Exploring a Lead‐free Semiconducting Hybrid Ferroelectric with a Zero‐Dimensional Perovskite‐like Structure

Perovskite lead halides (CH₃NH₃PbI₃) have recently taken a promising position in photovoltaics and optoelectronics because of remarkable semiconducting properties and possible ferroelectricity. However, the potential toxicity of lead arouses great environmental concern for widespread application. A new chemically tailored lead‐free semiconducting hybrid ferroelectric is reported, N‐methylpyrrolidinium)₃Sb₂Br₉ ( 1 ), which consists of a zero‐dimensional (0‐D) perovskite‐like anionic framework connected by corner‐ sharing SbBr₆ coordinated octahedra. It presents a large ferroelectric spontaneous polarization of approximately 7.6 μC cm^?2, as well as notable semiconducting properties, including positive temperature‐dependent conductivity and ultraviolet‐sensitive photoconductivity. Theoretical analysis of electronic structure and energy gap discloses a dominant contribution of the 0‐D perovskite‐like structure to the semiconducting properties of the material. This finding throws light on the rational design of new perovskite‐like hybrids, especially lead‐free semiconducting ferroelectrics.     

Switchable Charge‐Transfer in the Photoelectrochemical Energy‐Conversion Process of Ferroelectric BiFeO3 Photoelectrodes

Instead of conventional semiconductor photoelectrodes, herein, we focus on BiFeO₃ ferroelectric photoelectrodes to break the limits imposed by common semiconductors. As a result of their prominent ferroelectric properties, the photoelectrodes are able to tune the transfer of photo‐excited charges generated either in BiFeO₃ or the surface modifiers by manipulating the poling conditions of the ferroelectric domains. At 0 V vs Ag/AgCl, the photocurrent could be switched from 0 μA cm^?2 to 10 μA cm^?2 and the open‐circuit potential changes from 33 mV to 440 mV, when the poling bias of pretreatment is manipulated from ?8 V to +8 V. Additionally, the pronounced photocurrent from charge injection of the excited surface modifiers could be quenched by switching the poling bias from +8 V to ?8 V.     

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).     

Room‐Temperature Ferroelectric Material Composed of a Two‐Dimensional Metal Halide Double Perovskite for X‐ray Detection

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.     

A Molecular Ferroelectric Showing Room‐Temperature Record‐Fast Switching of Spontaneous Polarization

Fast switching of spontaneous polarization (P_s) is one of the most essential requirements for ferroelectrics used in the field of data storage. However, in contrast to inorganic counterparts, the low operating frequency (<500 Hz) for molecular ferroelectrics severely hinders their large‐scale applications. Herein, for the first time, we achieved the room‐temperature fastest switching of the P_s in a new molecular ferroelectric, N‐methylmorpholinium trinitrophenolate ( 1 ), which displays notable ferroelectricity (P_s=3.2 μc cm^?2). Strikingly, electric polarizations of 1 have been switched under a record‐high frequency of 263 kHz, and this performance remains stable without any obvious fatigue after ca. 2×10⁵ switching cycles. To our knowledge, 1 is the first organic ferroelectric to switch polarization at such a high operating frequency, exceeding the majority of organic ferroelectrics, which opens up new possibilities for its potential in the field of non‐volatile memory.     

Potassium 1,1′‐Dinitramino‐5,5′‐bistetrazolate: A Primary Explosive with Fast Detonation and High Initiation Power

Adequate primary explosives such as lead azide mostly contain toxic ingredients, which have to be replaced. A new candidate that shows high potential, potassium 1,1′‐dinitramino‐5,5′‐bistetrazolate (K₂DNABT), was synthesized by a sophisticated synthetic procedure based on dimethylcarbonate and glyoxal. It was intensively characterized for its chemical (X‐ray diffraction, EA, NMR and vibrational spectroscopy) and physico‐chemical properties (sensitivity towards impact, friction, and electrostatic, DSC). The obtained primary explosive combines good thermal stability with the desired mechanical stability. Owing to its high heat of formation (326 kJ mol^?1) and density (2.11 g cm^?3), impressive values for its detonation velocity (8330 m s^?1) and pressure (311 kbar) were computed. Its superior calculated performance output was successfully confirmed and demonstrated by different convenient energetic test methods.     

