A room-temperature antiferroelectric in hybrid perovskite enables highly efficient energy storage at low electric fields

Renewing Halogen Substitution Strategy for the Rational Design of High-Curie Temperature Metal-Free Molecular Antiferroelectrics

Metal-free molecular antiferroelectric (AFE) holds a promise for energy storage on account of its unique physical attributes. However, it is challenging to explore high-curie temperature (Tc) molecular AFEs, due to the lack of design strategies regarding the rise of phase transition energy barriers. By renewing the halogen substitution strategy, we have obtained a series of high-Tc molecular AFEs of the halogen-substituted phenethylammonium bromides (x-PEAB, x=H/F/Cl/Br), resembling the binary stator-rotator system. Strikingly, the p-site halogen substitution of PEA+ cationic rotators raises their phase transition energy barrier and greatly enhances Tc up to ~473 K for Br-PEAB, on par with the record-high Tc values for molecular AFEs. As a typical case, the member 4-fluorophenethylammonium bromide (F-PEAB) shows notable AFE properties, including high Tc (~374 K) and large electric polarization (~3.2 μC/cm2). Further, F-PEAB also exhibits a high energy storage efficiency (η) of 83.6 % even around Tc, catching up with other AFE oxides. This renewing halogen substitution strategy in the molecular AFE system provides an effective way to design high-Tc AFEs for energy storage devices.

Ferroics in Hybrid Organic-Inorganic Perovskites: Fundamentals, Design Strategies, and Implementation

Hybrid organic-inorganic perovskites (HOIPs) afford highly versatile structure design and lattice dimensionalities; thus, they are actively researched as material platforms for the tailoring of ferroic behaviors. Unlike single-phase organic or inorganic materials, the interlayer coupling between organic and inorganic components in HOIPs allows the modification of strain and symmetry by chirality transfer or lattice distortion, thereby enabling the coexistence of ferroic orders. This review focuses on the principles for engineering one or multiple ferroic orders in HOIPs, and the conditions for achieving multiferroicity and magnetoelectric properties. The prospects of multilevel ferroic modulation, chiral spin textures, and spin orbitronics in HOIPs are also presented.

Phase Transitions and Dynamics in Mixed Three- and Low-Dimensional Lead Halide Perovskites

Lead halide perovskites are extensively investigated as efficient solution-processable materials for photovoltaic applications. The greatest stability and performance of these compounds are achieved by mixing different ions at all three sites of the APbX3 structure. Despite the extensive use of mixed lead halide perovskites in photovoltaic devices, a detailed and systematic understanding of the mixing-induced effects on the structural and dynamic aspects of these materials is still lacking. The goal of this review is to summarize the current state of knowledge on mixing effects on the structural phase transitions, crystal symmetry, cation and lattice dynamics, and phase diagrams of three- and low-dimensional lead halide perovskites. This review analyzes different mixing recipes and ingredients providing a comprehensive picture of mixing effects and their relation to the attractive properties of these materials.

Investigating the Structure-property Relationships of Two Cd-based Hybrid Multifunctional Compounds with High Tc, Bright Fluorescence and Wide Band-gap

Organic-inorganic hybrid multifunctional materials have shown significant application in lighting and sensor fields, owing to their prominent performance and diversity structures. Herein, we synthesized two multifunctional compounds: (propyl-quinuclidone)2 CdBr4 (1) and (F-butyl-quinuclidone)2 CdBr4 (2). By introducing light-emitting organic cation with flexible long chain, 1 and 2 exhibit excellent transition properties and bright blue-white fluorescence. Then, combine fluorescence lifetime and first-principal calculation, providing evidence for the electron transfer emission. Subsequently, investigated the impact of substituent carbon chain length (methyl to butyl), structural rigidity (C-C to C-F) and halide framework (Cl to I) on the fluorescence properties. Results indicate that Cd⋅⋅⋅Cd distance and structural rigidity play an important role in fluorescence. Overall, our research provides valuable insight and example for chemical modifications enhance compound performance.

Silver/Antimony-Base Multifunctional Double Perovskite with H/F Substitution Enhance Properties

Two-dimensional double perovskites have experienced rapid development due to their outstanding optoelectronic properties and diverse structural characteristics. However, the synthesis of high-performance multifunctional compounds and the regulation of their properties still lack relevant examples. Herein, we synthesized two multifunctional compounds, (C6H14N)4AgSbBr8 (1) and (F2-C6H12N)4AgSbBr8 (2), which exhibit high solid-state phase transition temperature, bistable dielectric constant switching, second harmonic generation (SHG), and bright emission. Through H/F substitution, the transition temperature increases and achieves a smaller band gap attributed to reduced interlayer spacing. Furthermore, we investigated the broad emission mechanism of the compounds through first-principles calculation and variable-temperature fluorescence, confirming the presence of the STE1 emission. Our work provides insight into the further development of multifunctional compounds and chemical modification that enhances compound properties.

