Effect of Caffeine Copigmentation of Anthocyanin Dyes on DSSC Efficiency

Abstract

Caffeine is known to influence the absorbance spectrum of anthocyanin dyes. Such dyes are often used as sensitizers in dye-sensitized solar cells (DSSCs). Natural dyes, like anthocyanins, yield only small DSSC efficiencies, but are of high interest since they are usually non-toxic and inexpensive. Here we report on the influence of copigmentation of anthocyanins, taken from commercially available tea, with caffeine. In this way, the efficiencies were increased for measurements with a solar simulator as well as with ambient light. In addition, the well-known pH dependence of the efficiency of DSSCs dyed with anthocyanins was shifted—while a pH value of 1–2 was ideal for pure anthocyanins used as dyes, a higher pH value of 2–3 was sufficient to reach the maximum efficiencies for caffeine-copigmented dyes. This means that instead of reducing the pH value by adding an acid, adding caffeine can also be used to increase the efficiency of DSSCs prepared with anthocyanins. Finally, a comparison of several literature sources dealing with anthocyanin-based DSSCs allows for evaluation of our results with respect to the work of other groups.

Electrospinning a Dye-Sensitized Solar Cell

“…Instead, the ideas discussed below to make fully electrospun DSSCs more efficient concentrate on morphological and material optimization approaches based on non-toxic materials. An additional reduction of the efficiency due to the relatively large cell area, as opposed to most other studies [21], can also not be avoided since larger cell areas make upscaling to larger scales easier than an approach based on smallest DSSC areas.…”

“…Depending on the cell area, the solvents used, the choice whether platinum or graphite is used as the catalyst, the electrolyte, and a possible nanostructure of the semiconducting layer, efficiencies between 0.0002% and 2.3% are typical for natural dyes as sensitizers [11][12][13][14][15][16][17][18][19]. It should be mentioned that in many cases the given efficiencies are prone to calculation errors, typically by one order of magnitude, sometimes by larger factors [20,21], and should thus be treated with care.…”

Recent advances in anthocyanin dyes extracted from plants for dye sensitized solar cell

“…Moreover, the cells with co-pigmented dyes were observed to be more stable than the cells with pure anthocyanin, i.e. they showed a smaller drop of efficiency during the observation period [130].…”

“…Irén Juhász Junger et al [134] studied the influence of caffeine as a co-pigmentation of anthocyanin on the energy conversion efficiency of anthocyanin based DSSCs. They stated that the efficiency of anthocyanin based DSSCs when co-pigmented with caffeine is dependent upon the pH contents of the solution due to either hyperchromic or hypochromic effects.…”

Solarstrom aus Früchtetee

“…natürlicher Farbstoffe findet (einige Beispiele sind in [6] und [8] aufgeführt). Durch die regelmäßige Wiederholung solcher Rechenfehler scheinen auch Gutachter von Publikationen sich an angebliche Wirkungsgrade von einigen Prozent zu gewöhnen und diese Werte nicht mehr nachzurechnen.…”