Highly efficient dye-sensitized solar cells by TiCl4 surface modification of ZnO nano-flower thin film

Abstract

In dye-sensitized solar cells (DSSCs), the semiconductor photo-anode film plays a significant role in enhancing the overall power conversion efficiency. ZnO is considered as the futuristic hope for photoanodes in DSSCs due to manifold properties over TiO2. However, the power conversion efficiency of ZnO-based DSSCs is still low due to its poor chemical stability and surface defects. In this work, we reported the synthesis of ZnO nano-flowers as well as its surface modification of with TiCl4 at different concentration. In DSSCs, the enhancement in power conversion efficiency results suggested that surface modification of ZnO film by TiCl4 leads to the deposition of TiO2 which subsequently increases the roughness factor of film as well as scattering layer. This preferential surface modification of ZnO film facilitates the accumulation of large number of photo-injected electrons in the HOMO of the photoanode with rapid transfer of charge carriers to FTO via ZnO layer by lowering the recombination of photo-injected electrons with the redox electrolyte as well as oxidized dye. The intensity-modulated photocurrent spectroscopy (IMVS) and intensity-modulated photovoltage spectroscopy (IMPS) study also indicated that the recombination rate decreased considerably during the electron transportation. The ZnO film surface modified by TiCl4 achieved a power conversion efficiency of 4.48%, which is two times higher than that of the non-modified ZnO photoanode.