Millisecond Spin Relaxation Times of Distinct Electron and Hole Subensembles in MA x FA 1− x PbI ₃ Perovskite Crystals

The unique combination of outstanding optical quality and attractive spin properties opens new avenues for optical spin control in hybrid organic‐inorganic perovskite semiconductors. Using the optically detected magnetic resonance technique, we study the spins of electrons and holes in mixed‐cation single crystals with and 0.8. Multiple distinct spin subensembles with absolute values of ‐factor spanning from 2.9 to 3.5 for electrons and from 0.5 to 1.6 for holes are resolved, revealing diverse localization environments. We measure the longitudinal spin relaxation times, , reaching 2 ms and remaining in the range even for weakly localized carriers at cryogenic temperatures. The magnetic‐field dependence of is dominated by the random nuclear (Overhauser) fields with strengths of mT for electrons and mT for holes. The corresponding correlation times of the hyperfine field are determined by carrier hopping between shallow localization sites. The temperature dependence of reveals a weak localization potential of the charge carriers and shows a correlation between and the inhomogeneity of the spin ensemble. These results establish mixed‐A‐site perovskite single crystals as a promising solid‐state platform with long‐lived spin states for quantum information applications.