A Semiconducting Organic–Inorganic Hybrid Perovskite‐type Non‐ferroelectric Piezoelectric with Excellent Piezoelectricity

Piezoelectric materials are a class of important functional materials applied in high‐voltage sources, sensors, vibration reducers, actuators, motors, and so on. Herein, [(CH₃)₃S]₃[Bi₂Br₉]( 1 ) is a brilliant semiconducting organic–inorganic hybrid perovskite‐type non‐ferroelectric piezoelectric with excellent piezoelectricity. Strikingly, the value of the piezoelectric coefficient d₃₃ is estimated as ≈18 pC N^?1. Such a large piezoelectric coefficient in non‐ferroelectric piezoelectric has been scarcely reported and is comparable with those of typically one‐composition non‐ferroelectric piezoelectrics such as ZnO (3pC N^?1) and much greater than those of most known typical materials. In addition, 1 exhibits semiconducting behavior with an optical band gap of ≈2.58 eV that is lower than the reported value of 3.37 eV for ZnO. This discovery opens a new avenue to exploit molecular non‐ferroelectric piezoelectric and should stimulate further exploration of non‐ferroelectric piezoelectric due to their high stability and low loss characteristics.     

Pressure‐Dependent Polymorphism and Band‐Gap Tuning of Methylammonium Lead Iodide Perovskite

We report the pressure‐induced crystallographic transitions and optical behavior of MAPbI₃ (MA=methylammonium) using in situ synchrotron X‐ray diffraction and laser‐excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin‐orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO₃‐type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase‐mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction.     

An Above‐Room‐Temperature Ferroelectric Organo–Metal Halide Perovskite: (3‐Pyrrolinium)(CdCl3)

Hybrid organo–metal halide perovskite materials, such as CH₃NH₃PbI₃, have been shown to be some of the most competitive candidates for absorber materials in photovoltaic (PV) applications. However, their potential has not been completely developed, because a photovoltaic effect with an anomalously large voltage can be achieved only in a ferroelectric phase, while these materials are probably ferroelectric only at temperatures below 180 K. A new hexagonal stacking perovskite‐type complex (3‐pyrrolinium)(CdCl₃) exhibits above‐room‐temperature ferroelectricity with a Curie temperature T_c=316 K and a spontaneous polarization P_s=5.1 μC cm^?2. The material also exhibits antiparallel 180° domains which are related to the anomalous photovoltaic effect. The open‐circuit photovoltage for a 1 mm‐thick bulky crystal reaches 32 V. This finding could provide a new approach to develop solar cells based on organo–metal halide perovskites in photovoltaic research.     

Experimental Evidence for a Triboluminescent Antiperovskite Ferroelectric: Tris(trimethylammonium) catena‐Tri‐μ‐chloro‐manganate(II) Tetrachloromanganate(II)

The perovskite structure is rich in ferroelectricity. In contrast, ferroelectric antiperovskites have been scarcely confirmed experimentally since the discovery of M₃AB‐type antiperovskites in the 1930s. Ferroelectricity is now revealed in an organic–inorganic hybrid X₃AB antiperovskite structure, which exhibits a clear ferroelectric phase transition 6/mmmF6mm with a high Curie point of 480 K. The physical properties across the phase transition are obviously changed along with the symmetry requirements, providing solid experimental evidence for the ferroelectric phase transition. More interestingly, the discovered antiperovskite shows intense photoluminescence and triboluminescence properties. The confirmation of the triboluminescent ferroelectric antiperovskite will open new avenues to explore excellent optoelectronic properties in the antiperovskite family.     

Two-Step Structure Phase Transition,Dielectric Anomalies,and Thermochromic Luminescence Behavior in a Direct Band Gap 2D Corrugated Layer Lead Chloride Hybrid of [(CH3)4N]4Pb3Cl10

A direct band gap 2D corrugated layer lead chloride hybrid, [(CH₃)₄N]₄Pb₃Cl₁₀ ( 1 ), shows analogous topology to the {Mg₃F₁₀⁴⁻}_∞ layer in Cs₄Mg₃F₁₀, and with the (CH₃)₄N⁺ cations locating in the inorganic layer voids and between the interlayers. Two reversible structural phase transitions occur in 1 at 225/210 K and 328/325 K upon heating/cooling, respectively. On going from the low- to intermediate-temperature phase, the space group changes from P2₁/c to Cmca, and the crystallographic axis perpendicular to the layers is doubled with the order–disorder transformation of (CH₃)₄N ⁺ cations between the interlayers. The intermediate- and high-temperature phases are isomorphic with similar cell parameters and packing structure; their main difference concerns the disorder degree of the (CH₃)₄N ⁺ cations between the interlayers. The two-step structural phase transitions lead to dielectric anomalies around the corresponding T_c. Interestingly, 1 shows multiband emission, originating from the recombination of exciton and emission of defects. Moreover, 1 exhibits divergent thermochromic luminescent features around the T_c on the intermediate to low temperature transition.     

