Hybrid Organic-inorganic Metal Halide Research Articles

The Pnictogen Bond, Together with Other Non-Covalent Interactions, in the Rational Design of One-, Two- and Three-Dimensional Organic-Inorganic Hybrid Metal Halide Perovskite Semiconducting Materials, and Beyond.

The pnictogen bond, a somewhat overlooked supramolecular chemical synthon known since the middle of the last century, is one of the promising types of non-covalent interactions yet to be fully understood by recognizing and exploiting its properties for the rational design of novel functional materials. Its bonding modes, energy profiles, vibrational structures and charge density topologies, among others, have yet to be comprehensively delineated, both theoretically and experimentally. In this overview, attention is largely centered on the nature of nitrogen-centered pnictogen bonds found in organic-inorganic hybrid metal halide perovskites and closely related structures deposited in the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD). Focusing on well-characterized structures, it is shown that it is not merely charge-assisted hydrogen bonds that stabilize the inorganic frameworks, as widely assumed and well-documented, but simultaneously nitrogen-centered pnictogen bonding, and, depending on the atomic constituents of the organic cation, other non-covalent interactions such as halogen bonding and/or tetrel bonding, are also contributors to the stabilizing of a variety of materials in the solid state. We have shown that competition between pnictogen bonding and other interactions plays an important role in determining the tilting of the MX6 (X = a halogen) octahedra of metal halide perovskites in one, two and three-dimensions. The pnictogen interactions are identified to be directional even in zero-dimensional crystals, a structural feature in many engineered ordered materials; hence an interplay between them and other non-covalent interactions drives the structure and the functional properties of perovskite materials and enabling their application in, for example, photovoltaics and optoelectronics. We have demonstrated that nitrogen in ammonium and its derivatives in many chemical systems acts as a pnictogen bond donor and contributes to conferring stability, and hence functionality, to crystalline perovskite systems. The significance of these non-covalent interactions should not be overlooked, especially when the focus is centered on the rationale design and discovery of such highly-valued materials.

Coupling Intracompound Charge Transfer and Cluster‐Centered Excited States in Cu(I) Halide Hybrids for Efficient White Light Emission

Abstract0D hybrid organic–inorganic metal halides have attracted significant interest due to their unique optoelectronic properties, but attainment of efficient and stable white light emission (WLE) in such compounds remains a challenge. Here, efficient WLE via a molecular design that couples intracompound charge transfer and cluster‐centered excited states in 0D halide hybrids is demonstrated. Two Cu(I) halide hybrids, K(18‐crown‐6)Cu2Br3 and Na4(18‐crown‐6)5In2Cu4Br14·8H2O, are synthesized wherein luminescent [Cu4Br6]2− clusters are isolated from each other and surrounded by 18‐crown‐6 coordinated alkali metal cations. In the case of K(18‐crown‐6)Cu2Br3, [Cu4Br6]2− clusters are only partially isolated, leading to strong orange emission with a photoluminescence quantum yield (PLQY) of 53% under UV excitation. Strikingly, to a larger extent of isolation as that, in Na4(18‐crown‐6)5In2Cu4Br14·8H2O as a result of the incorporation of nonemissive [InBr4]− clusters, intense white light emission with a PLQY of 97% is achieved. The dual cluster‐centered states, coupled with a mixed metal‐to‐ligand and halide‐to‐ligand charge transfer state, are responsible for this bright white luminescence. This work provides new design principles for expanding the materials library for single‐component, solid‐state WLE.

Organic Cation Modulation Triggered Second Harmonic Response in Manganese Halides with Bright Fluorescence.

Zero-dimensional (0D) hybrid manganese halides have been recently synthesized and exhibited rich functional properties including fluorescence, ferroelectrics, and ferromagnetism. However, few studies on second-harmonic generation (SHG) behaviors of manganese halide crystals have been reported, presumably owing to the d-d transitions. Here, we report three manganese bromides, [TEA]2MnBr4 (TEA+ = tetraethylammonium; 1), [BTEA]2MnBr4 (BTEA+ = benzyltriethylammonium; 2), and [BTMA]2MnBr4 (BTMA+= benzyltrimethylammonium; 3), with linear and nonlinear optical properties via benzyl or ethyl/methyl substitution strategies. They feature 0D structures containing isolated [MnBr4]2- anions and quaternary ammonium cations with different sizes inserted for charge balance. They all show green phosphorescence, and 2 possesses good luminescence efficiency with a quantum yield of 97.8%, which is larger than those of 1 (79%) and 3 (72%). Specifically, acentric 1 and 3 present effective SHG responses about 0.48 and 0.59 times that of KDP, respectively. The result throws light on the new properties of the hybrid manganese halides and provides a new way to develop novel nonlinear optical-active organic-inorganic hybrid metal halides.

