High-Performance Field-Effect Transistors Fabricated with Donor–Acceptor Copolymers Containing S···O Conformational Locks Supplied by Diethoxydithiophenethenes

Constructing planar π-conjugated backbone is of critical importance for polymeric semiconductors to obtain high charge carrier mobility. In this regard, suitable introduction of noncovalent interactions is one of useful approaches. Herein, we report a series of donor–acceptor copolymers based on diethoxydithiophenethene (EDTE), namely PEDTE<i>n</i> (<i>n</i> = 1, 2, and 3), containing multiple O···H–C and S···O conformational locks, where the latter ones are supplied by the EDTE units. PEDTE<i>n</i> owns planar conjugated backbones with suitable HOMO energy levels (ca. – 5.20 eV) and strong absorption behaviors along with enhanced solution processability. High-performance field-effect transistors based on the copolymers exhibited a high hole mobility of up to 5.37 cm² V^–1 s^–1, which is among the highest values of semiconducting polymers based on the concept of conformational locks. AFM and GIXRD experiments reveal that PEDTE<i>n</i> could form crystalline and close packing thin films with a π–π stacking distance of down to 3.78 Å

Etching-Controlled Growth of Graphene by Chemical Vapor Deposition

Graphene growth and etching are reciprocal processes that can reach a dynamic balance during chemical vapor deposition (CVD). Most commonly, the growth of graphene is the dominate process, while the etching of graphene is a recessive process often neglected during CVD growth of graphene. We show here that through the rational design of low-pressure CVD of graphene in hydrogen-diluted methane and regulation of the flow rate of H₂, the etching effect during the growth process of graphene could be prominent and even shows macroscopic selectivity. On this basis, etching-controlled growth and synthesis of graphene with various morphologies from compact to dendritic even to fragmentary have been demonstrated. The morphology–selection mechanism is clarified through phase-field theory based on simulations. This study not only presents an intriguing case for the fundamental mechanism of CVD growth but also provides a facile method for the synthesis of high-quality graphene with trimmed morphologies

Improving the Photovoltaic Performance of Polymer Solar Cells Based on Furan-Flanked Diketopyrrolopyrrole Copolymers via Tuning the Alkyl Side Chain

Two furan-flanked diketopyrrolopyrrole copolymers, poly­(3,6-difuran-2-yl-2,5-di­(alkyl)-pyrrolo­[3,4-<i>c</i>]­pyrrole-1,4-dione-altthienylenevinylene) with different alkyl side chains (PDVFs), have been synthesized and applied as a donor in polymer solar cells (PSCs). The PSC based on a blend of PDVF-8 with 2-octyldodecyl and [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁BM) as an active layer has shown a better device performance than the PSC based on a blend of PDVF-10 with 2-decyltetradecyl and PC₇₁BM. Tuning the alkyl side chains attached on the PDVFs leads to an increase of power conversion efficiency from 3.57% (PDVF-10) to 4.56% (PDVF-8) due to enhancements of short circuit current and fill factor. The effect of different alkyl side chains on the phase separation of the PDVF/PC₇₁BM thin film has been investigated by using atomic force microscopy, transmission electron microscopy, and X-ray photoemission spectroscopy depth profiling in details. Furthermore, impedance spectroscopy was used to analyze the relationship between the phase separation of the PDVF/PC₇₁BM blend films and the PSCs performance

Fluorodiphenylethene-Containing Donor–Acceptor Conjugated Copolymers with Noncovalent Conformational Locks for Efficient Polymer Field-Effect Transistors

The diphenylethene moiety is a versatile building block that offers several chemically functionalizable sites, allowing easy modulation of electronic properties of the resulting polymers and providing numerous opportunities for discovering related structure–property relationships. In this study, we report a series of difluoro­diphenylethene-based copolymers with noncovalent conformational locks for applications in polymer field-effect transistors. Different fluorination positions lead to different type of intra- and intermolecular interactions, backbone conformations, and eventually different device performances. 2,2′-Difluoro­diphenylethene-based copolymers P2DFPE-<i>n</i> containing F···H–C conformation locks exhibit obviously enhanced hole mobilities of 1.3–1.5 cm² V^–1 s^–1, whereas 3,3′-difluoro­diphenylethene-based copolymers P3DFPE-<i>n</i> containing F···H–C and F···S conformation locks show lower mobilities of 0.2–0.4 cm² V^–1 s^–1. AFM and 2D-GRXD investigations indicate that P2DFPE-<i>n</i> takes predominantly edge-on orientation packing mode, forming crystalline and highly ordered thin films with small π–π stacking distances of 3.59–3.68 Å. However, P3DFPE-<i>n</i> adopts random close molecular packing mode in solid states

