Search

The chemical diversity and structural flexibility of lead halide perovskites (LHPs) offer tremendous opportunities to tune their optical properties through internal molecular engineering and external stimuli. Herein, we report the wide‐range and ultrapure photoluminescence emissions in a family of homologous 2D LHPs, [MeOPEA]2PbBr4−4xI4x (MeOPEA=4‐methoxyphenethylammonium; x=0, 0.2, 0.425, 0.575, 1) enabled through internal chemical pressure and external hydrostatic pressure. The chemical pressure, induced by the C−H⋅⋅⋅π interactions and halogen doping/substitution strengthens the structural rigidity to give sustained narrow emissions, and regulates the emission energy, respectively. Further manipulation of physical pressure leads to wide‐range emission tuning from 412 to 647 nm in a continuous and reversible manner. This work could open up new pathways for developing 2D LHP emitters with ultra‐wide color gamut and high color purity which are highly useful for pressure sensing. [ABSTRACT FROM AUTHOR]

2D hybrid organic–inorganic perovskites (HOIPs) are highly responsive to external stimuli and therefore have application potential as sensing materials. Though their optical properties upon singular thermal or pressure stimulation have been recently investigated, their dual‐stimuli‐responsive behaviors have not yet been explored. Here, the dual‐stimuli‐responsive luminescence of a pair of new enantiomeric 2D Dion–Jacobson HOIPs, R+[(4‐aminophenyl)ethylamine]PbI4 and S‐[(4‐aminophenyl)ethylamine]PbI4, is reported. The photoluminescence results show that their 485 nm emissions can be red‐shifted by ≈6 nm upon heating, and further increased to 529 nm under pressure. Such dual‐stimuli‐responsive emissions expand their Commission Internationale de L'Eclairage coordinates successively from (0.140, 0.272) to (0.283, 0.473). Detailed structural analysis and first principles calculations reveal that the temperature‐ and pressure‐responsive behaviors arise from the predominant electron–phonon interactions over thermal expansion effect and pressure‐induced in‐plane PbI bond contraction, respectively. The findings open up a new pathway to successively tune the optical emission of 2D HOIPs via a dual‐stimuli‐responsive approach. [ABSTRACT FROM AUTHOR]

Piezoelectric hybrid organic–inorganic perovskites have attracted significant attention due to their outstanding piezoelectricity comparable to perovskite oxides. However, their elastic properties, which determine the piezoelectric performance, have not yet been explored. Here, the elastic properties of a perovskite ferroelectric TMCM-CdCl3 (TMCM = trimethylchloromethyl ammonium) with a large piezoelectric effect are comprehensively investigated. High-pressure synchrotron powder x-ray diffraction experiments reveal that it exhibits a low bulk modulus of 14.58 GPa, which is an order of magnitude lower than those of perovskite oxides. In addition, Young's moduli and shear moduli were calculated using density functional theory, and their values are significantly smaller than perovskite piezoceramics. Furthermore, the acoustic properties of TMCM-CdCl3 were calculated. Its longitudinal wave velocity is 3.86 km s−1–4.94 km s−1, and the corresponding specific acoustic impedance is 8.28 MRayl–10.21 MRayl. These maximum values are, respectively, 31.5%, 74.4%, and 8.4%, 73.1% lower than those from BaTiO3 and PbTiO3. Our findings disclose the soft nature and low acoustic impedance of hybrid perovskite piezoelectrics, which are critical to their applications in energy conversion devices. [ABSTRACT FROM AUTHOR]

Two-dimensional lead halide perovskites (2D LHPs) can be generally categorized into the Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases, with unbiased and biased structural packing manners, respectively. To distinguish the two different phases during materials discovery, the synthesis has heavily relied on the traditional trial-and-error methods which severely delay the rapid development of these emerging 2D materials. In this work, we applied machine learning (ML) to accelerate the synthetic development of (100)-oriented 2D A 2 BX 4 and ABX 4 LHPs (A = organic amine cation, B = Pb, X = halide). The experimentally available 264 crystal structures were used as training data for our ML model to identify the descriptors influencing the formation of the RP- and DJ-phases. The number of nitrogen atoms able to be protonated, the heteroatom type, and the nitrogen content of the organic amine are identified as the most influential factors. To validate our model, three organic amines were tested by growing single crystals and two of the three new structures are consistent with our ML results. This study takes one step further toward the rational synthesis of RP- and DJ-phase hybrid 2D LHPs via an approach of ML. [Display omitted] [ABSTRACT FROM AUTHOR]