Continuous electron transport pathways constructed in TiO2 sub-microsphere films for high-performance dye-sensitized solar cells

Abstract

TiO₂ sub-microspheres applied as photoanodes in dye-sensitized solar cells (DSSCs) have been reported to have dual functions with high specific surface areas and light scattering capabilities. Large voids are left in the sub-microsphere film and lead to the poor connectivity between the neighboring sub-microspheres, which will limit the enhancement of the short-circuit current density (J_sc) and the power conversion efficiency (η). Herein, we develop a closely linked network by introducing TiO₂ nanocrystallines into the voids to construct a continuous electron transport pathway. It is found that pore sizes, porosity, and specific surface area could be effectively tuned by simply adjusting the content of TiO₂ nanocrystallines. As confirmed by the intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) and electrochemical impedance spectra (EIS), when the content of TiO₂ nanocrystallines in the sub-microspheres is 10 wt% (NP10), the electron transport time, electron collection efficiency, and electron diffusion length are optimized compared with the other contents. As a result, the η of the optimized NP10 photoanode based DSSC is up to 11.22%, which is higher than the 10.58% efficiency demonstrated by the pure sub-microsphere photoanode based cell.