A Titanium‐Doped SiOx Passivation Layer for Greatly Enhanced Performance of a Hematite‐Based Photoelectrochemical System

This study introduces an in situ fabrication of nanoporous hematite with a Ti‐doped SiO_x passivation layer for a high‐performance water‐splitting system. The nanoporous hematite with a Ti‐doped SiO_x layer (Ti‐(SiO_x/np‐Fe₂O₃)) has a photocurrent density of 2.44 mA cm^?2 at 1.23 V_RHE and 3.70 mA cm^?2 at 1.50 V_RHE. When a cobalt phosphate co‐catalyst was applied to Ti‐(SiO_x/np‐Fe₂O₃), the photocurrent density reached 3.19 mA cm^?2 at 1.23 V_RHE with stability, which shows great potential of the use of the Ti‐doped SiO_x layer with a synergistic effect of decreased charge recombination, the increased number of active sites, and the reduced hole‐diffusion pathway from the hematite to the electrolyte.     

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.     

Dual‐Doped Molybdenum Trioxide Nanowires: A Bifunctional Anode for Fiber‐Shaped Asymmetric Supercapacitors and Microbial Fuel Cells

A novel in situ N and low‐valence‐state Mo dual doping strategy was employed to significantly improve the conductivity, active‐site accessibility, and electrochemical stability of MoO₃, drastically boosting its electrochemical properties. Consequently, our optimized N‐MoO_3?x nanowires exhibited exceptional performances as a bifunctional anode material for both fiber‐shaped asymmetric supercapacitors (ASCs) and microbial fuel cells (MFCs). The flexible fiber‐shaped ASC and MFC device based on the N‐MoO_3?x anode could deliver an unprecedentedly high energy density of 2.29 mWh cm^?3 and a remarkable power density of 0.76 μW cm^?1, respectively. Such a bifunctional fiber‐shaped N‐MoO_3?x electrode opens the way to integrate the electricity generation and storage for self‐powered sources.     

Conjugated Copper–Catecholate Framework Electrodes for Efficient Energy Storage

A conjugated copper(II) catecholate based metal–organic framework (namely Cu‐DBC) was prepared using a D₂‐symmetric redox‐active ligand in a copper bis(dihydroxy) coordination geometry. The π‐d conjugated framework exhibits typical semiconducting behavior with a high electrical conductivity of ca. 1.0 S m^?1 at room temperature. Benefiting from the good electrical conductivity and the excellent redox reversibility of both ligand and copper centers, Cu‐DBC electrode features superior capacitor performances with gravimetric capacitance up to 479 F g^?1 at a discharge rate of 0.2 A g^?1. Moreover, the symmetric solid‐state supercapacitor of Cu‐DBC exhibits high areal (879 mF cm^?2) and volumetric (22 F cm^?3) capacitances, as well as good rate capability. These metrics are superior to most reported MOF‐based supercapacitors, demonstrating promising applications in energy‐storage devices.     

Magnetothermal Microfluidic‐Assisted Hierarchical Microfibers for Ultrahigh‐Energy‐Density Supercapacitors

Chemical architectures with an ordered porous backbone and high charge transfer are significant for fiber‐shaped supercapacitors (FSCs). However, owing to the sluggish ion kinetic diffusion and storage in compacted fibers, achieving high energy density remains a challenge. An innovative magnetothermal microfluidic method is now proposed to design hierarchical carbon polyhedrons/holey graphene (CP/HG) core–shell microfibers. Owing to highly magnetothermal etching and microfluidic reactions, the CP/HG fibers maintain an open inner‐linked ionic pathway, large specific surface area, and moderate nitrogen active site, facilitating more rapid ionic dynamic transportation and accommodation. The CP/HG FSCs show an ultrahigh energy density (335.8 μWh cm^?2) and large areal capacitance (2760 mF cm^?2). A self‐powered endurance application with the integration of chip‐based FSCs is designed to profoundly drive the durable motions of an electric car and walking robot.     

