Resolving the Controversy in Biexciton Binding Energy of Cesium Lead Halide Perovskite Nanocrystals through Heralded Single-Particle Spectroscopy

Abstract

Understanding exciton−exciton interaction in multiply excited nanocrystals is crucial to their utilization as functional materials. Yet, for lead halide perovskite nanocrystals, which are promising candidates for nanocrystal-based technologies, numerous contradicting values have been reported for the strength and sign of their exciton−exciton interaction. In this work, we unambiguously determine the biexciton binding energy in single cesium lead halide perovskite nanocrystals at room temperature. This is enabled by the recently introduced single-photon avalanche diode array spectrometer, capable of temporally isolating biexciton−exciton emission cascades while retaining spectral resolution. We demonstrate that CsPbBr 3 nanocrystals feature an attractive exciton−exciton interaction, with a mean biexciton binding energy of 10 meV. For CsPbI 3 nanocrystals, we observe a mean biexciton binding energy that is close to zero, and individual nanocrystals show either weakly attractive or weakly repulsive exciton−exciton interaction. We further show that, within ensembles of both materials, single-nanocrystal biexciton binding energies are correlated with the degree of charge-carrier confinement.

Biexciton dynamics in halide perovskite nanocrystals

“…159 In many studies on the biexciton binding energy in LHP NCs, it has been reported that the exciton-exciton interaction is attractive and DE XX is a few tens of millielectronvolts or less. 70,74,[160][161][162] The value of DE XX has been mainly investigated by using transient absorption spectroscopy and time-resolved PL spectroscopy of NC ensembles. The reported values in CsPbBr 3 NCs are scattered over a wide range 69,160,161 and even a negative value (the repulsive exciton-exciton interaction) has been reported.…”

“…159 In many studies on the biexciton binding energy in LHP NCs, it has been reported that the exciton–exciton interaction is attractive and Δ E XX is a few tens of millielectronvolts or less. 70,74,160–162…”

Excitonic Bloch–Siegert shift in CsPbI3 perovskite quantum dots

“…Therefore, with decreasing QD size, both μ 01 and μ 12 become smaller, whereas E XX is enhanced, which are consistent with the physical properties of QDs. We note that some recent studies reported repulsive biexciton interactions in lead halide perovskite QDs, [46][47][48] which are still under debate are out of the scope of our current study. By contrast, recent single-dot PL measurements at cryogenic temperatures allow to directly readout exciton and biexciton emission lines, which gave biexciton binding energies of ~20 meV for weakly-confined (~10 nm) CsPbI 3 QDs.…”

Nonlocal screening dictates the radiative lifetimes of excitations in lead halide perovskites

“…1c at intermediate electron-hole distances must arise from the lattice. An effective electron-hole repulsion has been speculated in lead halide perovskites previously, [37][38][39] but had defied direct observation or theoretical validation.…”

“…For example, this repulsion may help explain observations of anti-binding of biexcitons. 38,39 The identification of a repulsive electronhole interaction generated from the soft, polar modes of the perovskite lattice offers a key new design principle for photovoltaic materials. Searching for other systems that admit this type of interaction represents a promising new direction for materials discovery.…”