Crystal Phase Control of Luminescing α‐NaGdF4:Eu3+and β‐NaGdF4:Eu3+ Nanocrystals

NaGdF₄:Eu³⁺, NaEuF₄, and NaGdF₄ nanocrystals were synthesized in the high‐boiling coordinating solvent N‐(2‐hydroxyethyl)‐ethylenediamine (HEEDA). Phase pure nanomaterials, crystallizing either in the cubic α‐phase or the hexagonal β‐phase, were obtained by adjusting one reaction parameter only, i.e., the molar ratio between metal and fluoride ions in the synthesis. The hexagonal β‐phase is formed, if this molar ratio is close to stoichiometric, whereas the cubic α‐phase is obtained in the presence of excess metal ions. The optical properties of the Eu³⁺ doped samples are different for the two crystal phases. The results indicate an increased number of oxygen impurities close to Eu³⁺ ions, if excess metal ions are used in the synthesis.     

Towards General Guidelines for Aligned,Nanoscale Assemblies of Hairy‐Rod Polyfluorene

This account highlights recent progress towards understanding the complex hierarchical levels of solid‐state structure in a prototypical helical hairy‐rod polyfluorene, poly[9,9‐bis(2‐ethylhexyl)fluorene‐2,7‐diyl] (or PF2/6). This branched‐side‐chain containing polyfluorene undergoes a systematic intermolecular self‐assembly and liquid‐crystalline phase behavior in combination with uniaxial and biaxial alignment. The latter processes yield full three‐dimensional orientation of the crystallites and polymer chains. Also reviewed are the impact of the molecular structure and phase behavior on surface morphology, anisotropic film formation, and, ultimately, the overall impact of these physical attributes on optical constants. This particular polyfluorene also represents a model system for demonstrating the applicability of mean‐field theory in detailing the self‐organization of aligned hairy‐rod block‐copolymer systems. These results of PF2/6 are compared to those of other archetypical π‐conjugated hairy‐rod polymers. General guidelines of how molecular weight influences nanostructure, phase behavior, alignment, and surface morphology are given.     

Ambipolar Charge Transport in Air‐Stable Polymer Blend Thin‐Film Transistors

Ambipolar thin‐film transistors based on a series of air‐stable, solution‐processed blends of an n‐type polymer poly(benzobisimidazobenzophenanthroline) (BBL) and a p‐type small molecule, copper phthalocyanine (CuPc) are demonstrated, where all fabrication and measurements are performed under ambient conditions. The hole mobilities are in the range of 6.0 × 10^–6 to 2.0 × 10^–4 cm² V^–1 s^–1 and electron mobilities are in the range of 2.0 × 10^–6 to 3.0 × 10^–5 cm² V^–1 s^–1, depending on the blend composition. UV‐vis spectroscopy and electron diffraction show crystallization of CuPc in the metastable α‐crystal form within the semicrystalline BBL matrix. These CuPc domains develop into elongated ribbon‐like crystalline nanostructures when the blend films are processed in methanol, but not when they are processed in water. On methylene chloride vapor annealing of the blend films, a phase transformation of CuPc from the α‐form to the β‐form is observed, as shown by optical absorption spectroscopy and electron diffraction. Ambipolar charge transport is only observed in the blend films where CuPc crystallized in the elongated ribbon‐like nanostructures (α‐form). Ambipolar behavior is not observed with CuPc in the β‐polymorph. Unipolar hole mobilities as high as 2.0 × 10^–3 cm² V^–1 s^–1 are observed in these solution‐processed blend field‐effect transistors (FETs) on prolonged treatment in methanol, comparable to previously reported hole mobilities in thermally evaporated CuPc FETs. These results show that ambipolar charge transport and carrier mobilities in multicomponent organic semiconductors are intricately related to the phase‐separated nanoscale and crystalline morphology.     

