Counter electrodes for DSCs
Counter electrode (CE) is the layer to reduce the redox species oxidized at the working electrode. 
Normally, platinum (Pt) is used for this layer due to its high catalytic property. A thin layer of Pt nanoparticles is deposited on FTO by thermal decomposition, sputtering or electrochemical deposition.
Its charge transfer resistance, which is strongly related to fill factor in the solar cells, is characterized by Impedance spectroscopy.
By improving the catalytic property and
by increasing the surface area, the charge
transfer resistance at counter electrode can
be reduced. Preparation conditions and new
materials are investigated to improve the fill
factor for DSCs.