Structural Diversity in White-Light-Emitting Hybrid Lead Bromide Perovskites

Water-Stable 1D Hybrid Tin(II) Iodide Emits Broad Light with 36% Photoluminescence Quantum Efficiency

The optical and light emission properties of tin and lead halide perovskites are remarkable because of the robust room-temperature (RT) performance, broad wavelength tunability, high efficiency, and good quenching resistance to defects. These highly desirable attributes promise to transform current light-emitting devices, phosphors, and lasers. One disadvantage in most of these materials is the sensitivity to moisture. Here, we report a new air-stable one-dimensional (1D) hybrid lead-free halide material (DAO)Sn₂I₆ (DAO, 1,8-octyldiammonium) that is resistant to water for more than 15 h. The material exhibits a sharp optical absorption edge at 2.70 eV and a strong broad orange light emission centered at 634 nm, with a full width at half-maximum (fwhm) of 142 nm (0.44 eV). The emission has a long photoluminescence (PL) lifetime of 582 ns, while the intensity is constant over a very broad temperature range (145-415 K) with a photoluminescence quantum yield (PLQY) of at least 20.3% at RT. Above 415 K the material undergoes a structural phase transition from monoclinic (C2/c) to orthorhombic (Ibam) accompanied by a red shift in the band gap and a quench in the photoluminescence emission. Density functional theory calculations support the trend in the optical properties and the 1D electronic nature of the structure, where the calculated carrier effective masses along the inorganic chain are significantly lower than those perpendicular to the chain. Thin films of the compound readily fabricated from solutions exhibit the same optical properties, but with improved PLQY of 36%, for a 60 nm thick film, among the highest reported for lead-free low-dimensional 2D and 1D perovskites and metal halides.

Broadband Photoluminescence in 2D Organic-Inorganic Hybrid Perovskites: (C7H18N2)PbBr4 and (C9H22N2)PbBr4

Organic-inorganic hybrid perovskites have aroused intense research interest because of their excellent physical performance and potential for use in optoelectronic field. Herein, we report two new 2D hybrid lead bromides, (C₇H₁₈N₂)PbBr₄ [C₇H₁₈N₂ is 1,7-diaminoheptane] and (C₉H₂₂N₂)PbBr₄ [C₉H₂₂N₂ is 1,9-diaminononane], both of which possess ⟨100⟩-oriented inorganic layers consisting of corner-sharing octahedra. The optical bandgaps are experimentally determined to be 2.76 eV for (C₇H₁₈N₂)PbBr₄ and 2.78 eV for (C₉H₂₂N₂)PbBr₄. Upon 390 nm excitation, (C₇H₁₈N₂)PbBr₄ exhibits white-light emission centered at 600 nm, and (C₉H₂₂N₂)PbBr₄ exhibits red-light emission centered at 620 nm. These broad photoluminescent spectra originate from the synergistic emission of free excitons (FEs) and self-trapped excitons (STEs). This work provides a strategy for realizing single-component white-light emission and efficient red-light emission in two-dimensional perovskites, demonstrating the vast application prospects of 2D perovskites in photoelectric devices.

[(N-AEPz)ZnCl4]Cl: A "Green" Metal Halide Showing Highly Efficient Bluish-White-Light Emission

Benefiting from their structural flexibility and solution processability, organic-inorganic metal halide hybrids with efficient white-light emission present a great promise for solid-state lighting and display applications. However, most of these reported high-performance single-component white-light materials contain lead. Herein, we report a "green" organic zinc halide, [(N-AEPz)ZnCl₄]Cl (1; N-AEPz = N-aminoethylpiperazine), exhibiting prominent bluish-white-light emission with a photoluminescence quantum efficiency as high as 11.52%. Such a value is among the highest in the reported metal halide white-light emitters. Mechanism studies disclose that the broad-band emission is ascribed to the synergistic work of organic salts and inorganic clusters. This work would incent research on single-component white-light materials for next-generation display and lighting technologies.

