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.
Highlights
Dye-sensitized solar cells (DSSCs) have been investigated by diverse research groups since their first presentation in the scientific literature [1]
We have investigated DSSCs dyed with anthocyanins and found a significant efficiency improvement when the pH value of the dye extract was decreased to 1.1 [12]
In this study we investigated DSSCs dyed with anthocyanins co-pigmented by caffeine
Summary
Dye-sensitized solar cells (DSSCs) have been investigated by diverse research groups since their first presentation in the scientific literature [1]. A large advantage of DSSCs, as opposed to common silicon-based solar cells, is the possibility to produce them from non-toxic, low-cost materials without a cleanroom. The highest conversion efficiencies are reached with very specialized materials, which typically lack these advantages [2]. During the integration of DSSCs into textiles, the use of toxic materials should be avoided, for example through a replacement of the widely used ruthenium based dyes by natural dyes. DSSCs with natural dyes are known to yield low energy conversion efficiencies. In order to eliminate this handicap, different natural dyes and dye sources were examined by many research groups. For example, efficiencies up to 0.011% were reached [6], while curcumin resulted in an efficiency of
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