Photoinduced large polaron transport and dynamics in organic–inorganic hybrid lead halide perovskite with terahertz probes

Organic-inorganic hybrid metal halide perovskites (MHPs) have attracted tremendous attention for optoelectronic applications. The long photocarrier lifetime and moderate carrier mobility have been proposed as results of the large polaron formation in MHPs. However, it is challenging to measure the effective mass and carrier scattering parameters of the photogenerated large polarons in the ultrafast carrier recombination dynamics. Here, we show, in a one-step spectroscopic method, that the optical-pump and terahertz-electromagnetic probe (OPTP) technique allows us to access the nature of interplay of photoexcited unbound charge carriers and optical phonons in polycrystalline CH3NH3PbI3 (MAPbI3) of about 10 μm grain size. Firstly, we demonstrate a direct spectral evidence of the large polarons in polycrystalline MAPbI3. Using the Drude–Smith–Lorentz model along with the Frӧhlich-type electron-phonon (e-ph) coupling, we determine the effective mass and scattering parameters of photogenerated polaronic carriers. We discover that the resulting moderate polaronic carrier mobility is mainly influenced by the enhanced carrier scattering, rather than the polaron mass enhancement. While, the formation of large polarons in MAPbI3 polycrystalline grains results in a long charge carrier lifetime at room temperature. Our results provide crucial information about the photo-physics of MAPbI3 and are indispensable for optoelectronic device development with better performance.

Environmental-friendly lead-free chiral Mn-based metal halides with efficient circularly polarized photoluminescence at room temperature

In recent years, chiral organic-inorganic hybrid metal halides have attracted more and more attention from researchers. However, most chiral metal halides are based on toxic Pb elements. In this work, we first successfully prepared a pair of lead-free manganese-based metal halide enantiomers (R/S-1-PPA) 2 MnBr 4 (R/S-1-PPA=R/S-1-Phenylpropan-1-amine). Under the excitation of 365 nm UV light, (R/S-1-PPA) 2 MnBr 4 exhibited bright green emission, which can be attributed to the spin-forbidden d-d transition of Mn 2+ . In addition, the decay lifetimes were as high as 32.57 μs and 33.60 μs for (R-1-PPA) 2 MnBr 4 and (S-1-PPA) 2 MnBr 4 , respectively. (R/S-1-PPA) 2 MnBr 4 showed notable circular dichroism (CD) signals and displayed highly efficient circularly polarized photoluminescence (CPPL) at room temperature with the large g lum of − 0.01 and 0.008, respectively. The high g lum enables them to be a series of very promising materials for the development of chiral optoelectronic devices based on chiral hybrid metal halides. Finally, the white LED device constructed with (R-1-PPA) 2 MnBr 4 also showed a wide color gamut, as high as 107% of NTSC, and a "warm" white light-correlated color temperature of 6883 K, which indicated it has good competitiveness in the application of white light LED devices. • We synthesized a pair of Pb-free Mn-based chiral metal halides (R/S-1-PPA) 2 MnBr 4 . • The halides emitted green CPPL, with g lum of − 0.01 and 0.008 at room temperature. • The g lum represent the maximum of the reported Mn-based metal halides.

Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites

The continuous progress in the synthesis and characterization of materials in the vast family of hybrid organic-inorganic metal halide perovskites (HOIPs) has been pushed by their exceptional properties mainly in optoelectronic applications. These works highlight the peculiar role of lattice vibrations, which strongly interact with electrons, resulting in coupled states affecting the optical properties. Among these materials, layered (2D) HOIPs have emerged as a promising material platform to address some issues of their three-dimensional counterparts, such as ambient stability and ion migration. Layered HOIPs consist of inorganic layers made of metal halide octahedra separated by layers composed of organic cations. They have attracted much interest not only for applications, but also for their rich phenomenology due to their crystal structure tunability. Here, we give an overview of the main experimental findings achieved via Raman spectroscopy in several configurations and set-ups, and how they contribute to shedding light on the complex structural nature of these fascinating materials. We focus on how the phonon spectrum comes from the interplay of several factors. First, the inorganic and organic parts, whose motions are coupled, contribute with their typical modes which are very different in energy. Nonetheless, the interaction between them is relevant, as it results in low-symmetry crystal structures. Then, the role of external stimuli, such as temperature and pressure, which induce phase transitions affecting the spectrum through change in symmetry of the lattice, octahedral tilting and arrangement of the molecules. Finally, the relevant role of the coupling between the charge carriers and optical phonons is highlighted.

Highly Reversible Moisture‐Induced Bright Self‐Trapped Exciton Emissions in a Copper‐Based Organic–Inorganic Hybrid Metal Halide

AbstractMetal halide perovskites are promising optoelectronic materials due to their unique luminescent properties. However, their practical application is limited by their poor chemical stability, especially in humid environments. Moisture can cause phase changes or chemical decomposition, resulting in significant fluorescence quenching. In this study, a copper‐based organic–inorganic hybrid metal halide (t‐BA)3Cu6I9 is synthesized (t‐BA+ is the tert‐butyl‐ammonium ion (C(CH3)3NH3+)). This material exhibits water‐induced luminescence, and its chemical stability in humid environments is being investigated. Tetragonal t‐BA3Cu6I9 is not luminescent, but it reacts quickly with water in the air. The resultant (t‐BA)2Cu2I4·H2O has a broad green emission peak at 520 nm, high photoluminescence quantum yield of 59.4%. Remarkably, (t‐BA)2Cu2I4·H2O is converted back to t‐BA3Cu6I9 at temperatures above 40 °C. This phase conversion is highly repeatable, and the luminescent intensity can be fully recovered after 50 transformation cycles. The mechanism of luminescence is investigated through temperature‐dependent photoluminescence spectra and theoretical calculation, which suggests that (t‐BA)2Cu2I4·H2O has a more localized charge distribution and sufficient polyhedral distortion, resulting in a bright and efficient emission from self‐trapped excitons. This is the first report of water‐induced luminescence in copper‐based metal halides, and it paves the way for stable luminescent materials that are responsive to humidity.

Exciton-Phonon Coupling of Chiral One-Dimensional Lead-Free Hybrid Metal Halides at Room Temperature.

The interaction between organic cations and inorganic metal halide octahedral units strongly affects the properties of organic-inorganic hybrid metal halides. The "soft" property of the lattice provides the possibility of its strong exciton-phonon interaction. Here we report one-dimensional (1D) lead-free chiral organic-inorganic hybrid metal halide single crystals of (R/S)-methylbenzylamine bismuth iodide (R/S-MBA)2Bi2I8, which exhibits a high level of octahedral bond distortion. The introduction of chiral amines leads to a strong chiroptical response in the range of 200-600 nm. The strong exciton-phonon coupling can be observed through the coherent oscillation spectrum of transient absorption dynamics at room temperature. The coherent phonon oscillation frequencies are ∼97 and ∼130 cm-1, corresponding to the symmetrical stretching or bending of the Bi-I octahedron. Our work provides new insights for the study of exciton-phonon coupling in 1D chiral hybrid metal halides.

Tailoring Photoluminescence by Strain-Engineering in Layered Perovskite Flakes.

Strain is an effective strategy to modulate the optoelectronic properties of 2D materials, but it has been almost unexplored in layered hybrid organic-inorganic metal halide perovskites (HOIPs) due to their complex band structure and mechanical properties. Here, we investigate the temperature-dependent microphotoluminescence (PL) of 2D (C6H5CH2CH2NH3)2Cs3Pb4Br13 HOIP subject to biaxial strain induced by a SiO2 ring platform on which flakes are placed by viscoelastic stamping. At 80 K, we found that a strain of <1% can change the PL emission from a single peak (unstrained) to three well-resolved peaks. Supported by micro-Raman spectroscopy, we show that the thermomechanically generated strain modulates the bandgap due to changes in the octahedral tilting and lattice expansion. Mechanical simulations demonstrate the coexistence of tensile and compressive strain along the flake. The observed PL peaks add an interesting feature to the rich phenomenology of photoluminescence in 2D HOIPs, which can be exploited in tailored sensing and optoelectronic devices.

