Past Events

Abstract:

In recent years, the shortage of oil supplies, fossil fuels, air pollution and global warming, aroused our awareness of the urgency of finding alternative renewable energy sources. Undoubtedly, the most suitable candidate energy source is solar energy. Due to its usefulness, many of attempts have been made by scientists to invent efficient solar cells, which can generate electricity in a clean way. The most efficient solar cells invented up to now are multilayer thin film solar cells. However, they have high fabrication cost, difficulties fabricating a large device area, complicated fabrication processes, and result in pollutant generation during fabrication of semiconductors. Thus, many researchers are now finding alternative methods to fabricate low-cost solar cells with reasonable high power conversion efficiency. Dye sensitized solar cells (DSSC), which were invented by B.O’Regan and M. Gratzel, seem to be a desirable choice.

A typical DSSC consists of a semiconductor oxide layer, dye, electrolyte and electrodes. The semiconductor layer plays an important role in the performance of the solar cell, and its surface chemistry and electronic properties determine the quantities of dye adsorption, electron injection and carrier transport. The nanosized TiO₂ porous semiconductor layer could achieve a ~11 % light-to-electricity conversion efficiency in spite of the poor electron transport within interpenetrated random network and intrinsic defects at the boundaries of sintered TiO₂ nanoparticles’ porous structure. Therefore, in recent years, considerable research has been devoted to the replacement of the porous structure with a 1D crystalline semiconductor layer or other morphologies that have good electron transport and with a high surface area for dye coverage. Further improvements of DSSCs can be achieved by optimizing the semiconductor layer morphology with more dye coverage, better electron injection and carrier transport in DSSCs. Therefore, in my research, I have investigated the effects of the TiO₂ nanotubes and nanowires produced by the anodization and assisted oxidation growth methods on DSSCs. I have also studied the effect of the annealing condition, i.e., different annealing temperatures and annealing atmospheres, in order to investigate their influence on DSSC’s performance.

From the results of the study, it can be concluded that anatase TiO₂ results in better photovoltaic performance compared to rutile. Also, while 1D nanostructures typically exhibit efficient electron transport. To further improve the efficiency, it is necessary to increase the surface area and the dye adsorption. This can be achieved using mixed morphology. The best efficiency in this work was achieved for TiO₂ nanotubes filled with porous TiO₂ network subjected to a TiCl₄ treatment.