Giant Piezoelectric Coefficients in Relaxor Piezoelectric Ceramic PNN‐PZT for Vibration Energy Harvesting

It is well known that the piezoelectric performance of ferroelectric Pb(Zr,Ti)O₃ (PZT) based ceramics is far inferior to that of ferroelectric single crystals due to ceramics' polycrystalline nature. Herein, it is reported that piezoelectric stress coefficient e₃₃ = 39.24 C m^?2 (induced electric displacement under applied strain) in the relaxor piezoelectric ceramic 0.55Pb(Ni_1/3Nb_2/3)O₃–0.135PbZrO₃–0.315PbTiO₃ (PNN‐PZT) prepared by the solid state reaction method exhibits the highest value among various reported ferroelectric ceramic and single crystal materials. In addition, its piezoelectric coefficient d₃₃* = 1753 pm V^?1 is also comparable with that of the commercial Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (PMN‐PT) piezoelectric single crystal. The PNN‐PZT ceramic is then assembled into a cymbal energy harvester. Notably, its maximum output current at the acceleration of 3.5 g is 2.5 mA_pp, which is four times of the PMN‐PT single crystal due to the large piezoelectric e₃₃ constants; while the maximum output power is 14.0 mW, which is almost the same as the PMN‐PT single crystal harvester. The theoretical analysis on force‐induced power output is also presented, which indicates PNN‐PZT ceramic has great potential for energy device application.     

弛豫铁电陶瓷最佳退火条件的正交试验法

采用正交试验法,通过计算水平均值和极差,运用直观分析来确定因素的最佳水平组合和因素的主次顺序,寻求退火的最佳实验条件。根据最小二乘法原理,给出了测量数据真值的最佳估计值。采用正交试验法获得的最佳退火条件对Pb(Zn1/3Nb2/3)O3-PbTiO3-BaTiO3弛豫铁电陶瓷试样进行热处理,介电常数显著提高,最大增幅达137%,高于已有的报道130%[J.Appl.Phys.2002,92(5)]。实验结果表明:运用正交试验法进行退火是研究弛豫铁电陶瓷改性的一种有效途径。     

(Na,K,Li)(Nb,Sb)O3无铅压电陶瓷的性能

采用传统的固相反应法和普通烧结工艺,制备了A位和B位复合的(Na0.5+xK0.44Li0.06–x)Nb0.95Sb0.05O3(x=0,0.006,0.012)系无铅压电陶瓷样品,并对样品的压电、机电性能进行了研究。结果表明:该陶瓷系列具有很高的压电应变常数(x=0.006时d33=243pC/N)、低的介质损耗(tanδ<2×10–2)、较高的机电耦合系数(x=0.012时,k33=0.632)、高的铁电顺电相变温度(tC约400℃)。这些性能显示了它是一种替代铅基PZT的具有很好应用前景的无铅压电陶瓷。     

Solution‐Processed Highly Efficient Alternating Current‐Driven Field‐Induced Polymer Electroluminescent Devices Employing High‐k Relaxor Ferroelectric Polymer Dielectric

Organic thin‐film electroluminescent (EL) devices, such as organic light‐emitting diodes (OLEDs), typically operate using constant voltage or direct current (DC) power sources. Such approaches require power converters (introducing power losses) and make devices sensitive to dimensional variations that lead to run away currents at imperfections. Devices driven by time‐dependent voltages or alternating current (AC) may offer an alternative to standard OLED technologies. However, very little is known about how this might translate into overall performance of such devices. Here, a solution‐processed route to creating highly efficient AC field‐induced polymer EL (FIPEL) devices is demonstrated. Such solution‐processed FIPEL devices show maximum luminance, current efficiency, and power efficiency of 3000 cd m^?2, 15.8 cd A^?1, and 3.1 lm W^?1 for blue emission, 13 800 cd m^?2, 76.4 cd A^?1, and 17.1 lm W^?1 for green emission, and 1600 cd m^?2, 8.8 cd A^?1, and 1.8 lm W^?1 for orange‐red emission. The high luminance and efficiency, and solution process pave the way to industrial roll‐to‐roll manufacturing of solid state lighting and display.     

