Templated-Assembly of CsPbBr3 Perovskite Nanocrystals into 2D Photonic Supercrystals with Amplified Spontaneous Emission

Abstract

Perovskite nanocrystals (NCs) have revolutionized optoelectronic devices because of their versatile optical properties. However, controlling and extending these functionalities often requires a light-management strategy involving additional processing steps. Herein, we introduce a simple approach to shape perovskite nanocrystals (NC) into photonic architectures that provide light management by directly shaping the active material. Pre-patterned polydimethylsiloxane (PDMS) templates are used for the template-induced self-assembly of 10 nm CsPbBr₃ perovskite NC colloids into large area (1 cm² ) 2D photonic crystals with tunable lattice spacing, ranging from 400 nm up to several microns. The photonic crystal arrangement facilitates efficient light coupling to the nanocrystal layer, thereby increasing the electric field intensity within the perovskite film. As a result, CsPbBr₃ 2D photonic crystals show amplified spontaneous emission (ASE) under lower optical excitation fluences in the near-IR, in contrast to equivalent flat NC films prepared using the same colloidal ink. This improvement is attributed to the enhanced multi-photon absorption caused by light trapping in the photonic crystal.

Keywords: 2D photonic crystals; PDMS template; amplified spontaneous emission (ASE); perovskite nanocrystals; self-assembly.

Figure 1

a) Schematic illustration of PDMS template‐assisted fabrication of 2D photonic supercrystals made of perovskite NCs. b),c) Representative SEM images of 2D photonic supercrystals made of CsPbBr₃ arrays with lattice parameters of 600 nm and 1700 nm, respectively. The inset in (b) is a photograph of different CsPbBr₃ SC arrays on glass substrates, displaying diffraction under white light illumination.

Figure 2

SEM characterization of photonic crystals prepared by self‐assembly of NCs from dispersions at concentrations of a)–c) 100 d)–f) 50 and g)–i) 10 mg mL⁻¹. The concentration of NCs and ligands has a strong influence on the viscosity of the sample, altering the distribution of NCs along the surface. Isolated pillars are formed at low concentrations, while a residual layer of NCs is formed all over the sample at 100 mg mL⁻¹.

Figure 3

Lattice resonances and field enhancement: Experimental (a) and theoretical (b) extinction (1−T, where T is transmittance) spectra for a NC thin film (green curve) and for different PhCs with lattice parameters of 400 (blue), 500 (black) and 600 nm (red). The vertical dashed line in (a) corresponds to the 800 nm laser excitation wavelength used in the nonlinear experiments. c)–f) FDTD simulated spatial distribution of the electric field enhancement illustrating the effect of light diffraction, for the case of 600 nm lattice parameter versus a perovskite flat film (e,f).

Figure 4

a) SEM close view of SC arrangement in a perovskite PhC obtained from a 100 mg mL⁻¹ NC dispersion, used for ASE studies. b) Photoluminescence spectra obtained from inside the patterned area (red), outside of the patterned area (blue) and from the initial colloidal dispersion (green).

Figure 5

a) Fluence‐dependent PL (evolution of ASE) of CsPbBr₃ 2D photonic crystals film and b) the corresponding emission intensity obtained by integration of the spectra. The inset in (a) is a photograph of the photonic crystal film showing waveguiding above excitation threshold for ASE. The dotted lines in (b) are the best linear fits for intensities below (green) and above (red) threshold. The spectra were acquired with 800 nm femtosecond laser excitation.