Alloying n ‐Butylamine into CsPbBr 3 To Give a Two‐Dimensional Bilayered Perovskite Ferroelectric Material

Exceptional structural phase transition near room temperature in an organic-inorganic hybrid ferroelectric

An organic-inorganic hybrid ferroelectric, (C6H5CH2CH2NH3)2[HgI4], undergoes an exceptional structural phase transition near room temperature, triggered by a flip of half the organic cations and an order-disorder transition of the inorganic anions, and may be regarded as a displacive-type ferroelectric. This finding provides a new structural phase transition mechanism in molecule-based ferroelectrics.

Monolayer-to-Multilayer Dimensionality Reconstruction in a Hybrid Perovskite for Exploring the Bulk Photovoltaic Effect Enables Passive X-ray Detection

Halide hybrid perovskites are attracting considerable attention as highly promising candidates for directly sensing X-ray radiation, but it is challenging to realize passive X-ray detection without an external power supply. However, the bulk photovoltaic effect (BPVE) in ferroelectrics promotes the independent separation of photoexcited carriers. Herein, by dimensionality reconstruction of a pure-two-dimensional (P-2D) monolayered perovskite (CH₃ OC₃ H₉ N)₂ PbBr₄ , we obtained a quasi-two-dimensional (Q-2D) ferroelectric (CH₃ OC₃ H₉ N)₂ CsPb₂ Br₇ . Converting P-2D into Q-2D perovskite stimulates a significant BPVE associated with robust ferroelectricity, as well as an enhanced mobility lifetime product. These features show the potential of the first passive X-ray detector based on ferroelectrics with an impressive sensitivity up to 410 μC Gy^-1  cm^-2 at zero bias, which is even superior to the value of the state-of-the-art α-Se detector operated at relatively high bias.

Incorporating Guanidinium as Perovskitizer-Cation of Two-Dimensional Metal Halide for Crystal-Array Photodetectors

Two-dimensional (2D) hybrid perovskites are recently emerging as a potential family of semiconductors for versatile optoelectronic applications. Currently, the "perovskitizer" moieties are rigidly limited to small-size cations, while few 2D metal-halides containing guanidinium cations inside perovskite cages have been studied for photodetection. Herein, we present a new 2D hybrid perovskite, (i-BA)₂ (G)Pb₂ I₇ (where G is guanidinium and i-BA is isobutylammonium), which adopts a bilayered framework of {GPb₂ I₇ }. Single-crystal structure analyses disclose that G cations act as the perovskitizer, confined in the flexible perovskite cages formed by the distorted PbI₆ octahedra. Such inorganic sheets are crucial to the superior semiconducting properties and optical bandgap, as verified by the density functional theory calculation. Furthermore, its planar crystal-array photodetector shows fascinating photoelectric performance, including a quite low dark current (∼4.6×10^-11  A), a large current switching ratio (∼1.0×10³ ), and a notable photo-responsivity of ∼0.72 A W^-1 , suggesting great potential of (i-BA)₂ (G)Pb₂ I₇ for photodetection.

Exploring a Fatigue-Free Layered Hybrid Perovskite Ferroelectric for Photovoltaic Non-Volatile Memories

Through a functional unit-transmutation strategy, a fatigue-free layered hybrid perovskite ferroelectric (C₆ H₅ CH₂ NH₃ )₂ CsPb₂ Br₇ (BCPB) has been developed, which demonstrates stable spontaneous polarization (P_s ) of 6.5 μC cm^-2 and high Curie temperature up to 425 K. Meanwhile, BCPB shows splendid bulk photovoltaic effect (BPVE) properties with noticeable zero-bias photocurrent density (5 μA cm^-2 ), and high on/off switching ratio of current (over 3×10⁵ ); these merits even overmatch the most known ferroelectric semiconductor BiFeO₃ . The unique structure with self-regulated net electrical charged layers gives rise to the fatigue-free feature of P_s and BPVE (no significant fatigue after 10⁸ polarity switching cycles), promoting the potential applications of BCPB in photovoltaic non-volatile memories. This work offers an efficient approach for exploring fatigue-free semiconducting ferroelectrics as well as excavates their further applications in next-generation electronic devices.