Ge‐Mediated Modification in Ta3N5 Photoelectrodes with Enhanced Charge Transport for Solar Water Splitting

Ta₃N₅ is a promising photoanode candidate for photoelectrochemical water splitting, with a band gap of about 2.1 eV and a theoretical solar‐to‐hydrogen efficiency as high as 15.9 % under AM 1.5 G 100 mW cm^?2 irradiation. However, the presently achieved highest photocurrent (ca. 7.5 mA cm^?2) on Ta₃N₅ photoelectrodes under AM 1.5 G 100 mW cm^?2 is far from the theoretical maximum (ca. 12.9 mA cm^?2), which is possibly due to serious bulk recombination (poor bulk charge transport and charge separation) in Ta₃N₅ photoelectrodes. In this study, we show that volatilization of intentionally added Ge (5 %) during the synthesis of Ta₃N₅ promotes the electron transport and thereby improves the charge‐separation efficiency in bulk Ta₃N₅ photoanode, which affords a 320 % increase of the highest photocurrent comparing with that of pure Ta₃N₅ photoanode under AM 1.5 G 100 mW cm^?2 simulated sunlight.     

Synthesis and characterization of poly(1,4‐bis((E)‐2‐(3‐dodecylthiophen‐2‐yl)vinyl)benzene) derivatives

New amorphous semiconducting copolymers, poly(9,9‐dialkylfluorene)‐alt‐(3‐dodecylthienyl‐divinylbenzene‐3‐dodecylthienyl) derivatives (PEFTVB and POFTVB), were designed, synthesized, and characterized. The structure of copolymers was confirmed by H NMR, IR, and elemental analysis. The copolymers showed very good solubility in organic solvents and high thermal stability with high T_g of 178–185 °C. The weight average molecular weight was found to be 107,900 with polydispersity of 3.14 for PEFTVB and 76,700 with that of 3.31 for POFTVB. UV–vis absorption studies showed the maximum absorption at 428 nm (in solution) and 435 nm (in film) for PEFTVB and at 430 nm (in solution) and 436 nm (in film) for POFTVB. Photoluminescence studies showed the emission at 498 nm (in solution) and 557 nm (in film) for PEFTVB and at 498 nm (in solution) and 536 nm (in film) for POFTVB. The solution‐processed thin‐film transistors showed the carrier mobility of 2 × 10^?4 cm² V^?1 s^?1 for PEFTVB‐based devices and 2 × 10^?5 cm² V^?1 s^?1 for POFTVB‐based devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3942–3949, 2010     

Centimeter‐Sized Single Crystal of Two‐Dimensional Halide Perovskites Incorporating Straight‐Chain Symmetric Diammonium Ion for X‐Ray Detection

Two‐dimensional (2D) AA′_n?1M_nX_3n+1 type halide perovskites incorporating straight‐chain symmetric diammonium cations define a new type of structure, but their optoelectronic properties are largely unexplored. Reported here is the synthesis of a centimeter‐sized AA′_n?1M_nX_3n+1 type perovskite, BDAPbI₄ (BDA=NH₃C₄H₈NH₃), single crystal and its charge‐transport properties under X‐ray excitation. The crystal shows a staggered configuration of the [PbI₆]^4? layers, a band gap of 2.37 eV, and a low trap density of 3.1×10⁹ cm^?3. The single‐crystal X‐ray detector exhibits an excellent sensitivity of 242 μC Gy_air^?1 cm^?2 under the 10 V bias (0.31 V μm^?1), a detection limit as low as 430 nGy_air s^?1, ultrastable response current, a stable baseline with the lowest dark current drift of 6.06×10^?9 nA cm^?1 s^?1 V^?1, and rapid response time of τ_rise=7.3 ms and τ_fall=22.5 ms. These crystals are promising candidates for the next generation of optoelectronic devices.     

Board‐like Fused‐Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis,Self‐Assembly,p‐Type Semiconductivity,and Photoluminescence

Fused‐thiophene discotic liquid crystals were designed and easily synthesized by Suzuki coupling and FeCl₃ oxidized tandem cyclodehydrogenation reactions, including homo‐ and cross‐coupling reactions. The resulting hexagonal and rectangular columnar mesomorphic supramolecular structures formed were characterized by polarizing optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering. The charge carrier transport properties in the mesophases of two of the synthesized fused‐thiophene discogens were measured by transient photocurrent time‐of‐flight (TOF) technique, revealing fast hole transport values in the range of 10^?3 to 10^?2 cm² V^?1 s^?1, thus demonstrating potential applications in electronic devices. The luminescent sanidic mesogens, with different extended π‐conjugated systems, also emit blue, green, or red light, with absolute photoluminescent quantum yields as high as 18 %.     