Self‐Trapped Exciton Emission with High Thermal Stability in Antimony‐Doped Hybrid Manganese Chloride

AbstractSelf‐trapped exciton (STE) emission in some metal halides has acquired great interest in recent years due to their broadband emission, large Stokes shift, and high photoluminescence quantum yield (PLQY). However, severe thermal quenching of STE emission is still a critical bottleneck that impedes their application in light‐emitting field. Herein, a novel zero‐dimensional hybrid metal halide, Sb3+‐doped (BTPP)2MnCl4 (BTPP = Benzyltriphenylphosphonium), is accordingly synthesized to address this issue. This compound exhibits excitation‐dependent dual emissions including STE emission of antimony chloride tetrahedron and 4T1‐6A1 transition of Mn2+ ions, resulting in a tunable emission color from green to orange. More importantly, the PL intensity of STE emission at 420 K in (BTPP)2MnCl4:2.0%Sb can maintain 72.5% of its ambient value, which is superior to current organic–inorganic hybrid metal halides. Temperature‐dependent and time‐resolved spectroscopy results suggest that the high thermal stability of STE emission originates from the efficient energy transfer from (BTPP)2MnCl4 host to antimony chloride tetrahedron, which promotes the formation of STEs. The white light‐emitting diode based on this (BTPP)2MnCl4:2.0%Sb phosphor exhibits high‐performance warm white light with a correlated color temperature of 4827 K and a color rendering index of 88.7, which demonstrates its potential in solid‐state lighting applications.

Corrugated 1D Hybrid Metal Halide [C6H7ClN]CdCl3 Exhibiting Broadband White-Light Emission.

Organic-inorganic hybrid metal halides (OIMHs) exhibiting white-light emission are a splendid class of emitters and are regarded as desired phosphors for solid-state lighting applications. Here we report a single-component white-light-emitting hybrid metal halide, namely, [C6H7ClN]CdCl3 (C6H7ClN = 4-(chloromethyl)pyridinium), which features a corrugated 1D anionic double chain composed of edge-shared CdCl6 octahedrons and exhibits broadband white-light emission with a photoluminescence quantum yield of 12.3% under 365 nm UV light irradiation. Density functional theory calculations and temperature-dependent emission spectral analysis unveil that the broadband emission of [C6H7ClN]CdCl3 is ascribed to self-trapped excitons. Moreover, a single-component white-light-emitting diode device with a correlated color temperature of 5214 K and color rendering index of 83.7 can be fabricated via coating [C6H7ClN]CdCl3 on a 365 nm UV light-emitting diode chip. Such a promising luminescent material provides guidance for the design and synthesis of OIMHs with unique structures and desired properties.

Crystal structure and optical properties of in situ synthesized organic-inorganic hybrid metal halides

In recent years, low-dimensional organic-inorganic metal halides have been widely used in photoluminescent diodes, solar cells, lasers, photodetectors, and other fields because of their rich structures and excellent optoelectronic properties. In this paper, organic cations H2DAB (DAB = benzidine) and H2TMB (TMB = 3, 3′, 5, 5′-tetramethylbenzidine) are used as structural templates and cations to regulate the structure of inorganic anions (0D, 1D) and then regulate the luminescence properties of the materials. Among them, the materials with one-dimensional inorganic structures show typical semiconductor behavior, and their electrical conductivity increases with the increase of temperature. The inorganic part of this series of compounds has large structural distortion, large bandgap, significant Stokes shift, and wideband emissions. It has a long fluorescence lifetime, ranging from nanosecond to millisecond. More interestingly, they realize the controllable adjustment of the colour of fluorescent light emitted from yellow-green light, yellow light, orange-red light to near-white light. This work provides a new structure model for understanding the structure-activity relationship between structure and luminescence properties.

