Halide double perovskites have recently emerged as a promising environmentally friendly optoelectronic and photovoltaic material for their inherent thermodynamic stability, high defect tolerance, and ...appropriate band gaps. However, to date, no ferroelectric material based on halide double perovskites has been discovered. Herein, by hetero‐substitution of lead and cation intercalation of n‐propylamine, the first halide double perovskite ferroelectric, (n‐propylammonium)2CsAgBiBr7 (1), is reported and it exhibits distinct ferroelectricity with a notable saturation polarization of about 1.5 μC cm−2. More importantly, single‐crystal photodetectors of 1 exhibit extraordinary performance with containing high on/off ratios of about 104, fast response rates of 141 μs, and detectivity as high as 5.3×1011 Jones. This finding opens a new way to design high‐performance perovskite ferroelectrics, and provides a viable approach in the search for stable and lead‐free optoelectronic materials as an alternative to the lead‐containing system.
Lead free: The first halide double perovskite ferroelectric was rationally designed by the substitution of the lead component and cation intercalation of n‐propylamine. The material exhibits fascinating ferroelectricity with a notable saturation polarization of about 1.5 μC cm−2, as well as extraordinary semiconducting performance, including high on/off ratios of about 104, fast response rates of 141 μs, and detectivity as high as 5.3×1011 Jones.
In terms of strong light-polarization coupling, ferroelectric materials with bulk photovoltaic effects afford a promising avenue for optoelectronic devices. However, due to severe polarization ...deterioration caused by leakage current of photoexcited carriers, most of ferroelectrics are merely capable of absorbing 8-20% of visible-light spectra. Ferroelectrics with the narrow bandgap (<2.0 eV) are still scarce, hindering their practical applications. Here, we present a lead-iodide hybrid biaxial ferroelectric, (isopentylammonium)
(ethylammonium)
Pb
I
, which shows large spontaneous polarization (~5.2 μC/cm
) and a narrow direct bandgap (~1.80 eV). Particularly, the symmetry breaking of 4/mmmFmm2 species results in its biaxial attributes, which has four equivalent polar directions. Accordingly, exceptional in-plane photovoltaic effects are exploited along the crystallographic 001 and 010 axes directions inside the crystallographic bc-plane. The coupling between ferroelectricity and photovoltaic effects endows great possibility toward self-driven photodetection. This study sheds light on future optoelectronic device applications.
Although two‐dimensional (2D) metal–halide double perovskites display versatile physical properties due to their huge structural compatibility, room‐temperature ferroelectric behavior has not yet ...been reported for this fascinating family. Here, we designed a room‐temperature ferroelectric material composed of 2D halide double perovskites, (chloropropylammonium)4AgBiBr8, using an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity, including a Curie temperature of 305 K and a notable spontaneous polarization of ≈3.2 μC cm−2, triggered by dynamic ordering of the organic cation and the tilting motion of heterometallic AgBr6/BiBr6 octahedra. Besides, the alternating array of inorganic perovskite sheets and organic cations endows large mobility‐lifetime product (μτ=1.0×10−3 cm2 V−1) for detecting X‐ray photons, which is almost tenfold higher than that of CH3NH3PbI3 wafers. As far as we know, this is the first study on an X‐ray‐sensitive ferroelectric material composed of 2D halide double perovskites. Our findings afford a promising platform for exploring new ferroelectric materials toward further device applications.
Perovskite with new properties: A room‐temperature ferroelectric 2D metal–halide double perovskite, (CPA)4AgBiBr8, exhibits a notable spontaneous polarization of 3.2 μC cm−2 and a Curie temperature of 305 K. Its 2D alternating array of inorganic perovskite frameworks and organic cations endows it with a large mobility‐lifetime product (≈1.0×10−3 cm2 V−1) for detecting X‐ray photons.
Two‐dimensional (2D) layered hybrid perovskites have shown great potential in optoelectronics, owing to their unique physical attributes. However, 2D hybrid perovskite ferroelectrics remain rare. The ...first hybrid ferroelectric with unusual 2D multilayered perovskite framework, (C4H9NH3)2(CH3NH3)2Pb3Br10 (1), has been constructed by tailored alloying of the mixed organic cations into 3D prototype of CH3NH3PbBr3. Ferroelectricity is created through molecular reorientation and synergic ordering of organic moieties, which are unprecedented for the known 2D multilayered hybrid perovskites. Single‐crystal photodetectors of 1 exhibit fascinating performances, including extremely low dark currents (ca. 10−12 A), large on/off current ratios (ca. 2.5×103), and very fast response rate (ca. 150 μs). These merits are superior to integrated detectors of other 2D perovskites, and compete with the most active CH3NH3PbI3.
A 2D multilayered perovskite hybrid ferroelectric was constructed by alloying mixed organic cations into the 3D perovskite prototype of CH3NH3PbBr3. Ferroelectric single‐crystal photodetectors show exceptional behavior, including extremely low dark current (ca. 10−12 A), large on/off current ratio (ca. 2.5×103), and a very fast response rate (ca. 150 μs).
To switch bulk nonlinear optical (NLO) effects represents an exciting new branch of NLO material science, whereas it remains a great challenge to achieve high contrast for “on/off” of quadratic NLO ...effects in crystalline materials. Here, we report the supereminent NLO-switching behaviors of a single-component plastic crystal, 2-(hydroxymethyl)-2-nitro-1,3-propanediol (1), which shows a record high contrast of at least ∼150, exceeding all the known crystalline switches. Such a breakthrough is clearly elucidated from the slowing down of highly isotropic molecular motions during plastic-to-rigid transition. The deep understanding of its intrinsic plasticity and superior NLO property allows the construction of a feasible switching mechanism. As a unique class of substances with short-range disorder embedded in long-range ordered crystalline lattice, plastic crystals enable response to external stimuli and fulfill specific photoelectric functions, which open a newly conceptual avenue for the designing of new functional materials.
