Showing papers by "Yeong Don Park published in 2019"

Effect of Crystallization Modes in TIPS-pentacene/Insulating Polymer Blends on the Gas Sensing Properties of Organic Field-Effect Transistors

Abstract: Blending organic semiconductors with insulating polymers has been known to be an effective way to overcome the disadvantages of single-component organic semiconductors for high-performance organic field-effect transistors (OFETs). We show that when a solution processable organic semiconductor (6,13-bis(triisopropylsilylethynyl)pentacene, TIPS-pentacene) is blended with an insulating polymer (PS), morphological and structural characteristics of the blend films could be significantly influenced by the processing conditions like the spin coating time. Although vertical phase-separated structures (TIPS-pentacene-top/PS-bottom) were formed on the substrate regardless of the spin coating time, the spin time governed the growth mode of the TIPS-pentacene molecules that phase-separated and crystallized on the insulating polymer. Excess residual solvent in samples spun for a short duration induces a convective flow in the drying droplet, thereby leading to one-dimensional (1D) growth mode of TIPS-pentacene crystals. In contrast, after an appropriate spin-coating time, an optimum amount of the residual solvent in the film led to two-dimensional (2D) growth mode of TIPS-pentacene crystals. The 2D spherulites of TIPS-pentacene are extremely advantageous for improving the field-effect mobility of FETs compared to needle-like 1D structures, because of the high surface coverage of crystals with a unique continuous film structure. In addition, the porous structure observed in the 2D crystalline film allows gas molecules to easily penetrate into the channel region, thereby improving the gas sensing properties.

Aqueous Lithium-Ion Battery of Nano-LiFePO 4 with Antifreezing Agent of Ethyleneglycol for Low-Temperature Operation

Abstract: Low-temperature performance of the rechargeable batteries is limited because of a narrow temperature range of the electrolyte. Despite the aqueous electrolyte having a lower freezing point than the...

Uniform and Reliable Dip-Coated Conjugated Polymers for Organic Transistors as Obtained by Solvent Vapor Annealing

Abstract: Dip-coating is a useful technique to prepare a thin film of an organic semiconductor; however, achieving homogeneous film properties is sometimes challenging because of the experimental configurati...

Influence of Molecular Weight on the Solidification of a Semiconducting Polymer during Time-Controlled Spin-Coating

Abstract: Molecular weight (Mw) is a key material parameter governing a variety of interesting characteristics of macromolecules. Here, we systematically studied the effects of the Mw of a semiconducting pol...

Metal–organic frameworks in a blended polythiophene hybrid film with surface-mediated vertical phase separation for the fabrication of a humidity sensor

Abstract: A facile, reliable, fast-response poly(3-hexylthiophene-2,5-diyl) (P3HT)-based humidity sensor was developed by introducing metal–organic frameworks (MOFs), HKUST-1, into the semiconducting layer. HKUST-1 displayed an excellent ability to capture water molecules, thereby generating and attracting charge carriers derived from the water molecules present in the active layer. The HKUST-1/P3HT hybrid film showed excellent device sensitivity with an enhanced electrical current and a threshold voltage shift as a function of the relative humidity due to the superior gas capture properties and the porosity of HKUST-1. The surface energy of the substrate altered the distribution and location of HKUST-1 in the active layer, which improved the sensitivity of the hydrophilic surface. A dynamic gas sensing test revealed that the hybrid film displayed a reliable and stable performance with fast response and recovery times. The introduction of MOFs into a conjugated polymer stabilized and sensitized the devices, providing a facile method of improving gas sensor technologies based on organic semiconductors.