Lead-Free Tin(IV)-Based Organic-Inorganic Metal Halide Hybrids with Excellent Stability and Blue-Broadband Emission

Lead-free zero-dimensional (0D) organic-inorganic metal halide hybrids have recently attracted special attention as luminescent materials. However, their structural stability is still a challenge for the further development. Here, we select Sn⁴⁺ as the B-site inorganic cation and obtain a new tin(IV)-based organic-inorganic metal halide hybrids (C₆N₂H₁₆Cl)₂SnCl₆ with remarkable air stability. (C₆N₂H₁₆Cl)₂SnCl₆ exhibits a blue broadband emission originating from self-trapping excitons (STEs) and the emission intensity remains stable for over three months. When the temperature rises to 450 K, the intensity of photoluminescence can maintain about 50%, indicating the good thermal stability of (C₆N₂H₁₆Cl)₂SnCl₆. This work presents a new strategy toward the tin(IV)-based photoluminescent organic-inorganic metal halide hybrids with environmentally friendly, high stability characteristics.

A Three-Dimensional Lead Halide Perovskite-Related Ferroelectric

Three-dimensional (3D) organic-inorganic lead halides represented by [CH₃NH₃]PbI₃ perovskite have attracted great interest for their diverse functional properties and promising optoelectronic applications. However, 3D lead halides are still very rare and their ferroelectricity remains controversial. Here, we report an unprecedented 3D lead halide perovskite-related ferroelectric [2-trimethylammonioethylammonium]Pb₂Cl₆ ([TMAEA]Pb₂Cl₆), which contains a 3D lead chloride framework of corner- and edge-sharing PbCl₆ octahedral, with the [TMAEA]⁺ cations occupying the voids of the framework. [TMAEA]Pb₂Cl₆ shows a ferroelectric-to-paraelectric phase transition with the Curie temperature as high as 412 K, a typical ferroelectric hysteresis loop at 293 K with a spontaneous polarization of 1 μC/cm², and a clear ferroelectric domain switching. To the best of our knowledge, [TMAEA]Pb₂Cl₆ is the first 3D lead halide showing such an excellent ferroelectricity. Additionally, it also exhibits a semiconducting property with a direct band gap of 3.43 eV. This finding enriches the family of 3D hybrid lead halides and inspires the exploration of 3D lead halide ferroelectrics.

Structure-Dependent Photoluminescence in Low-Dimensional Ethylammonium, Propylammonium, and Butylammonium Lead Iodide Perovskites

Hybrid organic-inorganic perovskites have attracted great attention as the next generation materials for photovoltaic and light-emitting devices. However, their environment instability issue remains as the largest challenge for practical applications. Recently emerging two-dimensional (2D) perovskites with Ruddlesden-Popper structures are found to greatly improve the stability and aging problems. Furthermore, strong confinement of excitons in these natural quantum-well structures results in the distinct and narrow light emission in the visible spectral range, enabling the development of spectrally tunable light sources. Besides the strong quasi-monochromatic emission, some 2D perovskites composed of the specific organic cations and inorganic layer structures emit a pronounced broadband emission. Herein, we report the light-emitting properties and the degradation of low-dimensional perovskites consisting of the three shortest alkylammonium spacers, mono-ethylammonium (EA), n-propylammonium (PA), and n-butylammonium (BA). While (BA)₂PbI₄ is known to form well-oriented 2D thin films consisting of layers of corner-sharing PbI₆ octahedra separated by a bilayer of BA cations, EA with shorter alkyl chains tends to form other types of lower-dimensional structures. Nevertheless, optical absorption edges of as-prepared fresh EAPbI₃, (PA)₂PbI₄, and (BA)₂PbI₄ are obviously blue-shifted to 2.4-2.5 eV compared to their 3D counterpart, methylammonium lead iodide (MAPbI₃) perovskite, and they all emit narrow excitonic photoluminescence. Furthermore, by carefully optimizing deposition conditions, we have achieved a predominantly 2D structure for (PA)₂PbI₄. However, unlike (BA)₂PbI₄, upon exposure to ambient environment, (PA)₂PbI₄ readily transforms to a different crystal structure, exhibiting a prominently broadband light from ∼500 to 800 nm and a gradual increase in intensity as structural transformation proceeds.

