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 tau(oc) and for the combined process of recombination and ch arge collection tau(sc) 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 tau(oc) and tau(sc) from the stead y-state electron-concentration profiles in the TiO2 film n(x) calculated fo r constant light intensity. The continuity equation is modified to account for charge trapping and detrapping and the nonlinearity of the recombinatio n rate on n. A simple expression is derived for calculating the charge-coll ection efficiency from the measured values of tau(oc)/tau(sc) and the light intensity dependence of tau(oc).