Kinked Star‐Shaped Fluorene/ Triazatruxene Co‐oligomer Hybrids with Enhanced Functional Properties for High‐Performance,Solution‐Processed,Blue Organic Light‐Emitting Diodes

A novel series of kinked star‐shaped oligofluorene/triazatruxene hybrids are conveniently prepared via a powerful microwave‐enhanced multiple coupling methodology. Constructing kinked star‐shaped architectures can effectively suppress crystallization and aggregation. The resulting materials are highly amorphous, showing stable amorphous morphology against crystallization. A triazatruxene core endows the materials with elevated highest occupied molecular orbital (HOMO) levels that are well matched to the anode work function, leading to a significantly improved hole‐injection property. They hybrids are highly luminescent in both solution (quantum yield is 0.52–0.80) and the solid‐state (quantum yield is 0.45–0.76) with bright blue emission. Remarkably, solution‐processed devices displaying single‐layer electroluminescence (EL) based on these oligomers exhibit efficient blue EL and demonstrate striking color stability, almost unchanged with increasing driving voltage. The best device performance has a rather low turn‐on voltage (3.3 V) and a high device efficiency (2.16 % @ 2382 cd m^–2) as well as a high brightness (7714 cd m^–2 @ 10 V) with CIE coordinates of (0.16, 0.15); it shows remarkably better EL performance than devices based on linear oligofluorene or polyfluorene counterparts. The results prove that an oligomer with kinked star‐shaped architecture is extremely promising for efficient and stable blue EL. The reasons for the enhanced functional properties and the improved color stability are discussed in relation to the chemical structures and components.     

Silicon thin‐film solar cells with rectangular‐shaped grating couplers

As an alternative to randomly textured transparent conductive oxides as front contact for thin‐film silicon solar cells the application of transparent grating couplers was studied. The grating couplers were prepared by sputtering of aluminium‐doped zinc oxide (ZnO) on glass substrate, a photolithography and a lift‐off process and were used as periodically textured substrates. The period size and groove depth of these transparent gratings were tuned independently from each other and varied between 1 and 4 μm and 100–600 nm. The optical properties of rectangular‐shaped gratings and the opto‐electronic behaviour of amorphous and microcrystalline silicon solar cells with integrated grating couplers as a function of the grating parameters (period size P and groove depth h_g) are presented. The optical properties of the gratings are discussed with respect to randomly textured substrates and the achieved solar cell results are compared with the opto‐electronic properties of solar cells deposited on untextured (flat) and randomly textured substrates. Copyright © 2005 John Wiley & Sons, Ltd.     

Controlled Synthesis of Ultrathin 2D β‐In2S3 with Broadband Photoresponse by Chemical Vapor Deposition

β‐In₂S₃ is a natural defective III–VI semiconductor attracting considerable interests but lack of efficient method for its 2D form fabrication. Here, for the first time, this paper reports controlled synthesis of ultrathin 2D β‐In₂S₃ flakes via a facile space‐confined chemical vapor deposition method. The natural defects in β‐In₂S₃ crystals, clearly revealed by optical spectra and optoelectronic measurement, strongly modulate the (opto)‐electronic of as‐fabricated β‐In₂S₃ and render it a broad detection range from visible to near‐infrared. Particularly, the as‐fabricated β‐In₂S₃ photodetector shows a high photoresponsivity of 137 A W^?1, a high external quantum efficiency of 3.78 × 10⁴%, and a detectivity of 4.74 × 10¹⁰ Jones, accompanied with a fast rise and decay time of 6 and 8 ms, respectively. In addition, an interesting linear response to the testing power intensities range is observed, which can also be understood by the presence of natural defects. The unique defective structure and intrinsic optical properties of β‐In₂S₃, together with its controllable growth, endow it with great potential for future applications in electronics and optoelectronics.     

Threshold Reduction in Polymer Lasers Based on Poly(9,9‐dioctylfluorene) with Statistical Binaphthyl Units

We introduce novel statistical copolymers of poly(9,9‐dioctylfluorene), PFO, which contain various concentrations of 6,6′‐(2,2′‐octyloxy‐1,1′‐binaphthyl) spacer groups. We demonstrate that, owing to the large dihedral angle (> 60°) between neighboring naphthalene units, we could hinder the formation of the highly ordered β‐phase in thin films of the copolymers. In low‐temperature photoluminescence measurements, the typical signature of the PFO β‐phase at 442 nm is no longer observed for copolymers with a binaphthyl concentration of about 12 %. Moreover, the optical properties of the copolymers resembled those of the glassy α‐phase PFO. Second‐order distributed feedback (DFB) lasers based on thin films of the homopolymer PFO showed a minimum lasing threshold of 11.7 μJ cm^–2 (λ_max = 452 nm, excitation at λ = 337 nm with 500 ps pulses). With increasing binaphthyl concentration in the copolymer backbone, the lasing threshold steadily decreased to 3 μJ cm^–2 for a binaphthyl concentration of about 12 %. Therefore, our novel copolymers provide a vast improvement for PFO‐based optoelectronics.     