[DMEDA]PbCl4: a one-dimensional organic lead halide perovskite with efficient yellow emission

By using a simple room temperature solution reaction, we prepared a new type of one-dimensional (1D) hybrid lead halide [DMEDA]PbCl₄. The compound gives a bright yellow emission with efficient photoluminescence quantum efficiency (PLQE) and optical stability.

Broadband white light emission from one-dimensional zigzag edge-sharing perovskite

We reported 1D (AMP)PbBr₄ and (AMP)PbCl₄ perovskites, which consisted of the 1D zigzag edge-sharing [PbBr₄²⁻ (or PbCl₄²⁻)]_∞ infinite inorganic chains with AMP²⁺ cations, for the white-light emission.

Strongly emissive white-light-emitting silver iodide based inorganic–organic hybrid structures with comparable quantum efficiency to commercial phosphors

A series of one-dimensional silver iodide based inorganic–organic hybrid structures with tunable white light emissions and high quantum efficiency have been synthesized by Cu substitution.

Broadband yellow light emitting performance based on zero-dimensional hybrid lead bromide trimers

Two new zero-dimensional organic–inorganic hybrid lead halides based on linear [Pb₃Br₁₂]⁶⁻ trimers display broadband yellow light emissions with high photoluminescence quantum yields, exhibiting potential in the fabrications of white-light emitting diodes.

Tetrameric cluster assembled one-dimensional hybrid lead halides with broadband light emission

A series of new types of 1D lead halide perovskites have been synthesized based on [Pb₄X₁₆] tetrameric clusters. The 1D crystal lattice exhibits broadband yellow light emission arising from the self-trapped excitons with potential application in WLEDs.

Locally collective hydrogen bonding isolates lead octahedra for white emission improvement

As one of next-generation semiconductors, hybrid halide perovskites with tailorable optoelectronic properties are promising for photovoltaics, lighting, and displaying. This tunability lies on variable crystal structures, wherein the spatial arrangement of halide octahedra is essential to determine the assembly behavior and materials properties. Herein, we report to manipulate their assembling behavior and crystal dimensionality by locally collective hydrogen bonding effects. Specifically, a unique urea-amide cation is employed to form corrugated 1D crystals by interacting with bromide atoms in lead octahedra via multiple hydrogen bonds. Further tuning the stoichiometry, cations are bonded with water molecules to create a larger spacer that isolates individual lead bromide octahedra. It leads to zero-dimension (0D) single crystals, which exhibit broadband ‘warm’ white emission with photoluminescence quantum efficiency 5 times higher than 1D counterpart. This work suggests a feasible strategy to modulate the connectivity of octahedra and consequent crystal dimensionality for the enhancement of their optoelectronic properties.

Low dimensional lead halide perovskites possess intriguing optical properties that are still under debate. Here Cui et al. use hydrogen bonds containing spacers to synthesize highly luminescent perovskites with fully isolated lead-bromide octahedras and shed light on the origin of the emission.

Ruddlesden-Popper Perovskites: Synthesis and Optical Properties for Optoelectronic Applications

Ruddlesden-Popper perovskites with a formula of (A')2(A) n -1B n X3 n +1 have recently gained widespread interest as candidates for the next generation of optoelectronic devices. The variations of organic cation, metal halide, and the number of layers in the structure lead to the change of crystal structures and properties for different optoelectronic applications. Herein, the different synthetic methods for 2D perovskite crystals and thin films are summarized and compared. The optoelectronic properties and the charge transfer process in the devices are also delved, in particular, for light-emitting diodes and solar cells.

