Proceedings of nanoGe September Meeting 2015 (NFM15)
Publication date: 8th June 2015
Understanding the nature of the photoconductivity in methylammomnium lead halide perovskites is mandatory in order to further promote the development of low cost-solution processed solar converters. Here, we use THz spectroscopy to unravel the nature of pump induced photoconductivity in chlorine based methylammonium lead iodide perovskite films as a function of temperature in the range between 300K-150K (tetragonal phase) and 150K-77K (orthorhombic phase). Room temperature ultra-broad band frequency resolved complex photoconductivity measurements (in the range 0-12THz) reveal that: (i) free charge carriers (no excitons) are the main photoproduct after light excitation and (ii) that free carriers do not experience any confinement (e.g. due to backscattering at grain boundaries). Applying the Drude model, the temperature dependent measurements in the 0-2THz range reveal scattering times increasing from ~4 fs at 300 K (tetragonal phase; mobility of ~27 cm2 V-1 s-1) to almost ~25 fs at 77 K (orthorhombic phase, mobility of ~150 cm2 V-1 s-1). The inferred scattering rates show a temperature dependence of ~T-3/2 in the tetragonal phase. These indicate that phonon-electron (rather than impurity) scattering is the main physical mechanism limiting charge mobility in these materials.