Coordinatable and High Charge‐Carrier‐Mobility Water‐Soluble Conjugated Copolymers for Effective Aqueous‐Processed Polymer–Nanocrystal Hybrid Solar Cells and OFET Applications

A water‐soluble conjugated polymer (WCP) poly[(3,4‐dibromo‐2,5‐thienylene vinylene)‐co‐(p‐phenylene‐vinylene)] (PBTPV), containing thiophene rings with high charge‐carrier mobility and benzene rings with excellent solubility is designed and prepared through Wessling polymerization. The PBTPV precursor can be easily processed by employing water or alcohols as the solvents, which are clean, environmentally friendly, and non‐toxic compared with the highly toxic organic solvents such as chloroform and chlorobenzene. As a novel photoelectric material, PBTPV presents excellent hole‐transport properties with a carrier mobility of 5 × 10^?4 cm² V^?1 s^?1 measured in an organic field‐effect transistor device. By integrating PBTPV with aqueous CdTe nanocrystals (NCs) to produce the active layer of water‐processed hybrid solar cells, the devices exhibit effective power conversion efficiency up to 3.3%. Moreover, the PBTPV can form strong coordination interactions with the CdTe NCs through the S atoms on the thiophene rings, and effective coordination with other nanoparticles can be reasonably expected.     

Quantum‐Dot‐Functionalized Poly(styrene‐co‐acrylic acid) Microbeads: Step‐Wise Self‐Assembly,Characterization, and Applications for Sub‐femtomolar Electrochemical Detection of DNA Hybridization

A novel nanoparticle label capable of amplifying the electrochemical signal of DNA hybridization is fabricated by functionalizing poly(styrene‐co‐acrylic acid) microbeads with CdTe quantum dots. CdTe‐tagged polybeads are prepared by a layer‐by‐layer self‐assembly of the CdTe quantum dots (diameter = 3.07 nm) and polyelectrolyte on the polybeads (diameter = 323 nm). The self‐assembly procedure is characterized using scanning and transmission electron microscopy, and X‐ray photoelectron, infrared and photoluminescence spectroscopy. The mean quantum‐dot coverage is (9.54 ± 1.2) × 10³ per polybead. The enormous coverage and the unique properties of the quantum dots make the polybeads an effective candidate as a functionalized amplification platform for labelling of DNA or protein. Herein, as an example, the CdTe‐tagged polybeads are attached to DNA probes specific to breast cancer by streptavidin–biotin binding to construct a DNA biosensor. The detection of the DNA hybridization process is achieved by the square‐wave voltammetry of Cd²⁺ after the dissolution of the CdTe tags with HNO₃. The efficient carrier‐bead amplification platform, coupled with the highly sensitive stripping voltammetric measurement, gives rise to a detection limit of 0.52 fmol L^?1 and a dynamic range spanning 5 orders of magnitude. This proposed nanoparticle label is promising, exhibits an efficient amplification performance, and opens new opportunities for ultrasensitive detection of other biorecognition events.     

High‐Yield Fabrication and Electrochemical Characterization of Tetrapodal CdSe,CdTe, and CdSexTe1–x Nanocrystals

