Conjugated Polyelectrolytes as Multifunctional Passivating and Hole‐Transporting Layers for Efficient Perovskite Light‐Emitting Diodes

Metal halide perovskites (MHPs) have attracted significant attention as light‐emitting materials owing to their high color purities and tunabilities. A key issue in perovskite light‐emitting diodes (PeLEDs) is the fabrication of an optimal charge transport layer (CTL), which has desirable energy levels for efficient charge injection while blocking opposite charges and enabling perovskite layer growth with reduced interfacial defects. Herein, two poly(fluorene‐phenylene)‐based anionic conjugated polyelectrolytes (CPEs) with different counterions (K⁺ and tetramethylammonium (TMA⁺)) are presented as multifunctional passivating and hole‐transporting layers (HTLs). The crystal growth of MHPs grown on different HTLs is investigated through X‐ray photoelectron spectroscopy, X‐ray diffraction, and density functional theory calculation. The CPE bearing the TMA⁺ counterions remarkably improves the growth of perovskites with suppressed interfacial defects, leading to significantly enhanced emission properties and device performance. The luminescent properties are further enhanced via aging and electrical stress application with effective rearrangement of the counterions on the interfacial defects in the perovskites. Finally, efficient formamidinium lead tribromide‐based quasi‐2D PeLEDs with an external quantum efficiency of 10.2% are fabricated. Using CPEs with varying counterions as a CTL can serve as an effective method for controlling the interfacial defects and improving perovskite‐based optoelectronic device properties.     

Development of an Electrophoretic Deposition Method for the In Situ Fabrication of Ultra-Thin Composite-Polymer Electrolytes for Solid-State Lithium-Metal Batteries

All-solid-state lithium-metal batteries offer higher energy density and safety than lithium-ion batteries, but their practical applications have been pushed back by the sluggish Li⁺ transport, unstable electrolyte/electrode interface, and/or difficult processing of their solid-state electrolytes. Li⁺-conducting composite polymer electrolytes (CPEs) consisting of sub-micron particles of an oxide solid-state electrolyte (OSSE) dispersed in a solid, flexible polymer electrolyte (SPE) have shown promises to alleviate the low Li⁺ conductivity of SPE, and the high rigidity and large interfacial impedance of OSSEs. Solution casting has been by far the most widely used procedure for the preparation of CPEs in research laboratories; however, this method imposes several drawbacks including particle aggregation and settlement during a long-term solvent evaporation step, excessive use of organic solvents, slow production time, and mechanical issues associated with handling of ultra-thin films of CPEs (<50 µm). To address these challenges, an electrophoretic deposition (EPD) method is developed to in situ deposit ultra-thin CPEs on lithium-iron-phosphate (LFP) cathodes within just a few minutes. EPD-prepared CPEs have shown better electrochemical performance in the lithium-metal battery than those CPEs prepared by solution casting due to a better dispersion of OSSE within the SPE matrix and improved CPE contact with LFP cathodes.     

基于三维芳纶纳米纤维骨架的柔性高压复合电解质膜及其固态锂金属电池

聚合物电解质在锂金属电池中的应用受限于锂枝晶生长、电化学不稳定性及较低的离子电导率.为解决这些问题,本文通过向三维多孔芳纶纳米纤维(ANF)中填充聚环氧乙烷(PEO)-双三氟甲基磺酰亚胺锂(LiTFSI)电解质,制备了基于三维芳纶纳米纤维网络骨架的柔性ANF/PEO-LiTFSI复合电解质薄膜.由于其独特的构造及离子在三维ANF/PEO-LiTFSI界面中的连续输运,该复合电解质膜具有比PEO-LiTFSI电解质膜更高的力学强度(10.0 MPa)、热稳定性、电化学稳定性(60℃下达4.6 V)和离子电导率,以及较强的抑制锂枝晶能力.基于该复合电解质的固态LiFePO4/Li电池表现出优异的循环性能(在0.4 C下充放电百次后的容量达130 mA h g-1、保持率为93%).该研究提供了一种基于三维骨架设计和制备高性能电解质的有效方法,有望应用于固态锂金属电池.     

