Nanoparticle/dye interface optimization in dye-sensitized solar cells

Abstract

A critical component in the development of highly efficient dye-sensitized solar cells is the interface between the ruthenium bipyridyl complex dye and the surface of the mesoporous titanium dioxide film. In spite of many studies aimed at examining the detailed anchoring mechanism of the dye on the titania surface, there is as yet no commonly accepted understanding. Furthermore, it is generally believed that a single monolayer of strongly attached molecules is required in order to maximize the efficiency of electron injection into the semiconductor. In this study, the amount of adsorbed dye on the mesoporous film is maximised, which in turn increases the light absorption and decreases carrier recombination, resulting in improved device performance. A process that increases the surface concentration of the dye molecules adsorbed on the TiO2 surface by up to 20% is developed. This process is based on partial desorption of the dye after the initial adsorption, followed by readsorption. This desorption/adsorption cycling process can be repeated multiple times and yields a continual increase in dye uptake, up to a saturation limit. The effect on device performance is directly related and a 23% increase in power conversion efficiency is observed. Surface enhanced Raman spectroscopy, infrared spectroscopy, and electrochemical impedance analysis were used to elucidate the fundamental mechanisms behind this observation. The surface concentration of N719 dye molecules on mesoporous TiO2 films is increased by up to 20% using an adsorption/desorption cycling process. After the initial adsorption of dye, a partial desorption is accomplished by immersing the sample in water. Cycling this process results in a continual overall increase in dye uptake. Ultimately, a 23% increase in dye-sensitized solar cell performance is observed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.