Effect of Electron Donor Groups on Optoelectronic Properties of Betalain Dyes: A DFT Study

Density functional theory (DFT) and time-dependent-DFT analyses show that the modified betalain dyes exhibit λ_{m a x} of 400–442 nm and light-harvesting efficiencies >93%. Upon binding to (TiO₂)₆H₃, absorption peaks red shift to 461–470 nm. Binding energies range from −1.39 to −0.03 eV. TPA-Beet and p-dme-N-pBeet show superior optoelectronic performance and are strong candidates for DSSC applications.

A sensitizer is a vital component of dye-sensitized solar cells (DSSCs); it absorbs incident photons, excites electrons, and facilitates charge transfer to the semiconductor. In the present work, modification of betalain dyes through grafting of electron donor groups has been performed. The reported optoelectronic properties of the investigated dyes are determined using density functional theory (DFT) and time-dependent DFT methods. The investigated sensitizers exhibit maximum absorption between 400 and 442 nm with light-harvesting efficiencies exceeding 93%. Favorable interactions are observed between the dyes and the hydrogenated TiO₂ cluster, (TiO₂)₆H₃. The obtained binding energies range from −1.39 to −0.97 eV in the gas phase and −0.31 to −0.03 eV in water. The electronic spectra of the dye@TiO₂ complexes show broader and intensive bands with bathochromic shifts when compared to the individual dyes. The charge density distribution in the complexes indicates appropriate ability of the dyes for charge injection to the semiconductor. Among the considered dyes, the most promising candidates for use in DSSCs have been selected.

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