Improved water repellency and environmental stability of perovskite solar cells by encapsulating with paraffin wax

Hybrid organic-inorganic metal halide perovskite solar cells are the fastest growing cost-effective photovoltaic technology because of their solution processability and lightweight properties. However, the poor stability of perovskite materials in presence of moisture is the main hindrance to their outdoor applications. Here, paraffin wax is explored as an encapsulating material for improving the water repellency of perovskite solar cells. For this purpose, the drop of paraffin from a burning candle is placed on the device area composed of methylammonium lead iodide as a perovskite material and doped poly(3-hexylthiophene) as a hole-transporting layer. The encapsulation does not affect the photovoltaic performance of the tested devices in ambient conditions, exhibiting the same performance as in an inert atmosphere. Moreover, the photovoltaic performance of the encapsulated solar cells remains unchanged even after 2160 h under ambient conditions with continuous exposure to the relative humidity in the range of 70–85%. The encapsulation is so robust that the photovoltaic performance of the cells does not change even after immersing the encapsulated cell in water or after heating at 85 °C. This performance of paraffin coating is superior to many reported sealing agents, which are deposited using costly instruments or by multistep processes. Thus, the paraffin exhibits the potential to be used as an alternative low-cost coating material for perovskite solar cells.

The magnetic polaron modulated luminescence bands of organic-inorganic hybrid ferroelectric anti-perovskite (C3H9N)3Cd2Cl7 doped with Mn2+

Recently, the excellent optical properties of organic-inorganic hybrid metal halides have attracted much attention in the optoelectronic field. However, their complicated preparation processes seriously influence their properties and applications. In this work, we developed a series of organic-inorganic hybrid metal halides (C3H9N)3Cd2Cl7:x%Mn2+ with an antiperovskite structure with ferroelectrics in an early report, giving tunable emissions contemporarily with different manganese (Mn)2+ concentrations via a simple mechanochemical method. Meanwhile, their single crystals were also grown by a slow thermal evaporation method. The as-grown products with Mn dopants exhibited diluted magnetic semiconductor behavior and varied emission profiles by different excitation wavelengths, which could be modified by the heat treatment. All the emission bands come from the different magnetic polarons with enhanced electron-phonon coupling or self-trapped exciton formation. Ferromagnetic coupling Mn–Mn pairs or clusters in the doped lattice favor the magnetic polaron and red emission at room temperature and even give much stronger emission above room temperature. The excitonic magnetic polaron and local excitonic magnetic polaron were detected at about 309 nm and 398 nm, respectively, with Mn doping. Without Mn2+ dopant, the weak emission band at about 398 nm can also be detected from an intrinsically bound exciton or confined exciton from the amine incorporated metal chlorides. This Mn-doped anti-perovskite Cd halides may find applications in the solid display and lighting, as well as the magneto-optical devices.

Light Emission Enhancement of (C3H10N)4Pb1-xMnxBr6 Metal-Halide Powders by the Dielectric Confinement Effect of a Nanosized Water Layer.

Organic-inorganic hybrid metal halides have been widely studied as a kind of phosphor materials for high-performance white light-emitting diodes. In this paper, a series of organic-inorganic metal-halide (C3H10N)4Pb1-xMnxBr6 powders with different Mn2+ ion doping concentrations were synthesized by mechanochemical methods, giving broadband white light emission with a photoluminescence quantum yield of 36.1% at room temperature, which turn green with a much larger intensity at 80 K. Interestingly, its emission converted from white to red after 100 °C treatments and turned back to white again when exposed to moist air for a while. This emission variation was caused by the adsorbed water layer on the surface of product powders via the dielectric confinement. The red emission from no water powders is identified to occur from the Mn ferromagnetic pair in point-shared octahedral sites, while the broadband white emission originated from the surface water-assisted dielectric confinement and surface polarization which combine the self-trapped excitons and d-d transitions of Mn ions and Mn pairs in the product. Moreover, this white emission can transform into green color at 80 K with a much stronger intensity, caused by the even efficient surface dielectric confinement by the adsorbed frozen water layer. This special compound has the advantages of simple preparation, low cost, and good stability and even contains water molecule in the air, giving a near-perfect white emission, with CIE of (0.33, 0.35) and correlated color temperatures at around 5733 K, which may be used for different applications such as sensing, solid-state lighting, and display.

Effect of Temperature and Pressure on Structural and Optical Properties of Organic-Inorganic Hybrid Manganese Halides.

