Efficiency enhancement for ZnO tetrapod dye-sensitized solar cells by TiO2 coating and ammonium treatment

Dye sensitized solar cells (DSSCs) have aroused much interest in recent years. However, the efficiency still needs improvement. In order to enhance the performance of the cells it is important to increase the active surface area for dye adsorption so as to increase the light absorbance. In this work, zinc oxide (ZnO) tetrapods, which have four legs extending from a common core, were used to fabricate the photoanode due to its large surface area. Also, it is important to reduce the recombination rate and increase the carrier transport rate so that a higher efficiency can be achieved. Therefore, the effect on the performance of cells after coating a titanium oxide (TiO2) film and ammonium treatment on the ZnO nanostructures were investigated, too. The former helped suppress the recombination rate while the latter helped improve the carrier concentration and charge transport. Moreover, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy were performed on the as-grown and ammonia annealed samples. Under optimal conditions, AM 1.5 power conversion efficiency of 1.02% was achieved.