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Low-dimensional halide perovskites exhibit intriguing excitonic properties and emerge as an important class of self-activated luminescent materials. However, the ability to manipulate and optimize their luminescent properties is limited by the lack of the microscopic understanding of the exciton relaxation and emission and the inconsistency in the theoretical results in the literature. In this work, based on first-principles calculations, we studied excitons in 1D lead halide perovskites, C4N2H14PbBr4 and C4N2H14PbCl4, which are both bright visible-light emitters. We find that, in both compounds, the polaron-pair exciton (EX-PP) is more stable than the onsite exciton (EX-OS) and only the EX-PP emission energy from the calculation is close to the main photoluminescence (PL) peak observed in the experiment. The EX-OS is found to emit UV light in both compounds. Therefore, the EX-PP is responsible for the experimentally observed visible light emission in both C4N2H14PbBr4 and C4N2H14PbCl4. Furthermore, the calculated small energy difference between the EX-PP and EX-OS in C4N2H14PbBr4 suggests that the metastable EX-OS can be thermally populated at room temperature (RT); the calculated EX-OS emission energy agrees well with the energy of a minor PL peak observed at RT but not at 77 K. The validity our approach in the exciton calculation is supported by the benchmark of the calculated exciton emission energies against the experimental results in 13 0D and 1D metal halides. The discrepancies between this work and a recent theoretical study in the literature are also discussed. [ABSTRACT FROM AUTHOR]

Herein, a new family of hybrid metal halides, (DMAP)2MBr4 (M = Cu, Zn), featuring zero‐dimensional (0D), pseudo‐layered crystal structures containing isolated molecular 4‐dimethylaminopyridinium (DMAP, C7H11N2+) cations and MBr42− tetrahedral anions are reported. (DMAP)2MBr4 show remarkable long‐term stability, with no signs of degradation after one year of ambient air exposure. The reported solution synthesis affords large crystals measuring up to 1 cm, which showed significant response to soft 8 keV X‐ray photons when implemented into X‐ray detectors. Furthermore, (DMAP)2ZnBr4 demonstrates tunable color light emission properties, which is attributed to the organic molecular units based on our combined experimental and computational results. The measured photoluminescence quantum yield (PLQY) for (DMAP)2ZnBr4 is 7.35 %, a remarkable enhancement of emission efficiency as compared to a weak emission from the organic precursor. The inexpensive and earth‐abundant chemical compositions and ease of preparation of the new hybrid metal halides make them promising candidates for optical and electronic applications. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and characterization is reported of (C9NH20)2SnBr4, a novel organic metal halide hybrid with a zero‐dimensional (0D) structure, in which individual seesaw‐shaped tin (II) bromide anions (SnBr42−) are co‐crystallized with 1‐butyl‐1‐methylpyrrolidinium cations (C9NH20+). Upon photoexcitation, the bulk crystals exhibit a highly efficient broadband deep‐red emission peaked at 695 nm, with a large Stokes shift of 332 nm and a high quantum efficiency of around 46 %. The unique photophysical properties of this hybrid material are attributed to two major factors: 1) the 0D structure allowing the bulk crystals to exhibit the intrinsic properties of individual SnBr42− species, and 2) the seesaw structure enabling a pronounced excited state structural deformation as confirmed by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

The rich chemistry of organic metal halide hybrids has enabled the development of a variety of new functional materials with crystal structures beyond perovskites. In article number 1801474, Biwu Ma and co‐workers report a novel bulk assembly of one‐dimensional (1D) organic metal halide hybrid, C5H16N2Pb2Br6, in which lead bromide octahedrons form a corrugated chain structure via non‐planar edge‐sharing. This 1D material exhibits a broadband yellow emission peaked at 554 nm with a full width at half maximum of 155 nm with a photoluminescence quantum efficiency of around 10%, due to exciton self‐trapping. [ABSTRACT FROM AUTHOR]

The family of molecular level low‐dimensional organic metal halide hybrids has expanded significantly over the last few years. Here a new type of 1D metal halide structure is reported, in which metal halide octahedra form a corrugated double‐chain structure via nonplanar edge‐sharing. This material with a chemical formula of C5H16N2Pb2Br6 exhibits a broadband yellow emission under ultraviolet light excitation with a photoluminescence quantum efficiency of around 10%. The light‐yellow emission is considered to be attributed to self‐trapping excitons. Theoretical calculations show that the unique alignment of the octahedra leads to small band dispersion and large exciton binding energy. Together with previously reported 1D metal halide wires and tubes, this new bulk assembly of 1D metal halides suggests the potential to develop a library of bulk assemblies of metal halides with controlled structures and compositions. A novel molecularly 1D metal halide C5H16N2Pb2Br6 is discovered, in which metal halide octahedra employ a double‐chain structure in the bulk crystals. C5H16N2Pb2Br6 exhibits a broadband yellow emission with a photoluminescence quantum efficiency of ≈10% due to exciton self‐trapping. [ABSTRACT FROM AUTHOR]

Organic-inorganic metal halide hybrids are an important class of crystalline materials with exceptional structural and property tunability. Recently metal halide perovskites with ABX 3 structure have been extensively investigated as new generation semiconductors for various optoelectronic devices, including photovoltaic cells, light emitting diodes, photodetectors, and lasers, for their exceptional optical and electronic properties. By controlling the morphological dimensionality, low dimensional metal halide perovskites, including 2D perovskite nanoplatelets, 1D perovskite nanowires, and 0D perovskite quantum dots, have been developed to exhibit distinct properties from their bulk counterparts, due to quantum size effects. Besides ABX 3 perovskites, organic-inorganic metal halide hybrids, containing the same fundamental building block of metal halide octahedra (BX 6), can also be assembled to possess other types of crystallographic structures. Using appropriate organic and inorganic components, low dimensional organic-inorganic metal halide hybrids with 2D, quasi-2D, corrugated-2D, 1D, and 0D structures at the molecular level have been developed and studied. Due to the strong quantum confinement and site isolation, these low dimensional metal halide hybrids at the molecular level exhibit remarkable and unique properties that are significantly different from those of ABX 3 perovskites. In light of the rapid development of low dimensional metal halide perovskites and hybrids, it is indeed timely to review the recent progress in these areas. Also, there is a need to clarify the difference between morphological low dimensional metal halide perovskites and molecular level low dimensional metal halide hybrids, as currently the terminologies of low dimensional perovskites are not appropriately used in many cases. In this review article, we discuss the synthesis, characterization, application, and computational studies of low dimensional metal halide perovskites and hybrids. [ABSTRACT FROM AUTHOR]