Y-shape structured azo dyes with self-transforming feature to zwitterionic form as sensitizer for DSSC and DFT investigation of their photophysical and charge transfer properties.

Two novel azo dyes with D-π-A-π-D structures were designed and synthesized to investigate the relationship between molecular structure and sensitizing performance on applying for dye-sensitized solar cells (DSSCs) in comparison with their linear counterparts. Introducing hydroxyl auxiliary groups and arranging π-conjugation length as two parallel and series structural architectures, Y-shape and linear, led to red shift in absorption wavelength and increase in absorption intensity for the Y-shape pattern providing an efficient charge transfer pathway and improved Jsc and η of the DSSCs. Emerging a zwitterionic form, azonium structure, of the sensitizer in parallel configuration for the dyes 1a.p and 1b.p, enhanced light absorption domain and changed anchoring fashion could engendering improved electronic overlapping. The easily-synthesized dyes were evaluated for photophysical and electrochemical properties and turned out that the parallel-decorated dyes displayed better results than the series types as photosensitizers for DSSCs. ATR and Raman spectra clearly showed the adsorption of these dyes on the TiO2 surface. Operational tests of DSSCs, coated by titled azo dyes, illustrated that decorating π-conjugation pattern as parallel structure as well as accessorizing the donor unit with hydroxyl groups improved the photovoltaic performance. Optimized band gap due to participating the azonium structure and restricted electron recombination as well as rectified dye regeneration were proposed as main elements in enhancing performance parameters. A higher solar conversion efficiency was recorded for DSSCs based on the Y-shape dyes compared to other meta azo dye-based cells that were previously reported. Computational calculations were used to corroborate the opto-electrochemical traits of the dyes with a special concern on the influence of structural pattern on photovoltaic features.

Improving the optoelectronic efficiency of novel meta-azo dye-sensitized TiO2 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 λonset 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 TiO2 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 TiO2 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.