Density of photoinduced free carriers in perovskite thin films via purely optical detection
The great strides of perovskite-based photovoltaic devices galvanize an increasing number of material studies. We revealed the photoinduced steady-state free carrier densities of perovskite films through a purely optical detection method. The method avoided the possible interference from strong ionic conductivity within perovskite materials. The densities were measured at the order of 1015 cm−3 and 1016 cm−3 for CH3NH3PbI3 films without and with chlorine introduction, respectively. Long free carrier lifetimes were figured out according to the densities. The densities were found to increase, as observed from the illumination, following a sublinear power law. This indicates sub-bandgap trapping states involved in the charge accumulation mechanism. In addition, the densities presented an abnormal temperature sensitivity revealing a thermally activated recombination channel above ∼240 K.