Progress in light harvesting and charge injection of dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on nanocrystalline semiconductors such as TiO2 are of great interest as an alternative to the conventional solar cells because of their high performance, low-cost production, and environmental advantages. The DSSCs consist of dye molecule coated wide bandgap semiconductor layer, electrolyte, and transparent conducting oxide (TCO) film. When the DSSCs are exposed to solar light, an incident photon creates a bound electron–hole pair in dye sensitizers. Electrons then flow into the oxide nanoparticle anode due to a difference in the energy levels. On the other hand, holes move to the counter electrode through sequential redox reactions in the electrolyte. Therefore, the cell performance is influenced by parameters such as the morphology and optical properties of nanocrystalline oxide films, the electrochemical characteristics of redox electrolytes, and the photochemical properties of molecular sensitizers. In this article, we review the major components of DSSCs such as the oxide semiconductor film, sensitizing dyes, electrolytes, and TCO and discuss their progress to maximize light harvesting and charge injection efficacy. Their electrical, optical, and chemical properties are well correlated to optimize the light harvesting and charge injection of DSSCs. We have also shown recent efforts to improve the energy conversion efficiency, long term stability, sustainability and affordability by modifying or revolutionizing the components of DSSCs. This includes a prospect on the potential commercialization of DSSCs.