Spin Correlated-Plasmons at Room Temperature Driven by Electronic Correlations in Lead-Free 2D Hybrid Organic–Inorganic Perovskites

Abstract

Hybrid organic−inorganic perovskites (HOIPs) have emerged to the forefront of optoelectronic material advancements for the past few years. However, our understanding on electronic structure and correlations are still lacking. Herewith, by simultaneously analyzing complex dielectric function, loss functions, and reflectivity directly obtained from spectroscopic ellipsometry and supported with theoretical calculations, we report new spin correlated-plasmons with low loss in (MA) 2 CuCl 4 . Photoluminescence and time-resolved photoluminescence measurements show a broadband emission band originating from the self-trapped emission excitons. Through X-ray absorption spectroscopy and resonant photoemission spectroscopy measurements at the C K-edge, a resonance enhancement peak is observed and unravels a charge transfer event due to the opening of an extra autoionization channel. Our result shows the importance of coupling between spin correlated-plasmons and electron−hole pairs together with spin-dependent exchange interaction in determining electronic structure and optical properties of HOIPS.

Tailoring the Optical and Electronic Properties of 2D Hybrid Dion–Jacobson Copper Chloride Perovskites

“…Interestingly, the full width at half maximum (FWHM) of BDACuCl 4 displays a reduction from 183 nm (sample A) to 73.4 nm (sample C) for the intense peak, evidencing a fingerprint emission attributed to the recombination of free excitons (FE) . On the other hand, the linewidth broadening of the other two components shows typical FWHM close to 150 nm, which is comparable to that of the previous HOIP reports − and our recent work . We associate such broadband emission arising from the self-trapped excitons (STE) to the strong carrier–phonon interactions typically found in the 2D-HOIP structure. − In addition, the physical origin of such STE emission in 2D copper halides can be associated to the Jahn–Teller effect mediated by the out-of-plane distortion within the Cu octahedral sheets. , Since the STE is heavily modulated from the number exciton–phonon coupling, we therefore attribute the observation to the competition between the in-plane and out-of-plane distortions within the hybrid DJ perovskite structure.…”

“…Typically, deconvoluted XPS peaks in copper perovskites share a charge disproportion of Cu cations in 1+ and 2+ valence states as previously reported in the literature and our previous work. 52,61,62 Here, we correlate that such a charge profile introduces a means to tune different local chemical environments within this layered perovskite structure. Since the conventional phenomenology of disproportionation involves the absence of transition metal atom charge ordering, the creation of different Cu−Cl bond lengths ("bond alternation") for different local environments could slightly "corrugate" the inorganic sheet arrangement of the 2D DJ copper perovskite.…”

“…47 On the other hand, the linewidth broadening of the other two components shows typical FWHM close to 150 nm, which is comparable to that of the previous HOIP reports 48−51 and our recent work. 52 We associate such broadband emission arising from the self-trapped excitons (STE) to the strong carrier−phonon interactions typically found in the 2D-HOIP structure. 53−58 In addition, the physical origin of such STE emission in 2D copper halides can be associated to the Jahn−Teller effect mediated by the out-ofplane distortion within the Cu octahedral sheets.…”

Mechanochemical Synthesis, Optical and Magnetic Properties of Pb-Free Ruddlesden–Popper-Type Layered Rb2CuCl2Br2 Perovskite

“…At 77 K, a narrower PL band centered at 640 nm appeared along with an additional relatively broader peak near 695 nm, which are separated by 55 nm (∼150 meV). The low-energy second peak observed at low temperature is due to the bound excitonic emission, which generally originated from the intrinsic defect sites just below the band-edge (such as shallow trap states). − Such low temperature-induced dual emission was earlier reported for several low-dimensional halide perovskite systems, such as (MA) 2 CuCl 4 , Cu-doped Cs 2 ZnBr 4 , Cs 3 Sb 2 I 9 , (C 4 H 9 NH 3 I) 2 (PbI 2 ), (PEA) 2 PbX 4 , and (PEA) 2 CsSn 2 I 7 . ,− During the temperature elevation from 77 to 298 K, the high energy emission band remains at the expense of the low energy band. This event implies that, with increasing temperature, the trapped excitons acquire sufficient thermal energy to overcome the energy barrier between two emitting excited states and finally emerge as one asymmetric emission at 298 K .…”

Insights into the spectroscopic and structural features of methylammonium copper halide perovskites and theoretical view

“…The surface morphology of the (CH 3 NH 3 ) 2 CuCl 4 (MA 2 CuCl 4 ) (hereafter named PG 80) was studied using transmission electron microscopy (TEM) is shown in figure 1. Based on the x-ray diffraction spectrum and the sharp intensity of the peaks, which directly correlates with the interplanar spacing of low-dimensional single crystals [21], our sample has been conclusively identified as a layered 2D perovskite and is shown in figure 2. The observed diffraction peaks at 9.5°, 19.1°, 29.5°, 38.7°, and 48.8°can be unambiguously attributed to the formation of PG 80, with each peak corresponding to the planes: (001), (002), (003), (004), and (005) [22].…”