Defect-Related Broadband Emission in Two-Dimensional Lead Bromide Perovskite Microsheets

Abstract

Low-dimensional hybrid lead halide perovskites (LHPs) with broadband emission (BE) have been developed as promising candidates for single-source white-light-emitting diodes. However, the underlying origin of such BE is poorly understood. Herein, dual-emissive [NH3(CH2)8NH3]­PbBr4 perovskite microsheets (PMSs) with good dispersibility are successfully prepared. Besides the general narrowband emission (NE) originating from free excitons, BE (∼522 nm) is generated under a Br-poor condition, which is not observed in the single-crystal sample. Unlike self-trapped exciton emission, the BE observed in PMSs is experimentally determined to be related to bromide vacancies (VBr), thereby exhibiting quasisaturation under high excitation intensity. Femtosecond transient absorption spectroscopy first shows that the trapping time of the photogenerated electrons by acceptor-like VBr– is ∼15 ps, slower than that by surface defects (<1 ps). This study provides new insight into the underlying mechanism of BE and an effective approach to manipulating the optical properties of 2D perovskites.

Regulation of the luminescence mechanism of two-dimensional tin halide perovskites

“…15 ), However, for the (PEA) 2 SnI 4 and (HA) 2 SnI 4 samples, the TA spectra were characterized by a redshift and a gradual increase in the intensity of the bleaching peak at the band edge with decreasing temperature between 340 and 77 K. Here (PEA) 2 SnI 4 is still applied as the representative material. The redshift of the bleaching peak of component I with a subpicosecond lifetime (277 fs) usually involves different physical processes, such as bandgap renormalization 42 , 43 , optical Stark effect 44 , exciton formation 42 , 45 , and trap states trapping 19 , 46 , 47 . In the recent study of TA kinetics, the component I was attributed to the surface defect trapping exciton process (<1 ps) in 2D (CH 3 (CH 2 ) 8 NH 3 ) 2 PbBr 4 perovskite 47 , the surface trap states trapping exciton process (600 fs) for monolayer MoS 2 materials 46 , and the exciton formation (<1 ps) in monolayer WS 2 materials 42 , 48 .…”

“…The redshift of the bleaching peak of component I with a subpicosecond lifetime (277 fs) usually involves different physical processes, such as bandgap renormalization 42 , 43 , optical Stark effect 44 , exciton formation 42 , 45 , and trap states trapping 19 , 46 , 47 . In the recent study of TA kinetics, the component I was attributed to the surface defect trapping exciton process (<1 ps) in 2D (CH 3 (CH 2 ) 8 NH 3 ) 2 PbBr 4 perovskite 47 , the surface trap states trapping exciton process (600 fs) for monolayer MoS 2 materials 46 , and the exciton formation (<1 ps) in monolayer WS 2 materials 42 , 48 . Several reports have shown that the temperature affects the dielectric shielding effect in the material 49 , 50 , i.e., in the low-temperature phase, the exciton binding energy increases, inducing an increase in the proportion and the formation rate of excitons 50 .…”

White-light defect emission and enhanced photoluminescence efficiency in a 0D indium-based metal halide

“…Besides, the spectrum also contains a long tail extending up to 800 nm, which is different from those of the low-dimensional lead–halide hybrids displaying a single sharp excitonic band at absorption onset. 18,53–57 The long tail might be associated with the interband absorption, stemming from multiple defect states. Upon UV light excitation, (C 6 H 8 N) 6 InBr 9 crystals exhibit a warm white-light emission with a color temperature of 5500 K and CIE chromaticity coordinates of (0.33, 0.37), as displayed in Fig.…”

“…The formed shallow and deep defects in the band gap play different roles in determining the materials’ photophysical processes, and it is known that the deep-level defects might be nonradiative recombination centers, shortening the carrier lifetimes and deteriorating the optical properties, while the shallow-level defects may be PL centers. 37–42 Nevertheless, reports on 0D metal halides with defect-assisted PL are rare, 43–45 and the understanding of the defect properties in this type of material is still in its infancy; thus, there remain many open questions to be solved.…”

Free and self-trapped exciton emission in perovskite CsPbBr3 microcrystals

“…[34][35][36][37][38][39] The double perovskites and low-dimensional perovskites were found to have strong STE emission. [40][41][42][43][44][45][46][47][48] Since the lattice deformation in these structures is easy to occur. In the fully inorganic Cs-Pb-Br systems, the STE emission was mainly discussed in zero-dimensional Cs 4 PbBr 6 , [49][50][51] in which the [PbBr 6 ] À octahedrons are isolated.…”