Chapter 8 - Potential of nanooxidic materials and structures of photoanodes for DSSCs

Abstract

A dye-sensitized solar cell (DSSC) is a piece of optoelectronic equipment that uses semiconductor materials and works on the principles of electrochemistry. The semiconductor in the photoanode of the DSSC is covered by dye molecules that function as a matrix for the solar and artificial absorption of electromagnetic radiation, particularly in the visible region. The problem with DSSCs is their lower efficiency compared to conventional solar cells due to the electron transfer barrier caused by the grain boundary in the semiconductor. Numerous semiconductor materials have been investigated for use as photoanodes in DSSCs, such as nanooxidic photoanode materials (TiO2, ZnO, SnO2). These oxide materials must have a fast charge mobility rate to minimize losses of photogenerated charges, and high porosity with large surface area can result in more dye molecules being adsorbed on the metal oxides. Generally, nanoparticles of TiO2 are utilized in the photoanode of DSSCs because of the very high specific surface areas. However, the light-scattering ability of TiO2 nanoparticles is weak and this limits the efficiency of the dye molecules to harvest light. Furthermore, grain boundary trapping sites prevent fast electron transport and this can lead to electron recombination in the electrolyte. Therefore optimization of functional properties such as the shape and structure modulation of the photoanode materials is needed to improve DSSC performance. A lot of work has been done to overcome the drawbacks of TiO2 nanoparticles. These include the synthesis of one-dimensional (1D) nanostructures such as fibers and rods. Compared with nanoparticle films, 1D nanostructures can help to increase charge carrier collection through direct carrier transport pathways to the external circuit. 1D nanostructured material has a lower recombination rate so that load transport takes place faster and results in better DSSC performance.