Appl Phys A (2010) 100: 1169–1176
DOI 10.1007/s00339-010-5731-z
Growth of nanocrystalline TiO
2
films by pulsed-laser-induced
liquid-deposition method and preliminary applications
for dye-sensitized solar cells
Guo-Bing Wang · Min-Gong Fu · Bin Lu ·
Guo-Ping Du · Li Li · Xiao-Mei Qin · Wang-Zhou Shi
Received: 5 January 2010 / Accepted: 20 April 2010 / Published online: 19 May 2010
© Springer-Verlag 2010
Abstract A novel technique, the pulsed-laser-induced liq-
uid-deposition (PLLD) method, has been employed to grow
nanocrystalline TiO
2
films on fluorine-doped tin-oxide-
coated (FTO) glass substrates at room temperature. The
PLLD method was implemented by directing a pulsed laser
into a liquid precursor and depositing the photosynthesized
nanocrystalline TiO
2
on an FTO glass substrate immersed
in the liquid precursor. The as-grown nanocrystalline TiO
2
films were found to have a rutile crystal structure and con-
sist of a number of flower-like TiO
2
crystal units arrayed
together on the FTO glass substrate. Each of the flower-like
TiO
2
crystal units was composed of many nanostructured
TiO
2
whiskers, and their building blocks were found to be
bundles of TiO
2
nanorods with diameter of about 5 nm. The
growth of these TiO
2
nanorods is highly anisotropic, with
the preferential growth direction along [001]. As-grown
nanocrystalline TiO
2
films were annealed at 450°C in air for
30 min for the applications of dye-sensitized solar cells, and
the nanostructured characteristics with good porosity were
preserved after annealing. A preliminary dye-sensitized so-
lar cell was built based on the annealed nanocrystalline TiO
2
film. The results suggest that the PLLD method is a promis-
ing technique for growing nanocrystalline TiO
2
films for
photovoltaic applications.
G.-B. Wang · M.-G. Fu · G.-P. Du (
) · L. Li · X.-M. Qin ·
W.-Z. Shi
Key Laboratory of Optoelectronic Materials and Devices and
Department of Physics, Shanghai Normal University,
Shanghai 200234, China
e-mail: gpdu999@163.com
B. Lu
College of Life and Environment Sciences, Shanghai Normal
University, Shanghai 200234, China
1 Introduction
Dye-sensitized solar cells (DSSCs) have been attracting
considerable attention because of their relatively high con-
version efficiency, low production cost, and simple fabrica-
tion process [1, 2]. At present, DSSCs based on nanocrys-
talline TiO
2
films have achieved solar energy conversion ef-
ficiencies beyond 10%, which is comparable to or higher
than the current commercial thin film solar cells, such as
CdTe, and amorphous Si based solar cells [3–6]. A DSSC
typically consists of five primary constituents [2], which
are the transparent conducting oxide (TCO) electrode, the
nanocrystalline TiO
2
porous film (ZnO or other oxide semi-
conductors may also be used), the dye sensitizer anchored
on the nanocrystalline TiO
2
, the redox electrolyte, and the
counterelectrode coated with a thin layer of catalyst such as
platinum, carbon, or others [7].
Light is absorbed by the anchored dye on the surfaces
of TiO
2
. Due to the higher electron affinity of TiO
2
,the
charge separation takes place at the interfaces between the
dye and the TiO
2
as the photoinduced electrons are injected
from the dye into the conduction band (CB) of TiO
2
. Hence,
the performance of a DSSC is strongly dependent on the
surface-area-to-volume ratio afforded by the TiO
2
film. An
optimal performance of a DSSC is possible only when the
TiO
2
film has a huge surface-area-to-volume ratio, which,
in turn, is determined by the morphology of the TiO
2
film.
The morphology of the TiO
2
film influences dye adsorption,
interfacial electron transfer, and carrier transport [8]. As a
result, intensive research effort is being devoted to devel-
oping novel techniques for fabricating nanocrystalline TiO
2
porous films, which provide the optimal performances in
DSSCs [9, 10].
At present, nanocrystalline TiO
2
porous films have been
mainly produced via colloidal synthesis of TiO
2
nanoparti-
cles and subsequent placement of the TiO
2
colloidal slurry