Photoinduced Large Polaron Transport and Dynamics in Organic-inorganic Hybrid Lead Halide Perovskite with Terahertz Probes

Organic-inorganic hybrid metal halide perovskites (MHPs) have attracted tremendous attention for optoelectronic applications. The long photocarrier lifetime and moderate carrier mobility have been proposed as results of the large polaron formation in MHPs. However, it is challenging to measure the effective mass and carrier scattering parameters of the photogenerated large polarons in the ultrafast carrier recombination dynamics. Here, we show, in a one-step spectroscopic method, that the optical-pump and terahertz-electromagnetic probe (OPTP) technique allows us to access the nature of interplay of photoexcited unbound charge carriers and optical phonons in polycrystalline CHNHPbI (MAPbI) of about 10 μm grain size. Firstly, we demonstrate a direct spectral evidence of the large polarons in polycrystalline MAPbI. Using the Drude-Smith-Lorentz model along with the Frӧhlich-type electron-phonon (e-ph) coupling, we determine the effective mass and scattering parameters of photogenerated polaronic carriers. We discover that the resulting moderate polaronic carrier mobility is mainly influenced by the enhanced carrier scattering, rather than the polaron mass enhancement. While, the formation of large polarons in MAPbI polycrystalline grains results in a long charge carrier lifetime at room temperature. Our results provide crucial information about the photo-physics of MAPbI and are indispensable for optoelectronic device development with better performance.