Cyanocarbazole Derivatives for High‐Performance Electroluminescent Devices

3‐Cyano‐9‐diarylamino carbazoles have been synthesized. These new compounds emit in the blue to green region. Double‐layer electroluminescent devices using these compounds as the hole‐transport/emitting materials are highly efficient. Two of the compounds can be fabricated into single‐layer devices with good performance. Green‐ and blue‐emitting devices with good performance were also fabricated using one of the compounds as the hole‐injection layer.     

In Search of High‐Performance Platinum(II) Phosphorescent Materials for the Fabrication of Red Electroluminescent Devices

The rational design and syntheses of Pt(iqdz)₂ ( 1 ) and Pt(pydz)₂ ( 2 ) bearing isoquinolinyl indazole (iqdz)H or pyridyl indazole (pydz)H groups on the coordinating ligands are reported. Single‐crystal X‐ray diffraction studies of 1 reveal a square planar geometry, in which two iqdz ligands adopt a trans‐configuration. Short N…H contacts (～2.21 Å) are detected between the ortho‐hydrogen atom of isoquinoline and the adjacent N atom of the indazole fragment, making the overall molecular geometry analogous to that of the platinum(II ) porphyrinato complexes. The lowest absorption bands for both complexes reveal strong state mixings between singlet and triplet (metal‐to‐ligand charge transfer and intra‐ligand) manifolds. This, in combination with the introduction of a camphor‐like structure to avoid the stacking effect, leads to phosphorescence with unprecedented brightness both in solution and in the solid state. Organic light‐emitting diode (OLED) devices fabricated using 1 as a dopant emitter have been achieved in a multilayer configuration. The results constitute the first highly efficient Pt^II‐based red OLED.     

Direct Growth of Pyramid‐Textured Perovskite Single Crystals: A New Strategy for Enhanced Optoelectronic Performance

Even though there have been a few reports of substrate surface texturing of thin film perovskite solar cells to enhance their light trapping, there has been no direct texturing of the perovskite material, let alone perovskite single crystals (SCs). Herein, a method to prepare a pyramid‐structured perovskite CH₃NH₃PbX₃ (CH₃NH₃⁺ = MA, X = I, Br) SC surface with minimized light reflection and maximized incident light harvesting is reported. Specifically, a hard template is used to directly transfer the pyramidal texture onto the MAPbX₃ SC during its growth. A well‐shaped pyramidal texture is formed on the single‐crystal surface leading to improved light trapping. The textured MAPbBr₃ SC shows good crystallinity, prolonged carrier lifetime, and improved carrier mobility. Furthermore, the photodetector made from the textured SC shows enhanced responsivity of 321 A W^?1 and external quantum efficiency of 7191%, about two times higher than that of a control device. This method may be used to directly fabricate desired textures on general single crystal surfaces.     

High‐Tg Carbazole Derivatives as Blue‐Emitting Hole‐Transporting Materials for Electroluminescent Devices

A series of dicarbazolyl derivatives bridged by various aromatic spacers and decorated with peripheral diarylamines were synthesized using Ullmann and Pd‐catalyzed C–N coupling procedures. These derivatives emit blue light in solution. In general, they possess high glass‐transition temperatures (T_g > 125 °C) which vary with the bridging segment and methyl substitution on the peripheral amine. Double‐layer organic light‐emitting devices were successfully fabricated using these molecules as hole‐transporting and emitting materials. Devices of the configuration ITO/HTL/TPBI/Mg:Ag (ITO: indium tin oxide; HTL: hole‐transporting layer; TPBI: 1,3,5‐tris(N‐phenylbenzimidazol‐2‐yl)benzene) display blue emission from the HTL layer. The EL spectra of these devices appear slightly distorted due to the exciplex formation at the interfaces. However, for the devices of the configuration ITO/HTL/Alq₃/Mg:Ag (Alq₃ = tris(8‐hydroxyquinoline)aluminum) a bright green light from the Alq₃ layer was observed. This clearly demonstrates the facile hole‐transporting property of the materials described here.     

