Jieun Ghim

Bio: Jieun Ghim is an academic researcher from Gwangju Institute of Science and Technology. The author has contributed to research in topics: Pentacene & Organic semiconductor. The author has an hindex of 12, co-authored 12 publications receiving 901 citations.

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

Polarity Effects of Polymer Gate Electrets on Non‐Volatile Organic Field‐Effect Transistor Memory

Abstract: These func-tionalities arise from field-effect modulation by the chargesstored in chargeable polymer gate dielectrics, referred to aspolymer electrets.An electret is a piece of dielectric material that exhibits aquasi-permanent electrical charges or dipolar polarization,including ferro-, piezo-, and pyro-electric polymers.

Effect of light irradiation on the characteristics of organic field-effect transistors

Abstract: The effect of light irradiation on the characteristics of organic field-effect transistors containing sexithiophene (6-T) and pentacene was examined. Organic phototransistors (OPTs) in which 6-T and pentacene were incorporated were fabricated. Their response behaviors were investigated under conditions of irradiation by either modulated or continuous ultraviolet light with various intensities. Both devices showed two distinguishable responses, i.e., fast and slow responses from photoconductive and photovoltaic effects, respectively. The fast response is mainly the result of the generation of mobile carriers by the absorption of a photon energy higher than the band gap energy of the semiconductor and, subsequently, an increase in conductance via a greater flow of photogenerated mobile carriers into the channel layer. On the other hand, the slow response, which was confirmed by a light induced shift in the threshold voltage (Vth) or the switch-on voltage (VO), is the result of a slow release of accumulated ...

Effect of rubbed polyimide layer on the field-effect mobility in pentacene thin-film transistors

Abstract: We investigated preferentially oriented pentacene grains on rubbed polyimide (PI) layers under various conditions, such as substrate temperature and cumulative rubbing number. In case of pentacene thin films deposited on rubbed PI at room temperature (RT), compared to unrubbed, the field-effect mobilities were improved by two- to threefold in contrast to the cases of elevated temperature. From the results of crystalline in-plane orientation and thin-film versus bulk-phase ratio, we proposed that pentacence crystalline orientation on a rubbed PI layer could be more favorable at RT, whereas the heating energy might weaken the interaction energy between pentacene molecules and aligned PI layer.

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.

Quantitative determination of organic semiconductor microstructure from the molecular to device scale.

Abstract: The authors would like to thank M. Chabinyc, H. Ade, B. Collins, R. Noriega, K. Vandewal, and D. Duong for fruitful discussions in the preparation of this review. Stanford Synchrotron Radiation Lightsource (SSRL) is a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. This publication was partially supported by the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST).

Arylamine organic dyes for dye-sensitized solar cells

Abstract: Arylamine organic dyes with donor (D), π-bridge (π) and acceptor (A) moieties for dye-sensitized solar cells (DSCs) have received great attention in the last decade because of their high molar absorption coefficient, low cost and structural variety. In the early stages, the efficiency of DSCs with arylamine organic dyes with D–π–A character was far behind that of DSCs with ruthenium(II) complexes partly due to the lack of information about the relationship between the chemical structures and the photovoltaic performance. However, exciting progress has been recently made, and power conversion efficiencies over 10% were obtained for DSCs with arylamine organic dyes. It is thus that the recent research and development in the field of arylamine organic dyes employing an iodide/triiodide redox couple or polypyridyl cobalt redox shuttles as the electrolytes for either DSCs or solid-state DSCs has been summarized. The cell performance of the arylamine organic dyes are compared, providing a comprehensive overview of arylamine organic dyes, demonstrating the advantages/disadvantages of each class, and pointing out the field that needs to reinforce the research direction in the further application of DSCs.

Organic photoresponse materials and devices

Abstract: Organic photoresponse materials and devices are critically important to organic optoelectronics and energy crises. The activities of photoresponse in organic materials can be summarized in three effects, photoconductive, photovoltaic and optical memory effects. Correspondingly, devices based on the three effects can be divided into (i) photoconductive devices such as photodetectors, photoreceptors, photoswitches and phototransistors, (ii) photovoltaic devices such as organic solar cells, and (iii) optical data storage devices. It is expected that this systematic analysis of photoresponse materials and devices could be a guide for the better understanding of structure–property relationships of organic materials and provide key clues for the fabrication of high performance organic optoelectronic devices, the integration of them in circuits and the application of them in renewable green energy strategies (critical review, 452 references).