Abstract

This study comes up with a new architecture of multi-layered photoanode electrodes containing two thick layers (i.e., 6 µm) of nanocrystalline TiO₂ particles and two thin layers (i.e., 1 µm) of uniform TiO₂ aggregates, which are alternately deposited. The aggregates layers are deposited by a straightforward gel process, developed for the preparation of uniform and sponge-like light scattering layer for dye-sensitized solar cells (DSSCs) applications. The aggregates layers are composed of uniform spherical particles with average diameter of 2 µm, containing small nanoparticles with the average grain size of 20 nm. The nanocrystalline layers contain 20-nm-diameter TiO₂ nanoparticles. X-ray diffraction reveals that the nanocrystalline layers have a pure anatase phase, whereas the aggregates layers show a mixture of anatase and rutile phases. Diffuse reflectance spectroscopy demonstrates that the multi-layered electrode enjoys better light scattering ability than that of mono-layered electrode due to the incorporation of a thin light scattering layer into the nanocrystalline film. The multi-layered DSSC shows the highest power conversion efficiency of 7.69 % as a result of higher light harvesting and less recombination which is demonstrated by electrochemical impedance spectroscopy. From IPCE measurement, the external quantum efficiency of the multi-layered cell is equal 88 %, which is higher than that of mono-layered cell (i.e., 78 %).