The high‐yield fabrication of tetrapodal CdSe, CdTe, and CdSe_xTe_1–x nanocrystals is systematically studied. CdSe nanocrystals are prepared by first controlling the synthesis of high‐quality wurtzite CdSe and zinc blende CdSe nanocrystals at a relatively high temperature (260 °C) by selecting different ligands. Then, based on the phase control of the CdSe nanocrystals, two nanoparticle‐tailoring routes (i.e., a seed‐epitaxial route and ligand‐dependent multi‐injecting route) are used, and a high yield of CdSe tetrapods is obtained. CdTe nanocrystals are prepared by adjusting the ligand composition and the ratio of Cd to Te; CdTe tetrapods are synthesized in high yield using a mixed ligand that does not contain alkylphosphonic acids. Moreover, the nanoscale Te powder (Te nanowires/nanorods), which is highly soluble in the ligand solvent, is first used as a Te source to synthesize CdTe nanocrystals, which remarkably enhanced the output of the CdTe nanocrystals in one reaction. Furthermore, composition‐tunable ternary CdSe_xTe_1–x alloyed tetrapods are synthesized on a large scale, for the first time, by thermolyzing the mixture of the organometallic Cd precursor and the mixed (Se + Te) source in a mixed‐ligand solution. The CdSe, CdTe, and CdSe_xTe_1–x nanocrystals are characterized by transmission electron microscopy (TEM), high‐resolution TEM, selected‐area electron diffraction, X‐ray diffraction, and UV‐vis and photoluminescence (PL) spectroscopy. Interesting nonlinear, composition‐dependent absorption and PL spectra are observed for the ternary CdSe_xTe_1–x alloyed nanocrystals. The band‐edge positions of the nanocrystals of CdSe, CdSe_xTe_1–x, and CdTe are systematically studied by cyclic voltammetry.     

A New Carbazole‐Constructed Hyperbranched Polymer: Convenient One‐Pot Synthesis,Hole‐Transporting Ability,and Field‐Effect Transistor Properties

A new hyperbranched polymer ( HB‐car ), constructed fully by carbazole moieties, is successfully synthesized through a one‐pot Suzuki coupling reaction. The resultant polymer is well‐characterized, and its hole‐transporting ability is studied carefully. The device, in which HB‐car is utilized as a hole‐transporting layer and tris‐(8‐hydroxyquinoline) aluminum as an electron‐emitting layer as well as electron‐transporting layer, gives a much higher efficiency (3.05 cd A^–1), than that of a poly(N‐vinylcarbazole) based device (2.19 cd A^–1) under similar experimental conditions. The remarkable performance is attributed to its low energy barrier and enhanced hole‐drifting ability in the HB‐car based device. In addition, for the first time, a field‐effect transistor (FET) based on the hyperbranched polymer is fabricated, and the organic FET device shows that HB‐car is a typical p‐type FET material with a saturation mobility of 1 × 10^–5 cm² V^–1 s^–1, a threshold voltage of –47.1 V, and an on‐to‐off current ratio of 10³.     

Multifunctional Fluorene‐Based Oligomers with Novel Spiro‐Annulated Triarylamine: Efficient,Stable Deep‐Blue Electroluminescence,Good Hole Injection,and Transporting Materials with Very High Tg

A series of fluorene‐based oligomers with novel spiro‐annulated triarylamine structures, namely DFSTPA, TFSTPA, and TFSDTC, are synthesized by a Suzuki cross‐coupling reaction. The spiro‐configuration molecular structures lead to very high glass transition temperatures (197–253 °C) and weak intermolecular interactions, and consequently the structures retain good morphological stability and high fluorescence quantum efficiencies(0.69–0.98). This molecular design simultaneously solves the spectral stability problems and hole‐injection and transport issues for fluorene‐based blue‐light‐emitting materials. Simple double‐layer electroluminescence (EL) devices with a configuration of ITO/TFSTPA (device A) or TFSDTC (device B)/ TPBI/LiF/Al, where TFSTPA and TFSDTC serve as hole‐transporting blue‐light‐emitting materials, show a deep‐blue emission with a peak around 432 nm, and CIE coordinates of (0.17, 0.12) for TFSTPA and (0.16, 0.07) for TFSDTC, respectively, which are very close to the National Television System Committee (NTSC) standard for blue (0.15, 0.07). The maximum current efficiency/external quantum efficiencies are 1.63 cd A^?1/1.6% for device A and 1.91 cd A^?1/2.7% for device B, respectively. In addition, a device with the structure ITO/DFSTPA/Alq₃/LiF/Al, where DFSTPA acts as both the hole‐injection and ‐transporting material, is shown to achieve a good performance, with a maximum luminance of 14 047 cd m^?2, and a maximum current efficiency of 5.56 cd A^?1. These values are significantly higher than those of devices based on commonly usedN,N′‐di(1‐naphthyl)‐N,N′‐diphenyl‐[1,1′‐biphenyl]‐4,4′‐diamine (NPB) as the hole‐transporting layer (11 738 cd m^?2 and 3.97 cd A^?1) under identical device conditions.     