All-Inorganic CsCu2 I3 Single Crystal with High-PLQY (≈15.7%) Intrinsic White-Light Emission via Strongly Localized 1D Excitonic Recombination

Energy-saving white lighting from the efficient intrinsic emission of semiconductors is considered as a next-generation lighting source. Currently, white-light emission can be composited with a blue light-emitting diode and yellow phosphor. However, this solution has an inevitable light loss, which makes the improvement of the energy utilization efficiency more difficult. To deal with this problem, intrinsic white-light emission (IWE) in a single solid material gives a possibility. Here, an all-inorganic lead-free CsCu₂ I₃ perovskite single crystal (SC) with stable and high photoluminescence quantum yield (≈15.7%) IWE through strongly localized 1D exciton recombination is synthesized. In the CsCu₂ I₃ , the Cu-I octahedron, which provides most of electron states, is isolated by Cs atoms in two directions to form a 1D electronic structure, resulting a high radiation recombination rate of excitons. With this electronic structure design, the CsCu₂ I₃ SCs have great potential in energy-saving white lighting.

Broadband white-light emission from supramolecular piperazinium-based lead halide perovskites linked by hydrogen bonds

We demonstrate white-light emission using lead halide perovskites: (pip)2PbBr6 (pip = piperazine), (pip)2Pb4Cl12, (1mpz)2PbBr6 (1mpz = 1-methylpiperazine), and (2,5-dmpz)0.5PbBr3·2((CH3)2SO) (2,5-dmpz = trans-2,5-dimethylpiperazine, abbreviated as (2,5-dmpz)0.5PbBr3), in which the inorganic frameworks were connected by piperazinium dications through hydrogen bonds, forming a three-dimensional supramolecular network. From single-crystal X-ray diffraction measurements and Raman spectroscopy, we identified the crystal structures and local environmental vibrational modes in the inorganic framework, finding that (pip)2PbBr6 crystallized in the centrosymmetric orthorhombic space group Pnnm, whereas (pip)2Pb4Cl12 crystallized in the trigonal/rhombohedral space group R3. The zero-dimensional (1mpz)2PbBr6 structure crystallized in the centrosymmetric monoclinic space group P2/n, whereas the [PbBr6]4- octahedron was separated by a 1-methylpiperazine dication. (2,5-dmpz)0.5PbBr3·2((CH3)2SO) contained half a cation, which was completed by inversion symmetry, along with two dimethyl sulfoxide solvent molecules that crystallized in the monoclinic space group P21/c. Among the perovskites, (2,5-dmpz)0.5PbBr3·2((CH3)2SO) exhibited the longest carrier lifetime (42 ns), the lowest band gap (2.34 eV), and the highest photoluminescence quantum yield (58.02%). This is because it forms a 1D corner-sharing structure and has localized electronic states near the conduction band minimum, which contributes to the high photoluminescence quantum yield and white-light emission.

Broadband emission of double perovskite Cs2Na0.4Ag0.6In0.995Bi0.005Cl6:Mn2+ for single-phosphor white-light-emitting diodes

In this Letter, we report the broadband photoluminescence of lead-free double perovskite Cs₂Na_0.4Ag_0.6In_0.95Bi_0.05Cl₆:Mn²⁺. Under ultraviolet excitation, the white phosphor shows two emission peaks at 550 nm and 610 nm from self-trapped exciton and doped Mn²⁺ ions, respectively, leading to a broad emission spectrum over the whole visible spectrum suitable for lighting application. The white-light-emitting diodes exhibit high light quality with CIE coordinates (0.38, 0.42) and color rendering index of 82.6. The mechanism of luminescence of this double perovskite is also discussed in this Letter.