Novel Film‐Casting Method for High‐Performance Flexible Polymer Electrodes

A new film‐casting method for polymer electrodes is reported, in which thickness‐controlled drop‐casting (TCDC), using polyaniline doped with camphorsulfonic acid (PANI:CSA) is used. By combining the advantages of conventional spin‐casting and drop‐casting methods, and by rigorously controlling the film formation parameters, flexible polymer electrodes with high conductivity and excellent transmittance can be produced. The PANI:CSA electrodes cast by the TCDC method exhibited constant thickness‐independent conductivities of ～600 S cm^?1 down to a film thickness of 0.2 μm, and a high optical transmittance of about 85% at 550 nm. Furthermore, the new casting method significantly reduced the sheet resistance (～90 Ω/square) of the PANI:CSA electrodes compared with the conventional spin‐cast films, enhancing the performance of the devices deposited on plastic substrates. The flexible polymer light‐emitting diode produced a brightness of 6000 cd m^?2, and the flexible polymer solar cell exhibited a power conversion efficiency of 2%, both of which were much higher than those of the devices fabricated by the conventional spin‐casting method.     

High‐Performance Carbon‐LiMnPO4 Nanocomposite Cathode for Lithium Batteries

A cathode material of an electrically conducting carbon‐LiMnPO₄ nanocomposite is synthesized by ultrasonic spray pyrolysis followed by ball milling. The effect of the carbon content on the physicochemical and electrochemical properties of this material is extensively studied. A LiMnPO₄ electrode with 30 wt% acetylene black (AB) carbon exhibits an excellent rate capability and good cycle life in cell tests at 55 and 25 °C. This electrode delivers a discharge capacity of 158 mAh g^?1 at 1/20 C, 126 mAh g^?1 at 1 C, and 107 mAh g^?1 at 2 C rate, which are the highest capacities reported so far for this type of electrode. Transmission electron microscopy and Mn dissolution results confirm that the carbon particles surrounding the LiMnPO₄ protect the electrode from HF attack, and thus lead to a reduction of the Mn dissolution that usually occurs with this electrode. The improved electrochemical properties of the C‐LiMnPO₄ electrode are also verified by electrochemical impedance spectroscopy.     

A DCM‐Type Red‐Fluorescent Dopant for High‐Performance Organic Electroluminescent Devices

2‐(2‐tert‐Butyl‐6‐((E)‐2‐(2,6,6‐trimethyl‐2,4,5,6‐tetrahydro‐1H‐pyrrolo[3,2,1‐ij]quinolin‐8‐yl)vinyl)‐4H‐pyran‐4‐ylidene)malononitrile (DCQTB) is designed and synthesized in high yield for application as the red‐light‐emitting dopant in organic light‐emitting diodes (OLEDs). Compared with 4‐(dicyanomethylene)‐2‐tert‐butyl‐6‐(1,1,7,7,‐tetramethyljulolidyl‐9‐enyl)‐4H‐pyran (DCJTB), one of the most efficient red‐emitting dopants, DCQTB exhibits red‐shifted fluorescence but blue‐shifted absorption. The unique characteristics of DCQTB with respect to DCJTB are utilized to achieve a red OLED with improved color purity and luminous efficiency. As a result, the device that uses DCQTB as dopant, with the configuration: indium tin oxide (ITO)/N,N′‐bis(1‐naphthyl)‐N,N′‐diphenyl‐1,1′‐biphenyl‐4,4′‐diamine (NPB; 60 nm)/tris(8‐quinolinolato) aluminum (Alq₃):dopant (2.3 wt %) (7 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 12 nm)/Alq₃(45 nm)/LiF(0.3 nm):Al (300 nm), shows a larger maximum luminance (L_max = 6021 cd m^–2 at 17 V), higher maximum efficiency (η_max = 4.41 cd A^–1 at 11.5 V (235.5 cd m^–2)), and better chromaticity coordinates (Commission Internationale de l'Eclairage, CIE, (x,y) = (0.65,0.35)) than a DCJTB‐based device with the same structure (L_max = 3453 cd m^–2 at 15.5 V, η_max = 3.01 cd A^–1 at 10 V (17.69 cd m^–2), and CIE (x,y) = (0.62,0.38)). The possible reasons for the red‐shifted emission but blue‐shifted absorption of DCQTB relative to DCJTB are also discussed.     

State‐of‐the‐Art Neutral Tint Multichromophoric Polymers for High‐Contrast See‐Through Electrochromic Devices

Two new multichromophoric electrochromic polymers featuring a conjugated EDOT/ProDOT copolymer backbone (PXDOT) and a reversible Weitz‐type redox active small molecule electrochrome (WTE) tethered to the conjugated chain are reported here. The careful design of the WTEs provides a highly reversible redox behavior with a colorless red switching that complements the colorless blue switching of the conjugated backbone. Subtractive color mixing successfully provides high performing solution processable polymeric layers with colorless neutral tint switchable limiting states for application in see‐through electrochromic devices. Design, synthesis, comprehensive chemical and spectroelectrochemical characterization as well as the preparation of a proof‐of‐concept device are discussed.     

