Defect-Induced Narrowband Light Emission from a 2D Hybrid Lead Iodide Perovskite

The formation of color centers capable of emitting narrowband light emission from solution-phase precursors would enable a new direction in the design and characterization of single photon emitters for quantum information processors. In this study, we present an experimental approach through which we form defective samples of the two-dimensional hybrid organic–inorganic perovskite hexyl ammonium lead iodide whose light emission spectra possess narrow peaks below the optical gap. We use temperature-dependent photoluminescence (PL) spectroscopic studies to show the electronic states participating in the radiative relaxation processes leading to these narrow peaks stem from thermal activation over at least one energy barrier from the self-trapped exciton state whose height matches vibrations of the molecular cation. In addition, power-dependent PL measurements allow us to show two correlated peaks in the subgap light emission spectra likely stem from a similar defect state and can be assigned to an exciton and charge bound to a defect site. We use first-principles electronic structure calculations to attribute the light emission peak to iodine and hydrogen vacancies, which produce a localized electronic state in an energetic vicinity consistent with our experimental results. These results show the promise solution-processed, self-assembled quantum materials hold in the wide distribution of single, near-infrared photon emitters for information processing and storage.