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.