Self‐Doping Cathode Interfacial Material Simultaneously Enabling High Electron Mobility and Powerful Work Function Tunability for High‐Efficiency All‐Solution‐Processed Polymer Light‐Emitting Diodes

A variety of N ‐hydrogenated/N ‐methylated pyridinium salts are elaborately designed and synthesized. Thermogravimetric and X‐ray photoelectron spectra analysis indicate the intensities of the N? H covalent bonds are strengthened step‐by‐step from 3,3′‐(5′‐(3‐(pyridin‐3‐yl)phenyl)‐[1,1′:3′,1″‐terphenyl]‐3,3″‐diyl)dipyridine (Tm)‐HCl to Tm‐HBr and then Tm‐TfOH, which results in gradually improved cathode interfacial modification abilities. The larger dipole moments of N⁺? H containing moieties compared to those of the N⁺? CH₃ endow them with more preferable interfacial modification abilities. Electron paramagnetic resonance signals reveal the existence of radical anions in the solid state of Tm‐TfOH, which enables its self‐doping property and high electron mobility up to 1.67 × 10^?3 cm² V^?1 s^?1. Using the Tm‐TfOH as the cathode interfacial layers (CILs), the phenyl‐substituted poly(para ‐phenylene vinylene)‐based all‐solution‐processed polymer light‐emitting diodes (PLEDs) achieve more preferable device performances than the poly[(9,9‐bis(3′‐(N ,N ‐dimethylamino)propyl)‐2,7‐fluorene)‐alt ‐2,7‐(9,9‐dioctylfluorene)]‐based ones, i.e., high current density of nearly 300 mA cm^?2, very high luminance over 15 000 cd m^?2 at a low bias of 5 V. Remarkably, the thickness of the CILs has little impact on the device performance and high efficiencies are maintained even at thicknesses up to 85 nm, which is barely realized in PLEDs with small‐molecule‐based electron transporting layers.     

Progression of metalorganic chemical vapour‐deposited CdTe thin‐film PV devices towards modules

This paper reports important developments achieved with CdTe thin‐film photovoltaic devices produced using metalorganic chemical vapour deposition at atmospheric pressure. In particular, attention was paid to understand the enhancements in solar cell conversion efficiency, to develop the cell design, and assess scalability towards modules. Improvements in the device performance were achieved by optimising the high‐transparency window layer (Cd_0.3Zn_0.7S) and a device‐activation anneal. These increased the fill factor and open‐circuit voltage to 77 ± 1% and 785 ± 7 mV, respectively, compared with 69 ± 3% and 710 ± 10 mV for previous baseline devices with no anneal and thicker Cd_0.3Zn_0.7S. The enhancement in these parameters is associated with the two fold to three fold increase in the net acceptor density of CdTe upon air annealing and a decrease in the back contact barrier height from 0.24 ± 0.01 to 0.16 ± 0.02 eV. The optimum thickness of the window layer for maximum photocurrent was 150 nm. The cell size was scaled from 0.25 to 2 cm² in order to assess its impact on the device series resistance and fill factor. Finally, micro‐module devices utilising series‐connected 2‐cm² sub‐cells were fabricated using a combination of laser and mechanical scribing techniques. An initial module‐to‐cell efficiency ratio of 0.9 was demonstrated for a six‐cell module with the use of the improved device structure and processing. Prospects for CdTe photovoltaic modules grown by metalorganic chemical vapour deposition are commented on. Copyright © 2015 John Wiley & Sons, Ltd.     