Uniform and Reliable Dip-Coated Conjugated Polymers for Organic Transistors as Obtained by Solvent Vapor Annealing

Abstract: Dip-coating is a useful technique to prepare a thin film of an organic semiconductor; however, achieving homogeneous film properties is sometimes challenging because of the experimental configuration of dip-coating under the strong influence of solvent vapor. In this work, we studied the effect of solvent vapor on dip-coated film uniformity during the dip-coating process. We demonstrate that solvent vapor released from the solution reservoir strongly affects film crystallinity at each relative position in the vertical direction. We also propose a novel method that utilizes the inevitable solvent vapor to anneal dip-coated films by adding some residual time during the dip-coating process, which results in highly uniform and crystalline films. Field-effect transistors constructed using films prepared by this dip-coating technique show a uniform, reliable field effect. This work provides a general principle and systematic guideline to prepare highly crystalline and uniform films of organic semiconductors via dip-coating. This method substantially reduces operational complexity in the dip-coating process, enables easy operation, and thus meets the demands of being low-cost for large-area fabrication without a postprocess. We therefore expect this method to be highly meaningful for the fabrication of organic electronics as well as for the assembly of other materials via solution processes.

Tailoring the crystallinity of solution-processed 6,13-bis(triisopropylsilylethynyl)pentacene via controlled solidification.

Abstract: Solution processing is one of the most important techniques for producing large-area, uniform films for printed electronics via a low-cost process. Herein, we propose a time-controlled spin-coating method to improve the crystallinity of films of the solution-processable organic small-molecule semiconductor 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene). A key factor in this process was to halt spinning before drying had begun. We used microscopic and spectroscopic analyses to systematically investigate the effect of spinning time on the evaporation rate of solvent at different spinning rates. We found that the crystallinity of the TIPS-pentacene thin films was substantially enhanced when the spinning time was limited to a few seconds, without post-treatment. We fabricated field-effect transistors using thin films deposited by this method and found that the field-effect mobility was enhanced ∼100-fold compared with that of a device fabricated using a film deposited by the conventional spin-coating method.

Highly crystalline and uniform conjugated polymer thin films by a water-based biphasic dip-coating technique minimizing the use of halogenated solvents for transistor applications

Abstract: The commercialization of organic electronics will require minimizing the use of halogenated solvents used to solution-process organic semiconductors, which is a crucial step for large-area coating methods, such as the dip-coating method. Here, we report a novel biphasic dip-coating method which uses a water-based biphasic solution and produces a uniform, smooth, and crystalline conjugated polymer thin film in the presence of a solvent additive. We demonstrated that a solvent additive with a high boiling point and solubility parameter similar to that of the solution affected the solvent evaporation rate and improved the crystallinity of the dip-coated polymer thin film. The method used to add the solvent strongly influenced how the solvent additive diffused into the polymer solution, which affected the resulting film morphology. The crystallinity and morphology of the polymer films were correlated with the electrical characteristics, and the most crystalline film displayed a high hole field effect mobility of 0.0391 cm2 V−1 s−1 when processed from the solvent mixture without post-treatment. Our findings provide a direction for the development of reliable and promising organic thin film transistor technologies.

Built-in Water Capture in a Polythiophene Film Blended with Metal-Organic Frameworks

Abstract: We introduced a metal-organic framework (MOF), HKUST-1, to a conjugated polymer layer, poly(3-hexylthiopene-2,5-diyl) (P3HT), and systematically investigated the effects of HKUST-1 in the P3HT active layer on the performances of fieldeffect transistor (FET) devices under humid conditions over 21 days. The performances of a P3HT film blended with HKUST-1 in an FET remained relatively stable under humid conditions over a long period of time. As the water molecules diffused into the bulk conjugated polymer layer, the HKUST-1 crystals in the P3HT film captured water molecules and prevented water adsorption by the P3HT backbones, suggesting an efficient approach to improving the environmental stability of polymer FETs. Furthermore, HKUST-1/P3HT blended films exposed to humidity displayed recovered device performances under vacuum. The device stability conveyed by the HKUST-1 in the presence of humidity was closely related to the superior ability of the HKUST-1 to capture water, which was based on the water adsorption characteristics of HKUST-1.