Angular‐Shaped 4,9‐Dialkyl α‐ and β‐Naphthodithiophene‐Based Donor–Acceptor Copolymers: Investigation of Isomeric Structural Effects on Molecular Properties and Performance of Field‐Effect Transistors and Photovoltaics

Two angular‐shaped 4,9‐didodecyl α‐aNDT and 4,9‐didodecyl β‐aNDT isomeric structures have been regiospecifically designed and synthesized. The distannylated α‐aNDT and β‐aNDT monomers are copolymerized with the Br‐DTNT monomer by the Stille coupling to furnish two isomeric copolymers, PαNDTDTNT and PβNDTDTNT, respectively. The geometric shape and coplanarity of the isomeric α‐aNDT and β‐aNDT segments in the polymers play a decisive role in determining their macroscopic device performance. Theoretical calculations show that PαNDTDTNT possesses more linear polymeric backbone and higher coplanarity than PβNDTDTNT. The less curved conjugated main chain facilitates stronger intermolecular π–π interactions, resulting in more redshifted absorption spectra of PαNDTDTNT in both solution and thin film compared to the PβNDTDTNT counterpart. 2D wide‐angle X‐ray diffraction analysis reveals that PαNDTDTNT has more ordered π‐stacking and lamellar stacking than PβNDTDTNT as a result of the lesser curvature of the PαNDTDTNT backbone. Consistently, PαNDTDTNT exhibits a greater field effect transistor hole mobility of 0.214 cm² V^?1 s^?1 than PβNDTDTNT with a mobility of 0.038 cm² V^?1 s^?1. More significantly, the solar cell device incorporating the PαNDTDTNT:PC₇₁BM blend delivers a superior power conversion efficiency (PCE) of 8.01% that outperforms the PβNDTDTNT:PC₇₁BM‐based device with a moderate PCE of 3.6%.     

The Roles of the Ge‐Te Core Network and the Sb‐Te Pseudo Network During Rapid Nucleation‐Dominated Crystallization of Amorphous Ge2Sb2Te5

Ge₂Sb₂Te₅ (GST) has demonstrated its outstanding importance among rapid phase‐change (PC) materials, being applied for optical and electrical data storage for over three decades. The mechanism of nanosecond phase change in GST, which is vital for its application, has long been disputed: various, quite diverse scenarios have been proposed on the basis of various experimental and theoretical approaches. Nevertheless, one central question still remains unanswered: why is amorphous GST stable at room temperature for long time while it can rapidly transform to the crystalline phase at high temperature? Here it is revealed for the first time, by modelling the amorphous structure based on synchrotron radiation anomalous X‐ray scattering data, that germanium and tellurium atoms form a “core” Ge‐Te network with ring formation. It is also suggested that the Ge‐Te network can stabilize the amorphous phase at room temperature and can persist in the crystalline phase. On the other hand, antimony does not contribute to ring formation but constitutes a “pseudo” network with tellurium, in which the characteristic Sb–Te distance is somewhat longer than the covalent Sb–Te bond distance. This suggests that the Sb‐Te pseudo network may act as a precursor to forming critical nuclei during the crystallization process. The findings conclude that the Ge‐Te core network is responsible for the outstanding stability and rapid phase change of the amorphous phase while the Sb‐Te pseudo network is responsible for triggering critical nucleation.     

