RESUMEN
How to orient polymers homeotropically in thin films has been a long-standing issue in polymer science because polymers intrinsically prefer to lie down. Here we provide a design principle for polymers that are processable into a 2D homeotropic order. The key to this achievement was a recognition that cylindrical polymers can be designed to possess oppositely directed local dipoles in their cross-section, which possibly force polymers to tightly connect bilaterally, affording a 2D rectangular assembly. With a physical assistance of the surface grooves on Teflon sheets that sandwich polymer samples, homeotropic ordering is likely nucleated and gradually propagates upon hot-pressing towards the interior of the film. Consequently, the 2D rectangular lattice is constructed such that its b axis (side chains) aligns along the surface grooves, while its c axis (polymer backbone) aligns homeotropically on a Teflon sheet. This finding paves the way to molecularly engineered 2D polymers with anomalous functions.
RESUMEN
The slow-down in traditional silicon complementary metal-oxide-semiconductor (CMOS) scaling (Moore's law) has created an opportunity for a disruptive innovation to bring the semiconductor industry into a postsilicon era. Due to their ultrathin body and ballistic transport, carbon nanotubes (CNTs) have the intrinsic transport and scaling properties to usher in this new era. The remaining challenges are largely materials-related and include obtaining purity levels suitable for logic technology, placement of CNTs at very tight (â¼5 nm) pitch to allow for density scaling and source/drain contact scaling. This review examines the potential performance advantages of a CNT-based computing technology, outlines the remaining challenges, and describes the recent progress on these fronts. Although overcoming these issues will be challenging and will require a large, sustained effort from both industry and academia, the recent progress in the field is a cause for optimism that these materials can have an impact on future technologies.
RESUMEN
Thin films of carbon nanotubes (CNTs) are fabricated from solution using a one-step directed assembly strategy. Very high surface selectivity and exceptionally high CNT densities can be observed in small features with complex shapes. This directed assembly technique makes use of minimum amounts of CNTs and low toxicity solvents, and can be applied to metallic, semiconducting and mixed CNTs for fabrication of thin films over macroscopic areas. The thin films obtained with this approach are used for thin-film transistor (TFT) fabrication, and their electrical characterization is described.
RESUMEN
A thin-film transistor: An n-type polymer semiconductor, poly(2,3-bis(perfluorohexyl)thieno[3,4-b]pyrazine), was synthesized through a Pd-catalyzed polycondensation employing a perfluorinated multiphase solvent system. This is the first example of an n-type polymer semiconductor with exclusive solubility in fluorinated solvents. The fabrication of organic field effect transistors containing this new n-type polymer semiconductor is shown.
RESUMEN
The motivation of this study is to determine if small amounts of designer additives placed at the polymer-fullerene interface in bulk heterojunction (BHJ) solar cells can influence their performance. A series of AB-alternating side-chain-functionalized poly(thiophene) analogues, P1-6, are designed to selectively localize at the interface between regioregular poly(3-hexylthiophene) (rr-P3HT) and PC(n)BM (n = 61, 71). The side chains of every other repeat unit in P1-6 contain various terminal aromatic moieties. BHJ solar cells containing ternary mixtures of rr-P3HT, PC(n)BM, and varying weight ratios of additives P1-6 are fabricated and studied. At low loadings, the presence of P1-6 consistently increases the short circuit current and decreases the series resistance of the corresponding devices, leading to an increase in power conversion efficiency (PCE) compared to reference P3HT/PC(61)BM cells. Higher additive loadings (>5 wt %) lead to detrimental nanoscale phase separation within the active layer blend and produce solar cells with high series resistances and low overall PCEs. Small-perturbation transient open circuit voltage decay measurements reveal that, at 0.25 wt % incorporation, additives P1-6 increase charge carrier lifetimes in P3HT/PC(61)BM solar cells. Pentafluorophenoxy-containing polymer P6 is the most effective side-chain-functionalized additive and yields a 28% increase in PCE when incorporated into a 75 nm thick rr-P3HT/PC(61)BM BHJ at a 0.25 wt % loading. Moreover, devices with 220 nm thick BHJs containing 0.25 wt % P6 display PCE values of up to 5.3% (30% PCE increase over a control device lacking P6). We propose that additives P1-6 selectively localize at the interface between rr-P3HT and PC(n)BM phases and that aromatic moieties at side-chain termini introduce a dipole at the polymer-fullerene interface, which decreases the rate of bimolecular recombination and, therefore, improves charge collection across the active layer.