Effect of TiO2 microbead pore size on the performance of DSSCs with a cobalt based electrolyte

Abstract

Mesoporous TiO₂ microbeads with well-defined intra-bead pore sizes (14 nm, 23 nm or 33 nm) were employed to investigate the effect of pore size on the performance of dye-sensitized solar cells constructed with an organic dye (MK2) and a [Co(bpy)₃]^2+/3+ (bpy = 2,2′-bipyridine)-based electrolyte. The TiCl₄ post treatment and film thickness were optimized for the TiO₂ electrodes made from beads with 33 nm intra-bead pores, and an overall energy conversion efficiency of 8.5% was achieved for a device with a 6.5 μm thick TiO₂ film treated with a 20 mM TiCl₄ solution. Although beads with larger pores had a smaller specific surface area, devices derived from these beads produced better photovoltaic performance. This is attributed to the improved diffusion of cobalt species inside the working electrode, as evidenced by a higher electron lifetime and dye regeneration rate recorded on these solar cells.