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
$\hbox{TiO}_{2}$
photoanodes as a function of laser-integrated fluence
$\Phi$
. We show that the electron lifetime
$\tau_{\rm oc}$
in the
$ \hbox{TiO}_{2}$
film extracted from EIS spectra monotonically increases with laser sintering fluence both at constant illumination and, even more significantly, at constant photoinduced charge
$Q_{\rm oc}$
. The increase in
$\tau_{\rm oc}$
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
$Q_{\rm oc}$
. A strong correlation between
$\tau_{\rm oc}$
and the cell electrical parameters is observed, although device efficiency peaks with
$\Phi$
whereas
$\tau_{\rm oc}$
does not. The rise of
$\tau_{\rm oc}$
with
$\Phi$
indicates improved electromechanical bonding between
$ \hbox{TiO}_{2}$
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
$\tau_{\rm oc}$
indicates that laser processing may also have significant potential in many other device applications that require high-surface-area
$\hbox{TiO}_{2}$
coupled with good electronic transduction.