The frequency-dependent photocurrent response of dye-sensitized
TiO2 cells to modulated illumination is
analyzed. Analytical expressions are derived that describe
generation, collection, and recombination of electrons
in a thin layer nanocrystalline solar cell under conditions of steady
illumination and with a superimposed
small amplitude modulation. The analysis considers illumination
from the contact side and from the counter
electrode side, and characteristic differences in the
intensity-modulated photocurrent response are predicted
for the two cases. The attenuation of the ac photocurrent by
the RC time constant of the cell is also
considered.
The theoretical analysis shows that intensity modulated
photocurrent spectroscopy (IMPS) can provide new
insight into the dynamics of electron transport and collection in the
dye-sensitized solar cell. Experimental
IMPS data measured for high-efficiency dye-sensitized cells are fitted
to the theoretical model using Bode
plots in order to derive values of the lifetime (2 ×
10-2 s) and diffusion coefficient (5 ×
10-5 cm2
s-1) of
photoinjected electrons.
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