Two donor-π-spacer-acceptor (D-π-A) organic dyes were designed as photochromic dyes with the same π-spacer and acceptor but different donors, based on their electron-donating strength. Various structural, electronic, and optical properties, chemical reactivity parameters, and certain crucial factors that affect short-circuit current density (Jsc) and open circuit voltage (Voc) were investigated computationally using density functional theory and time-dependent density functional theory. The trans-cis isomerization of these azobenzene-based dyes and its effect on their properties was studied in detail. Furthermore, the dye-(TiO2)9 anatase nanoparticle system was simulated to understand the electronic structure of the interface. Based on the results, we justified how the trans-cis isomerization and different donor groups influence the physical properties as well as the photovoltaic performance of the resultant dye-sensitized solar cells (DSSCs). These theoretical calculations can be used for the rapid screening of promising dyes and their optimization for photochromic DSSCs.

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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.

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Naturally abundant dyes are very attractive for the development of dye-sensitized solar cells (DSSCs). Hydroxycinnamic acid derivatives, such as caffeic acid (CA), ferulic acid (FA), and p-coumaric acid (PA), were considered for the selective harvesting of ultraviolet A (UVA) (315–400 nm) photons. Their spectroscopic and electrochemical properties were investigated both theoretically and experimentally. They were further successfully adopted as photosensitizers in UV-selective and visibly transparent DSSCs, which exhibited a power conversion efficiency of 0.22–0.38% under AM (air mass) 1.5G (global) illumination (100 mW/cm2) and 3.40–3.62% under UVA irradiation (365 nm, 115.22 mW/cm2), with a corresponding visible light transmittance (VLT) of 49.07–43.72% and a general color rendering index (Ra) of 93–90.