Extreme Electron-Photon Interaction in Disordered Perovskites

Abstract

The interaction of light with solids can be dramatically enhanced owing to electron-photon momentum matching. This mechanism manifests when light scattering from nanometer-sized clusters including a specific case of self-assembled nanostructures that form a long-range translational order but local disorder (crystal-liquid duality). In this paper, a new strategy based on both cases for the light-matter-interaction enhancement in a direct bandgap semiconductor - lead halide perovskite CsPbBr₃ - by using electric pulse-driven structural disorder, is addressed. The disordered state allows the generation of confined photons, and the formation of an electronic continuum of static/dynamic defect states across the forbidden gap (Urbach bridge). Both mechanisms underlie photon-momentum-enabled electronic Raman scattering (ERS) and single-photon anti-Stokes photoluminescence (PL) under sub-band pump. PL/ERS blinking is discussed to be associated with thermal fluctuations of cross-linked [PbBr₆]^4- octahedra. Time-delayed synchronization of PL/ERS blinking causes enhanced spontaneous emission at room temperature. These findings indicate the role of photon momentum in enhanced light-matter interactions in disordered and nanostructured solids.

Keywords: Raman blinking; crystal‐liquid duality; disordered perovskite; electronic Raman scattering; electron‐photon interaction; near‐field photon momentum; photoluminescence blinking.

Figure 1

a) Artistic illustration of a CsPbBr₃ pad, whose left and right corners are top‐covered with SWCNT electrodes, b) SEM image of the CsPbBr₃ perovskite pad (top view). c) Photocurrent map across the perovskite pad under 633 nm cw illumination when dc bias off. d,e) Sketches of PL mechanisms when external dc voltage bias off and on.

Figure 2

a) A confocal optical image of a CsPbBr₃ pad consisting of disordered and ordered regions separated with the DOI. b) Raman spectra of a CsPbBr₃ pad exposed to 633 nm excitation pump with the intensity of 0.4 MW cm⁻² and different dc bias, registered at the DOI (red spot in Figure 2a). c) A plot of PL peak position versus cross section shown in Figure 2a. d) aS‐PL, l‐ERS and h‐ERS kinetics along a cross section marked in Figure 2a. e) Autocorrelation function for three processes registered at the DOI. f) 1D Raman map versus time. g) A PL spectrum at the spot marked in Figure 2f and its numerical decomposition into the ESPL (dashed blue curve) and spontaneous bunching PL (SBPL) (solid red curve) bands. h) Pump‐dependent PL intensity at the DOI after 3 s and 30 s.

Figure 3

a) Energy band structure of CsPbBr₃. b) Schematic illustration of optical transitions at the DOI (not to scale).

Figure 4

a) 1D Raman intensity map, b) a photocurrent distribution curve and c) 1D EL map at dc bias of 7 V along the cross section highlighted in Figure 2a. The inset in the left panel shows the aS‐PL and h‐ERS at the DOI when the circuit is on and off. The dotted straight lines mark the h‐ERS maximum. The arrow indicates an additional aS‐PL flare while circuit off.