Improving the optoelectronic efficiency of novel meta-azo dye-sensitized TiO semiconductor for DSSCs.

A series of novel azo dyes possessing varying conjugation lengths and different donor moieties, based on 5-amino isophthalic acid were designed and synthesized. Azobenzene unites were utilized as the π-spacer part to extend the conjugation range and connect the donor to acceptor unit. When the dialkylamino substituent was changed from dimethyl to diethanol, a red shift in the absorption spectra and λ was observed. The photophysical and electrochemical properties of the straightforward-synthesized dyes were investigated in solution and on photoanode surface which promised the suitability of the dyes as photosensitizers for dye sensitized solar cells (DSSCs). Increased dye adsorption strength on the TiO surface as well as light harvesting capability was expected due to bearing two anchoring-electron accepting groups which could lead to enhanced electron transfer (ET). The ATR absorption spectra clearly showed that these dyes were adsorbed on the TiO surface. It was realized that increasing π-conjugation length as well as hydroxyl containing donor group gave rise to improved photovoltaic performance of DSSCs. Reduced band gap along with suppressed electron recombination and amended dye regeneration were recognized to play an important role in enhancing performance parameters. DSSCs based on these dyes exhibited higher solar conversion efficiency in comparison with efficiency of other meta azo dyes that were previously synthesized. Theoretical calculations (DFT/TDDFT) expressed that among the dyes, members 3a and 3b possessed localized and non-continuous electron distribution in their frontier orbitals as well as maximum amount of oscillator strength.