Organic-inorganic hybrid metal halides have recently attracted attention in the global research field for their bright light emission, tunable photoluminescence wavelength, and convenient synthesis method. This study reports the detailed properties of (C10H16N)2MnBr4, which emits bright green light with a high photoluminescence quantum yield. Results of powder X-ray diffraction, photoluminescence, thermogravimetric analysis, and Raman spectra show the phase transition of (C10H16N)2MnBr4 at 430 K. This phase transition was identified as the solid to liquid state of (C10H16N)2MnBr4. Moreover, the pressure- and temperature-induced relationship between structural and optical properties in (C10H16N)2MnBr4 can be identified. This investigation provides deep insights into the luminescent properties of metal halide crystals and promotes further research.

Chiral Hybrid Copper(I) Halides for High Efficiency Second Harmonic Generation with a Broadband Transparency Window.

Chiral hybrid organic-inorganic metal halides (HOMHs) with intrinsic noncentrosymmetry have shown great promise for applications in second-order nonlinear optics (NLO). However, established chiral HOMHs often suffer from their relatively small band gaps, which lead to negative impacts on transparent window and laser-induced damage thresholds (LDT). Here, we have synthesized two chiral HOMHs based on CuI halides, namely (R-/S-MBA)CuBr2 , which feature well-balanced NLO performances with a highly efficient SHG response, outstanding optical transparency, and high LDT. The effective second-order NLO coefficient of (R-MBA)CuBr2 has been determined to be ≈24.7 pm V-1 , which is two orders of magnitude higher than that of their CuII counterparts. This work shows the promising potential of CuI -based chiral HOMHs for nonlinear photonic applications in wide wavelength regions.

Chiral Hybrid Copper(I) Halides for High Efficiency Second Harmonic Generation with a Broadband Transparency Window

AbstractChiral hybrid organic–inorganic metal halides (HOMHs) with intrinsic noncentrosymmetry have shown great promise for applications in second‐order nonlinear optics (NLO). However, established chiral HOMHs often suffer from their relatively small band gaps, which lead to negative impacts on transparent window and laser‐induced damage thresholds (LDT). Here, we have synthesized two chiral HOMHs based on CuI halides, namely (R‐/S‐MBA)CuBr2, which feature well‐balanced NLO performances with a highly efficient SHG response, outstanding optical transparency, and high LDT. The effective second‐order NLO coefficient of (R‐MBA)CuBr2 has been determined to be ≈24.7 pm V−1, which is two orders of magnitude higher than that of their CuII counterparts. This work shows the promising potential of CuI‐based chiral HOMHs for nonlinear photonic applications in wide wavelength regions.

Regulating Optical Activity and Anisotropic Second-Harmonic Generation in Zero-Dimensional Hybrid Copper Halides.

Structural engineering permits the introduction of chirality into organic-inorganic hybrid metal halides (HMHs), which creates a promising and exclusive material for applications in various optoelectronics. However, the optical activity regulation of chiral HMHs remains largely unexplored. In this work, we have synthesized two pairs of lead-free chiral HMHs with a zero-dimensional tetrahedral arrangement, i.e., (R- and S-1-(1-naphthyl)ethylammonium)2CuCl4 and (R- and S-1-(2-naphthyl)ethylammonium)2CuCl4. The magnitude of optical activity in these HMHs can be efficiently modulated as a result of the different magnetic transition dipole moments. Furthermore, these HMHs exhibited effective second-harmonic generation (SHG) and distinct SHG-circular dichroism (CD), with (R-1-(1-naphthyl)ethylammonium)2CuCl4 having an anisotropy factor (gSHG-CD) of up to 0.41. This work not only provides insights into regulating the optical activity and anisotropic SHG effect of lead-free chiral HMHs but also confirms the feasibility of SHG-CD spectroscopy as a promising tool for characterizing the intrinsic optical activity of chiral materials.

Broadband white-light emission from a novel two-dimensional metal halide assembled by Pb–Cl hendecahedrons

The abundant selection of organic molecules and inorganic units has allowed for the fabrication of organic–inorganic hybrid metal halides (OIMHs) of various morphologies and crystal structures with controllable molecular dimensions and unique photoelectric properties.