Unveiling the Impact of Organic Spacer Cations on Auger Recombination in Layered Halide Perovskites

A library of large organic cation spacers is available for engineering the performance of layered two-dimensional (2D) halide perovskite devices. Despite extensive photophysics studies, there remains a research gap over the structure-function relations in 2D perovskites, especially the underlying factors influencing the Auger recombination (AR) process. Herein, the contributions of exciton binding energy, exciton-phonon coupling, and defects/film morphology to the AR process in 2D perovskites are examined. Phenyl-alkyl-ammonium cations with different lengths of attached alkyl groups, commonly used in blue light-emitting diodes, are investigated. The findings reveal an order of magnitude higher threshold carrier density for the AR onset as well as a reduced AR in cations with longer alkyl chain length. Although possessing similar exciton binding energies, the exciton-phonon coupling strength is found to play a major role in reducing the AR rate, with a smaller contribution from the defect states/film morphology. The findings can help provide further guidance on organic spacer cation engineering for highly efficient 2D perovskite light emitters.