The Role of Interfaces in Polyethylene/Metal‐Oxide Nanocomposites for Ultrahigh‐Voltage Insulating Materials

Recent progress in the development of polyethylene/metal‐oxide nanocomposites for extruded high‐voltage direct‐current (HVDC) cables with ultrahigh electric insulation properties is presented. This is a promising technology with the potential of raising the upper voltage limit in today's underground/submarine cables, based on pristine polyethylene, to levels where the loss of energy during electric power transmission becomes low enough to ensure intercontinental electric power transmission. The development of HVDC insulating materials together with the impact of the interface between the particles and the polymer on the nanocomposites electric properties are shown. Important parameters from the atomic to the microlevel, such as interfacial chemistry, interfacial area, and degree of particle dispersion/aggregation, are discussed. This work is placed in perspective with important work by others, and suggested mechanisms for improved insulation using nanoparticles, such as increased charge trap density, adsorption of impurities/ions, and induced particle dipole moments are considered. The effects of the nanoparticles and of their interfacial structures on the mechanical properties and the implications of cavitation on the electric properties are also discussed. Although the main interest in improving the properties of insulating polymers has been on the use of nanoparticles, leading to nanodielectrics, it is pointed out here that larger microscopic hierarchical metal‐oxide particles with high surface porosity also impart good insulation properties. The impact of the type of particle and its inherent properties (purity and conductivity) on the nanocomposite dielectric and insulating properties are also discussed based on data obtained by a newly developed technique to directly observe the charge distribution on a nanometer scale in the nanocomposite.     

添加无机粒子的P(VDF-HFP)-PMMA复合聚合物电解质的性能

研究了以PP/PE/PP(聚丙烯/聚乙烯/聚丙烯)膜为支撑体,P(VDF-HFP)(聚(偏二氟乙烯-六氟丙烯))-PMMA(聚甲基丙烯酸甲酯)为聚合物基体,与纳米级SiO2、CaCO3进行复合构成的聚合物电解质膜(CPE)的性能。借助X射线衍射、电化学阻抗、电池的首次充放电、倍率放电和充放电循环测试,考察了复合聚合物电解质CPE(SiO2)和CPE(CaCO3)的结构以及它们与LiFePO4正极材料、金属锂的相容性。结果表明:无机粒子的加入没有改变原来聚合物P(VDF-HFP)-PMMA非晶结构;两种电解质构成的电池的首次充放电性能相差不大,但是循环性能后者优于前者;LiFePO4/CPE(CaCO3)/Li构成的电池的倍率放电性能、放电容量和容量保持率均优于LiFePO4/CPE(SiO2)/Li电池;CPE(CaCO3)与LiFePO4、金属锂的相容性更好。     

Li+‐Containing,Continuous Silica Nanofibers for High Li+ Conductivity in Composite Polymer Electrolyte

Solid‐state electrolytes have recently attracted significant attention toward safe and high‐energy lithium chemistries. In particular, polyethylene oxide (PEO)‐based composite polymer electrolytes (CPEs) have shown outstanding mechanical flexibility and manufacturing feasibility. However, their limited ionic conductivity, poor electrochemical stability, and insufficient mechanical strength are yet to be addressed. In this work, a novel CPE supported by Li⁺‐containing SiO₂ nanofibers is developed. The nanofibers are obtained via sol–gel electrospinning, during which lithium sulfate is in situ introduced into the nanofibers. The uniform doping of Li₂SO₄ in SiO₂ nanofibers increases the Li⁺ conductivity of SiO₂, generates mesopores on the surface of SiO₂ nanofibers, and improves the wettability between SiO₂ and PEO. As a result, the obtained SiO₂/Li₂SO₄/PEO CPE yields high Li⁺ conductivity (1.3 × 10^?4 S cm^?1 at 60 °C, ≈4.9 times the Li₂SO₄‐free CPE) and electrochemical stability. Furthermore, the all‐solid‐state LiFePO₄‐Li full cell demonstrates stable cycling with high capacities (over 80 mAh g^?1, 50 cycles at C/2 at 60 °C). The Li⁺‐containing mesoporous SiO₂ nanofibers show great potential as the filler for CPEs. Similar methods can be used to incorporate Li salts into other filler materials for CPEs.     

Multiply Charged Conjugated Polyelectrolytes as a Multifunctional Interlayer for Efficient and Scalable Perovskite Solar Cells

A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene-co-phenylene) by varying the side-chain ionic density from two to six per repeat units (MPS2-TMA, MPS4-TMA, and MPS6-TMA). The effect of MPS2, 4, 6-TMA as interlayers on top of a hole-extraction layer of poly(bis(4-phenyl)-2,4,6-trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device-to-device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS-TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open-circuit voltage increases from 1.06 V for the PeSC with MPS2-TMA to 1.11 V for the PeSC with MPS6-TMA. The trap densities of the PeSCs with MPS2,4,6-TMA are further analyzed using frequency-dependent capacitance measurements. Finally, a large-area (1 cm²) PeSC is successfully fabricated with MPS6-TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s.     

Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li⁺ extraction from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li⁺ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li⁺ conductivity on crossing the polymer/polymer interface.     

