Luminescence Fine Structures in Single Lead Halide Perovskite Nanocrystals: Size Dependence of the Exciton-Phonon Coupling

Lead halide perovskite nanocrystals (NCs) have superior photoluminescence (PL) properties, such as high PL quantum yields and wide PL wavelength tunability, for optoelectronic applications. Here, we report the PL spectra of single formamidinium lead halide perovskite FAPbX(3) (X = Br, I) NCs examined by single-dot spectroscopy at low temperature. We found four PL peaks in the low-energy region below the strong exciton PL peak that originate from two longitudinal-optical (LO) phonon replicas of the exciton PL, biexcitons, and charged excitons (trions). The binding energies of the biexcitons and trions become larger as the NCs decrease in size. The LO phonon energies show no size dependence, but the Huang-Rhys factors, which reflect the strength of the exciton-phonon coupling, become larger for smaller NCs. Our findings provide important insights into the exciton properties of perovskite NCs.

Automated summary

Lead halide perovskite nanocrystals exhibit excellent photoluminescence properties, with high quantum yields and tunable wavelengths. Single-dot spectroscopy was used to explore the photoluminescence spectra of formamidinium lead halide perovskite NCs, revealing multiple peaks below the exciton peak. As the size of the NCs decreases, the binding energies of biexcitons and trions increase, while the phonon energies show no size dependence but the exciton-phonon coupling strength increases for smaller NCs. This study provides valuable insights into the exciton properties of perovskite NCs.