Strongly (001) Oriented Bimorph PZT Film on Metal Foils Grown by rf‐Sputtering for Wrist‐Worn Piezoelectric Energy Harvesters

For piezoelectric energy harvesters, a large volume of piezoelectric material with a high figure of merit is essential to obtain a higher power density. The work describes the growth of highly (001) oriented sputtered lead zirconate titanate (PZT) films (f ≈ 0.99) exceeding 4 µm in thickness on both sides of an Ni foil to produce a bimorph structure. These films are incorporated in novel wrist‐worn energy harvesters (<16 cm²) in which piezoelectric beams are plucked magnetically using an eccentric rotor with embedded magnets to implement frequency up‐conversion. The resulting devices successfully convert low‐frequency vibration sources (i.e., from walking, rotating the wrist, and jogging) to higher frequency vibrations of the PZT beams (100–200 Hz). Measured at resonance, six beams producing an output of 1.2 mW is achieved at 0.15 G acceleration. For magnetic plucking of a wrist‐worn nonresonant device, 40–50 µW is produced during mild activity.     

Hierarchically Divacancy Defect Building Dual‐Activated Porous Carbon Fibers for High‐Performance Energy‐Storage Devices

Renewable and environmentally friendly biomass‐based carbon electrode materials naturally possess fast ion transport, high adsorption, and excellent chemical stability for high‐performance energy‐storage devices. However, intelligently building the effectively biomass‐transferred carbon materials for the requirement of high energy density is still a big challenge to date. Here, a hierarchically divacancy defect building platform is reported for effectively biomass‐transferred and highly interconnected 3D dual‐activated porous carbon fibers (DACFs) based on the internal?external dual‐activation function of the pre‐embedded KOH and CO₂ molecular. This uniquely interconnected frameworks not only fully provide the abundant active sites for ion interaction, but also efficiently guarantee the substantial accommodation for ion storage. Based on this, the as‐prepared DACFs‐based supercapacitors deliver a high energy density of 61.3 Wh kg^?1 at a power density of 875 W kg^?1 in the EMIMBF₄ ionic liquid. This work not only provides a simple and efficient technique to enhance the energy density of carbon materials, but also probably promotes its additional application in environmental remediation.     

Naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole‐Containing π‐Conjugated Compound: Nonfullerene Electron Acceptor for Organic Photovoltaics

The development of nonfullerene acceptor materials applicable to organic photovoltaics (OPVs) has attracted considerable attention for the achievement of a high power conversion efficiency (PCE) in recent years. However, it is still challenging due to the insufficiency of both the variety of effective electron‐deficient units and certain guidelines for the design of such materials. This work focusses on naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NTz) as a key electron‐deficient unit. Therefore, a new electron‐accepting π‐conjugated compound (NTz‐Np), whose structure is based on the combination of NTz and the fluorene‐containing imide‐annelated terminal units (Np), is designed and synthesized. The NTz‐Np compound exhibits a narrow optical energy gap (1.73 eV), a proper energy level (?3.60 eV) of the lowest unoccupied molecular orbital, and moderate electron mobility (1.6 × 10^?5 cm² V^?1 s^?1), indicating that NTz‐Np has appropriate characteristics as an acceptor against poly(3‐hexylthiophene) (P3HT), a representative donor. OPV devices based on NTz‐Np under the blend with P3HT show high photovoltaic performance with a PCE of 2.81%, which is the highest class among the P3HT/nonfullerene‐based OPVs with the conventional device structure. This result indicates that NTz unit can be categorized as a potential electron‐deficient unit for the nonfullerene acceptors.     

