DYNAMIC-RESPONSE OF DYE-SENSITIZED NANOCRYSTALLINE SOLAR-CELLS - CHARACTERIZATION BY INTENSITY-MODULATED PHOTOCURRENT SPECTROSCOPY

The frequency-dependent photocurrent response of dye-sensitized TiO2 c ells to modulated illumination is analyzed. Analytical expressions are derived that describe generation, collection, and recombination of el ectrons in a thin layer nanocrystalline solar cell under conditions of steady illumination and with a superimposed small amplitude modulatio n. The analysis considers illumination from the contact side and from the counter electrode side, and characteristic differences in the inte nsity-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 intensit y modulated photocurrent spectroscopy (IMPS) can provide new insight i nto the dynamics of electron transport and collection in the dye-sensi tized solar cell. Experimental IMPS data measured for high-efficiency dye-sensitized cells are fitted to the theoretical model using Bode pl ots in order to derive values of the lifetime (2 x 10(-2) s) and diffu sion coefficient (5 x 10(-5) cm(2) s(-1)) of photoinjected electrons.