Theoretical Study of the Effect of Introducing pi-Conjugation and/or an Electron Withdrawing Unit in a Heteroleptic Dual-Electron Donor-Based Dye Sensitizer

Abstract

In this study, three triphenylamine (TPA)-based dye sensitizers with phenothiazine (PTZ) and TPA as dual-electron donors, benzothiadiazole (BTD) as an electron withdrawing unit, and cyanoacetic acid as an electron acceptor (dye1, dye2, dye3, dye4) were designed and investigated. To decrease the energy band gap of dye1, we added pi-conjugation between the PTZ donor and the TPA donor in dye1 and/or BTD between the TPA and thiophen in dye1. Using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, we gained insight into the factors responsible for photovoltaic performance. Due to the different energy band gaps of each dye, the absorption spectra of the dyes each showed a different form. Among the dyes, dye4 showed the most red-shifted and broadest absorption spectra. It is expected that dye4 would have better photovoltaic properties than the others. This work indicates that adding pi-conjugation or a withdrawing unit into dye would result in good photovoltaic properties for dye-sensitized solar cells (DSSCs).