Metal halide perovskites have emerged as highly promising materials for optoelectronics and spintronics over the past decade. However, a complete understanding of their fundamental physical characteristics, such as thermal bandgap evolution, spin relaxation mechanisms, and transport properties, remains elusive. This knowledge gap is currently hindering the development of advanced pervoskite-based devices.

In the first part of the talk, we systematically studied ultrafast spin coherence, spin relaxation and bandgap revolution with temperature in two hybrid organic-inorganic perovskites MA_0.3FA_0.7PbI₃ and MA_0.3FA_0.7Pb_0.5Sn_0.5I₃. We observed contrasting spin lifetimes between the two samples, suggesting that the spin relaxation is likely due to scattering with defects via the Elliot-Yafet mechanism at low temperatures and the spin decoherence suffers from g-factor inhomogeneity due to impurities and vacancies. By measuring carrier spin lifetimes at elevated temperatures, we specify possible roles of defects and phonons in the spin relaxation channels. Our temperature-dependent experiments revealed drastic changes in both electron and hole Landé g-factors. We propose that this effect is dominated by the enhancement of dynamic lattice distortions (lattice vibrations) with increasing temperature, resulting in strong modifications of not only the bandgap but also the interband transition matrix and the spin-orbit splitting gap. [1,2]

In the second part of the talk, we directly monitored exciton diffusive transport from low temperature to room temperature using high-purity CsPbBr₃ single crystals and contact-free transient grating spectroscopy. We then converted the diffusion into an effective exciton mobility (\mu) using the Einstein relation. As the temperature (T) increases, the mobility decreases rapidly below 100 K with a scaling \mu~T^-3.0, and then follows a more gradual \mu~T^-1.7 trend at higher temperatures. Our first-principles calculations perfectly reproduce this experimental trend and reveal that optical phonon scattering governs carrier mobility shifts over the entire temperature range, with a single longitudinal optical mode dominating room-temperature transport. [3]

Our findings unambiguously resolve previous theory-experiment discrepancies, providing benchmarks for the future design of optoelectronic and spintronic perovskite devices.