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Seo, Jooyeok,Nam, Sungho,Jeong, Jaehoon,Lee, Chulyeon,Kim, Hwajeong,Kim, Youngkyoo American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.1
<P>We report planar liquid crystal-gated-organic field-effect transistors (LC-<I>g</I>-OFETs) with a simple in-plane drain–source–gate electrode structure, which can be cost-effectively prepared by typical photolithography/etching processes. The LC-<I>g</I>-OFET devices were fabricated by forming the LC layer (4-cyano-4′-pentylbiphenyl, 5CB) on top of the channel layer (poly(3-hexylthiophene), P3HT) that was spin-coated on the patterned indium–tin oxide (ITO)-coated glass substrates. The LC-<I>g</I>-OFET devices showed p-type transistor characteristics, while a current saturation behavior in the output curves was achieved for the 50–150 nm-thick P3HT (channel) layers. A prospective on/off ratio (>1 × 10<SUP>3</SUP>) was obtained regardless of the P3HT thickness, whereas the resulting hole mobility (0.5–1.1 cm<SUP>2</SUP>/(V s)) at a linear regime was dependent on the P3HT thickness. The tilted ordering of 5CB at the LC-P3HT interfaces, which is induced by the gate electric field, has been proposed as a core point of working mechanism for the present LC-<I>g</I>-OFETs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-1/am506609s/production/images/medium/am-2014-06609s_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am506609s'>ACS Electronic Supporting Info</A></P>
Jooyeok Seo,Sungho Nam,Soohyeong Park,Chulyeon Lee,Jaehun Park,Hwajeong Kim,Youngkyoo Kim IEEE 2017 IEEE journal of selected topics in quantum electro Vol.23 No.4
<P>Terahertz spectroscopy was employed to investigate the charge carrier dynamics of aniline-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films. The measured charge carrier lifetime was correlated with the performances of organic solar cells with the aniline-treated PEDOT:PSS hole-collecting layers. The result showed that the charge carrier lifetime was sensitive to the aniline content. The longest charge carrier lifetime was achieved for 1.2 mol.% aniline, which led to the highest power conversion efficiency of 8.83%. In particular, the trend of the charge carrier lifetime was found to be strongly affected by the surface morphology of the aniline-treated PEDOT:PSS layers.</P>
Seo, Jooyeok,Song, Myeonghun,Jeong, Jaehoon,Nam, Sungho,Heo, Inseok,Park, Soo-Young,Kang, Inn-Kyu,Lee, Joon-Hyung,Kim, Hwajeong,Kim, Youngkyoo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.36
<P>We report broadband pH-sensing organic field-effect transistors (OFETs) with the polymer-dispersed liquid crystal (PDLC) sensing layers. The PDLC layers are prepared by spin-coating using ethanol solutions containing 4-cyano-4'-pentyl-biphenyl (503) and a diblock copolymer (PAA-b-PCBOA) that consists of LC-philic block [poly(4-cyanobiphenyl-4-oxyundecyl acrylate) (PCBOA)] and acrylic acid block [poly(acrylic acid) (PAA)]. The spin-coated sensing layers feature of SOB microdoniains (<5 mu m) encapsulated by the PAA-b-PCBOA polymer chains: The resulting LC-integrated-OFETs (PDLC-i-OFETs) can detect precisely and reproducibly a wide range of pH with only small amounts (10-40 mu L) of analyte solutions in both static and dynamic perfusion modes. The positive drain current change is measured for acidic solutions (pH < 7), whereas basic solutions (pH > 7) result in the negative change of drain current. The drain current trend in the present PDLC-i-OFET devices is explained by the shrinking expanding mechanism of the PAA chains in the diblock copolymer layers.</P>
Sooyong Lee,Jooyeok Seo,Jaehoon Jeong,Chulyeon Lee,Myeonghun Song,Hwajeong Kim,Youngkyoo Kim 한국태양광발전학회 2017 Current Photovoltaic Research Vol.5 No.3
Here we report the influence of thermal treatment on the performance of high efficiency polymer solar cells with the bulk heterojunction films of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b"] dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The crystalline nanostructure of PTB7-Th:PC71BM layers, which were annealed at three different temperatures, was investigated by employing synchrotron radiation grazing incidence X-ray diffraction (GIXD) technique. Results showed that the device performance was slightly reduced by thermal annealing at 50°C but became significantly poor by thermal annealing at 100°C. The poor device performance by thermal annealing was attributed to the collapse in the crystalline nanostructure of PTB7-Th in the PTB7-Th:PC71BM layers as evidenced by the GIXD measurements that exhibited huge reduction in the intensity of PTB7-Th (100) peak even at 50°C.
Han, Hyemi,Seo, Jooyeok,Song, Myeonghun,Kim, Hwajeong,Kim, Youngkyoo The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.17
<P>Here we report a strong addition effect of n-type conjugated polymer, which has a middle energy level between electron-donating polymers and electron-accepting fullerenes, on the enhanced power conversion efficiency (PCE) of inverted-type organic solar cells with bulk heterojunction (BHJ) layers of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-<I>b</I>:4,5-<I>b</I>′]dithiophene-<I>co</I>-3-fluorothieno[3,4-<I>b</I>]thiophene-2-carboxylate] (PTB7-Th) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). As a mid-energy level additive, poly(3-hexylthiophene-<I>co</I>-benzothiadiazole) end-capped with hexylthiophene (THBT-ht) was employed by varying its content up to 3 wt%. Results showed that the PCE of inverted-type PTB7-Th:PC71BM solar cells was enhanced from 8.77% to 9.81% (max: 10.02%) by adding only 0.5 wt% (1.47 mol%) THBT-ht. The pronounced improvement at 0.5 wt% has been assigned to the balanced charge transport and the drastic change of nanoscale morphology toward finer phase segregation and less hydrophobic smoother surface. The present finding is expected to contribute to further efficiency improvement of BHJ-based organic solar cells with various types of material systems.</P>