The selection of solvent for preparing a working electrode (and to act as the electrolyte) is known to influence the efficiency of dye-sensitized solar cells. In this topical review, results taken from a systematic study are presented from the authors’ own lab examining how protic and aprotic solvents, as well as solvent polarity, affect adsorption of carboxylic dyes on the titanium dioxide nanoparticle surface and electron injection from the dye to the semiconductor. Adsorption of dye molecules on nanoparticle surfaces is measured through second harmonic light scattering and electron injection through ultrafast transient mid-infrared absorption. It is revealed that protic solvents do not allow direct adsorption of the dye onto the semiconductor surface, due to hydrogen bonding with the dye and competitive binding to the semiconductor surface. Aprotic solvents, on the other hand, support solvation of the dye molecules but also facilitate dye adsorption on the semiconductor nanoparticle. Among aprotic solvents, it is found that solvents with higher polarity result in larger adsorption free energy for the dye and faster electron injection. Overall, these studies reveal that aprotic solvents with high solvent polarity (such as acetonitrile) yield more efficient solar cell devices.
The world of dyes and pigments is vast and there are innumerable varieties of these colorants to fulfill the requirements of varied industrial and commercial sectors. Acid dyes, basic dyes, solvent dyes, lake colors, pigment colors are just to name a few from the vast ocean of colors. This article will talk in brief about the solvent dye.
Solvent dye is a dye that is soluble in plastics or organic solvents. When it goes with an organic solvent the dyeing process occurs in a solution. As the molecules of solvent dyes have a very small polarity or none at all there is no ionization involved in the dyeing process as it does, say, with acid dyes. Solvent dyes are normally water insoluble. One commonly used organic solvent with solvent dyes that is non-polar is petrol.
As for the naming of solvent dyes a standardized pattern is followed. In the pattern, the first word is always ‘solvent’ which is followed by the dye color and then a distinguishing number. For example, the varied shades of red are segregated by the distinct number that comes after the shade name like ‘Solvent Red 49’, ‘Solvent Red 1’, and ‘Solvent Red 24’ and so on. Another example of the shade red occurring in another type of dye is Pigment Red 48 which is an azo derivative from naphthalene.
Solvent dyes are pretty versatile and have found their way into a number of applications. One of their common uses is in the automotive sector to impart color to petrol fuel and other lubricants. Varied hydrocarbon based non-polar materials such as waxes and candles, coatings and wood stains are colored with the aid of solvent dyes. In the printing industry they go towards marking inkjet inks, inks and glass coloration. Textile printing is followed by the media industry where the solvent dyes are used for magazines and newspapers.