Estimation of the Charge-Collection Efficiency of Dye-Sensitized Nanocrystalline TiO₂ Solar Cells

The dependence of the charge collection efficiency on the time constant for recombination τ_oc and for the combined process of recombination and charge collection τ_oc is calculated. The respective time constants can be obtained experimentally by intensity modulated photovoltage spectroscopy (IMVS) and intensity modulated photocurrent spectroscopy (IMPS) measurements. A new method is presented to determine τ_oc and τ_oc from the steady-state electron-concentration profiles in the TiO₂ film n(x) calculated for constant light intensity. The continuity equation is modified to account for charge trapping and detrapping and the nonlinearity of the recombination rate on n. A simple expression is derived for calculating the charge-collection efficiency from the measured values of τ_ocand the light intensity dependence of τ_oc.