Laser-Sintered $\hbox {TiO}_{2}$ Films for Dye Solar Cell Fabrication: An Electrical, Morphological, and Electron Lifetime Investigation

We have carried out a systematic and combined I- V, electrochemical impedance spectroscopy (EIS), and scanning emission microscopy (SEM) investigation of dye solar cells (DSCs) fabricated with laser-sintered TiO₂ photoanodes as a function of laser-integrated fluence Φ. We show that the electron lifetime τ_oc in the TiO₂ film extracted from EIS spectra monotonically increases with laser sintering fluence both at constant illumination and, even more significantly, at constant photoinduced charge Q_oc. The increase in τ_oc between the poorly sintered and the best laser-sintered devices is an order of magnitude at constant illumination (equivalent to the increase in device efficiency) and even greater at constant Q_oc. A strong correlation between τ_oc and the cell electrical parameters is observed, although device efficiency peaks with Φ whereas τ_oc does not. The rise of τ_oc with Φ indicates improved electromechanical bonding between TiO₂ nanoparticles due to the improved sintering carried out by the raster scanning laser process, as also confirmed by SEM images. The strong correlation between device performance and τ_oc indicates that laser processing may also have significant potential in many other device applications that require high-surface-area TiO₂ coupled with good electronic transduction.