Few‐Layer Nanosheets of n‐Type SnSe2

Layered p‐block metal chalcogenides are renowned for thermoelectric energy conversion due to their low thermal conductivity caused by bonding asymmetry and anharmonicity. Recently, single crystalline layered SnSe has created sensation in thermoelectrics due to its ultralow thermal conductivity and high thermoelectric figure of merit. Tin diselenide (SnSe₂), an additional layered compound belonging to the Sn‐Se phase diagram, possesses a CdI₂‐type structure. However, synthesis of pure‐phase bulk SnSe₂ by a conventional solid‐state route is still remains challenging. A simple solution‐based low‐temperature synthesis is presented of ultrathin (3–5 nm) few layers (4–6 layers) nanosheets of Cl‐doped SnSe₂, which possess n‐type carrier concentration of 2×10¹⁸ cm^?3 with carrier mobility of about 30 cm² V^?1 s^?1 at room temperature. SnSe₂ has a band gap of about 1.6 eV and semiconducting electronic transport in the 300–630 K range. An ultralow thermal conductivity of about 0.67 Wm^?1 K^?1 was achieved at room temperature in a hot‐pressed dense pellet of Cl‐doped SnSe₂ nanosheets due to the anisotropic layered structure, which gives rise to effective phonon scattering.     

Single‐Nanoparticle Collision Events: Tunneling Electron Transfer on a Titanium Dioxide Passivated n‐Silicon Electrode

Single‐nanoparticle collisions were observed on an n‐type silicon electrode (600 μm diameter) passivated by a thin layer of amorphous TiO₂, where the current steps occurred by tunneling electron transfer. The observed collision frequency was in reasonable agreement with that predicted from theory. The isolated electrode, after a collision experiment, with a Pt/TiO₂/n‐Si architecture was shown to retain the photoelectrochemical properties of n‐Si without photocorrosion or current decay. The Pt/TiO₂/n‐Si electrode produced 19 mA cm^?2 of photocurrent density under 100 mW cm^?2 irradiation from a xenon lamp during oxygen evolution without current fading for over 12 h.     

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.     

Exploiting the Bulk Photovoltaic Effect in a 2D Trilayered Hybrid Ferroelectric for Highly Sensitive Polarized Light Detection

Polarized light detection is attracting increasing attention for its wide applications ranging from optical switches to high‐resolution photodetectors. Two‐dimensional (2D) hybrid perovskite‐type ferroelectrics combining inherent light polarization dependence of bulk photovoltaic effect (BPVE) with excellent semiconducting performance present significant possibilities. Now, the BPVE‐driven highly sensitive polarized light detection in a 2D trilayered hybrid perovskite ferroelectric, (allyammonium)₂(ethylammonium)₂Pb₃Br₁₀ ( 1 ), is presented. It shows a superior BPVE with near‐band gap photovoltage of ca. 2.5 V and high on/off switching ratio of current (ca. 10⁴). Driven by the superior BPVE, 1 exhibits highly sensitive polarized light detection with a polarization ratio as high as ca. 15, which is far more beyond than those of structural anisotropy‐based monocomponent devices. This is the first realization of BPVE‐driven polarized light detection in hybrid perovskite ferroelectrics.     

Fuel‐Free Bio‐photoelectrochemical Cells Based on a Water/Oxygen Circulation System with a Ni:FeOOH/BiVO4 Photoanode

A bio‐photoelectrochemical cell (BPEC) based on a fuel‐free self‐circulation water–oxygen–water system was fabricated. It consists of Ni:FeOOH modified n‐type bismuth vanadate (BiVO₄) photoanode and laccase catalyzed biocathode. In this BPEC, irradiation of the photoanode generates photocurrent for photo‐oxidation of water to oxygen, which is reduced to water again at the laccase biocathode. Of note, the by‐products of two electrode reactions could continue to be reacted, which means the H₂O and O₂ molecules are retained in an infinite loop of water–oxygen–water without any sacrificial chemical components. As a result, the assembled fuel‐free BPEC exhibits good performance with an open‐circuit potential of 0.97 V and a maximum power density of 205 μW cm^?2 at 0.44 V. This BPEC based on a self‐circulation system offers a fuel‐free model to enhance multiple energy conversion and application in reality.