Colloidal Synthesis and Optical Properties of All-Inorganic Low-Dimensional Cesium Copper Halide Nanocrystals

Low-dimensional metal halides have recently attracted extensive attention owing to their unique structure and photoelectric properties. Herein, we report the colloidal synthesis of all-inorganic low-dimensional cesium copper halide nanocrystals (NCs) by adopting a hot-injection approach. Using the same reactants and ligands, but different reaction temperatures, both 1D CsCu₂ I₃ nanorods and 0D Cs₃ Cu₂ I₅ NCs can be prepared. Density functional theory indicates that the reduced dimensionality in 1D CsCu₂ I₃ compared to 0D Cs₃ Cu₂ I₅ makes the excitons more localized, which accounts for the strong emission of 0D Cs₃ Cu₂ I₅ NCs. Subsequent optical characterization reveals that the highly luminescent, strongly Stokes-shifted broadband emission of 0D Cs₃ Cu₂ I₅ NCs arises from the self-trapped excitons. Our findings not only present a method to control the synthesis of low-dimensional cesium copper halide nanocrystals but also highlight the potential of 0D Cs₃ Cu₂ I₅ NCs in optoelectronics.

Intrinsic Self-Trapped Emission in 0D Lead-Free (C4 H14 N2 )2 In2 Br10 Single Crystal

Low-dimensional lead halide perovskite materials recently have drawn much attention owing to the intriguing broadband emissions; however, the toxicity of lead will hinder their future development. Now, a lead-free (C₄ H₁₄ N₂ )₂ In₂ Br₁₀ single crystal with a unique zero-dimensional (0D) structure constituted by [InBr₆ ]^3- octahedral and [InBr₄ ]^- tetrahedral units is described. The single crystal exhibits broadband photoluminescence (PL) that spans almost the whole visible spectrum with a lifetime of 3.2 μs. Computational and experimental studies unveil that an excited-state structural distortion in [InBr₆ ]^3- octahedral units enables the formation of intrinsic self-trapped excitons (STEs) and thus contributing the broad emission. Furthermore, femtosecond transient absorption (fs-TA) measurement reveals that the ultrafast STEs formation together with an efficient intersystem crossing has made a significant contribution to the long-lived and broad STE-based emission behavior.

Lead-Free Halide Perovskites and Perovskite Variants as Phosphors toward Light-Emitting Applications

Lead halide perovskites have attracted tremendous research interests in the light-emitting field because of their high defect tolerance, solution processability, tunable spectrum, and efficient emission. In terms of luminescence types, both the narrowband emission derived from free-exciton (FE) and broadband white light emission from self-trapped exciton (STE) show great advantages in light-emitting applications. Despite the fascinating characteristics, their commercialization still suffers from the presence of toxic lead (Pb) and unsatisfactory stability. In this spotlight, we mainly focus on the lead-free candidates as phosphors for possible light-emitting applications. Thanks to the chemical diversity of metal halide perovskites and perovskite variants, many excellent lead-free light-emitting materials have recently been synthesized and characterized. We first classify these materials into three types according to material structures, including (1) double perovskites A₂B(I)B(III)X₆, (2) vacancy ordered perovskites A₂B(IV)X₆, (3) miscellaneous perovskite variants or halide semiconductors, which refer to halides without clear relation to the perovskite structure. We then highlight the importance of electronic dimensionality, defect passivation, and impurity doping in developing highly efficient perovskite-based emitters. We also discuss their applications in white light-emitting diodes (W-LED). Further challenges toward practical applications and potential applications are also included in a section on outlook and future challenges.

High-resolution remote thermometry and thermography using luminescent low-dimensional tin-halide perovskites

Although metal-halide perovskites have recently revolutionized research in optoelectronics through a unique combination of performance and synthetic simplicity, their low-dimensional counterparts can further expand the field with hitherto unknown and practically useful optical functionalities. In this context, we present the strong temperature dependence of the photoluminescence lifetime of low-dimensional, perovskite-like tin-halides and apply this property to thermal imaging. The photoluminescence lifetimes are governed by the heat-assisted de-trapping of self-trapped excitons, and their values can be varied over several orders of magnitude by adjusting the temperature (up to 20 ns °C^-1). Typically, this sensitive range spans up to 100 °C, and it is both compound-specific and shown to be compositionally and structurally tunable from -100 to 110 °C going from [C(NH₂)₃]₂SnBr₄ to Cs₄SnBr₆ and (C₄N₂H₁₄I)₄SnI₆. Finally, through the implementation of cost-effective hardware for fluorescence lifetime imaging, based on time-of-flight technology, these thermoluminophores have been used to record thermographic videos with high spatial and thermal resolution.

