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.