Soft crystal lattice and large anharmonicity facilitate the self-trapped excitonic emission in ultrathin 2D nanoplates of RbPb<sub>2</sub>Br<sub>5</sub>

Pradhan, Jayita; Das, Anustoop; Kundu, Kaushik; Chahat, .; Biswas, Kanishka

doi:10.1039/d2sc02992h

Cited by 9 publications

(14 citation statements)

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“…The 2D layered organic lead halide perovskites often show one more radiative decay channel called STE emission. − It is largely Stokes shifted compared with excitonic absorption and has a large spectral width. We have compared the low-temperature STE emission data of all four samples in Figure S13 of the SI.…”

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confidence: 99%

Emissive Dark Excitons in Monoclinic Two-Dimensional Hybrid Lead Iodide Perovskites

et al. 2023

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Typically, bright excitons (XB) emit light in two-dimensional (2D) layered hybrid perovskites. There are also dark excitons (XD), for which radiative recombination is spin-forbidden. Application of a magnetic field can somewhat relax the spin-rule, yielding XD emission. Can we obtain XD light emission in the absence of a magnetic field? Indeed, we observe unusually intense XD emission at ∼7 K for (Rac-MBA)2PbI4, (Rac-4-Br-MBA)2PbI4, and (R-4-Br-MBA)2PbI4 (Rac-MBA: racemic methylbenzylammonium), which crystallize in a lower symmetry monoclinic phase. For comparison, orthorhombic (R-MBA)2PbI4 does not exhibit XD emission. XD has a lower energy than XB, with energy difference ΔE. In monoclinic samples, ΔE ∼ 20 meV is large enough to suppress the thermal excitation of XD to XB, at temperatures <30 K. Consequently, XD recombines by emitting light with a long lifetime (∼205 ns). At higher temperatures, the emission switches to the spin-allowed XB (lifetime < 1 ns)

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confidence: 99%

Emissive Dark Excitons in Monoclinic Two-Dimensional Hybrid Lead Iodide Perovskites

et al. 2023

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“…To investigate the role of the inorganic moiety PbBr 2 in the mixed-halide perovskite thin film, the concentration of PbBr 2 was varied in the precursor solution. With 1:2 and 1:3 MAI:PbBr 2 , the resulting products are 2D MAPb 2 (IBr 4 ) perovskite and MAPb 3 (IBr 6 ) non-perovskite materials, respectively. , It is to be noted that the excess inorganic precursor within the mixed-halide perovskite solution also leads to a 2D structure in the form of APb 2 X 5 , in accord to a recent report by Pradhan et al . The schematic representation of 3D, 2D, and 1D perovskite crystal structures is shown in Figure b.…”

Section: Resultsmentioning

confidence: 95%

Dimension-Controlled Synthesis of Hybrid-Mixed Halide Perovskites for Solar Cell Application

Ghosh,

Gupta,

Nanda

et al. 2023

ACS Appl. Mater. Interfaces

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Despite the rapid improvement of photovoltaic (PV) efficiency in hybrid organic−inorganic metal halide perovskites (HOIPs), the fabrication procedure of a compact thin film in a large-area application is still a tedious work. Apart from the quality of the thin film, the stability of the perovskite materials and the expensive organic hole transport layer (HTL) within the HOIP-based PV device are the major issues that need to be addressed prior to their commercialization. Herein, a unique glass rod-based facile fabrication technique for producing a compact and stable thin film utilizing a mixed-halide-based perovskite precursor solution is demonstrated. The fabricated devices deliver high photoconversion efficiency (PCE) without the use of any HTL and show an excellent stability under ambient conditions. By varying the organic CH 3 NH 3 I (MAI) and inorganic PbBr 2 content, perovskite materials with different dimensions, i.e., 3D, 2D, and 1D, are synthesized to produce an active layer for PV devices. Although a 2D single-halide perovskite is reported earlier, herein two different mixed-halide 2D perovskites, i.e., MA 2 PbI 2 Br 2 and MAPb 2 IBr 4 , are synthesized successfully, and their performance is compared in detail along with that of 1D and 3D mixed-halide perovskites. The facile synthesized mixed-halide 2D-based MA 2 PbI 2 Br 2 perovskite shows a PCE of 10.14% with a high stability of 92% after 100 days without encapsulation, which is much superior as compared to that of the mixed-halide 3D MAPbIBr 2 . The semiconducting behavior as well as the nature of the bandgap of the synthesized compounds is examined by pursuing density functional theory calculations. Specifically, the role of iodine doping to modify the electronic band structure is investigated, and introduction of iodine is found to reduce the effective masses of both electrons and holes in the perovskite material.