Disphenoidal Zero-Dimensional Lead, Tin, and Germanium Halides: Highly Emissive Singlet and Triplet Self-Trapped Excitons and X-ray Scintillation

Low-dimensional metal halides have been researched as optoelectronic materials for the past two decades. Zero-dimensional halides of ns² elements (Sn, Pb, Sb) have recently gained attention as highly efficient broadband light emitters. These compounds comprise discrete metal halide centers, isolated by bulky organic cations. Herein, we report isostructural halide complexes of Ge(II), Sn(II), and Pb(II) with a 1-butyl-1-methyl-piperidinium cation (Bmpip), featuring unusual disphenoidal coordination with a highly stereoactive lone pair. Spectrally broad, bright emission from highly localized excitons, with quantum efficiencies of up to 75%, is observed in blue to red spectral regions for bromides (for Pb, Sn, and Ge, respectively) and extends into the near-infrared for Bmpip₂SnI₄ (peak at 730 nm). In the case of Sn(II) and Ge(II), both singlet and triplet excitonic emission bands have been observed. Furthermore, Bmpip₂SnBr₄ and Bmpip₂PbBr₄ exhibit X-ray-excited luminescence (radioluminescence) with brightness being commensurate with that of a commercial inorganic X-ray scintillator (NaI:Tl).

Pressure-Induced Emission (PIE) of One-Dimensional Organic Tin Bromide Perovskites

Low-dimensional halide perovskites easily suffer from the structural distortion related to significant quantum confinement effects. Organic tin bromide perovskite C₄N₂H₁₄SnBr₄ is a unique one-dimensional (1D) structure in which the edge sharing octahedral tin bromide chains [SnBr₄^2-]_∞ are embraced by the organic cations C₄N₂H₁₄²⁺ to form the bulk assembly of core-shell quantum wires. Some unusual phenomena under high pressure are accordingly expected. Here, an intriguing pressure-induced emission (PIE) in C₄N₂H₁₄SnBr₄ was successfully achieved by means of a diamond anvil cell. The observed PIE is greatly associated with the large distortion of [SnBr₆]^4- octahedral motifs resulting from a structural phase transition, which can be corroborated by in situ high-pressure photoluminescence, absorption, and angle-dispersive X-ray diffraction spectra. The distorted [SnBr₆]^4- octahedra would accordingly facilitate the radiative recombination of self-trapped excitons (STEs) by lifting the activation energy of detrapping of self-trapped states. First-principles calculations indicate that the enhanced transition dipole moment and the increased binding energy of STEs are highly responsible for the remarkable PIE. This work will improve the potential applications in the fields of pressure sensors, trademark security, and information storage.

Lead Halide Post-Perovskite-Type Chains for High-Efficiency White-Light Emission

Hybrid metal halides containing perovskite layers have recently shown great potential for applications in solar cells and light-emitting diodes. Such compounds exhibit quantum confinement effects leading to tunable optical and electronic properties. Thus, broadband white-light emission has been observed from diverse metal halides and, owing to high color rendering index, high thermal stability, and low-temperature solution processability, these materials have attracted interest for application in solid-state lighting. However, the reported quantum yields for white photoluminescence (PLQY) remain low (i.e., in the range 0.5-9%) and no approach has shown to successfully increase the intensity of this emission. Here, it is demonstrated that the quantum efficiencies of hybrid metal halides can be greatly enhanced if they contain a polymorph of the [PbX₄ ]^2- perovskite-type layers: the [PbX₄ ]^2- post-perovskite-type chains showing a PLQY of 45%. Different piperazines lead to a hybrid lead halide with either perovskite layers or post-perovskite chains influencing strongly the presence of self-trapped states for excitons. It is anticipated that this family of hybrid lead halide materials could enhance all the properties requiring the stabilization of trapped excitons.

