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SUMMARYDye-sensitized solar cells (DSSCs) have become a topic of significant research in the last two decades because of their scientific importance in the area of energy conversion. Currently, DSSC is using inorganic ruthenium (Ru)-based, metal-free organic dyes, quantum-dot sensitizer, perovskite-based sensitizer, and natural dyes as sensitizer. The use of metal-free, quantum-dot sensitizer, perovskite-based sensitizer, and natural dyes has become a viable alternative to expensive and rare Ru-based dyes because of low cost, ease of preparation, easy attainability, and environmental friendliness. Most of the alternatives to Ru-based dyes have so far proved inferior to the Ru-based dyes because of their narrow absorption bands (Δλ ≈ 100-250 nm), adverse dye aggregation, and instability. This review highlights the recent research on sensitizers for DSSC, including ruthenium complexes, metal-free organic dyes, quantum-dot sensitizer, perovskite-based sensitizer, mordant dyes, and natural dyes. It also details and tabulates all types of sensitizer with their corresponding efficiencies. Plot of progress in efficiency (η) of DSSC till date based on different types of sensitizers is also presented.

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Summary 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.

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Summary Natural dye‐sensitized solar cells (DSSCs) are becoming promising candidates for replacing synthetic dyes. Anthocyanins, a flavonoid pigment which is responsible for the coloration in fruits and flowers, have shown productive results in employing them as natural dye for DSSC. But unfortunately, they exhibit low efficiency compared with synthetic dyes. Probing the reasons for the low efficiency of anthocyanin paves way for finding solution to increase the efficiency. This paper lists the important factors that are responsible for anthocyanin instability in DSSC. As a remedial measure, this paper introduces two buffer layer made of algal byproducts—sodium alginate and Spirulina. Rutile phase TiO2 nanorods prepared by hydrothermal method were used as photoelectrode and are subsequently characterized by X ray diffraction, transmission electron microscopy, and optical studies. The use of sodium alginate above the photoelectrode has proved to improve the dye concentration in the film by introducing more hydroxyl groups on the surface of TiO2. Anthocyanins extracted from rose petals using citric acid as solvent were used as dye for DSSC. Prior to the sensitization process with anthocyanin dye, the TiO2 film (with sodium alginate) was sensitized with Spirulina. The chlorophylls, xanthophylls, phycocyanins, and amino acids present in Spirulina assist the anthocyanins to bond with TiO2 efficiently. This helps in enhancing the efficiency of anthocyanins of rose dye from 0.99% to 1.47%.

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