calculated results could provide a clear and intuitionistic strategy forexperimental synthesis of high performance dyes.