  Cu doped transparent ZnO thin films were spin coated on conductive glass
substrates. The samples were subsequently annealed in air for 1 hour at 500 0C
in order to form the phase of ZnO. ZnO samples were doped with different Cu
molar percentages up to 5%. The impedance and photovoltaic properties of sample
were measured. Photocurrent and photovoltage of doped and undoped samples were
measured in KI/I2 electrolyte. Adding a trace amount of Cu improved the
conducting properties of ZnO samples without changing other basic properties of
ZnO. The photocurrent gradually increases with the doping concentration due to
the high conducting properties of Cu. Investigation was carried out only up to
the doping concentration of 5%, because higher doping concentrations may
significantly influence the other properties of ZnO such as transparence of the
film. Impedance of samples was determined by fitting the data to an equivalent
circuit. The impedance reaches the maximum value at Cu concentrations of 3%.