Oligothiophene Assemblies Defined by DNA Interaction: From Single Chains to Disordered Clusters

The organization of conjugated polyelectrolytes (CPEs) interacting with biomolecules sets conditions for the biodetection of biological processes and identity, through the use of optical emission from the CPE. Herein, a well‐defined CPE and its binding to DNA is studied. By using dynamic light scattering and circular dichroism spectroscopy, it is shown that the CPE forms a multimolecule ensemble in aqueous solution that is more than doubled in size when interacting with a small DNA chain, while single chains are evident in ethanol. The related changes in the fluorescence spectra upon polymer aggregation are assigned to oscillator strength redistribution between vibronic transitions in weakly coupled H‐aggregates. An enhanced single‐molecule spectroscopy technique that allows full control of excitation and emission light polarization is applied to combed and decorated λDNA chains. It is found that the organization of combed CPE–λDNA complexes (when dry on the surface) allows considerable variation of CPE distances and direction relative to the DNA chain. By analysis of the polarization data energy transfer between the polymer chains in individual complexes is confirmed and their sizes estimated.     

Enhancing the Performance of the Half Tin and Half Lead Perovskite Solar Cells by Suppression of the Bulk and Interfacial Charge Recombination

In this article it is investigated how the hole extraction layer (HEL) influence the charge recombination and performance in half tin and half lead (FASn_0.5Pb_0.5I₃) based solar cells (HPSCs). FASn_0.5Pb_0.5I₃ film grown on PEDOT:PSS displays a large number of pin‐holes and open grain boundaries, resulting in a high defect density and shunts in the perovskite film causing significant bulk and interfacial charge recombination in the HPSCs. By contrast, FASn_0.5Pb_0.5I₃ films grown on PCP‐Na, an anionic conjugated polymer, show compact and pin‐hole free morphology over a large area, which effectively eliminates the shunts and trap states. Moreover, PCP‐Na is characterized by a higher work function, which determines a favorable energy alignment at the anode interface, enhancing the charge extraction. Consequently, both the interfacial and bulk charge recombination in devices using PCP‐Na HEL are considerably reduced giving rise to an overall improvement of all the device parameters. The HPSCs fabricated with this HEL display power conversion efficiency up to 16.27%, which is 40% higher than the efficiency of the control devices using PEDOT:PSS HEL (11.60%). Furthermore, PCP‐Na as HEL offers superior performance in larger area devices compared to PEDOT:PSS.     

Tumor‐Responsive Fluorescent Light‐up Probe Based on a Gold Nanoparticle/Conjugated Polyelectrolyte Hybrid

A tumor‐responsive nanoprobe based on a conjugated polyelectrolyte and gold nanoparticle (AuNP) hybrid was designed to response to the low pH extracellular microenvironment in tumor with light‐up fluorescence. AuNPs with positive surface charges were prepared by direct reducing Au salt with sodium borohydride and stabilized by cystamine. A pH triggered charge‐reversible polymer and a water‐soluble cationic conjugated polyelectrolyte (CPE) were sequentially deposited onto the AuNP surface through electrostatic interaction. The obtained hybrid probe is monodispersed with an average diameter of 68.3 nm by dynamic light scattering measurement. In physiological conditions (pH ≈ 7.4), the hybrid probe is almost non‐fluorescent due to the super‐quenching of CPE by AuNPs via energy/charge transfer and efficient exciton migration along the polymer backbone. When exposed to acidic extracellular microenvironments in tumor (pH_e ≈ 6.5), the acid‐labile amides hydrolyze into primary amines. The generated amine groups result in strong electrostatic repulsion between CPE and AuNPs, leading to recovered probe fluorescence. The fluorescence turn‐on is further utilized for tumor extracellular acidic microenvironment imaging. In addition, under in vivo conditions, the nanosized hybrid probe exhibits specific accumulation in tumor tissue with light‐up fluorescence, which provides new opportunities for easy tumor imaging and identification.     

Small Molecules Functionalized Zinc Oxide Interlayers for High Performance Low-Temperature Carbon-Based CsPbI2Br Perovskite Solar Cells

The charge recombination resulting from bulk defects and interfacial energy level mismatch hinders the improvement of the power conversion efficiency (PCE) and stability of carbon-based inorganic perovskite solar cells (C-IPSCs). Herein, a series of small molecules including ethylenediaminetetraacetic acid (EDTA) and its derivatives (EDTA-Na and EDTA-K) are studied to functionalize the zinc oxide (ZnO) interlayers at the SnO₂/CsPbI₂Br buried interface to boost the photovoltaic performance of low-temperature C-IPSCs. This strategy can simultaneously passivate defects in ZnO and perovskite films, adjust interfacial energy level alignment, and release interfacial tensile stress, thereby improving interfacial contact, inhibiting ion migration, alleviating charge recombination, and promoting electron transport. As a result, a maximum PCE of 13.94% with a negligible hysteresis effect is obtained, which is one of the best results reported for low-temperature CsPbI₂Br C-IPSCs so far. Moreover, the optimized devices without encapsulation demonstrate greatly improved operational stability.     