[C6H14N]PbBr3: An ABX3‐Type Semiconducting Perovskite Hybrid with Above‐Room‐Temperature Phase Transition

Organic–inorganic hybrid perovskites, with the formula ABX₃ (A=organic cation, B=metal cation, and X=halide; for example, CH₃NH₃PbI₃), have diverse and intriguing physical properties, such as semiconduction, phase transitions, and optical properties. Herein, a new ABX₃‐type semiconducting perovskite‐like hybrid, (hexamethyleneimine)PbBr₃ ( 1 ), consisting of one‐dimensional inorganic frameworks and cyclic organic cations, is reported. Notably, the inorganic moiety of 1 adopts a perovskite‐like architecture and forms infinite columns composed of face‐sharing PbBr₆ octahedra. Strikingly, the organic cation exhibits a highly flexible molecular configuration, which triggers an above‐room‐temperature phase transition, at T_c=338.8 K; this is confirmed by differential scanning calorimetry (DSC), specific heat capacity (C_p), and dielectric measurements. Further structural analysis reveals that the phase transition originates from the molecular configurational distortion of the organic cations coupled with small‐angle reorientation of the PbBr₆ octahedra inside the inorganic components. Moreover, temperature‐dependent conductivity and UV/Vis absorption measurements reveal that 1 also displays semiconducting behavior below T_c. It is believed that this work will pave a potential way to design multifeatured perovskite hybrids by utilizing cyclic organic amines.     

Bandgap‐Tunable Preparation of Smooth and Large Two‐Dimensional Antimonene

As a highly stable band gap semiconductor, antimonene is an intriguing two‐dimensional (2D) material in optoelectronics. However, its short layer distance and strong binding energy make it challenging to prepare high‐quality large 2D antimonene; therefore, its predicted tunable band gap has not been experimentally confirmed. Now, an approach to prepare smooth and large 2D antimonene with uniform layers that uses a pregrinding and subsequent sonication‐assisted liquid‐phase exfoliation process has been established. Mortar pregrinding provides a shear force along the layer surfaces, forming large, thin antimony plates, which can then easily be exfoliated into smooth, large antimonene, avoiding long sonication times and antimonene destruction. The resulting antimonene also enabled verification of the tunable band gap from 0.8 eV to 1.44 eV. Hole extraction and current enhancement by about 30 % occurred when the antimonene was used as a hole transport layer in perovskite solar cells.     

Alloying n‐Butylamine into CsPbBr3 To Give a Two‐Dimensional Bilayered Perovskite Ferroelectric Material

Cesium‐lead halide perovskites (e.g. CsPbBr₃) have gained attention because of their rich physical properties, but their bulk ferroelectricity remains unexplored. Herein, by alloying flexible organic cations into the cubic CsPbBr₃, we design the first cesium‐based two‐dimensional (2D) perovskite ferroelectric material with both inorganic alkali metal and organic cations, (C₄H₉NH₃)₂CsPb₂Br₇ ( 1 ). Strikingly, 1 shows a high Curie temperature (T_c=412 K) above that of BaTiO₃ (ca. 393 K) and notable spontaneous polarization (ca. 4.2 μC cm^?2), triggered by not only the ordering of organic cations but also atomic displacement of inorganic Cs⁺ ions. To our knowledge, such a 2D bilayered Cs⁺‐based metal–halide perovskite ferroelectric material with inorganic and organic cations is unprecedented. 1 also shows photoelectric semiconducting behavior with large “on/off” ratios of photoconductivity (>10³).     

Continuous and Segmented Semiconducting Fiber‐like Nanostructures with Spatially Selective Functionalization by Living Crystallization‐Driven Self‐Assembly

Fiber‐like π‐conjugated nanostructures are important components of flexible organic electronic and optoelectronic devices. To broaden the range of potential applications, one needs to control not only the length of these nanostructures, but the introduction of diverse functionality with spatially selective control. Here we report the synthesis of a crystalline‐coil block copolymer of oligo(p‐phenylenevinylene)‐b‐poly(2‐vinylpyridine) (OPV₅‐b‐P2VP₄₄), in which the basicity and coordinating/chelating ability of the P2VP segment provide a landscape for the incorporation of a variety of functional inorganic NPs. Through a self‐seeding strategy, we were able to prepare monodisperse fiber‐like micelles of OPV₅‐b‐P2VP₄₄ with lengths ranging from 50 to 800 nm. Significantly, the exposed two ends of OPV core of these fiber‐like micelles remained active toward further epitaxial deposition of OPV₅‐b‐PNIPAM₄₉ and OPV₅‐b‐P2VP₄₄ to generate uniform A‐B‐A and B‐A‐B‐A‐B segmented block comicelles with tunable lengths for each block. The P2VP domains in these (co‐)micelles can be selectively decorated with inorganic and polymeric nanoparticles as well as metal oxide coatings, to afford hybrid fiber‐like nanostructures. This work provides a versatile strategy toward the fabrication of narrow length dispersity continuous and segmented π‐conjugated OPV‐containing fiber‐like micelles with the capacity to be decorated in a spatially selective way with varying functionalities.     