High‐Performance,Air‐Stable,Top‐Gate,p‐Channel WSe2 Field‐Effect Transistor with Fluoropolymer Buffer Layer

High‐performance, air‐stable, p‐channel WSe₂ top‐gate field‐effect transistors (FETs) using a bilayer gate dielectric composed of high‐ and low‐k dielectrics are reported. Using only a high‐k Al₂O₃ as the top‐gate dielectric generally degrades the electrical properties of p‐channel WSe₂, therefore, a thin fluoropolymer (Cytop) as a buffer layer to protect the 2D channel from high‐k oxide forming is deposited. As a result, a top‐gate‐patterned 2D WSe₂ FET is realized. The top‐gate p‐channel WSe₂ FET demonstrates a high hole mobility of 100 cm²_­ V^?1 s^?1 and a I_ON/I_OFF ratio > 10⁷ at low gate voltages (V_GS ca. ?4 V) and a drain voltage (V_DS) of ?1 V on a glass substrate. Furthermore, the top‐gate FET shows a very good stability in ambient air with a relative humidity of 45% for 7 days after device fabrication. Our approach of creating a high‐k oxide/low‐k organic bilayer dielectric is advantageous over single‐layer high‐k dielectrics for top‐gate p‐channel WSe₂ FETs, which will lead the way toward future electronic nanodevices and their integration.     

Unveiling the Nanoparticle‐Seeded Catalytic Nucleation Kinetics of Perovskite Solar Cells by Time‐Resolved GIXS

Recently, a new seeding growth approach for perovskite thin films is reported to significantly enhance the device performance of perovskite solar cells. This work unveils the intermediate structures and the corresponding growth kinetics during conversion to perovskite crystal thin films assisted by seeding PbS nanocrystals (NCs), using time‐resolved grazing‐incidence X‐ray scattering. Through analyses of time‐resolved crystal formation kinetics obtained from synchrotron X‐rays with a fast subsecond probing time resolution, an important “catalytic” role of the seed‐like PbS NCs is clearly elucidated. The perovskite precursor‐capped PbS NCs are found to not only accelerate the nucleation of a highly oriented intermediate phase, but also catalyze the conversion of the intermediate phase into perovskite crystals with a reduced activation energy E_a = 47 (±5) kJ mol^?1, compared to 145 (±38) kJ mol^?1 for the pristine perovskite thin film. The reduced E_a is attributed to a designated crystal lattice alignment of the perovskite nanocrystals with perovskite cubic crystals; the pivotal heterointerface alignment of the perovskite crystals coordinated by the Pb NCs leads to an improved film surface morphology with less pinholes and enhanced crystal texture and thermal stability. These together contribute to the significantly improved photovoltaic performance of the corresponding devices.     

Red Phosphorescent Iridium Complex Containing Carbazole‐Functionalized β‐Diketonate for Highly Efficient Nondoped Organic Light‐Emitting Diodes

A novel red phosphorescent iridium complex containing a carbazole‐functionalized β‐diketonate, Ir(DBQ)₂(CBDK) (bis(dibenzo[f,h]quinoxalinato‐N,C²) iridium (1‐(carbazol‐9‐yl)‐5,5‐dimethylhexane‐2,4‐diketonate)) is designed, synthesized, and characterized. The electrophosphorescence properties of a nondoped device using the title complex as an emitter with a device configuration of indium tin oxide (ITO)/N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)‐1,1′‐diphenyl‐4,4′‐diamine (NPB; 20 nm)/iridium complex (20 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 5 nm)/tris(8‐hydroxyquinoline) (AlQ; 30 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) are examined. The results show that the nondoped device achieves a maximum lumen efficiency as high as 3.49 lm W^–1. To understand this excellent result observed, two reference complexes Ir(DBQ)₂(acac), where acac is the acetyl acetonate anion, and Ir(DBQ)₂(FBDK), [bis(dibenzo[f,h]quinoxalinato‐N,C²) iridium (1‐(9‐methyl‐fluoren‐9‐yl)‐6,6‐dimethylheptane‐3,5‐diketonate)], have also been synthesized, and as emitters they were examined under the same device configuration. The maximum lumen efficiency of the former compound is found to be 0.26 lm W^–1 while that for the latter is 0.37 lm W^–1, suggesting that the excellent performance of Ir(DBQ)₂(CBDK) can be attributed mainly to an improved hole‐transporting property that benefits the exciton transport. In addition, a bulky diketonate group separates the emitter centers from each other, which is also important for organic light‐emitting diodes.     

