Deyang Ji

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-sheared ultrathin films for highly-sensitive ammonia detection using organic thin-film transistors

The solution-shearing technique is utilized to fabricate large-area, ultrathin and continuous films of 1,4-bis((5′-hexyl-2,2′-bithiophen-5-yl)ethynyl)benzene (HTEB) for high-performance organic thin-film transistors (OTFTs), based on which highly sensitive, highly selective and reversible gas sensors exhibit outstanding response to NH3, with detection limit as low as 100 ppb.

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.

Solution-processed high-performance flexible 9, 10-bis(phenylethynyl)anthracene organic single-crystal transistor and ring oscillator

Organic semiconductor of 9, 10-bis(phenylethynyl)anthracene (BPEA) single crystal ribbon with ultra-long length has been prepared by solution drop casting method, where the growth direction was controlled with the seed crystal. The BPEA single crystal ribbon based field-effect transistors show high hole mobility up to 3.2 cm2/V·s, and the inverters exhibited the highest gain of 92. The complex device such as 5-stage ring oscillator consisting of 10 transistors was also constructed on a single crystal ribbon. This straightforward methodology was applied to fabricate plastic transistors on the flexible substrate, showing high performance even after repeatedly bending of 300 times.

Silver mirror reaction for organic electronics: towards high-performance organic field-effect transistors and circuits

A highly-conductive (conductivity: 1 × 105 S cm−1) silver film was produced via a silver mirror reaction at room temperature and then was successfully defined as source/drain electrodes and conductor sections in circuits with a photolithographic technique. High-performance bottom-gate bottom-contact (BGBC) organic field-effect transistors (OFETs) on glass substrates based on p-type pentacene were demonstrated, which were comparable to devices based on vacuum-evaporated silver electrodes. The device performance could be further significantly improved by modifying the silver electrodes with 7,7,8,8-tetracyanoquinodimethane (TCNQ) due to the reduced contact resistance. For pentacene-based transistors, the highest field-effect mobility was approaching 0.57 cm2 V−1 s−1 with the modified silver electrodes. Moreover, complex organic inverters and five-stage oscillators on glass substrates were first successfully manufactured through silver mirror reaction, and the gain and signal propagation delay was 17 and 400 μs for the inverters and oscillators, respectively. Our results demonstrated that the silver mirror reaction can be used as a promising simple and efficient approach to produce solution-processed electrodes and interconnections in low-cost and large-area organic circuits for industrial applications.

Surface Polarity and Self-Structured Nanogrooves Collaboratively Oriented Molecular Packing for High Crystallinity toward Efficient Charge Transport

Efficient charge transport in organic semiconductors is essential for construction of high performance optoelectronic devices. Herein, for the first time, we demonstrate that poly(amic acid) (PAA), a facilely deposited and annealing-free dielectric layer, can tailor the growth of organic semiconductor films with large area and high crystallinity toward efficient charge transport and high mobility in their thin film transistors. Pentacene is used as a model system to demonstrate the concept with mobility up to 30.6 cm2 V-1 s-1, comparable to its high quality single crystal devices. The structure of PAA has corrugations with OH groups pointing out of the surface, and the presence of an amide bond further allows adjacent polymer strands to interact via hydrogen bonding, leading to a self-rippled surface perpendicular to the corrugation. On the other hand, the strong polar groups (-COOH/-CONH) of PAA could provide repulsive forces between PAA and pentacene, which results in the vertical orientation of pentacene on the dielectric surface. Indeed, in comparison with its imidized counterpart polyimide (PI), PAA dielectric significantly enhances the film crystallinity, drastically increases the domain size, and decreases the interface trap density, giving rise to superior device performance with high mobility. This concept can be extended to more organic semiconducting systems, e.g., 2,6-diphenylanthracene (DPA), tetracene, copper phthalocyanine (CuPc), and copper hexadecafluorophthalocyanine (F16CuPc), demonstrating the general applicability. The results show the importance of combining surface nanogrooves with the strong polarity in orienting the molecular arrangement for high crystallinity toward efficient charge transport in organic semiconductors.

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 electrical properties of graphite oxide by plasma

The electrical properties of graphite oxide (GO) can be tuned consecutively by treating samples with ammonia and hydrogen plasma. When altering ammonia plasma time from 10 to 4.5 min, large area (greater than 100×100 μm2), n-type, ambipolar and p-type semiconducting reduced graphite oxide (RGO) sheets could be obtained. The highest mobilities of the electron and hole are 5.41 and 2.10 cm2 V−1 s−1 at low operational voltage (3 or −3 V, respectively). When treating a GO film with hydrogen:argon (9:1) plasma, high conductivity RGO was obtained with conductivity around 630 S cm−1. It is anticipated that this study could pave the way towards carbon-based electronics.

Poly(sodium-4-styrene sulfonate) (PSSNa)-assisted transferable flexible, top-contact high-resolution free-standing organic field-effect transistors

The development of high-integration, flexible and transferable devices is a very important premise to realize authentically wearable applications in the future. Here, we report how to fabricate flexible, free-standing and high-resolution (down to 5 μm) top-contact OFETs based on a polystyrene (PS) dielectric layer. In this process, we use a special sacrificial layer, poly(sodium-4-styrene sulfonate) (PSSNa). It is low-cost, dissolves quickly in water at room temperature and has good compatibility with most organic material processing techniques. With the help of this sacrificial layer, this kind of free-standing transistors can be successfully transferred onto arbitrary substrates. Furthermore, the degradation of the performance of the devices after multiple and successive transfer is tolerated.

Modulating the metal/organic interface via CuTCNQ decorated layer toward high performance bottom-contact single-crystal transistors

The organic single-crystal field-effect transistors using anthracene derivative, H-Ant as an active layer with source/drain electrodes decorated by metal charge transfer salt (CuTCNQ) were fabricated. We demonstrated that this bottom-contact structure displayed an obvious improvement in the electrical characteristics relative to their pristine copper and top-contact gold electrode counterparts. This observation could be ascribed to the lower contact resistance resulting from the energetic match between electrodes and semiconductor.