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