Dehydration Induced a Structural Transformation into a One-Dimensional Hybrid Perovskite with Second Harmonic Generation and Dual Dielectric Switching

Hybrid organic-inorganic perovskites with structural transformation have garnered continued interest in recent years for their potential as multifunctional materials in the field of optoelectronics and smart devices. Herein, we report a novel hybrid organic-inorganic halide, [C5NOH12]2[Cd1.5Cl5(H2O)] (1). Remarkably, the centrosymmetric compound 1 undergoes a structural transformation to a novel noncentrosymmetric hybrid perovskite [C5NOH12][CdCl3] (2) after dehydration. Accompanied by the chemical bond cleavage and reorganization, the zero-dimensional (0D) trinuclear cluster in compound 1 transforms into an intriguing one-dimensional (1D) hexagonal perovskite structure in compound 2, generating multiple optoelectronic switching behaviors. It is worth mentioning that compound 2 demonstrates successive structural phase transitions at 353 and 405 K, resulting in switchable second harmonic generation (SHG) and a dual dielectric response. In addition, compounds 1 and 2 both feature blue-light luminescence, with respective photoluminescence lifetimes of 0.73 and 1.42 ns. This work will offer a pioneering approach and expansive potential for the preparation and development of hybrid organic-inorganic perovskite materials with superior properties.

Excellent Switchable Properties, Broad-Band Emission, Ferroelectricity, and High Tc in a Two-Dimensional Hybrid Perovskite: (4,4-DCA)2PbBr4 Exploited by H/F Substitution

Switchable materials have gained significant attention due to their potential applications in data storage, sensors, and switching devices. Two-dimensional (2D) hybrid perovskites have demonstrated promising prospects for designing switchable materials, where the dynamic motion of the organic components coupled with the distortion of the inorganic framework provides the driving force for triggering multifunctional switchable properties. Herein, through the H/F substitution strategy, we report a polar 2D hybrid lead-based perovskite, (4,4-DCA)₂PbBr₄ (4,4-DCA = 4,4-difluorocyclohexylammonium) (1), which exhibits dual-stable behavior in a dielectric and second harmonic generation (SHG) response during the reversible phase transition process near the high Curie temperature T_c ∼ 409 K. The phase transition temperature is significantly increased by 41 K compared to the corresponding non-fluorinated (CHA)₂PbBr₄ (CHA = cyclohexylammonium). Remarkably, the material shows rare broad-band yellow emission under UV excitation, attributed to the induction of self-trapped exciton emission by the distortion of the [PbBr_6]^4- octahedra, as confirmed by the first-principles analysis. 1 also exhibited ferroelectricity with a saturation polarization value and a small coercive field. This study provides a new insight into the modification of multifunctional switchable materials through the H/F substitution strategy.

A high-temperature double perovskite molecule-based antiferroelectric with excellent anti-breakdown capacity for energy storage

Halide double perovskites have recently emerged as an environmentally green candidate toward electronic and optoelectronic applications owing to their non-toxicity and versatile physical merits, whereas study on high-temperature antiferroelectric (AFE) with excellent anti-breakdown property remains a huge blank in this booming family. Herein, we present the first high-temperature AFE of the lead-free halide double perovskites, (CHMA)₂CsAgBiBr₇ (1, where CHMA⁺ is cyclohexylmethylammonium), by incorporating a flexible organic spacer cation. The typical double P-E hysteresis loops and J-E curves reveal its concrete high-temperature AFE behaviors, giving large polarizations of ~4.2 μC/cm² and a high Curie temperature of 378 K. Such merits are on the highest level of molecular AFE materials. Particularly, the dynamic motional ordering of CHMA⁺ cation contributes to the formation of antipolar alignment and high electric breakdown field strength up to ~205 kV/cm with fatigue endurance over 10⁴ cycles, almost outperforming the vast majority of molecule counterparts. This is the first demonstration of high-temperature AFE properties in the halide double perovskites, which will promote the exploration of new "green" candidates for anti-breakdown energy storage capacitor.