  The surface states of the active TiO2 layer is crucial while fabricating an
efficient solar cell. This work experimentally analyses the effect of exposing
TiO2 based electron transport layer (ETL) to the ultraviolet-ozone (UV-O3) and
optimizes the exposure time for improving power conversion efficiency (PCE) of
fabricated dye-sensitized solar cells (DSSCs). These results demonstrate that
the performance of DSSCs can be improved significantly by UV-O3 exposure of
sintered TiO2 photoanode surface, with the duration of exposure being a
critical parameter. Fabricated devices show 33.01 % increase in PCE for the
optimum exposure. Nevertheless, overexposure of the sample beyond the optimum
time decreases the efficiency of the fabricated solar cells. The device with
optimum exposure exhibits the highest PCE of 8.34% with short circuit current
density (Jsc) of 15.15 mA/cm2, open circuit voltage (Voc) of 756 mV and Fill
factor (FF) of 71.10%. This increase in efficiency is attributed to the
enhanced crystallization and reduction in the organic contaminants C-C/C-H from
57.90 to 52.40% as shown by the X-ray diffraction (XRD) and X-ray photoelectron
spectroscopy (XPS), respectively. The XPS result further indicates an increase
in oxygen vacancy from 12.40 to 23.40% for O 1s state and from 9.30 to 14.30%
for Ti 2p state of Ti3+. Results from the Atomic Force Microscope (AFM) also
confirms the minimized surface roughness of 16.36 nm for the optimally exposed
TiO2 film, and increase in hydrophilicity leading to improved efficiency of the
solar cells which were optimally exposed to UV-O3.
