Spin Coherence and Relaxation Dynamics of Localized Electrons and Holes in FAPbI3 Films

We obtained highly stable polycrystalline thin films of FAPbI3 prepared under air ambient conditions. In these materials, the presence of Pb–O bonds prevents the propagation of α- to δ-FAPbI3 phase conversion and allowed addressing the study of the spin coherence and spin relaxation dynamics of the photogenerated carriers. We studied, at 2 K, the coherent evolution of electronic spins in FAPbI3 films by measuring the photoinduced Faraday rotation (PFR) under a transverse magnetic field. We identified two contributions to the measured signal that we associated with localized electrons and holes. The study of the Larmor spin precession as a function of magnetic field leads to Landé factors |ge| = 3.447 ± 0.006 for electrons and |gh| = 1.134 ± 0.003 for holes. We measured long spin coherence times of localized electrons (holes) of 3.3 ns (2.4 ns). PFR measurements in a longitudinal magnetic field yielded a carrier spin relaxation time of 17 ns at 32 mT. Finally, we were interested in experimentally estimating the value of the Kane energy, which is the key parameter to determine the band structure and the optical properties of halide perovskites, as well as the interaction of these materials with a magnetic field. From the experimentally determined hole g-factors and low-temperature absorption spectrum, we obtain the Kane energy parameter of FAPbI3, EP = 13.1 eV, a value slightly smaller than the calculated one ẼP = 14.7 eV. We, thus, experimentally establish a bridge between the optical and spin properties of halide perovskites.