Large‐size crystals of organic–inorganic hybrid perovskites (e.g., CH3NH3PbX3, X = Cl, Br, I) have gained wide attention since their spectacular progress on optoelectronic technologies. Although ...presenting brilliant semiconducting properties, a serious concern of the toxicity in these lead‐based hybrids has become a stumbling block that limits their wide‐scale applications. Exploring lead‐free hybrid perovskite is thus highly urgent for high‐performance optoelectronic devices. Here, a new lead‐free perovskite hybrid (TMHD)BiBr5 (TMHD = N,N,N,N‐tetramethyl‐1,6‐hexanediammonium) is prepared from facile solution process. Emphatically, inch‐size high‐quality single crystals are successfully grown, the dimensions of which reach up to 32 × 24 × 12 mm3. Furthermore, the planar arrays of photodetectors based on bulk lead‐free (TMHD)BiBr5 single crystals are first fabricated, which shows sizeable on/off current ratios (≈103) and rapid response speed (τrise = 8.9 ms and τdecay = 10.2 ms). The prominent device performance of (TMHD)BiBr5 strongly underscores the lead‐free hybrid perovskite single crystals as promising material candidates for optoelectronic applications.
A new lead‐free perovskite hybrid (TMHD)BiBr5 (TMHD = N,N,N,N‐Tetramethyl‐1,6‐hexanediammonium) is prepared from solution and high‐quality inch‐size single crystals are successfully grown with dimensions up to 32 × 24 × 12 mm3. Moreover, planar arrays of photodetectors based on bulk (TMHD)BiBr5 single‐crystal are first fabricated, which show prominent photodetection performance.
Poor stability has long been a major obstacle to the practical applications of metal–organic framework (MOF) photocatalysts. This problem can be overcome by the use of structural interpenetration. In ...this work, by modifying Ru metalloligands, we have rationally designed two Ru–polypyridine based MOFs (with non-interpenetrated and interpenetrated structures, respectively), both of which exhibit similar photocatalytic activities for CO2 photoreduction. Remarkably, the interpenetrated Ru-MOF possesses good photocatalytic durability and recyclability, and shows much higher thermal and photic stability in comparison with its non-interpenetrated counterpart. To the best of our knowledge, this is the first time that the stability of MOF photocatalysts was improved by using structural interpenetration.
Antiferroelectrics, characterized by the natural polarization-electric field (P–E) double hysteresis loops, has been developed as a promising branch for energy storage. Here, we present the first ...antiferroelectric in the booming family of lead iodide hybrid perovskites, (BA)2(EA)2Pb3I10 (1, where BA = n-butylammonium and EA = ethylammonium), which exhibits one of the highest Curie temperatures (∼363 K) for the majority of known molecular systems. Strikingly, its high-temperature antiferroelectricity, triggered by an antipolar alignment of adjacent dipoles, is confirmed by the characteristic double P–E hysteresis loops, thus enabling remarkable energy storage efficiencies in the range of 65%–83%. This merit is almost comparable to those of many inorganic counterparts, suggesting the great potential of 1 for energy storage. Another fascinating attribute is that 1 also acts as a room-temperature biaxial ferroelectric with spontaneous polarization of 5.6 μC·cm–2. As far as we know, this study on the high-temperature antiferroelectric, along with room-temperature biaxial ferroelectricity, is unprecedented for the versatile lead iodide hybrid perovskites, which sheds light on the design of new electric-ordered materials and facilitates their application of high-performance devices.
Abstract
Electrocaloric effect driven by electric fields displays great potential in realizing highly efficient solid-state refrigeration. Nevertheless, most known electrocaloric materials exhibit ...relatively poor cooling performance near room temperature, which hinders their further applications. The emerging family of hybrid perovskite ferroelectrics, which exhibits superior structural diversity, large heat exchange and broad property tenability, offers an ideal platform. Herein, we report an exceptionally large electrocaloric effect near room temperature in a designed hybrid perovskite ferroelectric (CH
3
)
2
CHCH
2
NH
3
2
PbCl
4
, which exhibits a sharp first-order phase transition at 302 K, superior spontaneous polarization (>4.8
μ
C/cm
2
) and relatively small coercive field (<15 kV/cm). Strikingly, a large isothermal entropy change Δ
S
of 25.64 J/kg/K and adiabatic temperature change Δ
T
of 11.06 K under a small electric field Δ
E
of 29.7 kV/cm at room temperature are achieved, with giant electrocaloric strengths of isothermal Δ
S
/Δ
E
of 0.86 J·cm/kg/K/kV and adiabatic Δ
T
/Δ
E
of 370 mK·cm/kV, which is larger than those of traditional ferroelectrics. This work presents a general approach to the design of hybrid perovskite ferroelectrics, as well as provides a family of candidate materials with potentially prominent electrocaloric performance for room temperature solid-state refrigeration.
Activation technique was applied for the measurement of ground-state and isomeric-state cross-sections in the
74
Se(n,2n)
73
Se reaction within the 13–15 MeV neutron energy range to resolve ...inconsistencies in the existing database.
γ
rays with energy of 253.7 keV from the decay of the
73
m
Se isomeric-state and energy of 361.2 keV from the
73
g
Se ground state were recorded using a high-resolution high-purity germanium (HPGe) detector. A monoenergetic neutron beam was produced via the T(d,n)
4
He. The cross-sections and isomeric ratios were also calculated using the TALYS-1.95 nuclear model code with different six-level density options at neutron energies varying from the reaction threshold to 20 MeV. Results are discussed and also compared with some corresponding values found in the literature.
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