Abstract

We present a new dandelion-like TiO2 spheres by a modified hydrothermal method for manufacture of dye-sensitized solar cells (DSSCs). This construct is composed of numerous nanowires for employment as the scattering layer of DSSCs. Such morphology is produced by nucleation-growth-assembly mechanism. The size of the dandelion-like spheres and their morphology can be tailored by controlling the processing parameters of the modified hydrothermal process. TiO2 nanoparticles with narrow size distribution are also synthesized by hydrothermal route for the active layer of DSSCs. The nanoparticles show pure anatase phase with average size of 40 nm, whereas the dandelion-like TiO2 spheres are pure rutile structure with average diameter in the range 5-9 mu m. A systematic study is performed in order to improve the photovoltaic performance of the DSSCs with different arrangement modes. First, the monolayer DSSCs with various thicknesses are prepared using pure nanoparticles. The highest power conversion efficiency (PCE) of 7.4% is obtained for the monolayer cell with thickness of 31 mu m. Second, the double layer DSSCs containing an under-layer and an over-layer are reported. The double layer DSSC made of nanoparticles as the under-layer (with thickness around 31 mu m) and mixtures of nanoparticles and dandelion-like spheres as the over-layer (as light scattering layer with thickness around 8 mu m) shows the highest PCE of 8.3%. The improvement of cell efficiency is explained by triple function mechanism including significant increase in light scattering, dye sensitization and photo-generated charge carriers. (C) 2015 Elsevier B.V. All rights reserved.