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Enhancement in the photostability of natural dyes for dye‐sensitized solar cell (DSSC) applications: a review

The advancements in the generation of solar cells have created a landmark to design a cost‐effective, less weight, biocompatible, and environmental‐friendly solar cell. Dye‐sensitized solar cells (DSSCs) have become a topic of significant research in the recent years because of their imperative role in the zone of harvesting energy from the renewable source, and it appears to be a promising candidate for the triumph because of its low cost and ease of preparation. The use of synthetic dyes as a sensitizer for DSSC provides better efficiency and high durability. Unfortunately, they suffer from several margins such as higher cost and usage of toxic materials. These downsides have opened up for alternative sensitizer such as biocompatible natural dyes. Natural dyes contain plant pigments such as carotenoid, flavonoid, betalains, and chlorophyll that act as sensitizers (dye) for DSSC. But, the efficiency of natural dyes is not up to the mark mainly due to photoinstability of natural dye in the presence of sunlight that leads to photodegradation. The stability issues are mainly due to interaction of natural dyes with photoelectrode. The photoelectrodes in DSSC are semiconductor materials with superior characteristic of photocatalytic activity (PCA). The PCA of titanium dioxide (TiO2) generates high energetic free electrons on the surface of film that produce free radical ions in contact with moisture. These free radical ions readily degrade the organic matter present nearby (natural dye in DSSC). Thus, the PCA of photoelectrode is responsible for the photodegradation of dyes causing photoinstability. The main objective of this review is to study the photoinstability of natural dyes in DSSC. In this regard, the DSSC is concentrated into sections, and the stability issues due to PCA of photoelectrode are studied individually in the view of considering the DSSC operating with iodide‐based electrolytes and platinum as counter electrode only. Various algae groups are featured as a study tool to overview the dye interaction with photoelectrode. It highlights the application of Z‐scheme of photosynthesis to DSSC to have a broader perception on the working of DSSC and also shows some of the ways for improving the stability of dyes by suppressing or reducing the PCA of photoelectrode. Copyright © 2017 John Wiley & Sons, Ltd.