Xiaotao Zhang

Tuning the Crystal Polymorphs of Alkyl Thienoacene via Solution Self‐Assembly Toward Air‐Stable and High‐Performance Organic Field‐Effect Transistors

The first example for thienoacene derivatives with selective growth of different crystal polymorphs is simply achieved by solution-phase self-assembly. Compared with platelet-shaped α-phase crystals, organic field-effect transistors (OFETs) based on microribbon-shaped β-phase crystals show a hole mobility up to 18.9 cm(2) V(-1) s(-1), which is one of the highest values for p-type organic semiconductors measured under ambient conditions.

Side-chain engineering of green color electrochromic polymer materials: toward adaptive camouflage application

The syntheses of adaptive camouflage devices based on novel side-chain engineered organic electrochromic materials have been demonstrated. Herein we report a molecule engineering approach for the tuning and syntheses of green-brown switchable electrochromic materials and also demonstrate their applications in chameleonic fabric devices. We have also successfully demonstrated the fabrication of chameleonic fabric devices.

Aggregation-induced emission enhancement based on 11,11,12,12,-tetracyano-9,10-anthraquinodimethane

By introducing phenyl groups into the 2- and 6-positions of 11,11,12,12-tetracyano-9,10-anthraquinodimethane, a material (dP-TCAQ) with aggregation-induced emission enhancement (AEE) characteristics was synthesized. The AEE phenomenon was explained by analysis of its solid-state packing mode. To our best knowledge, this is the first report regarding 11,11,12,12-tetracyano-9,10-anthraquinodimethane with AEE behaviour.

Characterizations of power loads on divertor targets for type-I, compound and small ELMs in the EAST superconducting tokamak

The Experimental Advanced Superconducting Tokamak (EAST) has recently achieved a variety of H-mode regimes with different edge-localized mode (ELM) dynamics, including type-I ELMs, compound ELMs, which are manifested by the onset of a large spike followed by a sequence of small spikes on Dα emissions, usual type-III ELMs, and very small ELMs. This newly observed very small ELMy H-mode appears to be similar to the type-II ELMy H-mode, with higher repetition frequency (~1 kHz) and lower amplitude than the type-III ELMy H-mode, exhibiting an intermediate confinement level between type-I and type-III ELMy H-modes. The energy loss and divertor power load are systematically characterized for these different ELMy H-modes to provide a physics basis for the next-step high-power long-pulse operations in EAST. Both type-I and compound ELMs exhibit good confinement (H98(y,2) ~ 1). A significant loss of the plasma stored energy occurs at the onset of type-I ELMs (~8%) and compound ELMs (~5%), while no noticeable change in the plasma stored energy is observed for the small ELMs, including both type-III ELMs and very small ELMs. The peak heat flux on divertor targets for type-I ELMs currently achieved in EAST is about 10 MW m−2, as determined from the divertor-embedded triple Langmuir probe system with high time resolution. As expected, type-III ELMs lead to much smaller divertor power loads with a peak heat flux of about 2 MW m−2. Peak power loads for compound ELMs are between those for type-I and type-III ELMs. It is remarkable that the new very small ELMy H-modes exhibit even lower target power deposition than type-III ELMs, with the peak heat flux generally below 1 MW m−2. These very small ELMs are usually accompanied by broadband fluctuations with frequencies ranging from 20 to 50 kHz, which may promote particle and power exhaust throughout the very small ELMy H-mode regime.

Substitution effect on molecular packing and transistor performance of indolo[3,2-b]carbazole derivatives

In this manuscript, two chloro-substituted derivatives of indolo[3,2-b]carbazole (ICZ), 2,8-dichloro-indolo[3,2-b]carbazole (CICZ) and 2,8-dichloro-5,11-dihexyl-indolo[3,2-b]carbazole (CHICZ) were designed and synthesized. The only difference between CICZ and CHICZ is at the N-5 and N-11 positions with or without long alkyl side chains. Interestingly, CICZ and CHICZ exhibited similar thermal, optical, and electrochemical properties, while their molecular packing motifs in solid state and corresponding charge transport properties were significantly different. The alkyl chains at N-5 and N-11 positions were proved not only enhancing the solubility and self-organization of the compounds but also shifting the molecular packing from herringbone (CICZ) to one-dimensional π–π stacking (CHICZ). Moreover, nearly no field-effect performance was observed for CICZ, while the mobility of CHICZ was as high as 0.14 cm2 V−1 s−1 for its thin films and 0.5 cm2 V−1 s−1 for its single crystals. These results confirmed that the chemical substitutions are a powerful molecular design tool to tune the molecular packing motifs of organic semiconductors and their corresponding electronic properties.

