  The use of graphene-based electrodes is burgeoning in a wide range of
applications, including solar cells, light emitting diodes, touch screens,
field-effect transistors, photodetectors, sensors and energy storage systems.
The success of such electrodes strongly depends on the implementation of
effective production and processing methods for graphene. In this work, we take
advantage of two different graphene production methods to design an advanced,
conductive oxide- and platinum-free, graphene-based counter electrode for
dye-sensitized solar cells (DSSCs). In particular, we exploit the combination
of a graphene film, produced by chemical vapor deposition (CVD) (CVD-graphene),
with few-layer graphene (FLG) flakes, produced by liquid phase exfoliation. The
CVD-graphene is used as charge collector, while the FLG flakes, deposited atop
by spray coating, act as catalyst for the reduction of the electrolyte redox
couple (i.e., I3-/I-- and Co+2/+3). The as-produced counter electrodes are
tested in both I3-/I-- and Co+2/+3-based semitransparent DSSCs, showing power
conversion efficiencies of 2.1% and 5.09%, respectively, under 1 SUN
illumination. At 0.1 SUN, Co+2/+3-based DSSCs achieve a power conversion
efficiency as high as 6.87%. Our results demonstrate that the electrical,
optical, chemical and catalytic properties of graphene-based dual films,
designed by combining CVD-graphene and FLG flakes, are effective alternatives
to FTO/Pt counter electrodes for DSSCs for both outdoor and indoor
applications.
