A review of photoanode materials, challenges, and outlook of dye-sensitized solar cells

Renewable energy, especially solar energy is extremely demandable to mitigate the current global issues (e.g., climate change) owing to less carbon dioxide-intensive, stable, continually accessible in nature etc. Therefore, third generation solar cells such as Dye-sensitized solar cells (DSSCs) have attracted global attention to the researchers in the field of energy than others because of their promising properties; low-cost, easy fabrication, use of non-toxic materials, environmentally friendly etc. The photoanode is one of the most crucial components of DSSCs and plays an essential role to improve the overall efficiency of the device. This review summarized the present state of the art in DSSCs and also included the new information about emerging the most prominent metal oxides, their morphology-based photoanodes and surface passivating organic materials. Firstly, we begin by discussing the fundamentals of energy, solar cells, and their generations. Then, the mostly used metal oxides as photoanode, such as TiO₂, ZnO, SnO₂, Nb₂O₅, WO₃, SrTiO₃, and Zn₂SnO₄ has been reviewed deeply with merits and demerits. These metal oxides-based nanostructures including zero dimensions (0D), one-dimensions (1D), two-dimensions (2D), three-dimensions (3D) are studied with the reason of highest efficiency. Thirdly, surface passivation with organic passivating compounds is discussed with proper statements to resolve the charge recombination, which is one of the main drawbacks for increasing the efficiency of the device. Finally, the main challenges of DSSCs for the commercialization, particular low efficiency, charge recombination, absorption ability, long-term stability, and fabrication cost are studied and the strategies for the overcome from these challenges are investigated.