Molecular Design And Theoretical Study On Novel2-pyrone Derivatives For Dye-sensitized Solar Cells

Dye-sensitized solar cells （DSSCs） have attracted considerable attention as a newgeneration of sustainable photovoltaic devices because of their relatively high incident solarlight-to-electricity conversion efficiency and low cost of production. Dye sensitizers havebeen recognized as one of the vital parts to achieve high performance among all thecomponents of the DSSC device. Metal-free organic dyes have been investigated intenselyowing to their advantages of high molar extinction coefficients, flexibility in structuretailoring, low-cost preparation process, and compliance with environmental issues. Therefore,in this work, we investigate the influence of2-pyrone moiety acting as Ï€ space on electronicand optical properties of organic dye before and after binding to TiO₂cluster using DFT andTDDFT calculations. The main results are summarized as follows:1. The coplanarity of molecular P1better than dye T and P2, although the geometry ofdye P2look very similar to T. After inserted a vinylene unit–CH=CH-, all the dyes obtainedhave an almost perfect copolanar structures in favor of intramolecular electron transfer.2. The energy level of the LUMO orbital of the dyes with2-Pyrone higher than theconduction band （CB） of the TiO₂electrode, and the energy level of the HOMO orbital of thenovel dyes lower than the I3-/I-redox potential. The results of calculated ΔGinject.and energylevel of orbitals shown that the new dyes have enough drive force to inject the electrons to theconduction band of the TiO₂.3. The absorption spectra for the dyes with2-Pyrone exhibit red shifts to some extentwith respect to that of the common dye-CHCH－T、CHCH－Ph、CHCH－F. The maxabsorption wavelengths of the dye OMe－CHCH－P2is540nm and the LHE of this dyeexceed0.98.4. The effects of semiconductor have been studied using the （TiO₂）8cluster as model. Allthe adsorption energies of the studies dyes are more than40kcal/mol. We computed thebidentate adsorption mode to be energetically favored compared to the monodentate one. The absorption spectra for the adsorped dyes exhibit red shifts with respect to that of the isolateddyes. The max absorption wavelengths of the adsorped dye OMe－CHCH－P2is617nm.In summary, our theoretical calcutions show that, the designed moleculars in which2-pyrone act as Ï€ space, comparing to the dyes with thiophene derivatives, are promising andeffective dye sensitizers for dye-sensitized solar cell.