First results from H-mode plasmas generated by ICRF heating in the EAST

Deuterium high-confinement (H-mode) plasmas, lasting up to 3.45 s, have been generated in the EAST by ion cyclotron range of frequency (ICRF) heating. H-mode access was achieved by coating the molybdenum-tiled first wall with lithium to reduce the hydrogen recycling from the wall. H-mode plasmas with plasma currents between 0.4 and 0.6 MA and axial toroidal magnetic fields between 1.85 and 1.95 T were generated by 27 MHz ICRF heating of deuterium plasma with hydrogen minority. The ICRF input power required to access the H-mode was 1.6–1.8 MW. The line-averaged density was in the range (1.83–2.3) × 1019 m−3. 200–500 Hz type-III edge localized mode activity was observed during the H-mode phase. The H-mode confinement factor, H98IPB(y, 2), was ~0.7.

Particle and power deposition on divertor targets in EAST H-mode plasmas

The effects of edge-localized modes (ELMs) on divertor particle and heat fluxes were investigated for the first time in the Experimental Advanced Superconducting Tokamak (EAST). The experiments were carried out with both double null and lower single null divertor configurations, and comparisons were made between the H-mode plasmas with lower hybrid current drive (LHCD) and those with combined ion cyclotron resonance heating (ICRH). The particle and heat flux profiles between and during ELMs were obtained from Langmuir triple-probe arrays embedded in the divertor target plates. And isolated ELMs were chosen for analysis in order to reduce the uncertainty resulting from the influence of fast electrons on Langmuir triple-probe evaluation during ELMs. The power deposition obtained from Langmuir triple probes was consistent with that from the divertor infra-red camera during an ELM-free period. It was demonstrated that ELM-induced radial transport predominantly originated from the low-field side region, in good agreement with the ballooning-like transport model and experimental results of other tokamaks. ELMs significantly enhanced the divertor particle and heat fluxes, without significantly broadening the SOL width and plasma-wetted area on the divertor target in both LHCD and LHCD + ICRH H-modes, thus posing a great challenge for the next-step high-power, long-pulse operation in EAST. Increasing the divertor-wetted area was also observed to reduce the peak heat flux and particle recycling at the divertor target, hence facilitating long-pulse H-mode operation. The particle and heat flux profiles during ELMs appeared to exhibit multiple peak structures, and were analysed in terms of the behaviour of ELM filaments and the flux tubes induced by modified magnetic topology during ELMs.

Initial results on plasma heating experiments in the ion cyclotron range of frequencies on EAST

Plasma heating using fast waves was successfully performed on the Experimental Advanced Superconducting Tokamak (EAST) in the H minority regime in deuterium plasmas at 27MHz and B-o = 2.0 T. With 1.0 MW of ion cyclotron range of frequency (ICRF) power injected at a line-averaged electron density of 4.0 x 10(19) m(-3), the electron temperature increased from 1.0 keV to above 2.0 keV and the loop voltage dropped. An increase in the stored energy by 30 kJ was obtained. The first H-mode plasma of 6.4 s was achieved with a combination of lower hybrid wave and ICRF heating. Density pump-out was observed during L-mode discharges at a high electron density of 4.0 x 10(19) m(-3). In these discharges, re-attachment of the plasma was observed when ICRF power was applied.

Pyridine-bridged diketopyrrolopyrrole conjugated polymers for field-effect transistors and polymer solar cells

Five wide or medium band gap diketopyrrolopyrrole (DPP)-based conjugated polymers with pyridine as bridges were developed for organic field-effect transistors (OFETs) and polymer solar cells (PSCs). By introducing copolymerized aromatic building blocks from strong electron-donating units to electron-deficient units into the conjugated backbone, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the DPP polymers were tailored to the low-lying position. Therefore, the polarity of charge transport in OFETs can be switched from p-type to n-type. The DPP polymer with a low-lying LUMO of −3.80 eV provides a hole-only mobility of 2.95 × 10−2 cm2 V−1 s−1, while an electron-only mobility of 1.24 × 10−3 cm2 V−1 s−1 is found in the DPP polymer with a LUMO of −4.22 eV. Further investigation of photovoltaic cells based on these DPP polymers shows a modest power conversion efficiency (PCE) of around 2%. Our results demonstrate that wide band gap pyridine-bridged DPP polymers have potential application in OFETs and OSCs by adjusting their energy level with alternated units on the conjugated backbone.

2D Organic Materials for Optoelectronic Applications

The remarkable merits of 2D materials with atomically thin structures and optoelectronic attributes have inspired great interest in integrating 2D materials into electronics and optoelectronics. Moreover, as an emerging field in the 2D-materials family, assembly of organic nanostructures into 2D forms offers the advantages of molecular diversity, intrinsic flexibility, ease of processing, light weight, and so on, providing an exciting prospect for optoelectronic applications. Herein, the applications of organic 2D materials for optoelectronic devices are a main focus. Material examples include 2D, organic, crystalline, small molecules, polymers, self-assembly monolayers, and covalent organic frameworks. The protocols for 2D-organic-crystal-fabrication and -patterning techniques are briefly discussed, then applications in optoelectronic devices are introduced in detail. Overall, an introduction to what is known and suggestions for the potential of many exciting developments are presented.