Tailoring Thickness of Conformal Conducting Polymer Decorated Aligned Carbon Nanotube Electrodes for Energy Storage

Aligned Carbon nanotubes (A‐CNT) based electrodes have emerged as high‐performance elements in electric energy storage and conversion devices. Morphological tailoring of conformal coatings of poly(ethylenedioxythiophene) (PEDOT) conductive polymer (CP) on the A‐CNT scaffold is demonstrated by controlling CP thickness at the nm scale. Results show that the CP nano‐films dominate the electrode capacitance in a supercapacitor application, contributing as much as 10x (pseudo)capacitance over the electric double layer of pristine A‐CNT due to volumetric vs. surface charge storage. Comparison to theoretical ion mobilities shows that the conformal CP films have active sites at ∼30% doping, indicating the CP quality is similar to thin films on flat substrates and that all these sites are accessed at all CP thickness values (up to 10 nm PEDOT thickness) and do not limit the rate of ion transport in and out of the CP film volume. Supercapacitor electrodes fabricated from these novel morphology‐controlled nanostructured composites provide a new route towards high‐performance next generation energy storage devices.     

High‐Performance,Solution‐Processed,and Insulating‐Layer‐Free Light‐Emitting Diodes Based on Colloidal Quantum Dots

Quantum‐dot light‐emitting diodes (QLEDs) may combine superior properties of colloidal quantum dots (QDs) and advantages of solution‐based fabrication techniques to realize high‐performance, large‐area, and low‐cost electroluminescence devices. In the state‐of‐the‐art red QLED, an ultrathin insulating layer inserted between the QD layer and the oxide electron‐transporting layer (ETL) is crucial for both optimizing charge balance and preserving the QDs' emissive properties. However, this key insulating layer demands very accurate and precise control over thicknesses at sub‐10 nm level, causing substantial difficulties for industrial production. Here, it is reported that interfacial exciton quenching and charge balance can be independently controlled and optimized, leading to devices with efficiency and lifetime comparable to those of state‐of‐the‐art devices. Suppressing exciton quenching at the ETL–QD interface, which is identified as being obligatory for high‐performance devices, is achieved by adopting Zn_0.9Mg_0.1O nanocrystals, instead of ZnO nanocrystals, as ETLs. Optimizing charge balance is readily addressed by other device engineering approaches, such as controlling the oxide ETL/cathode interface and adjusting the thickness of the oxide ETL. These findings are extended to fabrication of high‐efficiency green QLEDs without ultrathin insulating layers. The work may rationalize the design and fabrication of high‐performance QLEDs without ultrathin insulating layers, representing a step forward to large‐scale production and commercialization.     

Single molecular imaging and spectroscopy of conjugated polyelectrolytes decorated on stretched aligned DNA

DNA is the prototype template for building nanoelectronic devices by self-assembly. The electronic functions are made possible by coordinating electronic polymer chains to DNA. This paper demonstrates two methods for fabrication of aligned and ordered DNA nanowires complexed with conjugated polyelectrolytes (CPEs). The complex can be formed either in solution prior to stretching or after stretching of the bare DNA on a surface. Molecular combing was used to stretch the complexes on surface energy patterned surfaces, and PMMA for the bare DNA. Single molecular spectroscopy, in fluorescence, and microscopy, in atomic force microscopy, give evidence for coordination of the short CPE chains to the aligned DNA.     

Transition Metal Oxides for Organic Electronics: Energetics,Device Physics and Applications

During the last few years, transition metal oxides (TMO) such as molybdenum tri‐oxide (MoO₃), vanadium pent‐oxide (V₂O₅) or tungsten tri‐oxide (WO₃) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long‐term stable p‐type doping of wide band gap organic materials, charge‐generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi‐transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO‐based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution‐based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed.     