Structure–Property Relationship of Pyridine‐Containing Triphenyl Benzene Electron‐Transport Materials for Highly Efficient Blue Phosphorescent OLEDs

Three triphenyl benzene derivatives of 1,3,5‐tri(m‐pyrid‐2‐yl‐phenyl)benzene (Tm2PyPB), 1,3,5‐tri(m‐pyrid‐3‐yl‐phenyl)benzene (Tm3PyPB) and 1,3,5‐tri(m‐pyrid‐4‐yl‐phenyl)benzene (Tm4PyPB), containing pyridine rings at the periphery, are developed as electron‐transport and hole/exciton‐blocking materials for iridium(III) bis(4,6‐(di‐fluorophenyl)pyridinato‐N,C^2′)picolinate (FIrpic)‐based blue phosphorescent organic light‐emitting devices. Their highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) energy levels decrease as the nitrogen atom of the pyridine ring moves from position 2 to 3 and 4; this is supported by both experimental results and density functional theory calculations, and gives improved electron‐injection and hole‐blocking properties. They exhibit a high electron mobility of 10^?4–10^?3 cm² V^?1 s^?1 and a high triplet energy level of 2.75 eV. Confinement of FIrpic triplet excitons is strongly dependent on the nitrogen atom position of the pyridine ring. The second exponential decay component in the transient photoluminescence decays of Firpic‐doped films also decreases when the position of the nitrogen atom in the pyridine ring changes. Reduced driving voltages are obtained when the nitrogen atom position changes because of improved electron injection as a result of the reduced LUMO level, but a better carrier balance is achieved for the Tm3PyPB‐based device. An external quantum efficiency (EQE) over 93% of maximum EQE was achieved for the Tm4PyPB‐based device at an illumination‐relevant luminance of 1000 cd m^?2, indicating reduced efficiency roll‐off due to better confinement of FIrpic triplet excitons by Tm4PyPB in contrast to Tm2PyPB and Tm3PyPB.     

Overcoming the poor short wavelength spectral response of CdS/CdTe photovoltaic modules via luminescence down‐shifting: ray‐tracing simulations

The short‐wavelength response of cadmium sulfide/cadmium telluride (CdS/CdTe) photovoltaic (PV) modules can be improved by the application of a luminescent down‐shifting (LDS) layer to the PV module. The LDS layer contains a mixture of fluorescent organic dyes that are able to absorb short‐wavelength light of λ < 540 nm, for which the PV module exhibited low external quantum efficiency (EQE), and re‐emit it at a longer wavelength (λ > 540 nm), where the solar cell EQE is high. Ray‐tracing simulations indicate that a mixed LDS layer containing three dyes could lead to an increase in the short‐circuit current density from J_sc = 19.8 mA/cm² to J_sc = 22.9 mA/cm² for a CdS/CdTe PV module. This corresponds to an increase in conversion efficiency from 9.6% to 11.2%. This indicates that a relative increase in the performance of a production CdS/CdTe PV module of nearly 17% can be expected via the application of LDS layers, possibly without any making any alterations to the solar cell itself. Copyright © 2006 John Wiley & Sons, Ltd.     