Rational Molecular Design of Benzoquinone‐Derived Cathode Materials for High‐Performance Lithium‐Ion Batteries

p‐Benzoquinone (BQ) is a promising cathode material for lithium‐ion batteries (LIBs) due to its high theoretical specific capacity and voltage. However, it suffers from a serious dissolution problem in organic electrolytes, leading to poor electrochemical performance. Herein, two BQ‐derived molecules with a near‐plane structure and relative large skeleton: 1,4‐bis(p‐benzoquinonyl)benzene (BBQB) and 1,3,5‐tris(p‐benzoquinonyl)benzene (TBQB) are designed and synthesized. They show greatly decreased solubility as a result of strong intermolecular interactions. As cathode materials for LIBs, they exhibit high carbonyl utilizations of 100% with high initial capacities of 367 and 397 mAh g^?1, respectively. Especially, BBQB with better planarity presents remarkably improved cyclability, retaining a high capacity of 306 mAh g^?1 after 100 cycles. The cycling stability of BBQB surpasses all reported BQ‐derived small molecules and most polymers. This work provides a new molecular structure design strategy to suppress the dissolution of organic electrode materials for achieving high performance rechargeable batteries.     

A Continuous Carbon Nitride Polyhedron Assembly for High‐Performance Flexible Supercapacitors

Flexible supercapacitors with high power density, flexibility, and durability have shown enormous potential for smart electronics. Here, a continuous graphitic carbon nitride polyhedron assembly for flexible supercapacitor that is prepared by pyrolysis of carbon nanotubes wired zeolitic imidazolate framework‐8 (ZIF‐8) composites under nitrogen is reported. It exhibits a high specific capacitance of 426 F g^?1 at current density of 1 A g^?1 in 1 m H₂SO₄ and excellent stability over 10 000 cycles. The remarkable performance results from the continuous hierarchical structure with average pore size of 2.5 nm, high nitrogen‐doping level (17.82%), and large specific surface area (920 m² g^?1). Furthermore, a flexible supercapacitor is developed by constructing the assembly with interpenetrating polymer network electrolyte. Stemming from the synergistic effect of high‐performance electrode and highly ion‐conductive electrolyte, superior energy density of 59.40 Wh kg^?1 at 1 A g^?1 is achieved. The device maintains a stable energy supply under cyclic deformations, showing wide application in flexible and even wearable conditions. The work paves a new way for designing pliable electrode with excellent electronic and mechanic property for long‐lived flexible energy storage devices.     

Self‐Limited Epitaxial Growth of Ultrathin Nonlayered CdS Flakes for High‐Performance Photodetectors

2D nonlayered materials that possess appealing properties are entering the researchers' vision. However, direct access to the 2D level of these materials is still a great challenge due to the instrinsic isotropic chemical bond. This work presents the initially self‐limited epitaxial growth of ultrathin nonlayered CdS flakes (as thin as 6 nm) on mica substrate with a large domain size (>40 µm) by employing In₂S₃ as the passivation agent. Besides, the thickness and sizes of the products could be tunable by the addition level of In₂S₃ amount. The growth mechanism is evidenced via experiments and theoretical calculations, which is attributed to the surface distortion effect of In–S motif and the preference of local environments for In on the CdS (0001) surface. The photodetector designed on CdS flake demonstrates a high photoswitching ratio (up to 10³), a high detectivity (D* ≈ 2.71 × 10⁹ Jones), and fast photoresponse speed (τ_R = 14 ms, τ_D = 8 ms). The as‐proposed self‐limited epitaxial growth method opens a new avenue to synthetize 2D nonlayered materials and will promote their further applications in novel optoelectronic devices.     

Covalently Bonded Graphene–Carbon Nanotube Hybrid for High‐Performance Thermal Interfaces

The remarkable thermal properties of graphene and carbon nanotubes (CNTs) have been the subject of intensive investigations for the thermal management of integrated circuits. However, the small contact area of CNTs and the large anisotropic heat conduction of graphene have hindered their applications as effective thermal interface materials (TIMs). Here, a covalently bonded graphene–CNT (G‐CNT) hybrid is presented that multiplies the axial heat transfer capability of individual CNTs through their parallel arrangement, while at the same time it provides a large contact area for efficient heat extraction. Through computer simulations, it is demonstrated that the G‐CNT outperforms few‐layer graphene by more than 2 orders of magnitude for the c‐axis heat transfer, while its thermal resistance is 3 orders of magnitude lower than the state‐of‐the‐art TIMs. We show that heat can be removed from the G‐CNT by immersing it in a liquid. The heat transfer characteristics of G‐CNT suggest that it has the potential to revolutionize the design of high‐performance TIMs.