Zero‐Dimensional Hybrid Cd‐Based Perovskites with Broadband Bluish White‐Light Emissions

Recently, low‐dimensional organic‐inorganic hybrid metal halide perovskites acting as single‐component white‐light emitting materials have attracted extensive attention, but most studies concentrate on hybrid lead perovskites. Herein, we present two isomorphic zero‐dimensional (0D) hybrid cadmium perovskites, (HMEDA)CdX₄ (HMEDA=hexamethylenediamine, X=Cl ( 1 ), Br ( 2 )), which contain isolated [CdX₄]^2? anions separated by [HMEDA]²⁺ cations. Under UV light excitation, both compounds display broadband bluish white‐light emission (515 nm for 1 and 445 nm for 2 ) covering the entire visible light spectrum with sufficient photophysical stabilities. Remarkably, compound 2 shows a high color rendering index (CRI) of 83 enabling it as a promising candidate for single‐component WLED applications. Based on the temperature‐dependent, powder‐dependent and time‐resolved PL measurements as well as other detailed studies, the broadband light emissions are attributed to self‐trapped excitons stemming from the strong electron‐phonon coupling.     

Air‐Stable,Lead‐Free Zero‐Dimensional Mixed Bismuth‐Antimony Perovskite Single Crystals with Ultra‐broadband Emission

Lead‐free zero‐dimensional (0D) organic‐inorganic metal halide perovskites have recently attracted increasing attention for their excellent photoluminescence properties and chemical stability. Here, we report the synthesis and characterization of an air‐stable 0D mixed metal halide perovskite (C₈NH₁₂)₄Bi_0.57Sb_0.43Br₇?H₂O, in which individual [BiBr₆]^3? and [SbBr₆]^3? octahedral units are completely isolated and surrounded by the large organic cation C₈H₁₂N⁺. Upon photoexcitation, the bulk crystals exhibit ultra‐broadband emission ranging from 400 to 850 nm, which originates from both free excitons and self‐trapped excitons. This is the first example of 0D perovskites with broadband emission spanning the entire visible spectrum. In addition, (C₈NH₁₂)₄Bi_0.57Sb_0.43Br₇?H₂O exhibits excellent humidity and light stability. These findings present a new direction towards the design of environmentally‐friendly, high‐performance 0D perovskite light emitters.     

Air‐Stable,Lead‐Free Zero‐Dimensional Mixed Bismuth‐Antimony Perovskite Single Crystals with Ultra‐broadband Emission

Lead‐free zero‐dimensional (0D) organic‐inorganic metal halide perovskites have recently attracted increasing attention for their excellent photoluminescence properties and chemical stability. Here, we report the synthesis and characterization of an air‐stable 0D mixed metal halide perovskite (C₈NH₁₂)₄Bi_0.57Sb_0.43Br₇?H₂O, in which individual [BiBr₆]^3? and [SbBr₆]^3? octahedral units are completely isolated and surrounded by the large organic cation C₈H₁₂N⁺. Upon photoexcitation, the bulk crystals exhibit ultra‐broadband emission ranging from 400 to 850 nm, which originates from both free excitons and self‐trapped excitons. This is the first example of 0D perovskites with broadband emission spanning the entire visible spectrum. In addition, (C₈NH₁₂)₄Bi_0.57Sb_0.43Br₇?H₂O exhibits excellent humidity and light stability. These findings present a new direction towards the design of environmentally‐friendly, high‐performance 0D perovskite light emitters.     

A Zero‐Dimensional Organic Seesaw‐Shaped Tin Bromide with Highly Efficient Strongly Stokes‐Shifted Deep‐Red Emission

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 (SnBr₄^2?) 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 SnBr₄^2? species, and 2) the seesaw structure enabling a pronounced excited state structural deformation as confirmed by density functional theory (DFT) calculations.     

