Sensitized Molecular Triplet and Triplet Excimer Emission in Two-Dimensional Hybrid Perovskites

Two-dimensional (2D) organic–inorganic hybrid perovskites are promising materials for next-generation optoelectronic devices owning to their structural and functional versatility and enhanced ambient stability. Recent studies have started to focus on engineering the molecular properties of the organic cations to induce inorganic-to-organic energy/charge transfer for new functionalities, yet many puzzles regarding the inorganic–organic interaction mechanisms remain to be resolved. Here we fabricate 2D lead halide perovskites containing naphthalene methylamine (NMA) cations to study naphthalene triplet sensitization by inorganic excitons. We find that triplet sensitization proceeds via a two-step mechanism initiated by subpicosecond hole transfer from the inorganic layer to naphthalene. We also provide spectroscopic evidence for triplet excimer formation, i.e., the association between triplet and ground state molecules. The intensity ratio between the excimer and triplet emissions can be tuned via the percentage of the NMA cations in the organic layer, offering a route to tunable white-light emitters using 2D hybrid perovskites.