Low‐Temperature,Nontoxic Water‐Induced Metal‐Oxide Thin Films and Their Application in Thin‐Film Transistors

Here, a simple, nontoxic, and inexpensive “water‐inducement” technique for the fabrication of oxide thin films at low annealing temperatures is reported. For water‐induced (WI) precursor solution, the solvent is composed of water without additional organic additives and catalysts. The thermogravimetric analysis indicates that the annealing temperature can be lowered by prolonging the annealing time. A systematic study is carried out to reveal the annealing condition dependence on the performance of the thin‐film transistors (TFTs). The WI indium‐zinc oxide (IZO) TFT integrated on SiO₂ dielectric, annealed at 300 °C for 2 h, exhibits a saturation mobility of 3.35 cm² V^?1 s^?1 and an on‐to‐off current ratio of ≈10⁸. Interestingly, through prolonging the annealing time to 4 h, the electrical parameters of IZO TFTs annealed at 230 °C are comparable with the TFTs annealed at 300 °C. Finally, fully WI IZO TFT based on YO_x dielectric is integrated and investigated. This TFT device can be regarded as “green electronics” in a true sense, because no organic‐related additives are used during the whole device fabrication process. The as‐fabricated IZO/YO_x TFT exhibits excellent electron transport characteristics with low operating voltage (≈1.5 V), small subthreshold swing voltage of 65 mV dec^?1 and the mobility in excess of 25 cm² V^?1 s^?1.     

Nanodot‐Enhanced High‐Efficiency Pure‐White Organic Light‐Emitting Diodes with Mixed‐Host Structures

A relatively high‐efficiency, fluorescent pure‐white organic light‐emitting diode was fabricated using a polysilicic acid (PSA) nanodot‐embedded polymeric hole‐transporting layer (HTL). The diode employed a mixed host in the single emissive layer, which comprised 0.5 wt % yellow 5,6,11,12‐tetra‐phenylnaphthacene doped in the mixed host of 50 % 2‐(N,N‐diphenyl‐amino)‐6‐[4‐(N,N‐diphenylamino)styryl]naphthalene and 50 % N,N′‐bis‐(1‐naphthyl)‐N,N′‐diphenyl‐1,10‐biphenyl‐4‐4′‐diamine. By incorporating 7 wt % 3 nm PSA nanodot into the HTL of poly(3,4‐ethylene‐dioxythiophene)‐poly‐(styrenesulfonate), the efficiency at 100 cd m^–2 was increased from 13.5 lm W^–1 (14.7 cd A^–1; EQE: 7.2 %) to 17.1 lm W^–1 (17.6 cd A^–1; EQE: 8.3 %). The marked efficiency improvement may be attributed to the introduction of the PSA nanodot, leading to a better carrier‐injection‐balance.     

Nitrogen‐Doped Nanoporous Carbon/Graphene Nano‐Sandwiches: Synthesis and Application for Efficient Oxygen Reduction

A zeolitic‐imidazolate‐framework (ZIF) nanocrystal layer‐protected carbonization route is developed to prepare N‐doped nanoporous carbon/graphene nano‐sandwiches. The ZIF/graphene oxide/ZIF sandwich‐like structure with ultrasmall ZIF nanocrystals (i.e., ≈20 nm) fully covering the graphene oxide (GO) is prepared via a homogenous nucleation followed by a uniform deposition and confined growth process. The uniform coating of ZIF nanocrystals on the GO layer can effectively inhibit the agglomeration of GO during high‐temperature treatment (800 °C). After carbonization and acid etching, N‐doped nanoporous carbon/graphene nanosheets are formed, with a high specific surface area (1170 m² g^?1). These N‐doped nanoporous carbon/graphene nanosheets are used as the nonprecious metal electrocatalysts for oxygen reduction and exhibit a high onset potential (0.92 V vs reversible hydrogen electrode; RHE) and a large limiting current density (5.2 mA cm^?2 at 0.60 V). To further increase the oxygen reduction performance, nanoporous Co‐N_x/carbon nanosheets are also prepared by using cobalt nitrate and zinc nitrate as cometal sources, which reveal higher onset potential (0.96 V) than both commercial Pt/C (0.94 V) and N‐doped nanoporous carbon/graphene nanosheets. Such nanoporous Co‐N_x/carbon nanosheets also exhibit good performance such as high activity, stability, and methanol tolerance in acidic media.     

