Intra- and Interlayer Excitonic Fine Structure of the Two-Dimensional Perovskite (PEA)2PbI4

Two-dimensional halide perovskites host strongly bound excitons whose fine structure governs polarization selection rules and radiative recombination, yet spectral features in phenethylammonium lead iodide ((PEA)2PbI4) remain controversially assigned. Here, polarization-resolved low-temperature photoluminescence (PL) combined with first-principles G0W0+BSE calculations probes the intralayer and interlayer excitonic fine structure of this Ruddlesden–Popper perovskite. The low-energy multiplet is consistent with the intralayer excitonic fine structure governed by electron–hole exchange, crystal symmetry, and layer inequivalence in the two-layer unit cell, without requiring Rashba effects or exciton–polaron mechanisms as its primary origin. The weak doublet about 40 meV higher is best accounted for by interlayer excitons based on its energetics, splitting, and real-space character. Distortion-induced mixing of interlayer excitons with bright intralayer excitons provides a plausible explanation for the observed interlayer PL intensities and nearly orthogonal polarizations. These results support a layer-resolved excitonic picture encompassing both intralayer and interlayer states in (PEA)2PbI4.