Abstract Perovskite light-emitting diodes (PeLEDs) based on three-dimensional (3D) polycrystalline perovskites suffer from ion migration, which causes overshoot of luminance over time during ...operation and reduces its operational lifetime. Here, we demonstrate 3D/2D hybrid PeLEDs with extremely reduced luminance overshoot and 21 times longer operational lifetime than 3D PeLEDs. The luminance overshoot ratio of 3D/2D hybrid PeLED is only 7.4% which is greatly lower than that of 3D PeLED (150.4%). The 3D/2D hybrid perovskite is obtained by adding a small amount of neutral benzylamine to methylammonium lead bromide, which induces a proton transfer from methylammonium to benzylamine and enables crystallization of 2D perovskite without destroying the 3D phase. Benzylammonium in the perovskite lattice suppresses formation of deep-trap states and ion migration, thereby enhances both operating stability and luminous efficiency based on its retardation effect in reorientation.
Graphene is a distinct two-dimensional material that offers a wide range of opportunities for membrane applications because of ultimate thinness, flexibility, chemical stability, and mechanical ...strength. We demonstrate that few- and several-layered graphene and graphene oxide (GO) sheets can be engineered to exhibit the desired gas separation characteristics. Selective gas diffusion can be achieved by controlling gas flow channels and pores via different stacking methods. For layered (3- to 10-nanometer) GO membranes, tunable gas transport behavior was strongly dependent on the degree of interlocking within the GO stacking structure. High carbon dioxide/nitrogen selectivity was achieved by well-interlocked GO membranes in high relative humidity, which is most suitable for postcombustion carbon dioxide capture processes, including a humidified feed stream.
Controlled alignment and patterning of individual semiconducting nanowires at a desired position in a large area is a key requirement for electronic device applications. High-speed, large-area ...printing of highly aligned individual nanowires that allows control of the exact numbers of wires, and their orientations and dimensions is a significant challenge for practical electronics applications. Here we use a high-speed electrohydrodynamic organic nanowire printer to print large-area organic semiconducting nanowire arrays directly on device substrates in a precisely, individually controlled manner; this method also enables sophisticated large-area nanowire lithography for nano-electronics. We achieve a maximum field-effect mobility up to 9.7 cm(2) V(-1) s(-1) with extremely low contact resistance (<5.53 Ω cm), even in nano-channel transistors based on single-stranded semiconducting nanowires. We also demonstrate complementary inverter circuit arrays comprising well-aligned p-type and n-type organic semiconducting nanowires. Extremely fast nanolithography using printed semiconducting nanowire arrays provide a simple, reliable method of fabricating large-area and flexible nano-electronics.
A new silole‐containing low bandgap polymer is synthesized by replacing the 5‐position carbon of PCPDTBT with a silicon atom (PSBTBT). Through experiments and computational calculations, we show that ...the material properties, particular the packing of polymer chains, can be altered significantly. As a result, the polymer changes from amorphous to highly crystalline with the replacement of the silicon atom.
Polymer properties, such as their mechanical strength, barrier properties, and dielectric response, can be dramatically improved by the addition of nanoparticles. This improvement is thought to be ...because the surface area per unit mass of particles increases with decreasing particle size, R, as 1/R. This favorable effect has to be reconciled with the expectation that at small enough R the nanoparticles must behave akin to a solvent and cause a deterioration of properties. How does this transition in behavior from large solutes to the solvent limit occur? We conjecture that for small enough particles the layer of polymer affected by the particles (“bound” polymer layer) must be much smaller than that for large particles: the favorable effect of increasing particle surface area can thus be overcome and lead to the small solvent limit with unfavorable mechanical properties, for example. To substantiate this picture requires that we measure and compare the “bound polymer layer” formed on nanoparticles with those near large particles with equivalent chemistry. We have implemented a novel strategy to obtain uniform nanoparticle dispersion in polymers, a problem for many previous works. Then, by combining theory and a suite of experimental techniques, including differential scanning calorimetry and positron annihilation lifetime spectroscopy, we show that the immobilized poly(2-vinylpyridine) layer near 15 nm diameter silica particles (∼1 nm) is considerably thinner than that at flat silica surfaces (∼4 to 5 nm), which is the limit of an infinitely large particle. We have also determined that the changes in the polymer’s glass-transition temperature due to the presence of this strongly interacting surface are very small in both well-dispersed nanocomposites and thin films (<100 nm). Similarly, the polymer’s fragility, as determined by dielectric spectroscopy, is also found to be little affected in the nanocomposites relative to the pure polymer. While a systematic study of the dependence of the bound polymer layer thickness on particle size remains an outstanding challenge, this first study provides conclusive evidence for the hypothesis that the bound polymer layer can be significantly smaller around nanoparticles than at chemically similar flat surfaces.