High‐Purity‐Blue and High‐Efficiency Electroluminescent Devices Based on Anthracene

Novel blue‐light‐emitting materials, 9,10‐bis(1,2‐diphenyl styryl)anthracene (BDSA) and 9,10‐bis(4′‐triphenylsilylphenyl)anthracene (BTSA), which are composed of an anthracene molecule as the main unit and a rigid and bulky 1,2‐diphenylstyryl or triphenylsilylphenyl side unit, have been designed and synthesized. Theoretical calculations on the three‐dimensional structures of BDSA and BTSA show that they have a non‐coplanar structure and inhibited intermolecular interactions, resulting in a high luminescence efficiency and good color purity. By incorporating these new, non‐doped, blue‐light‐emitting materials into a multilayer device structure, it is possible to achieve luminance efficiencies of 1.43 lm W^–1 (3.0 cd A^–1 at 6.6 V) for BDSA and 0.61 lm W^–1 (1.3 cd A^–1 at 6.7 V) for BTSA at 10 mA cm^–2. The electroluminescence spectrum of the indium tin oxide (ITO)/copper phthalocyanine (CuPc)/1,4‐bis[(1‐naphthylphenyl)‐amino]biphenyl (α‐NPD)/BDSA/tris(9‐hydroxyquinolinato)aluminum (Alq₃)/LiF/Al device shows a narrow emission band with a full width at half maximum (FWHM) of 55 nm and a λ_max = 453 nm. The FWHM of the ITO/CuPc/α‐NPD/BTSA/Alq₃/LiF/Al device is 53 nm, with a λ_max = 436 nm. Regarding color, the devices showed highly pure blue emission ((x,y) = (0.15,0.09) for BTSA, (x,y) = (0.14,0.10) for BDSA) at 10 mA cm^–2 in Commission Internationale de l'Eclairage (CIE) chromaticity coordinates.     

Molecular Engineering of Blue Fluorescent Molecules Based on Silicon End‐Capped Diphenylaminofluorene Derivatives for Efficient Organic Light‐Emitting Materials

Blue fluorescent materials based on silicone end‐capped 2‐diphenylaminofluorene derivatives are synthesized and characterized. These materials are doped into a 2‐methyl‐9,10‐di‐[2‐naphthyl]anthracene host as blue dopant materials in the emitting layer of organic light‐emitting diode devices bearing a structure of ITO/DNTPD (60 nm)/NPB (30 nm)/emitting layer (30 nm)/Alq₃ (20 nm)/LiF (1.0 nm)/Al (200 nm). All devices exhibit highly efficient blue electroluminescence with high external quantum efficiencies (3.47%–7.34% at 20 mA cm^?2). The best luminous efficiency of 11.2 cd A^?1 and highest quantum efficiency of 7.34% at 20 mA cm^?2 are obtained in a device with CIE coordinates (0.15, 0.25). A deep‐blue OLED with CIE coordinates (0.15, 0.14) exhibits a luminous efficiency of 3.70 cd A^?1 and quantum efficiency of 3.47% at 20 mA cm^?2.     

