[Paper Review] Phonon-driven wavefunction localization promotes room-temperature, pure single-photon emission in large organic-inorganic lead-halide quantum dots

Leon G. Feld, Simon C. Boehme+14 more|arXiv (Cornell University)|Apr 24, 2024

Perovskite Materials and Applications4 citations

TL;DR

This study demonstrates that phonon-driven wavefunction localization in large organic-inorganic perovskite quantum dots (APbBr3) enables bright, stable, and pure single-photon emission at room temperature. Through anharmonic lattice vibrations and dynamic confinement, the A-cation induces phonon-mediated localization that avoids the trade-off between single-photon purity and stability seen in smaller quantum dots, achieving >95% purity and emission up to 10⁶ photons/s across 495–745 nm.

ABSTRACT

In lead halide perovskites (APbX3), the effect of the A-site cation on optical and electronic properties has initially been thought to be marginal. Yet, evidence of beneficial effects on solar cell performance and light emission is accumulating. Here, we report that the A-cation in soft APbBr3 colloidal quantum dots (QDs) controls the phonon-induced localization of the exciton wavefunction. Insights from ab initio molecular dynamics and single-particle fluorescence spectroscopy demonstrate that anharmonic lattice vibrations and the resulting polymorphism act as an additional confinement potential. Avoiding the trade-off between single-photon purity and optical stability faced by downsizing conventional QDs into the strong confinement regime, dynamical phonon-induced confinement in large organic-inorganic perovskite QDs enables bright (10^6 photons/s), stable (> 1h), and pure (> 95%) single-photon emission in a widely tuneable spectral range (495-745 nm). Strong electron-phonon interaction in soft perovskite QDs provides an unconventional route toward the development of scalable room-temperature quantum light sources.

Motivation & Objective

• To understand the role of the A-site cation in modulating excitonic properties in soft perovskite quantum dots.
• To address the long-standing trade-off between single-photon purity and photostability in quantum dots by avoiding strong quantum confinement.
• To explore how lattice dynamics and electron-phonon coupling can be harnessed for scalable room-temperature quantum light sources.
• To demonstrate stable, bright, and pure single-photon emission across a wide spectral range in large perovskite QDs.
• To establish phonon-induced wavefunction localization as a novel mechanism for excitonic confinement in soft materials.

Proposed method

• Employed ab initio molecular dynamics simulations to model anharmonic lattice vibrations and their impact on excitonic wavefunctions.
• Conducted single-particle fluorescence spectroscopy to probe emission properties and single-photon purity at the nanoscale.
• Synthesized large organic-inorganic perovskite quantum dots (APbBr3) with tunable size and composition to explore confinement effects.
• Analyzed the interplay between structural polymorphism and electron-phonon coupling to identify dynamic confinement mechanisms.
• Measured photoluminescence quantum yield, lifetime, and spectral stability over time to assess performance.
• Correlated structural dynamics with optical response to validate the phonon-driven localization model.

Experimental results

Research questions

• RQ1 How does the A-site cation influence excitonic wavefunction localization in soft perovskite quantum dots?
• RQ2 Can phonon-induced dynamic confinement replace strong quantum confinement to achieve high single-photon purity without sacrificing stability?
• RQ3 What is the role of anharmonic lattice vibrations and structural polymorphism in creating an effective confinement potential?
• RQ4 To what extent can large perovskite quantum dots maintain pure single-photon emission at room temperature?
• RQ5 Can electron-phonon coupling in soft perovskites enable scalable, bright, and stable room-temperature quantum light sources?

Key findings

• Phonon-driven wavefunction localization in large APbBr3 quantum dots enables room-temperature single-photon emission with purity exceeding 95%.
• The A-cation modulates anharmonic lattice vibrations that induce a dynamic confinement potential, reducing the need for strong quantum confinement.
• Large perovskite quantum dots exhibit stable emission for over 1 hour under continuous excitation, with brightness reaching 10⁶ photons per second.
• Single-photon emission is tunable across a broad spectral range from 495 to 745 nm, enabling application versatility.
• Ab initio molecular dynamics simulations confirm that polymorphism and lattice anharmonicity are key to the observed localization mechanism.
• The system avoids the typical trade-off between single-photon purity and photostability seen in conventional quantum dots by leveraging soft lattice dynamics.