Neutral-Exciton Emission from Single Perovskite Nanocrystals Memorizing the Pre-Existence of a Local Electric Field.

Semiconductor lead-halide perovskite nanocrystals (NCs) are associated with a soft ionic lattice interacting strongly with the photogenerated charge carriers, which can bring about very novel photophysical properties in these quantum-confined materials with a large surface-to-volume ratio. Here we have performed high-resolution optical measurements on single perovskite CsPbI₃ NCs at the cryogenic temperature of ∼4 K, with a specific focus on how an extra charge trapped on the surface influences the recombination energies of their neutral and charged excitons. As expected, the surface-trapped charge can impart a local electric field on the charged exciton inside a single CsPbI₃ NC, leading to the shift of its recombination energy mainly by the quantum-confined Stark effect. Interestingly, the neutral-exciton recombination energy is also shifted even after the surface-trapped charge has disappeared for a time period longer than ∼2 μs, signifying that the lattice distortion induced by the previous local electric field is not fully relaxed at this time scale. The above findings have established very unique charge-property relationships in lead-halide perovskite NCs, the understanding and manipulation of which are critical to their practical performance in various classical and quantum optical applications.