Polaron and Spin Dynamics in Organic–Inorganic Lead Halide Perovskite Nanocrystals

Abstract Long‐lived carrier population and spin‐based behavior in lead halide perovskite nanocrystals (NCs) are extremely interesting for implementing photovoltaic devices with efficiencies exceeding the Shockley–Queisser limit and quantum information processing, respectively. However, a comprehensive understanding of polaron‐mediated charge carrier interactions and an accurate description of the spin‐polarized states for spintronics are still lacking. Herein, the carrier and spin interactions are studied under controlled conditions in FAPbI₃ and Cs_0.01FA_0.99Pb(Br_0.11I_0.89)₃ NCs through ultrafast transient absorption (TA) spectroscopy. At early timescales, TA spectrum shows an asymmetric derivative feature originating from the hot carrier‐induced spectral redshift in FAPbI₃ NCs (55 ± 3 meV) and Cs_0.01FA_0.99Pb(Br_0.11I_0.89)₃ NCs (54 ± 2 meV) at the bandedges that stabilizes to 9 ± 1 and 11 ± 2 meV, respectively, at 1 ps due to the polaron formation. The kinetic analysis indicates that the polaron populations in FAPbI₃ and Cs_0.01FA_0.99Pb(Br_0.11I_0.89)₃ NCs decay with an average lifetime of 657 ± 34 and 532 ± 28 ps, respectively. The circular polarization‐resolved TA reveals that polaron formation can control spin relaxation in NCs, thus providing a powerful tool to explore the development of their prospective applications in spintronics.