Xiaolong Fu

25th Anniversary Article: Key Points for High‐Mobility Organic Field‐Effect Transistors

Remarkable progress has been made in developing high performance organic field-effect transistors (OFETs) and the mobility of OFETs has been approaching the values of polycrystalline silicon, meeting the requirements of various electronic applications from electronic papers to integrated circuits. In this review, the key points for development of high mobility OFETs are highlighted from aspects of molecular engineering, process engineering and interface engineering. The importance of other factors, such as impurities and testing conditions is also addressed. Finally, the current challenges in this field for practical applications of OFETs are further discussed.

Revealing the Charge-Transfer Interactions in Self-Assembled Organic Cocrystals: Two-Dimensional Photonic Applications

A new crystal of a charge-transfer (CT) complex was prepared through supramolecular assembly and it has unique two-dimensional (2D) morphology. The CT nature of the ground and excited states of this new Bpe-TCNB cocrystal (BTC) were confirmed by electron spin resonance measurements, spectroscopic studies, and theoretical calculations, thus providing a comprehensive understanding of the CT interactions in organic donor-acceptor systems. And the lowest CT1 excitons are responsible for the efficient photoluminescence (Φ(PL)=19%), which can actively propagate in individual 2D BTCs without anisotropy, thus implying that the optical waveguide property of the crystal is not related to the molecular stacking structure. This unique 2D CT cocrystal exhibits potential for use in functional photonic devices in the next-generation optoelectronic communications.

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.

Solution-Processed Large-Area Nanocrystal Arrays of Metal-Organic Frameworks as Wearable, Ultrasensitive, Electronic Skin for Health Monitoring.

Pressure sensors based on solution-processed metal-organic frameworks nanowire arrays are fabricated with very low cost, flexibility, high sensitivity, and ease of integration into sensor arrays. Furthermore, the pressure sensors are suitable for monitoring and diagnosing biomedical signals such as radial artery pressure waveforms in real time.

Quick Fabrication of Large-area Organic Semiconductor Single Crystal Arrays with a Rapid Annealing Self-Solution-Shearing Method

In this paper, we developed a new method to produce large-area single crystal arrays by using the organic semiconductor 9, 10-bis (phenylethynyl) anthracene (BPEA). This method involves an easy operation, is efficient, meets the demands of being low-cost and is independent of the substrate for large-area arrays fabrication. Based on these single crystal arrays, the organic field effect transistors exhibit the superior performance with the average mobility extracting from the saturation region of 0.2 cm2 V−1s−1 (the highest 0.47 cm2 V−1s−1) and on/off ratio exceeding 105. In addition, our single crystal arrays also show a very high photoswitch performance with an on/off current ratio up to 4.1 × 105, which is one of the highest values reported for organic materials. It is believed that this method provides a new way to fabricate single crystal arrays and has the potential for application to large area organic electronics.

Rubrene analogues with the aggregation-induced emission enhancement behaviour

In the light of the principle of aggregation-induced emission enhancement (AIEE), the rubrene analogue with orange light-emitting properties is designed and synthesized by substituting the phenyl side groups of rubrene with thienyl groups. To the best of our knowledge, this is the first report on the synthesis of rubrene with AIEE behaviour, thus paving the way for the development of light-emitting rubrene derivatives.

A novel method for photolithographic polymer shadow masking: toward high-resolution high-performance top-contact organic field effect transistors

A novel and universal method, based on water-soluble poly(4-styrene sulfonate), was introduced into the preparation of a polymer mask. Using this mask, high-resolution, high-performance, bottom-gate, top-contact OFETs can be achieved. There is no solvent intervention in the process of manufacturing these OFETs and the mask can be recycled.

Tuning charge transport from unipolar (n-type) to ambipolar in bis(naphthalene diimide) derivatives by introducing π-conjugated heterocyclic bridging moieties

A series of acceptor–donor–acceptor (A–D–A) conjugated molecules based on naphthalene diimide dimers bridged with different π-conjugated heterocyclic units (NDI–π–NDI) have been designed and synthesized. By an ingenious design strategy, the LUMO (the lowest unoccupied molecular orbital) of the NDI-based small molecules is well controlled to a relatively constant value of −3.8 to −3.9 eV, whereas their HOMO (the highest occupied molecular orbital) could be tuned over a wide range, from −6.5 eV (compound 1) to −5.5 eV (compound 5), leading to varied band gaps from 2.6 eV to 1.5 eV. Organic field-effect transistor (OFET) characterization of these NDI–π–NDI molecules shows that compounds 1, 2, and 3 have good n-type semiconducting properties in a N2 atmosphere with the maximum electron mobilities up to 0.15 cm2 V−1 s−1, 0.46 cm2 V−1 s−1 and 0.57 cm2 V−1 s−1, respectively. Compounds 4 and 5, due to the high-lying HOMO levels and reduced energy band gaps, have ambipolar semiconducting properties and OFETs based on 5 show the highest electron and hole mobilities up to 1.23 cm2 V−1 s−1 and 0.0074 cm2 V−1 s−1, respectively. Moreover, the performances are enhanced under thermal treatment because of the increased crystallinity as evidenced by X-ray diffraction (XRD) and atomic force microscopy (AFM). The easily tunable electronic energy levels make the NDI-based semiconductors promising n-channel and ambipolar components in organic devices.

A thienyl peripherally substituted rubrene analogue with constant emissions and good film forming ability

A new thienyl peripherally substituted rubrene analogue was synthesized. Different from rubrene quenching of fluorescence after aggregation, this compound emits constantly yellow-green light both in solution and in the aggregation state. Meanwhile, this rubrene analogue exhibits better film forming ability with the hole charge carrier mobility up to 0.01 cm2 V−1 s−1.