Free standing TiO2 nanotube array electrodes with an ultra-thin Al2O3 barrier layer and TiCl4 surface modification for highly efficient dye sensitized solar cells

Abstract

Dye sensitized solar cells were fabricated with free standing TiO₂ nanotube (TNT) array films, which were prepared by template assisted atomic layer deposition (ALD) with precise wall thickness control. Efforts to improve the photovoltaic performance were made by using Al₂O₃ barrier layer coating in conjunction with TiCl₄ surface modification. An Al₂O₃ thin layer was deposited on the TNT electrode by ALD to serve as the charge recombination barrier, but it suffers from the drawback of decreasing the photoelectron injection from dye into TiO₂ when the barrier layer became too thick. With the TiCl₄ treatment in combination with optimal thickness coating, this problem could be avoided. The co-surface treated electrode presents superior surface property with low recombination rate and good electron transport property. A high conversion efficiency of 8.62% is obtained, which is about 1.8 times that of the device without surface modifications.