High‐Mobility Air‐Stable Naphthalene Diimide‐Based Copolymer Containing Extended π‐Conjugation for n‐Channel Organic Field Effect Transistors

A high‐performance naphthalene diimide (NDI)‐based conjugated polymer for use as the active layer of n‐channel organic field‐effect transistors (OFETs) is reported. The solution‐processable n‐channel polymer is systematically designed and synthesized with an alternating structure of long alkyl substituted‐NDI and thienylene–vinylene–thienylene units (PNDI‐TVT). The material has a well‐controlled molecular structure with an extended π‐conjugated backbone, with no increase in the LUMO level, achieving a high mobility and highly ambient stable n‐type OFET. The top‐gate, bottom‐contact device shows remarkably high electron charge‐carrier mobility of up to 1.8 cm² V^?1 s^?1 (I_on/I_off = 10⁶) with the commonly used polymer dielectric, poly(methyl methacrylate) (PMMA). Moreover, PNDI‐TVT OFETs exhibit excellent air and operation stability. Such high device performance is attributed to improved π–π intermolecular interactions owing to the extended π‐conjugation, apart from the improved crystallinity and highly interdigitated lamellar structure caused by the extended π–π backbone and long alkyl groups.     

All‐Cellulose‐Based Quasi‐Solid‐State Sodium‐Ion Hybrid Capacitors Enabled by Structural Hierarchy

Na‐ion hybrid capacitors consisting of battery‐type anodes and capacitor‐style cathodes are attracting increasing attention on account of the abundance of sodium‐based resources as well as the potential to bridge the gap between batteries (high energy) and supercapacitors (high power). Herein, hierarchically structured carbon materials inspired by multiscale building units of cellulose from nature are assembled with cellulose‐based gel electrolytes into Na‐ion capacitors. Nonporous hard carbon anodes are obtained through the direct thermal pyrolysis of cellulose nanocrystals. Nitrogen‐doped carbon cathodes with a coral‐like hierarchically porous architecture are prepared via hydrothermal carbonization and activation of cellulose microfibrils. The reversible charge capacity of the anode is 256.9 mAh g^?1 when operating at 0.1 A g^?1 from 0 to 1.5 V versus Na⁺/Na, and the discharge capacitance of cathodes tested within 1.5 to 4.2 V versus Na⁺/Na is 212.4 F g^?1 at 0.1 A g^?1. Utilizing Na⁺ and ClO₄^? as charge carriers, the energy density of the full Na‐ion capacitor with two asymmetric carbon electrodes can reach 181 Wh kg^?1 at 250 W kg^?1, which is one of the highest energy devices reported until now. Combined with macrocellulose‐based gel electrolytes, all‐cellulose‐based quasi‐solid‐state devices are demonstrated possessing additional advantages in terms of overall sustainability.     

Multivalent‐Ion‐Mediated Stabilization of Hydrogen‐Bonded Multilayers

Hydrogen‐bonding interactions are an important alternative to electrostatic interactions for assembling multilayer thin films of uncharged components. Herein, a new method is reported for rendering such films stable at pH values close to physiological conditions. Multilayer films based on hydrogen bonding are assembled by the alternate deposition of poly[(styrene sulfonic acid)‐co‐(maleic acid)] (PSSMA) and poly(N‐isopropylacrylamide) (PNiPAAm) at pH 2.5. The use of PSSMA results in multilayers that contain free styrene sulfonate groups, as these moieties do not interact with the PNiPAAm functional groups. Subsequent infiltration of a multivalent ion (Ce⁴⁺ or Fe³⁺) leads to an increase in the total film mass, with little impact on the film morphology, as determined by using atomic force microscopy. To examine the film stability, the resulting films have been exposed to elevated pH (7.1). While there is substantial swelling of the multilayers (25 % and 55 % for Ce⁴⁺‐ and Fe³⁺‐stabilized films, respectively), film loss is negligible. This provides a stark contrast with non‐stabilized films, which disassemble almost immediately upon exposure to pH 7.1. This method represents a simple and effective strategy for stabilizing hydrogen‐bonded structures non‐covalently. Further, the multivalent ions also render the films responsive to changes in the local redox environment, as demonstrated by film disassembly after exposure of Fe³⁺‐treated films to iodide solutions.