Bright Blue Solution Processed Triple‐Layer Polymer Light‐Emitting Diodes Realized by Thermal Layer Stabilization and Orthogonal Solvents

The realization of fully solution processed multilayer polymer light‐emitting diodes (PLEDs) constitutes the pivotal point to push PLED technology to its full potential. Herein, a fully solution processed triple‐layer PLED realized by combining two different deposition strategies is presented. The approach allows a successive deposition of more than two polymeric layers without extensively redissolving already present layers. For that purpose, a poly(9,9‐dioctyl‐fluorene‐co‐N‐(4‐butylphenyl)‐diphenylamine) (TFB) layer is stabilized by a hard‐bake process as hole transport layer on top of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). As emitting layer, a deep blue emitting pyrene‐triphenylamine copolymer is deposited from toluene solution. To complete the device assembly 9,9‐bis(3‐(5′,6′‐bis(4‐(polyethylene glycol)phenyl)‐[1,1′:4′,1″‐terphenyl]‐2′‐yl)propyl)‐9′,9′‐dioctyl‐2,7‐polyfluorene (PEGPF), a novel polyfluorene‐type polymer with polar sidechains, which acts as the electron transport layer, is deposited from methanol in an orthogonal solvent approach. Atomic force microscopy verifies that all deposited layers stay perfectly intact with respect to morphology and layer thickness upon multiple solvent treatments. Photoelectron spectroscopy reveals that the offsets of the respective frontier energy levels at the individual polymer interfaces lead to a charge carrier confinement in the emitting layer, thus enhancing the exciton formation probability in the device stack. The solution processed PLED‐stack exhibits bright blue light emission with a maximum luminance of 16 540 cd m^?2 and a maximum device efficiency of 1.42 cd A^?1, which denotes a five‐fold increase compared to corresponding single‐layer devices and demonstrates the potential of the presented concept.     

High‐Performance Organic Photovoltaic Devices Using a New Amorphous Molecular Material with High Hole Drift Mobility,Tris[4‐(5‐phenylthiophen‐2‐yl)phenyl]amine

A new amorphous molecular material, tris[4‐(5‐phenylthiophen‐2‐yl)phenyl]amine (TPTPA), is synthesized and characterized. TPTPA forms a stable amorphous glass with a glass‐transition temperature of 83 °C when the melt sample is cooled. It also forms amorphous thin films by a thermal deposition technique. TPTPA exhibits a hole drift mobility of 1.0 × 10^?2 cm² V^?1 s^?1 at an electric field of 1.0 × 10⁵ V cm^?1 and at 293 K, as determined by the time‐of‐flight method, which is of the highest level among those of amorphous molecular materials. pn‐Heterojunction organic photovoltaic devices (OPVs) using TPTPA as an electron donor and C₆₀ or C₇₀ as an electron acceptor exhibit high performance with fill factors of 0.66～0.71 and power conversion efficiencies of 1.7～2.2% under air‐mass (AM) 1.5G illumination at an intensity of 100 mW cm^?2, which are of the highest level ever reported for OPVs using amorphous molecular materials.     

Green‐Chemical Synthesis of Ultrathin β‐MnOOH Nanofibers for Separation Membranes

Ultrathin β‐MnOOH nanofibers can be produced on a large scale via a green‐chemical method using an aqueous solution of very dilute Mn(NO₃)₂ and aminoethanol at room temperature. High‐magnification electron microscopy demonstrates that the β‐MnOOH nanofibers are 3–5 nm thin and up to 1 micrometer long and the nanofibers are parallel assembled into bundles with an average diameter of 25 nm. By a filtration process, ultrathin mesoporous membranes with strong mechanical, thermal, and chemical stabilities are prepared from the β‐MnOOH nanofiber bundles. The membranes can separate 10‐nm nanoparticles from water at a flux of 15120 L m^?2·h^?1·bar^?1, which was 2–3 times higher than that of commercial membranes with similar rejection properties. Based on the Young‐Laplace equation, β‐MnOOH nanofiber/polydimethylsiloxane composite membranes are developed through a novel downstream‐side evaporation process. From nanoporous to dense separation membranes can be achieved by optimizing the experimental conditions. The membranes show desirable separation performance for proteins, ethanol/water mixtures, and gases. The synthesis method of β‐MnOOH nanofibers is simple and environmentally friendly, and it is easily scalable for industry and applicable to other metal oxide systems. These composite membranes constitute a significant contribution to advanced separation technology.     