(4NPEA)2PbI4 (4NPEA = 4-Nitrophenylethylammonium): Structural, NMR, and Optical Properties of a 3 × 3 Corrugated 2D Hybrid Perovskite

(4NPEA)₂PbI₄ (4NPEA = 4-nitrophenylethylammonium) is the first 3 × 3 corrugated 2D organic-Pb/I perovskite. The nitro groups are involved in cation-cation and cation-iodide interactions. The structure contains both highly distorted and near-ideal PbI₆ octahedra, consistent with the observation of two ²⁰⁷Pb NMR resonances, while the optical properties resemble those of other 2D perovskites with distorted PbI₆ octahedra.

Atomistic Mechanism of Broadband Emission in Metal Halide Perovskites

Broadband emission is attributed to the formation of self-trapped excitons (STEs) due to the strong electron-phonon coupling. Interestingly, it has been observed in only certain three-dimensional and low-dimensional metal halide perovskites. Here, we show by density functional theory calculation that a low electronic dimensionality is a prerequisite for the formation of STE and, therefore, broadband emission. We further show that multiple STE structures exist in each perovskite exhibiting broadband emission. However, only the STE with Jahn-Teller-like octahedral distortion is mainly responsible for the observed broadband emission, though it may not be the lowest-energy structure. Our results provide important insights for designing perovskite materials for broadband emissions with preferred chromaticity coordinator or color temperature.

Designing a new family of oxonium-cation based structurally diverse organic–inorganic hybrid iodoantimonate crystals

We report proton-bound oxonium cation based iodoantimonate hybrid organic–inorganic crystals with diverse structure–property relationships.

Synthesis of a two-dimensional organic–inorganic bismuth iodide metalate through in situ formation of iminium cations

A new layered organic–inorganic iodido bismuthate is prepared from an in situ condensation reaction of acetone and dimethylammonium iodide.

Luminescent perovskites: recent advances in theory and experiments

This review summarizes previous research on luminescent perovskites, including oxides and halides, with different structural dimensionality. The relationship between the crystal structure, electronic structure and properties is discussed in detail.

Two-Dimensional Hybrid Halide Perovskites: Principles and Promises

Hybrid halide perovskites have become the "next big thing" in emerging semiconductor materials, as the past decade witnessed their successful application in high-performance photovoltaics. This resurgence has encompassed enormous and widespread development of the three-dimensional (3D) perovskites, spearheaded by CH₃NH₃PbI₃. The next generation of halide perovskites, however, is characterized by reduced dimensionality perovskites, emphasizing the two-dimensional (2D) perovskite derivatives which expand the field into a more diverse subgroup of semiconducting hybrids that possesses even higher tunability and excellent photophysical properties. In this Perspective, we begin with a historical flashback to early reports before the "perovskite fever", and we follow this original work to its fruition in the present day, where 2D halide perovskites are in the spotlight of current research, offering characteristics desirable in high-performance optoelectronics. We approach the evolution of 2D halide perovskites from a structural perspective, providing a way to classify the diverse structure types of the materials, which largely dictate the unusual physical properties observed. We sort the 2D hybrid halide perovskites on the basis of two key components: the inorganic layers and their modification, and the organic cation diversity. As these two heterogeneous components blend, either by synthetic manipulation (shuffling the organic cations or inorganic elements) or by application of external stimuli (temperature and pressure), the modular perovskite structure evolves to construct crystallographically defined quantum wells (QWs). The complex electronic structure that arises is sensitive to the structural features that could be in turn used as a knob to control the dielectric and optical properties the QWs. We conclude this Perspective with the most notable achievements in optoelectronic devices that have been demonstrated to date, with an eye toward future material discovery and potential technological developments.