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“…Clearly, the most intense PL zone (∼650 to 800 nm, marked by red color) widens up as the temperature increases from 15 to 300 K, with a prominent hypsochromic shift specifically after 225 K. This is because of the high extent of electron−phonon interaction feasible at relatively higher temperatures leading to an increase in the PL fwhm and stabilization of valence band with temperature due to lattice expansion at the same time. 24 It is notable that a single peak emission is observed at all of the temperatures. The PL emission remains broad (fwhm = 165 nm) even at 15 K which indicates that trapped or localized excitons are the origin of emission in CsPb 2 Br 5 .…”

Section: ■ Introductionmentioning

confidence: 91%

“…CsPb 2 Br 5 shows bulk modulus (B) of 8.59 GPa and shear modulus (G) of 7.07 GPa. Both of these values are extremely low and less than 3D halide perovskites 50,52 and even some 2D Ruddlesden−Popper perovskites 53 or non-perovskites 24 as well (Figure 4a,b).…”

Section: ■ Introductionmentioning

confidence: 99%

Curious Case of CsPb₂Br₅: Extremely Soft Structure-Induced Broadband Emission

Pradhan,

Das,

Panda

et al. 2024

Chem. Mater.

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Ever since the initial report on green emissive two-dimensional (2D) all-inorganic indirect band gap semiconductor, CsPb2Br5, arguments have arisen concerning its origin of photoluminescence, which has sparked continuous debate. Following the identification of the photoluminescence centers being primarily either strongly green emissive CsPbBr3 impurities or different amorphous lead-bromide ammonium complexes present at the surface of the solution-based synthesized product, here in this work, an all-solid-state synthesis approach has been implemented to avoid any involvement of incertitude that may arise from unwanted external particles. For the first time, we record the progressive formation of thermodynamically favored CsPb2Br5 phase over time, and interestingly, pristine CsPb2Br5 exhibits a highly Stokes-shifted broadband pinkish-red emission spanning from the visible-to-near infrared spectrum (∼500 to 850 nm). Emission wavelength-independent excitation and excitation wavelength-independent emission coupled with the similarity in the decay kinetics, all indicate toward the intrinsic nature of the broadband emission. The occurrence of low bulk and shear moduli (8.59 and 7.07 GPa, respectively) estimated from sound velocity measurements, the soft vibrational modes from Raman spectroscopy, and the significantly low Debye temperature (113 K) obtained from heat capacity (C p) measurements in the low-temperature range (2–31 K) reveal the structural softness on both global and local scales. These traits lead to the emergence of short-range elastic lattice deformation resulting from strong electron–phonon coupling upon photoexcitation, generating self-trapped excitonic emission in CsPb2Br5.

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Soft crystal lattice and large anharmonicity facilitate the self-trapped excitonic emission in ultrathin 2D nanoplates of RbPb₂Br₅

Abstract: Self-trapping of excitons (STE) and concomitant useful broadband emission in the low-dimensional metal halides occur due to strong electron-phonon coupling, which exhibit potential applications in optoelectronics and solid-state lighting. Lattice...

Cited by 9 publications

References 67 publications

Emissive Dark Excitons in Monoclinic Two-Dimensional Hybrid Lead Iodide Perovskites

Emissive Dark Excitons in Monoclinic Two-Dimensional Hybrid Lead Iodide Perovskites

Dimension-Controlled Synthesis of Hybrid-Mixed Halide Perovskites for Solar Cell Application

Curious Case of CsPb₂Br₅: Extremely Soft Structure-Induced Broadband Emission

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Soft crystal lattice and large anharmonicity facilitate the self-trapped excitonic emission in ultrathin 2D nanoplates of RbPb2Br5

Abstract: Self-trapping of excitons (STE) and concomitant useful broadband emission in the low-dimensional metal halides occur due to strong electron-phonon coupling, which exhibit potential applications in optoelectronics and solid-state lighting. Lattice...

Cited by 9 publications

References 67 publications

Emissive Dark Excitons in Monoclinic Two-Dimensional Hybrid Lead Iodide Perovskites

Emissive Dark Excitons in Monoclinic Two-Dimensional Hybrid Lead Iodide Perovskites

Dimension-Controlled Synthesis of Hybrid-Mixed Halide Perovskites for Solar Cell Application

Curious Case of CsPb2Br5: Extremely Soft Structure-Induced Broadband Emission

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Soft crystal lattice and large anharmonicity facilitate the self-trapped excitonic emission in ultrathin 2D nanoplates of RbPb₂Br₅

Curious Case of CsPb₂Br₅: Extremely Soft Structure-Induced Broadband Emission