Application of natural dyes in dye-sensitized solar cells

Abstract The booming demand for energy catastrophes is a huge challenge for the growth of economy and to address global climate change. These energy crises have been drastically increased during the last decades, and there is a dire need of renewable, cheaper, and eco-friendly sources of energy. The history revealed that for hundreds of years, humans have retrieved energy from natural sources. Amid different sources of energy, solar energy is the most feasible source of energy in terms of efficiency, low fabrication cost, and environmental friendliness. Natural dye-sensitized solar cells (NDSSC) are one of the promising sources for the conversion of solar photons to electrical charge. DSSC is categorized as a third generation energy production method. The most frequently used natural dyes are flavonoid pigments, chlorophyll, anthocyanin, carotenoid, and betalains, which are mostly extracted from different parts of plants. NDSSC energy conversion performance mainly depends on the characteristics of these pigments (mostly affected by extraction parameters), thickness of photo electrode, and annealing temperature. The natural dyes act as a sensitizer in these solar cells, by absorbing photons from sunlight and resulting in the excision of electrons. These energetic electrons are accepted by semiconductors (such as ZnO, TiO2, and Nb2O5), which result in the flow of electrons. With the increase in thickness of the surface, more natural dye is generally absorbed. This will result in more rushing of excised electrons. In this chapter, we cover different natural dyes and their applications in DSSC. In addition, we discuss how these natural dyes act as a sensitizer for solar cells by absorbing photons of sun light and convert them into electrical energy.