We investigated the effect of film thickness (geometrical confinement) on the structural evolution of sputtered indium-zinc-tin oxide (IZTO) films as high mobility n-channel semiconducting layers ...during post-treatment at different annealing temperatures ranging from 350 to 700 °C. Different thicknesses result in IZTO films containing versatile phases, such as amorphous, low-, and high-crystalline structures even after annealing at 700 °C. A 19-nm-thick IZTO film clearly showed a phase transformation from initially amorphous to polycrystalline bixbyite structures, while the ultra-thin film (5 nm) still maintained an amorphous phase. Transistors including amorphous and low crystalline IZTO films fabricated at 350 and 700 °C show reasonable carrier mobility (µ
) and on/off current ratio (I
) values of 22.4-35.9 cm
V
s
and 1.0-4.0 × 10
, respectively. However, their device instabilities against positive/negative gate bias stresses (PBS/NBS) are unacceptable, originating from unsaturated bonding and disordered sites in the metal oxide films. In contrast, the 19-nm-thick annealed IZTO films included highly-crystalline, 2D spherulitic crystallites and fewer grain boundaries. These films show the highest µ
value of 39.2 cm
V
s
in the transistor as well as an excellent I
value of 9.7 × 10
. Simultaneously, the PBS/NBS stability of the resulting transistor is significantly improved under the same stress condition. This promising superior performance is attributed to the crystallization-induced lattice ordering, as determined by highly-crystalline structures and the associated formation of discrete donor levels (~ 0.31 eV) below the conduction band edge.
Nano‐tailoring the shape and dimensions of the parabolic antireflective structure predicted by simulation has been successfully carried out to fabricate monolithic high‐performance antireflection ...(AR) polymer films. The average total reflectivity from an artificial antireflection film is lowered down to 0.64% at a wavelength range of 400 nm to 800 nm, which appears to be the best antireflection performance ever reported for transparent polymer antireflection films.
Organic synaptic transistors using intrinsic (i.e., non‐doped) organic semiconductors have demonstrated various synaptic functions to mimic biological synapses, but the devices show limited long‐term ...retention behaviors although long‐term memory is essential for neuromorphic computing. To achieve long‐term retention time, correlating the synaptic responses with the microstructures of polymer semiconductor is an imperative step. It is shown that synaptic plasticity in ion‐gel‐gated organic synaptic transistors (IGOSTs) can be modulated by controlling the microstructure of organic semiconductors and that long‐term memory retention can be significantly prolonged by increasing their crystallinity. The crystallinity of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) films that are spun‐cast on bare and self‐assembled monolayer is systematically controlled, before and after thermal treatments. Long‐term retention tends to extend, as the crystallinity increases. To evaluate synaptic current decay behaviors, it is suggested that the relaxation is a result of de‐doping of the polymer semiconductor over time. The recognition of handwritten digits is simulated and a high classification accuracy (>92%) is achieved with IGOSTs including high crystalline P3HT film. The study provides fundamental information about the effects of polymer microstructure on synaptic plasticity of IGOSTs, which may be applicable in neuromorphic electronics.
Long‐term memory retention in poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) ion‐gel‐gated organic synaptic transistors (IGOSTs) is prolonged by modulation of microstructure. Modulation of ordered structure of the organic semiconductor is a new strategy that affects ion spreading and trapping inside the organic semiconductor in an IGOST to achieve reliable long‐term memory retention of synaptic transistors for neuromorphic computing.
To enhance the electrical performance of pentacene‐based field‐effect transistors (FETs) by tuning the surface‐induced ordering of pentacene crystals, we controlled the physical interactions at the ...semiconductor/gate dielectric (SiO2) interface by inserting a hydrophobic self‐assembled monolayer (SAM, CH3‐terminal) of organoalkyl‐silanes with an alkyl chain length of C8, C12, C16, or C18, as a complementary interlayer. We found that, depending on the physical structure of the dielectric surfaces, which was found to depend on the alkyl chain length of the SAM (ordered for C18 and disordered for C8), the pentacene nano‐layers in contact with the SAM could adopt two competing crystalline phases—a “thin‐film phase” and “bulk phase” – which affected the π‐conjugated nanostructures in the ultrathin and subsequently thick films. The field‐effect mobilities of the FET devices varied by more than a factor of 3 depending on the alkyl chain length of the SAM, reaching values as high as 0.6 cm2 V−1 s−1 for the disordered SAM‐treated SiO2 gate‐dielectric. This remarkable change in device performance can be explained by the production of well π‐conjugated and large crystal grains in the pentacene nanolayers formed on a disordered SAM surface. The enhanced electrical properties observed for systems with disordered SAMs can be attributed to the surfaces of these SAMs having fewer nucleation sites and a higher lateral diffusion rate of the first seeding pentacene molecules on the dielectric surfaces, due to the disordered and more mobile surface state of the short alkyl SAM.
The crystalline phase and morphology of pentacene thin films deposited on a dielectric layer (see figure) can be controlled by changing the molecular ordering structure of organosilane SAMs adsorbed on the dielectric surface. Depending on the physical structure of the dielectric surface, the pentacene nanolayers can adopt two competing crystalline phases – “thin‐film” and “bulk” – that affect the π‐conjugated nanostructures, causing the field‐effect mobility to vary.
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