Organic-inorganic perovskites have opened a new ﬁeld in optoelectronics. Despite rapid progress in materials and device engineering, fundamental questions remain open concerning the underlying photophysics and transport. Several microscopic mechanisms have been proposed as sources of the extraordinarily long carrier lifetimes in the materials, including electron-hole separation in ferroelectric domains, suppression of electron-phonon scattering, large polaron formation, and lifetime enhancement by spin-polarization of electronic states. I will present results of photoemission experiments focusing on the latter effects. Static experiments ﬁnd a signiﬁcant Rashba splitting in (CH3NH3)PbBr3 single crystals, strong enough to put constraints on optical transitions. Additional, time-resolved experiments on (CH3NH3)PbI3 thin ﬁlms demonstrate ultrafast, sub-ps dynamics of the photoexcitation, followed by ≈ 100 ps of slow energetic relaxation of photoexcited electrons. The latter is consistent with suppression of electron-phonon coupling in the optically excited state.
Daniel Niesner received his doctoral degree in physics from the Friedrich-Alexander-University Erlangen-N¨urnberg, Germany in 2013 for his work on electron dynamics in gra-phene and topological insulators. As a postdoctoral fellow at the Department of Chemistry at Columbia University from 2013 to 2015 he started to focus on ultrafast dynamics in organic-inorganic perovskite compounds. He currently continues the research at University Erlangen-N¨urnberg, where he is a member of the Emerging Field Initiative ”Singlet Fission”.