Benign‐by‐Design Solventless Mechanochemical Synthesis of Three‐, Two‐, and One‐Dimensional Hybrid Perovskites

Organic–inorganic hybrid perovskites have attracted significant attention owing to their extraordinary optoelectronic properties with applications in the fields of solar energy, lighting, photodetectors, and lasers. The rational design of these hybrid materials is a key factor in the optimization of their performance in perovskite‐based devices. Herein, a mechanochemical approach is proposed as a highly efficient, simple, and reproducible method for the preparation of four types of hybrid perovskites, which were obtained in large amounts as polycrystalline powders with high purity and excellent optoelectronics properties. Two archetypal three‐dimensional (3D) perovskites (MAPbI₃ and FAPbI₃) were synthesized, together with a bidimensional (2D) perovskite (Gua₂PbI₄) and a “double‐chain” one‐dimensional (1D) perovskite (GuaPbI₃), whose structure was elucidated by X‐ray diffraction.     

The Significance of Ion Conduction in a Hybrid Organic–Inorganic Lead‐Iodide‐Based Perovskite Photosensitizer

The success of perovskite solar cells has sparked enormous excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such crystalline absorber materials. Far from being exhaustively studied in terms of solid‐state properties, these materials surprised by anomalies such as a huge apparent low‐frequency dielectric constant and pronounced hysteretic current–voltage behavior. Here we show that methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of iodine ions. In particular, we measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build‐up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into electrical charge transport in the hybrid organic–inorganic lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.     

Methylammonium Bismuth Iodide as a Lead‐Free,Stable Hybrid Organic–Inorganic Solar Absorber

Methylammonium lead halide (MAPbX₃) perovskites exhibit exceptional carrier transport properties. But their commercial deployment as solar absorbers is currently limited by their intrinsic instability in the presence of humidity and their lead content. Guided by our theoretical predictions, we explored the potential of methylammonium bismuth iodide (MBI) as a solar absorber through detailed materials characterization. We synthesized phase‐pure MBI by solution and vapor processing. In contrast to MAPbX₃, MBI is air stable, forming a surface layer that does not increase the recombination rate. We found that MBI luminesces at room temperature, with the vapor‐processed films exhibiting superior photoluminescence (PL) decay times that are promising for photovoltaic applications. The thermodynamic, electronic, and structural features of MBI that are amenable to these properties are also present in other hybrid ternary bismuth halide compounds. Through MBI, we demonstrate a lead‐free and stable alternative to MAPbX₃ that has a similar electronic structure and nanosecond lifetimes.     

Hydrogen-Bonded Polyrotaxane Cation Structure in Nickel Dithiolate Anion Radical Salts: Ferromagnetic and Semiconducting Behavior Associated with Structural Phase Transition

The pseudo-polyrotaxane structure of [(H-bpy⁺)- (DB-24-crown-8)]_∞ (H-bpy⁺ = monoprotonated 4,4-bipyridinium; DB-24-crown-8 = dibenzo-24-crown-8) has been incorporated into the anion radical salt [Ni(dmit)₂]⁻ (dmit²⁻ = 1,3-dithiole-2-thione-4,5-dithiolate). (H-bpy⁺)(DB-24-crown-8)[Ni(dmit)₂]⁻ crystallized as two polymorphs, crystals 1 and 2 . Crystal 1 was found to have a lower density and looser packing structure in which H-bpy⁺ forms a one-dimensional hydrogen-bonding chain that passes though the crown ether ring of DB-24-crown-8. DB-24-crown-8 adopts a U-shaped conformation in which two phenylene rings sandwich one of the pyridyl rings of H-bpy⁺ to stabilize the structure. The [Ni(dmit)₂]⁻ anions are arranged in a layer parallel to the (10) plane with uniform side-by-side interactions. A structural phase transition was observed at 235 K, accompanied by ordering of the polyrotaxane structure. In crystal 1 , at 173 K, H-bpy⁺ is twisted around the central C−C bond, which perturbs the arrangement of [Ni(dmit)₂]⁻ through short C−H⋅⋅⋅S contacts. As a result, the semiconducting behavior, with an activation energy of 0.21 eV, becomes insulating below 235 K. The crystal exhibits ferromagnetic interactions because of the weak side-by-side interactions between [Ni(dmit)₂]⁻ anions. Crystal 2 has a similar pseudo-polyrotaxane structure but showed no phase transition. This suggests that the looser crystal packing in crystal 1 induces the structural change of the pseudo-polyrotaxane, perturbing the electron system of [Ni(dmit)₂]⁻.     

Coexistence of Three Ferroic Orders in the Multiferroic Compound [(CH3)4N][Mn(N3)3] with Perovskite‐Like Structure

The perovskite azido compound [(CH₃)₄N][Mn(N₃)₃], which undergoes a first‐order phase change at T_t=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN₆] octahedral as well as order/disorder and off‐center shifts of the [(CH₃)₄N]⁺ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low‐temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH₃)₄N][Mn(N₃)₃] is a singular material in which three ferroic orders coexist even above room temperature.