Light‐Powered Directional Nanofluidic Ion Transport in Kirigami‐Made Asymmetric Photonic‐Ionic Devices

Nacre‐mimetic 2D nanofluidic materials with densely packed sub‐nanometer‐height lamellar channels find widespread applications in water‐, energy‐, and environment‐related aspects by virtue of their scalable fabrication methods and exceptional transport properties. Recently, light‐powered nanofluidic ion transport in synthetic materials gained considerable attention for its remote, noninvasive, and active control of the membrane transport property using the energy of light. Toward practical application, a critical challenge is to overcome the dependence on inhomogeneous or site‐specific light illumination. Here, asymmetric photonic‐ionic devices based on kirigami‐tailored graphene oxide paper are fabricated, and directional nanofluidic ion transport properties therein powered by full‐area light illumination are demonstrated. The in‐plane asymmetry of the graphene oxide paper is essential to the generation of photoelectric driving force under homogeneous illumination. This light‐powered ion transport phenomenon is explained based on a modified carrier diffusion model. In asymmetric nanofluidic structures, enhanced recombination of photoexcited charge carriers at the membrane boundary breaks the electric potential balance in the horizontal direction, and thus drives the ion transport in that direction under symmetric illumination. The kirigami‐based strategy provides a facile and scalable way to fabricate paper‐like photonic‐ionic devices with arbitrary shapes, working as fundamental elements for large‐scale light‐harvesting nanofluidic circuits.     

Ionic‐Liquid Doping Enables High Transconductance,Fast Response Time,and High Ion Sensitivity in Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) are highly attractive for applications ranging from circuit elements and neuromorphic devices to transducers for biological sensing, and the archetypal channel material is poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS. The operation of OECTs involves the doping and dedoping of a conjugated polymer due to ion intercalation under the application of a gate voltage. However, the challenge is the trade‐off in morphology for mixed conduction since good electronic charge transport requires a high degree of ordering among PEDOT chains, while efficient ion uptake and volumetric doping necessitates open and loose packing of the polymer chains. Ionic‐liquid‐doped PEDOT:PSS that overcomes this limitation is demonstrated. Ionic‐liquid‐doped OECTs show high transconductance, fast transient response, and high device stability over 3600 switching cycles. The OECTs are further capable of having good ion sensitivity and robust toward physical deformation. These findings pave the way for higher performance bioelectronics and flexible/wearable electronics.     

Carbons and Electrolytes for Advanced Supercapacitors

Electrical energy storage (EES) is one of the most critical areas of technological research around the world. Storing and efficiently using electricity generated by intermittent sources and the transition of our transportation fleet to electric drive depend fundamentally on the development of EES systems with high energy and power densities. Supercapacitors are promising devices for highly efficient energy storage and power management, yet they still suffer from moderate energy densities compared to batteries. To establish a detailed understanding of the science and technology of carbon/carbon supercapacitors, this review discusses the basic principles of the electrical double‐layer (EDL), especially regarding the correlation between ion size/ion solvation and the pore size of porous carbon electrodes. We summarize the key aspects of various carbon materials synthesized for use in supercapacitors. With the objective of improving the energy density, the last two sections are dedicated to strategies to increase the capacitance by either introducing pseudocapacitive materials or by using novel electrolytes that allow to increasing the cell voltage. In particular, advances in ionic liquids, but also in the field of organic electrolytes, are discussed and electrode mass balancing is expanded because of its importance to create higher performance asymmetric electrochemical capacitors.     

Fine‐Tuning the Energy Levels of a Nonfullerene Small‐Molecule Acceptor to Achieve a High Short‐Circuit Current and a Power Conversion Efficiency over 12% in Organic Solar Cells

Organic solar cell optimization requires careful balancing of current–voltage output of the materials system. Here, such optimization using ultrafast spectroscopy as a tool to optimize the material bandgap without altering ultrafast photophysics is reported. A new acceptor–donor–acceptor (A–D–A)‐type small‐molecule acceptor NCBDT is designed by modification of the D and A units of NFBDT. Compared to NFBDT, NCBDT exhibits upshifted highest occupied molecular orbital (HOMO) energy level mainly due to the additional octyl on the D unit and downshifted lowest unoccupied molecular orbital (LUMO) energy level due to the fluorination of A units. NCBDT has a low optical bandgap of 1.45 eV which extends the absorption range toward near‐IR region, down to ≈860 nm. However, the 60 meV lowered LUMO level of NCBDT hardly changes the V_oc level, and the elevation of the NCBDT HOMO does not have a substantial influence on the photophysics of the materials. Thus, for both NCBDT‐ and NFBDT‐based systems, an unusually slow (≈400 ps) but ultimately efficient charge generation mediated by interfacial charge‐pair states is observed, followed by effective charge extraction. As a result, the PBDB‐T:NCBDT devices demonstrate an impressive power conversion efficiency over 12%—among the best for solution‐processed organic solar cells.