Thiophene-bithiazole based metal-free dye as DSSC sensitizer: Effect of co-adsorbents on photovoltaic efficiency

Structure and Photoelectrical Properties of Natural Photoactive Dyes for Solar Cells

A series of natural photoactive dyes, named as D1–D6 were successfully extracted from six kinds of plant leaves for solar cells. The photoelectrical properties of dyes were measured via UV-Vis absorption spectra, cyclic voltammetry as well as photovoltaic measurement. To theoretically reveal the experimental phenomena, the chlorophyll was selected as the reference dye, where the ground and excited state properties of chlorophyll were calculated via density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The experimental results show that the absorption peaks of those dyes are mainly distributed in the visible light regions of 400–420 nm and 650–700 nm, which are consistent with the absorption spectrum of chlorophyll. The photoelectrical conversion efficiencies of the solar cells sensitized by the six kinds of natural dyes are in the order of D1 > D4 > D2 > D5 > D6 > D3. The dye D1 performance exhibits the highest photoelectrical conversion efficiency of 1.08% among the investigated six natural dyes, with an open circuit voltage of 0.58 V, a short-circuit current density of 2.64 mA cm−2 and a fill factor of 0.70.

Role of Voluminous Substituents in Controlling the Optical Properties of Disc/Planar-Like Small Organic Molecules: Toward Molecular Emission in Solid State

Inspired by the role of coadsorbents in dye-sensitized solar cells, a pathway to disfavor aggregation in disclike luminophores was studied to enhance solid-state emission. By restricting the intense π-π stacking using a multicyclic aliphatic ring system, we brought the lithocholic ring system as bulky side substitution into the fluorophore design. Compared to the small-size cyclohexyl substitution in BC-CY6, which exhibited a bathochromic shift in solid-state emission owing to the intermolecular interactions, lithocholic-substituted BC-LTH had reduced intense intermolecular interactions. This very bulky/voluminous side substitution (lithocholic unit) helped us extract intermolecular interaction-free molecular emission in solid state. The cyclohexyl substitution provided solid-state emission, and the broad and high Stokes shift provided an insight into stacking interactions. Face-to-face stacking-originated dimerlike species was observed in the crystal packing, which was studied by theoretical geometry optimization. The dimer species exhibited an intermolecular distance of 3.5 Å. The molecular sizes of the developed chromophores were estimated by geometry optimization, and it was concluded that the dimeric interactions in BC-LTH may not be formed owing to the voluminous nature of the side substitution present. Hence, we have been able to successfully establish through molecular level understanding the role of lithocholic functionality in tuning the optoelectronic properties of various emissive materials for different applications.