Seok-Ju Kang

Bio: Seok-Ju Kang is an academic researcher from Dongguk University. The author has contributed to research in topics: Field-effect transistor & Gate dielectric. The author has an hindex of 19, co-authored 31 publications receiving 2152 citations. Previous affiliations of Seok-Ju Kang include Gwangju Institute of Science and Technology.

A Thienoisoindigo-Naphthalene Polymer with Ultrahigh Mobility of 14.4 cm2/V·s That Substantially Exceeds Benchmark Values for Amorphous Silicon Semiconductors

Abstract: By considering the qualitative benefits associated with solution rheology and mechanical properties of polymer semiconductors, it is expected that polymer-based electronic devices will soon enter our daily lives as indispensable elements in a myriad of flexible and ultra low-cost flat panel displays. Despite more than a decade of research focused on designing and synthesizing state-of-the-art polymer semiconductors for improving charge transport characteristics, the current mobility values are still not sufficient for many practical applications. The confident mobility in excess of ∼10 cm2/V·s is the most important requirement for enabling the realization of the aforementioned near-future products. We report on an easily attainable donor–acceptor (D–A) polymer semiconductor: poly(thienoisoindigo-alt-naphthalene) (PTIIG-Np). An unprecedented mobility of 14.4 cm2/V·s, by using PTIIG-Np with a high-k gate dielectric poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)), is achieved from a simple coating p...

Organic Non-Volatile Memory Based on Pentacene Field-Effect Transistors Using a Polymeric Gate Electret**

Abstract: electrets. In this Communication, we report on OFET memory devices built on silicon wafers and based on films of pentacene and an SiO2 gate insulator that are separated by a thin layer of poly(a-methylstyrene) (PaMS), which acts as a polymeric gate dielectric. This OFET memory device displayed reversible shifts in the threshold voltage (VTh) when an appropriate gate voltage (Vg) was applied above a certain threshold via a relatively short switching time. Based on these reversible shifts in VTh, a non-volatile organic memory was demonstrated that takes advantage of the simple configuration of a typical OFET. This device showed a large memory window (about 90 V), a high on/off ratio (IOn/IOff) (10 5 ), a short switching time (less than 1 ls), and a long retention time (more than 100 h). These memory characteristics were obtained only when an appropriate polymeric gate electret layer (e.g., PaMS) was inserted between the SiO2 gate insulator and the pentacene channel in the typical OFET structure. Therefore, it is possible that this behavior originates from the modulation of the gate field by stored charges in the polymeric gate electret. Detailed reasons for these results and a possible operating mechanism for our OFET memory device are discussed. A cross-sectional view of the fabricated device structure is shown in Figure 1a. Further details concerning the fabrication of this device are discussed in the Experimental section. Figure 1b and c shows the output and transfer characteristics of the devices, respectively. The results indicate reasonably good OFET behavior, suggesting the additional PaMS layer does not degrade the performance of the devices. [14] From the conventional characterization equation, [15] the measured values of the typical field-effect mobility (lFET), VTh, and IOn/IOff were 0.51 cm 2 V –1 s –1 (maximum value, 0.89 cm 2 V –1 s –1 ), – 19 V, and 10 5 , respectively. These transistor properties could

Three-Dimensional Bulk Heterojunction Morphology for Achieving High Internal Quantum Efficiency in Polymer Solar Cells

Abstract: Here, an investigation of three-dimensional (3D) morphologies for bulk heterojunction (BHJ) films based on regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is reported. Based on the results, it is demonstrated that optimized post-treatment, such as solvent annealing, forces the PCBM molecules to migrate or diffuse toward the top surface of the BHJ composite films, which induces a new vertical component distribution favorable for enhancing the internal quantum efficiency (ηIQE) of the devices. To investigate the 3D BHJ morphology, novel time-of-flight secondary-ion mass spectroscopy studies are employed along with conventional methods, such as UV-vis absorption, X-ray diffraction, and high-resolution transmission electron microscopy studies. The ηIQE of the devices are also compared after solvent annealing for different times, which clearly shows the effect of the vertical component distribution on the performance of BHJ polymer solar cells. In addition, the fabrication of high-performance P3HT:PCBM solar cells using the optimized solvent-annealing method is reported, and these cells show a mean power-conversion efficiency of 4.12% under AM 1.5G illumination conditions at an intensity of 100 mW cm−2.

Dramatic inversion of charge polarity in diketopyrrolopyrrole-based organic field-effect transistors via a simple nitrile group substitution.

Abstract: A record-breaking high electron mobility of 7.0 cm(2) V(-1) s(-1) for n-channel polymer OFETs is reported. By the incorporation of only one nitrile group as an electron-withdrawing function in the vinyl linkage of the DPP-based copolymer, a dramatic inversion of majority charge-carriers from holes to electrons is achieved.

Mixed-dimensional van der Waals heterostructures

Abstract: The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. Given that any passivated, dangling-bond-free surface will interact with another through vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non-2D materials that adhere primarily through non-covalent interactions. We present a succinct and critical survey of emerging mixed-dimensional (2D + nD, where n is 0, 1 or 3) heterostructure devices. By comparing and contrasting with all-2D vdW heterostructures as well as with competing conventional technologies, we highlight the challenges and opportunities for mixed-dimensional vdW heterostructures.

Organic light detectors: photodiodes and phototransistors.

Abstract: While organic electronics is mostly dominated by light-emitting diodes, photovoltaic cells and transistors, optoelectronics properties peculiar to organic semiconductors make them interesting candidates for the development of innovative and disruptive applications also in the field of light signal detection. In fact, organic-based photoactive media combine effective light absorption in the region of the spectrum from ultraviolet to near-infrared with good photogeneration yield and low-temperature processability over large areas and on virtually every substrate, which might enable innovative optoelectronic systems to be targeted for instance in the field of imaging, optical communications or biomedical sensing. In this review, after a brief resume of photogeneration basics and of devices operation mechanisms, we offer a broad overview of recent progress in the field, focusing on photodiodes and phototransistors. As to the former device category, very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, and even though the simultaneous optimization of all these relevant parameters is demonstrated in a limited number of papers, real applications are within reach for this technology, as it is testified by the increasing number of realizations going beyond the single-device level and tackling more complex optoelectronic systems. As to phototransistors, a more recent subject of study in the framework of organic electronics, despite a broad distribution in the reported performances, best photoresponsivities outperform amorphous silicon-based devices. This suggests that organic phototransistors have a large potential to be used in a variety of optoelectronic peculiar applications, such as a photo-sensor, opto-isolator, image sensor, optically controlled phase shifter, and opto-electronic switch and memory.

25th Anniversary Article: A Decade of Organic/Polymeric Photovoltaic Research

Abstract: Organic photovoltaic (OPV) technology has been developed and improved from a fancy concept with less than 1% power conversion efficiency (PCE) to over 10% PCE, particularly through the efforts in the last decade. The significant progress is the result of multidisciplinary research ranging from chemistry, material science, physics, and engineering. These efforts include the design and synthesis of novel compounds, understanding and controlling the film morphology, elucidating the device mechanisms, developing new device architectures, and improving large-scale manufacture. All of these achievements catalyzed the rapid growth of the OPV technology. This review article takes a retrospective look at the research and development of OPV, and focuses on recent advances of solution-processed materials and devices during the last decade, particular the polymer version of the materials and devices. The work in this field is exciting and OPV technology is a promising candidate for future thin film solar cells.