Auger Recombination and Multiple Exciton Generation in Colloidal Two-Dimensional Perovskite Nanoplatelets: Implications for Light-Emitting Devices

Improving the understanding of multiple exciton interactions and dynamics in semiconductor nanostructures is mandatory for their successful use as photoactive materials in light convertors such as electroluminescent diodes, lasers, or single-photon sources. Here high-fluence and high-energy excitation effects are investigated in strongly confined two-dimensional (2D) lead iodide perovskite nanoplatelets (NPLs) using time-resolved photoluminescence and femtosecond transient absorption spectroscopy. Nonradiative Auger recombination (AR) is the dominant pathway for multiexciton recombination. Its dynamics are found to be subquadratic with the exciton density. Indeed, because of the limited exciton wave-function delocalization length, AR is limited by exciton diffusion in the 2D plane at moderate excitation fluence and takes place in several hundreds of picoseconds, with typical recombination rates on the order of 10^–2 cm²/s. At high excitation fluence leading to an average interexciton distance comparable with the exciton delocalization length, the measured “intrinsic” AR time is faster than 10 ps and independent of the NPL composition. The strong dependence of the AR rate on the interexciton distance allows us to identify the recombination resulting from multiple exciton generation, involving the reaction of “geminate biexcitons”, upon excitation at low fluence with high-energy photons.