Formation of a Ground‐State Charge‐Transfer Complex in Polyfluorene//[6,6]‐Phenyl‐C61 Butyric Acid Methyl Ester (PCBM) Blend Films and Its Role in the Function of Polymer/PCBM Solar Cells

Evidence is presented for the formation of a weak ground‐state charge‐transfer complex in the blend films of poly[9,9‐dioctylfluorene‐co‐N‐(4‐methoxyphenyl)diphenylamine] polymer (TFMO) and [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM), using photothermal deflection spectroscopy (PDS) and photoluminescence (PL) spectroscopy. Comparison of this polymer blend with other polyfluorene polymer/PCBM blends shows that the appearance of this ground‐state charge‐transfer complex is correlated to the ionization potential of the polymer, but not to the optical gap of the polymer or the surface morphology of the blend film. Moreover, the polymer/PCBM blend films in which this charge‐transfer complex is observed also exhibit efficient photocurrent generation in photovoltaic devices, suggesting that the charge‐transfer complex may be involved in charge separation. Possible mechanisms for this charge‐transfer state formation are discussed as well as the significance of this finding to the understanding and optimization of polymer blend solar cells.     

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant

New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λ_max = 421 nm/445 nm) and orange emission (λ_max = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m^–2, luminance efficiency of 7.30 cd A^–1, and power efficiency of 3.34 lm W^–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A^–1, power efficiency of 5.75 lm W^–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m^–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.     

White‐Light‐Emitting Diodes Based on Iridium Complexes via Efficient Energy Transfer from a Conjugated Polymer

Efficient white‐light‐emitting diodes (WLEDs) have been developed using a polyfluorene‐type blue‐emitting conjugated polymer doped with green and red phosphorescent dyes. The emission spectrum of the conjugated polymer, which has a very high luminescent efficiency, shows a large spectral overlap with the absorbance of green and red iridium complexes. Also, efficient energy transfer from the conjugated polymer to the iridium complexes is observed. Poly(N‐vinyl carbazole) is used to improve the miscibility between conjugated polymer and iridium complexes because of their poor chemical compatibility and phase separation. A white emission spectrum is easily obtained by varying the contents of the three materials and controlling the phase morphology. Moreover, these WLEDs show a voltage‐independent electroluminescence owing to the threshold and driving voltage of the three materials being similar as a result of energy transfer.     

Reversible Polarization Gratings on Thin Films of Polyoxetanes Bearing 4‐(N,N‐Diphenyl)amino‐4′‐nitroazobenzene Chromophores

Polarization gratings were fabricated by the two‐beam coupling method on the surface of a series of polyoxetanes containing 4‐(N,N‐diphenyl)amino‐4′‐nitroazobenzene pendants with the azobenzene chromophores either side‐on attached or end‐on attached through short or long spacers to the main chain. The dynamics of formation of the gratings or writings was studied in relation to the diffraction efficiency. The erasing behavior of the gratings was also examined, irradiating a linearly polarized single beam. The temporal stability of the diffraction efficiency was further studied after removing the coupled excitation beam. Both the mode of attachment of the chromophore to the main chain and the length of the side‐chain spacer greatly influenced the dynamic properties of the diffraction gratings. The presence of a long side‐chain spacer and side‐on attachment of the chromophore resulted in faster writing and erasing behavior. A preliminary study by solid‐state ¹³C NMR of the relaxational behavior of the main‐chain CH₂ groups and the pendant chromophores provided a reasonable picture to help explain the photo‐induced reorientation and relaxation of the azo chromophores at the molecular level.     

A Molecular Glass for Deep‐Blue Organic Light‐Emitting Diodes Comprising a 9,9′‐Spirobifluorene Core and Peripheral Carbazole Groups

Novel fluorene‐based compounds, TCPC‐6 and TCPC‐4, with rigid central spirobifluorene cores and peripheral carbazole groups are synthesized using the Suzuki coupling reaction. The optical, electrochemical, and thermal properties of these compounds are characterized. The compounds show strong deep‐blue emission both in solution and as thin films. Both TCPC‐6 and TCPC‐4 exhibit amorphous morphologies in the solid state with high glass transition temperatures (T_g) of 108 and 143 °C, respectively. Atomic force microscopy (AFM) measurements indicate that high‐quality amorphous films of these novel compounds can be prepared by spin‐coating. The oxidation potentials of TCPC‐6 and TCPC‐4 are significant lower than that of model compounds without peripheral carbazole groups, which suggests that these compounds have relatively high highest occupied molecular orbital (HOMO) energy levels and better hole‐injection capabilities. Light‐emitting devices fabricated by spin‐coating films of these molecules exhibit deep‐blue emission with Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (x, y) of (0.16, 0.05); the devices fabricated using spin‐coated TCPC‐6 and TCPC‐4 layers exhibit high luminance efficiencies of 1.35 and 0.90 cd A^–1 (with external quantum efficiencies of 3.72 and 2.47 %), respectively.     

