Charge Transport in Dye-Sensitized Solar Cells Based on Flame-made TiO2 Nanoparticles

The fundamental understanding on charge-transport properties of flame-synthesized TiO2 in dye-sensitized solar cells (DSSCs) is established in this work. By employing a one-step flame spray pyrolysis (FSP), predominantly anatase TiO2 nanoparticles with average nanoparticle sizes between 11 and 36 nm were achieved by varying the rate of combustion enthalpy (through varying liquid precursor feed flow rates) and using either an "open-flame" or "enclosed-flame" configuration. Electron diffusion coefficient (D), electron lifetime (tau), open circuit voltage (V-oc), and capacitance (C) measurements carried out on FSP TiO2-based DSSCs demonstrated that interband charge trap density decreased with increase in particle size. Compared to earlier studies, interband charge trap density could be controlled more independently of particle size. Under one-sun conditions, relatively high V-oc was measured with large particle size due to the lowering of interband charge trap density. This was true despite the associated shorter tau. Comparisons with commercial benchmark Nanoxide-T and Degussa P25 TiO2 were also carried out. The results from the current study have significant implications on the design of TiO2 nanoparticles by flame aerosol techniques, for DSSCs as well as other photoelectrochemical applications.