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We report the charge carrier recombination rate and spin coherence lifetimes in single crystals of two-dimensional (2D) Ruddlesden–Popper perovskites PEA2PbI4·(MAPbI3)n−1 (PEA, phenethylammonium; MA, methylammonium; n = 1, 2, 3, 4). Layer thickness-dependent charge carrier recombination rates are observed, with the fastest rates for n = 1 because of the large exciton binding energy, and the slowest rates are observed for n = 2. Room-temperature spin coherence times also show a nonmonotonic layer thickness dependence with an increasing spin coherence lifetime with increasing layer thickness from n = 1 to n = 4, followed by a decrease in lifetime from n = 4 to ∞. The longest coherence lifetime of ∼7 ps is observed in the n = 4 sample. Our results are consistent with two contributions: Rashba splitting increases the spin coherence lifetime going from the n = ∞ to the layered systems, while phonon scattering, which increases for smaller layers, decreases the spin coherence lifetime. The interplay between these two factors contributes to the layer thickness dependence.
Chen et al. (Tue,) studied this question.