Laser-Sintered TiO2 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 Phi. We show that the electron lifetime tau(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 tau(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 tau(oc) and the cell electrical parameters is observed, although device efficiency peaks with Phi whereas tau(oc) does not. The rise of tau(oc) with Phi 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 tau(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.