Sandwich-like design of TiO2 electrodes containing multiple light scattering layers for dye-sensitized solar cells applications

Abstract

This study comes up with a new architecture of multi-layered photoanode electrodes containing three thick layers (i.e., 4μm) of nanocrystalline TiO2 particles and three thin layers (i.e., 1μm) 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 (DSCs) applications. The aggregates layers are composed of uniform spherical particles with average diameter of 2μm, containing small nanoparticles with the average grain size of 20nm. The nanocrystalline layers contain 20-nm-diameter TiO2 nanoparticles. X-ray diffraction (XRD) 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 (DRS) 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 DSC shows the highest power conversion efficiency of 7.85% as a result of higher light harvesting and less recombination which is demonstrated by electrochemical impedance spectroscopy (EIS). From IPCE measurement, the external quantum efficiency of the multi-layered cell at 530nm is equal to 89%, which is higher than that of mono-layered cell (i.e., 78%).