Ordered Mesoporous Metastable α‐MoC1−x with Enhanced Water Dissociation Capability for Boosting Alkaline Hydrogen Evolution Activity

The sluggish reaction kinetics of the alkaline hydrogen evolution reaction (HER) remains an important challenge for water–alkali electrolyzers, which originates predominantly from the additional water dissociation step required for the alkaline HER. In this work, it is demonstrated theoretically and experimentally that metastable, face‐centered‐cubic α‐MoC_1?x phase shows superior water dissociation capability and alkaline HER activity than stable, hexagonal‐close‐packed Mo₂C phase. Next, high surface area ordered mesoporous α‐MoC_1?x (MMC) is designed via a nanocasting method. In MMC structure, the α‐MoC_1?x phase facilitates the water dissociation reaction, while the mesoporous structure with high surface area enables a high dispersion of metal NPs and efficient mass transport. As a result, Pt nanoparticles (NPs) supported on MMC (Pt/MMC) show substantially enhanced alkaline HER activity in terms of overpotentials, Tafel slopes, mass and specific activities, and exchange current densities, compared to commercial Pt/C and Pt NPs supported on particulate α‐MoC_1?x or β‐Mo₂C. Notably, Pt/MMC shows very low Tafel slope of 30 mV dec^–1, which is the lowest value among the reported Pt‐based alkaline HER catalysts, suggesting the critical role of MMC in enhancing the HER kinetics. The promotional effect of MMC support in the alkaline HER is further demonstrated with an Ir/MMC catalyst.     

Preparation and Memory Performance of a Nanoaggregated Dispersed Red 1‐Functionalized Poly (N‐vinylcarbazole) Film via Solution‐Phase Self‐Assembly

A nanoaggregated dispersed red 1‐grafted poly(N‐vinylcarbazole) (abbreviated PVDR) is self‐assembled via π–π stacking interactions of the carbazole groups in the polymer system after adding a solution of PVDR in N,N‐dimethylformamide to dichloromethane. Upon self‐assembly, the nanoaggregated PVDR film displays helical columnar stacks with large grain sizes, whereas a non‐aggregated PVDR film exhibits an amorphous morphology with smaller grain size. A write‐once read‐many‐times (WORM) memory device is shown whereby a pre‐assembled solution of PVDR is spin‐coated as the active layer and is sandwiched between an aluminum electrode and an indium‐tin‐oxide (ITO) electrode. This device shows very good memory performance, with an ON/OFF current ratio of more than 10⁵ and a low misreading rate through the precise control of the ON and OFF states. The stability of the nanoaggregated PVDR device is much higher than that of the non‐nanoaggregated PVDR device. This difference in device stability under constant voltage stress can be mainly attributed to the difference in the film crystallinity and surface morphology. No degradation in current density was observed for the ON‐ and OFF‐states after more than one hundred million (10⁸) continuous read cycles indicating that both states were insensitive to the read cycles. These results render the nanoaggregated PVDR polymer as promising components for high‐performance polymer memory devices.     

Metastable Copper‐Phthalocyanine Single‐Crystal Nanowires and Their Use in Fabricating High‐Performance Field‐Effect Transistors

This paper describes a simple, vapor‐phase route for the synthesis of metastable α‐phase copper‐phthalocyanine (CuPc) single‐crystal nanowires through control of the growth temperature. The influence of the growth temperature on the crystal structures, morphology, and size of the CuPc nanostructures is explored using X‐ray diffraction (XRD), optical absorption, and transmission electron microscopy (TEM). α‐CuPc nanowires are successfully incorporated as active semiconductors in field‐effect transistors (FETs). Single nanowire devices exhibit carrier mobilities and current on/off ratios as high as 0.4 cm² V^?1 s^?1 and >10⁴, respectively.