Continuous-wave perovskite polariton lasers

Abstract

Solution-processed semiconductor lasers are next-generation light sources for large-scale, bio-compatible and integrated photonics. However, overcoming their performance-cost trade-off to rival III-V laser functionalities is a long-standing challenge. Here, we demonstrate room-temperature continuous-wave perovskite polariton lasers exhibiting remarkably low thresholds of ~0.4 W cm^-2, enabled by a variable single-crystal perovskite microcavity. The threshold outperforms state-of-the-art III-V lasers by ~30 times under optical pumping, and is exceptional among solution-processed lasers. The ultralow-threshold lasing arises from steady-state exciton-polariton condensation, a macroscopic quantum phenomenon akin to Bose-Einstein condensation. The steady-state condensation is attained by fine-tuning the cavity photon-exciton energy separation near the degeneracy point for strong light-matter interactions. These mechanisms enabled the initial demonstration of an indirectly injected perovskite laser chip powered by a gallium nitride light-emitting diode. Our findings create exciting avenues toward on-chip integration of solution-processed lasers, opening opportunities for lasing with ultralow energy consumption and unprecedented performance.

Fig. 1.. Fabrication and material characterization of the perovskite polariton lasers.

(A) Schematic representation of a CW perovskite polariton laser. A perovskite single crystal is sandwiched between a pair of highly reflective DBRs, supporting CW lasing action through strong light-matter interactions. (B) Scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS) images of the DBR, showing bilayers of SiO₂ (blue regions) and TiO₂ (green regions). (C) Fabrication processes of the single-crystal perovskite microcavities. (D) Transient PL decay curves of perovskite samples (excitation wavelength: 400 nm; fluence: 42 nJ cm⁻²). FMPB denotes FA_0.1MA_0.9PbBr₃ perovskite. SC denotes single-crystal samples. PC denotes polycrystalline samples. (E) PLQY as a function of excitation intensity for various perovskite samples. (F) Absorption and PL spectra of a FA_0.1MA_0.9PbBr₃ single crystal (thickness: ~200 nm). (G) Scanning electron microscopy (SEM) image of a FA_0.1MA_0.9PbBr₃ single crystal. (H) Fluorescent microscope image of a FA_0.1MA_0.9PbBr₃ perovskite single crystal. (I) XRD patterns of FA_0.1MA_0.9PbBr₃ single crystal and polycrystalline samples.

Fig. 2.. CW polariton lasing from single-crystal perovskite microcavities at room temperature.

(A) Evolution of emission spectra under CW operation at different pump intensities. Single-crystal sample thickness: ~120 nm. (B) Light-output intensity, FWHM, and emission blue shift as functions of CW pump intensity (at ~300 K). (C) Temporal coherence of the CW polariton laser. The first-order coherence g¹(τ) above the threshold, measured using a Michelson interferometer. The red solid line represents a Gaussian fit to the data. The inset shows the Michelson interference pattern at zero time delay. Scale bar, 5 μm. (D) The angle-resolved PL spectra above the lasing threshold (3.0P_th). The straight line represents the dispersion relation of excitons. The solid parabolic curve represents the dispersion relation of cavity photons. The dashed curve represents the dispersion of the lower polariton branch. (E) Polariton occupancy in the ground and excited states, plotted in a semilogarithmic scale for pump intensities below (0.8P_th), around (~1.0P_th), and above (3.0P_th) the threshold (at ~300 K). The blue dashed line represents the Maxwell–Boltzmann distribution function with k_BT = 26 meV. (F) Comparison of CW lasing thresholds for lasers based on different classes of semiconductor materials. See table S1 for details. (G) Schematic illustration of an indirectly injected perovskite laser chip, powered by a 410-nm GaN LED. (H) Emission intensity and FWHM of the perovskite polariton laser chip as functions of driving current in the GaN LED (dc, at ~300 K). (I) Polariton lasing spectra from microcavities of variable lengths (adjusted using the single-crystal thickness). The second peak/shoulder in the spectrum of the device with the longest cavity length (red curve) can be attributed to the leakage of cavity-mode photons. The spectral linewidths are related to the detuning of the cavity.

Fig. 3.. Polariton to photon lasing transition in single-crystal perovskite microcavities.

(A) Emission intensity (I)–pump fluence (I₀) curve of a single-crystal perovskite microcavity, showing two thresholds at pump fluence of 0.3 μJ cm⁻² and 12.4 μJ cm⁻² corresponding to polariton lasing and photon lasing, respectively. The samples were pumped using a 400-nm fs laser (pulse width: 270 fs, repetition rate: 50 kHz, single-crystal thickness: ~130 nm). Above the first threshold, the increase in output intensity is super-linear with a power-law dependence of $I\propto {I_0}^{2.36}$. In the regime where photon lasing (light amplification by stimulated emission) occurs, the intensity increases more sharply with $I\propto {I_0}^{6.67}$. (B) FWHM and wavelength blue shift as functions of pump fluence, showing marked changes at the two thresholds. The shaded areas are regions near the thresholds. (C to F) Angle-resolved emission spectra of a single-crystal perovskite microcavity at different pump fluences: (C) P = 0.8P_th1, (D) P = 2P_th1, (E) P ~ P_th2, and (F) P = 1.6P_th2. (G) Emission spectra under pulsed pumping at 0.8P_th1 and 2.0P_th1. The emission blue shift (by ~0.6 meV) and linewidth narrowing (by ~2.3 meV) can be observed. (H) Spectra of spontaneous emission, polariton lasing, and photon lasing from the single-crystal perovskite. (I) The polarization characteristics.

Fig. 4.. The effects of detuning energy on polariton lasing.

(A to C) Angle-resolved emission spectra of single-crystal perovskite microcavities for different detuning energies of (A) ∆ = −12, (B) ∆ = −25, and (C) ∆ = −54 meV (at P = 3P_th). The thicknesses of single-crystal samples in (a)-(c) are 100 nm, 120 nm and 140 nm, respectively. (D) Polariton occupancy functions for different detuning energies (at P = 3P_th). (E) The emission intensity-pump intensity characteristics for different detuning energies (∆ = −54, −40, −25, and −12 meV). (F) Dependence of lasing threshold on detuning energy under pulsed (blue curve) and CW (red curve) pumping. CW polariton lasing is not observed for ∆ < −62 meV and ∆ > −10 meV, as shown in blue grade regions.