Fractal Etching of Graphene

An anisotropic etching mode is commonly known for perfect crystalline materials, generally leading to simple Euclidean geometric patterns. This principle has also proved to apply to the etching of the thinnest crystalline material, graphene, resulting in hexagonal holes with zigzag edge structures. Here we demonstrate for the first time that the graphene etching mode can deviate significantly from simple anisotropic etching. Using an as-grown graphene film on a liquid copper surface as a model system, we show that the etched graphene pattern can be modulated from a simple hexagonal pattern to complex fractal geometric patterns with sixfold symmetry by varying the Ar/H₂ flow rate ratio. The etched fractal patterns are formed by the repeated construction of a basic identical motif, and the physical origin of the pattern formation is consistent with a diffusion-controlled process. The fractal etching mode of graphene presents an intriguing case for the fundamental study of material etching

Naphthalenediimide-Based Copolymers Incorporating Vinyl-Linkages for High-Performance Ambipolar Field-Effect Transistors and Complementary-Like Inverters under Air

We report the synthesis of two novel donor–acceptor copolymers poly­{[<i>N</i>, <i>N</i>′-bis­(alkyl)-1,4,5,8-naphthalene diimide-2,6-diyl-<i>alt</i>-5,5′-di­(thiophen-2-yl)-2,2′-(<i>E</i>)-2-(2-(thiophen-2-yl)­vinyl)­thiophene]} (PNVTs) based on naphthalenediimide (NDI) acceptor and (<i>E</i>)-2-(2-(thiophen-2-yl)­vinyl)­thiophene donor. The incorporations of vinyl linkages into polymer backbones maintain the energy levels of the lowest unoccupied molecular orbits at −3.90 eV, therefore facilitating the electron injection. Moreover, the energy levels of the highest occupied molecular orbits increase from −5.82 to −5.61 eV, successfully decreasing the hole injection barrier. Atomic force microscopy measurements indicate that PNVTs thin films exhibit larger polycrystalline grains compared with that of poly­{[<i>N</i>, <i>N</i>′-bis­(2-octyldodecyl)-1,4,5,8-naphthalene diimide-2,6-diyl]-<i>alt</i>- 5,5′-(2,2′-bithiophene)} [P­(NDI2OD-T2)], consistent with the stronger <i>π</i>–<i>π</i> stacking measured by grazing incidence X-ray scatting. To optimize devices performance, field-effect transistors (FETs) with three devices configurations have been investigated. The results indicate that the electron mobility of the vinyl-containing PNVTs exhibit about 3–5 times higher than that of P­(NDI2OD-T2). Additionally, the vinyl-linkages in PNVTs remarkably enhance ambipolar transport of their top-gate FETs, obtaining high hole and electron mobilities of 0.30 and 1.57 cm² V^–1 s^–1, respectively, which are among the highest values reported to date for the NDI-based polymers. Most importantly, ambipolar inverters have been realized in ambient, exhibiting a high gain of 155. These results provide important progresses in solution-processed ambipolar polymeric FETs and complementary-like inverters

Large π‑Conjugated Quinacridone Derivatives: Syntheses, Characterizations, Emission, and Charge Transport Properties

Two 11-ring-fused quinacridone derivatives, TTQA and DCNTTQA, have been synthesized by ferric chloride mediated cyclization and Knoevenagel reaction. Replacement of the carbonyl groups (in TTQA) with dicyanoethylene groups (in DCNTTQA) not only red-shifted the emission to the near-infrared region but also led to a nonplanar skeleton that significantly improved the solubility of DCNTTQA. Moreover, dicyanoethylene groups rendered DCNTTQA low-lying HOMO and LUMO levels. DCNTTQA-based solution-processed field-effect transistors showed a hole mobility up to 0.217 cm² V^–1 s^–1