Higher Order Polaronic-Exciton Recombination in Two-Dimensional Dion–Jacobson-Type Perovskites

Understanding electronic and structural factors governing non-radiative recombination is key to developing hybrid low-dimensional materials for light-emitting applications. Here, we demonstrate that the ultrafast (0.6–5 ps) biexcitonic Auger process is the dominant exciton recombination pathway that occurs within the sub-picosecond to few picoseconds in two-dimensional Dion–Jacobson (2D DJ) hybrid perovskites. Studying two DJ perovskites with polaronic character and different exciton–phonon coupling, we reveal that ultrafast non-radiative recombination rates are primarily governed by strong exciton–phonon coupling and dielectric confinement in these materials. The third-order recombination rate reflects the interplay among exciton–phonon coupling, lattice distortion, band gap, and exciton binding energy. We show that Auger recombination occurs well below the Mott density in these 2D materials. We therefore establish a lower bound of 1.3 × 10¹⁹ cm^–3 for the Mott density, much higher than that of three-dimensional (3D) perovskites. This work highlights the intrinsically ultrafast higher order recombination of polaronic-excitons in 2D DJ perovskites, emphasizing their unique excitonic properties and fundamental differences from conventional 3D systems.