Computational Investigation of Tuning the Electron-Donating Ability in Metal-Free Organic Dyes Featuring an Azobenzene Spacer for Dye-Sensitized Solar Cells

Abstract

A series of donor–π-conjugated spacer–acceptor (D–π–A) organic dyes featuring an azobenzene spacer were designed as chromic dyes and investigated computationally. The electron-donating strength was modified by introducing electron-donating units to the donor side. In particular, the trans–cis isomerization of the azobenzene-based dyes and its effect on the optical and electronic properties were further scrutinized. In both trans and cis conformers, a gradual increase in electron-donating strength promoted the natural charge separation between donor and acceptor moieties, thereby allowing the absorption of a longer wavelength of visible light. Importantly, the conformational change of the azobenzene bridge resulted in different absorption spectra and light-harvesting properties. The azobenzene-based dyes will open up a new research path for chromic dye-sensitized solar cells.

Spectral Tuning and Photoisomerization Efficiency in Push–Pull Azobenzenes: Designing Principles

“…These ππ*/nπ* bands are separated enough to allow their selective irradiation: interestingly, excitation in the UV (ππ*) and in the visible region (nπ*) shows significantly different quantum yields (QYs), about 11% and 25%, respectively, in the trans case and 27% and 56% in the cis case in n -hexane . The QY wavelength dependence, which is in contrast with Kasha’s rule, suggests that different reaction mechanisms may take place starting from the ππ* or nπ* excited states (ESs), an issue that is still under discussion in experimental , and theoretical ,,− studies. Because of the reversibility of the isomerization, its speed, and the simplicity of incorporating azobenzene in complex structures, many studies are focused on red-shifting the intense ππ* bands, whose UV absorption is limiting technological and biological applications.…”

Metal‐free Organic Dyes Featuring an Azobenzene Bridge for Photochromic Dye‐Sensitized Solar Cells

“…[20][21][22][23] Furthermore, a few groups have explored asymmetric azobenzene derivatives for photoresponsive DSSCs, both theoretically and experimentally. [24][25][26][27][28] However, the photoswitching properties of these systems, which are related to trans-cis isomerization, are yet to be characterized in detail.…”

Dye-Sensitized Solar Cell (DSSC) Applications based on Cyano Functional Small Molecules Dyes

“…Donor-Acceptor type organic semiconductor materials (small molecules) are of great interest, especially since they are systems in which energy and electron transfer can be controlled [16,[23][24][25]. One of the advantages of these materials is that the p-doping and n-doping properties of the material are determined by controlling the energy of the conjugated π system with the regular repetition of donor and acceptor monomers in the chain, and the HOMO-LUMO band gap can be easily tuned [19,[26][27][28]. Because of these properties, it is common to use the donor-acceptor type materials in molecular electronics, nonlinear optical materials, and optoelectronic technology devices.…”