Highly-Anisotropic Dion-Jacobson Hybrid Perovskite by Tailoring Diamine into CsPbBr3 for Polarization-Sensitive Photodetection

2D materials with inherent attributes of structural anisotropy have been well applied in the field of polarization-sensitive photodetection. However, to explore new 2D members with strong polarized-light responses still remains a challenge. Herein, by alloying diamine molecule into the 3D prototype of CsPbBr₃ , a new Dion-Jacobson (DJ) type 2D perovskite of (HDA)CsPb₂ Br₇ (1, where HDA²⁺ is 1,6-hexamethylenediammonium), containing both inorganic Cs metal and organic cations is designed. The natural anisotropy characteristics of 1 are solidly elucidated by analyzing crystal structure, electric conductivity, and optical properties. Strikingly, distinct polarization-sensitive responses are observed in 1, owing to its strong anisotropy of optical absorption (the ratio of α_c /α_b ≈ 2.2). Consequently, crystal-based detectors of 1 exhibit fascinating photo-activities to polarized-light, including high detectivity (1.5 × 10⁹ Jones), large dichroism ratio (I_ph ^c /I_ph ^b ≈ 1.6) and fast responding rate (200 µs). All these polarization-sensitive performances along with intriguing phase stability make 1 a potential candidate for polarized-light detection. This work paves a pathway toward new functionalities of DJ-type 2D hybrid perovskites for their future optoelectronic device applications.

Dimensional Reduction of Cs2 AgBiBr6 : A 2D Hybrid Double Perovskite with Strong Polarization Sensitivity

By dimensional reduction of the 3D motif of Cs₂ AgBiBr₆ , a lead-free 2D hybrid double perovskite, (i-PA)₂ CsAgBiBr₇ (1, i-PA=isopentylammonium), was successfully designed. It adopts a quantum-confined bilayered structure with alternating organic and inorganic sheets. Strikingly, the unique 2D architecture endows it highly anisotropic nature of physical properties, including electric conductivity and optical absorption (the ratio α_b /α_c =1.9 at 405 nm). Such anisotropy attributes result in the strong polarization-sensitive responses with large dichroic ratios up to 1.35, being comparable to some 2D inorganic materials. This is the first study on the hybrid double perovskites with strong polarization sensitivity. A crystal device of 1 also exhibits rapid response speed (ca. 200 μs) and excellent stabilities. The family of 2D hybrid double perovskites are promising optoelectronic candidates, and this work paves a new pathway for exploring new green polarization-sensitive materials.

Polarization-Driven Self-Powered Photodetection in a Single-Phase Biaxial Hybrid Perovskite Ferroelectric

Self-powered photodetection driven by ferroelectric polarization has shown great potential in next-generation optoelectronic devices. Hybrid perovskite ferroelectrics that combine polarization and semiconducting properties have a promising position within this portfolio. Herein, we demonstrate the realization of self-powered photodetection in a new developed biaxial ferroelectric, (EA)₂ (MA)₂ Pb₃ Br₁₀ (1, EA is ethylammonium and MA is methylammonium), which displays high Curie temperature (375 K), superior spontaneous polarization (3.7 μC cm^-2 ), and unique semiconducting nature. Strikingly, without an external energy supply, 1 exhibits an direction-selectable photocurrent with fascinating attributes including high photocurrent density (≈4.1 μA cm^-2 ), high on/off switching ratio (over 10⁶ ), and ultrafast response time (96/123 μs); such merits are superior to those of the most active ferroelectric oxide BiFeO₃ . Further studies reveal that strong inversion symmetry breaking in 1 provides a desirable driving force for carrier separation, accounting for such electrically tunable self-powered photoactive behaviors. This work sheds light on exploring new multifunctional hybrid perovskites and advancing the design of intelligent photoelectric devices.

3D Organic-Inorganic Perovskite Ferroelastic Materials with Two Ferroelastic Phases: [Et3 P(CH2 )2 F][Mn(dca)3 ] and [Et3 P(CH2 )2 Cl][Mn(dca)3 ]

Organic-inorganic hybrid perovskite-type multiferroics have attracted considerable research interest owing to their fundamental scientific significance and promising technological applications in sensors and multiple-state memories. The recent achievements with divalent metal dicyanamide compounds revealed such malleable frameworks as a unique platform for developing novel functional materials. Herein, two 3D organic-inorganic hybrid perovskites [Et₃ P(CH₂ )₂ F][Mn(dca)₃ ] (1) and [Et₃ P(CH₂ )₂ Cl][Mn(dca)₃ ] (2) (dca=dicyanamide, N(CN)₂ ^- ) are presented. Accompanying the sequential phase transitions, they display a broad range of intriguing physical properties, including above room temperature ferroelastic behavior, switchable dielectricity, and low-temperature antiferromagnetic ordering (T_c =2.4 K for both 1 and 2). It is also worth noting that the spontaneous strain value of 1 is far beyond that of 2 in the first ferroelastic phase, as a result of the precise halogen substitution. From the point view of molecular design, this work should inspire further exploration of multifunctional molecular materials with desirable properties.

Successive near-room-temperature dielectric phase transitions in a lead-free hybrid perovskite-like compound

We have reported a lead-free organic–inorganic hybrid compound, (hexamethyleneimine)₂BiBr₅ (1), which undergoes three successive phase transitions in the vicinity of room temperature.