Carrier and exciton dynamics in halide perovskites

Abstract

Ever since the first perovskite-based solar cell (PSC) was reported in 2009, reported power conversion efficiencies (PCEs) of PSCs showed a rapid increase from 3.8% to now 25.5%. The reasons for the high PCEs include the large absorption coefficients, high carrier mobilities, and long balanced electron–hole diffusion lengths. Free carriers dominate at low excitation densities, while excitons at high excitation densities. The latter condition is widely used in light-emitting diodes and lasers. To determine the photovoltaic performance of PSCs, charge carrier transport properties of the perovskites should be characterized. In transient absorption (TA) spectroscopy, free carriers and excitons both contribute to the transient signals, while time-resolved THz spectroscopy (TRTS) is sensitive to both carriers and phonon modes in lead halide perovskites. Hence, these ultrafast techniques are useful tools to characterize the charge transport properties of lead halide perovskites. My thesis includes studies that use TA to disentangle the time-resolved free carrier and exciton contributions in mixed-cation lead mixed-halide perovskites, and also use TRTS to disentangle carrier and phonon dynamics in all-inorganic perovskites. Knowing the physics behind these materials after photoexcitation could give useful information to device scientists and sample growers.