Formation of Long-Lived Color Centers for Broadband Visible Light Emission in Low-Dimensional Layered Perovskites

Abstract

We investigate the origin of the broadband visible emission in layered hybrid lead-halide perovskites and its connection with structural and photophysical properties. We study ⟨001⟩ oriented thin films of hexylammonium (HA) lead iodide, (CHN)PbI, and dodecylammonium (DA) lead iodide, (CHN)PbI, by combining first-principles simulations with time-resolved photoluminescence, steady-state absorption and X-ray diffraction measurements on cooling from 300 to 4 K. Ultrafast transient absorption and photoluminescence measurements are used to track the formation and recombination of emissive states. In addition to the excitonic photoluminescence near the absorption edge, we find a red-shifted, broadband (full-width at half-maximum of about 0.4 eV), emission band below 200 K, similar to emission from ⟨110⟩ oriented bromide 2D perovskites at room temperature. The lifetime of this sub-band-gap emission exceeds that of the excitonic transition by orders of magnitude. We use X-ray diffraction measurements to study the changes in crystal lattice with temperature. We report changes in the octahedral tilt and lattice spacing in both materials, together with a phase change around 200 K in DAPbI. DFT simulations of the HAPbI crystal structure indicate that the low-energy emission is due to interstitial iodide and related Frenkel defects. Our results demonstrate that white-light emission is not limited to ⟨110⟩ oriented bromide 2D perovskites but a general property of this class of system, and highlight the importance of defect control for the formation of low-energy emissive sites, which can provide a pathway to design tailored white-light emitters.

Phase-Transition-Induced Carrier Mass Enhancement in 2D Ruddlesden–Popper Perovskites

“…More detail can be found in ref. 34 First-principles calculations are based on density functional theory (DFT) as implemented in the SIESTA package. 56,57 Calculations have been carried out on experimental structures 41 with the GGA functional in the revPBE form.…”

“…14,28,29 Moreover, the length and cross section of the organic ligands affect the distortion of the inorganic cages, modifying the band structure and the electron-phonon interaction. 23,24,[30][31][32][33][34] While the large variety of ways to tune the optical properties of 2D perovskites is undoubtedly their huge advantage, the interaction between different parameters hinders our fundamental understanding of their properties. To date their structural, dielectric, optical, and excitonic properties remain largely unexplored.Many of 2D perovskite family members exhibit complex absorption and emission spectra with many sidebands.…”

“…Films were spincoated from solutions of 20 mg/mL at 2000 rpm for 30 s and annealed for 15 min at 70 • C. All precursors were purchased from Sigma Aldrich. The crystals grow preferential with the lead iodide layers parallel to the glass substrate 34 Magneto-transmission measurements were performed in pulsed magnetic fields up to 68 T with a pulse duration of 500 ms. The broad band white light was provided by a tungsten halogen lamp.…”

Two‐Step Structure Phase Transition, Dielectric Anomalies, and Thermochromic Luminescence Behavior in a Direct Band Gap 2D Corrugated Layer Lead Chloride Hybrid of [(CH3)4N]4Pb3Cl10

“…Besides their exceptional optoelectrical properties, 2D lead/tin halide perovskites also show other fascinating functionalities, for example, piezoelectricity, nonlinear optical properties, dielectrics, and ferroelectrics . Thus, the lead halide‐based perovskites represent a large class of important materials, and these materials have the great chemical flexibility and outstanding multifunctionality for fundamental research as well as practical applications in optical, electronic, and energy‐based devices.…”

“…Both experimental and theoretical investigations demonstrate that the broad emission in visible spectrum is due to structural deformation, [16,32,34,35] self-localized emissive states, [36,37] defect states (like Freckle defects) [40] in the lattice of 2D lead/ tin halide perovskites. Besidest heir exceptionalo ptoelectrical properties, 2D lead/ tin halide perovskites alsos how other fascinating functionalities, for example, piezoelectricity, [34] nonlinearo ptical properties, [24,38] dielectrics, and ferroelectrics. [39,40] Thus, the lead halide-based perovskites represent al arge class of important materials, and these materials have the great chemical flexibility and outstanding multifunctionality for fundamental research as well as practical applications in optical, electronic, and energy-based devices.…”