Density of photoinduced free carriers in perovskite thin films via purely optical detection

Abstract

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.