Interrelationship between TiO2 nanoparticle size and kind/size of dyes in the mechanism and conversion efficiency of dye sensitized solar cells

Abstract

In order to provide a comprehensive investigation of TiO₂ nanoparticle size in relation with different dye types in DSSCs, three sizes of TiO₂ nanoparticles and two different dye types including a porphyrin dye (T2) and a ruthenium dye (N3) were synthesized. Steady state current–voltage (J–V) characteristics were investigated for the fabricated DSSCs and the results demonstrated that the optimum TiO₂ nanoparticle size changed with the dye type. The obtained J–V data were interpreted by cyclic voltammetry, UV-visible absorption spectroscopy, BET measurement, DFT calculation, IPCE measurement and impedance spectroscopy. The results for the N3 dye show that the surface area of the TiO₂ nanoparticles is a key factor for the N3 cells, which is restricted by TiO₂ pore diameter and surface state traps. In contrast, the density of localized states of the TiO₂ film under the LUMO state of the porphyrin dyes is the dominating factor for the performance of the solar cells, which is restricted by the surface area of the TiO₂ nanoparticles. These obtained results represent a significant advance in the development of porphyrin, ruthenium and even solid electrolyte DSSCs.