Trends in Metal Oxides Based Counter Electrode in Dye-Sensitized Solar Cells

Abstract

Solar cells are the prominent alternative energy resources in present era to replace the fossil-fuel-based energy resources. Solar cells using photovoltaic (PV) effect convert solar energy into electrical energy. The architecture of DSSCs (dye-sensitized solar cells) consists of several components, such as photoanode, electrolyte, and counter electrode (CE). The photoexcited electron from the dye reaches the external circuit through the photoanode and then the counter electrode collects the electron from an external circuit to catalyze the redox reduction in the electrolyte by reducing the overpotential. Therefore, counter electrodes play a significant role in boosting the performance of devices. So far, in counter electrodes, platinum (Pt) noble rare earth metal was used as the standard material because of its good catalytic property and long-term stability. However, it still 22lacks in transferring the technology because platinum is expensive. Hence, the researchers point out a different kind of materials possessing less expensive, easily available, long-term stability, and good catalyzing properties to replace the platinum metal. In this concern, metal oxides are found to be one of the best alternative materials to replace the conventional Pt counter electrode because of their cost-effectiveness and availability. Metal oxides have been easily synthesized using different approaches, thereby their structure, bandgap, and morphology can be tuned. For example, one-dimensional (1D) WO2 and CuO nanorods hold an excellent catalytic activity close to the conventional Pt. Similarly, ZnO nanowire array composites exhibit higher efficiency than Pt. In addition to all the above, metal oxides help to facilitate electron transport to the electrolyte for improving the reduction process of triiodide ions by means of creating oxygen vacancy. So, in this chapter, preparation of different metal oxides, tuning the bandgap, morphological aspects, the role of defects, catalytic property, and the role of counter electrodes in DSSCs are briefly discussed.