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Song, Seyeong,Lee, Kang Taek,Koh, Chang Woo,Shin, Hyebeom,Gao, Mei,Woo, Han Young,Vak, Doojin,Kim, Jin Young The Royal Society of Chemistry 2018 ENERGY AND ENVIRONMENTAL SCIENCE Vol.11 No.11
<P>Hot solution deposition has emerged as a promising strategy to achieve high performance polymer solar cells and many state-of-the-art devices have been recently fabricated by this approach in research laboratories. Currently, a major challenge in the photovoltaics community is translating such methodologies into industrially relevant processes so that progress can be made beyond the research community. In this work, hot deposition is developed <I>via</I> a slot die coating process, using a thermally robust and thickness tolerant photovoltaic polymer and a 3D printer-based slot die coater. This method uses not only hot substrates but also hot solutions. We find that controlling solution and substrate temperatures is critical to achieve optimum morphology and high device performance. Analysis of nano-morphology and molecular packing shows a clear influence of both solution and substrate temperatures. At optimal temperature conditions (80 °C head−80 °C substrate), slot die coated devices with an inverted configuration exhibited up to a 7.61% power conversion efficiency without using additives or other processing treatments, which are detrimental to stability and processing efficiency. The optimum temperature combination was readily scaled up using roll-to-roll processing equipment without further optimization, yielding flexible polymer solar cells with a 7.06% power conversion efficiency, demonstrating the potential of the hot slot die coating method from an industrial perspective.</P>
Song, Seyeong,Heo, Jungwoo,Lee, Tae Kyung,Park, Soojin,Walker, Bright,Kwak, Sang Kyu,Kim, Jin Young American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.33
<P>The application of localized surface plasmon resonance (LSPR) phenomena is an effective strategy to enhance the performance of polymer solar cells (PSCs) because of their ability to efficiently scatter light and dramatically increase light absorption in the active layer of PSCs. Unlike previous reports investigating LSPR materials in PSCs, we have approached the LSPR phenomenon from a physical perspective by examining the influence of the surrounding environment on LSPR properties. Uniformly ordered two-dimensional 10 nm Ag quantum dot arrays (2D Ag QAs) were prepared and utilized in PSCs. The 2D Ag QAs were incorporated into electron transport layers with different refractive indices, which showed a significant bathochromic shift as the refractive index increased and excellent agreement with theoretical calculations taking intrinsic size effects, nonlocal response, and plasmon coupling effects into account. When incorporated into PSCs, power conversion efficiencies of up to 8.51% were realizeda 12.5% enhancement compared to devices without Ag QAs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2017/jpccck.2017.121.issue-33/acs.jpcc.7b03763/production/images/medium/jp-2017-03763v_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b03763'>ACS Electronic Supporting Info</A></P>
Ko, Seo-Jin,Hoang, Quoc Viet,Song, Chang Eun,Uddin, Mohammad Afsar,Lim, Eunhee,Park, Song Yi,Lee, Byoung Hoon,Song, Seyeong,Moon, Sang-Jin,Hwang, Sungu,Morin, Pierre-Olivier,Leclerc, Mario,Su, Gregory Royal Society of Chemistry 2017 ENERGY AND ENVIRONMENTAL SCIENCE Vol.10 No.6
<P>A series of semi-crystalline, wide band gap (WBG) photovoltaic polymers were synthesized with varying number and topology of fluorine substituents. To decrease intramolecular charge transfer and to modulate the resulting band gap of D-A type copolymers, electron-releasing alkoxy substituents were attached to electron-deficient benzothiadiazole (A) and electron-withdrawing fluorine atoms (0-4F) were substituted onto a 1,4-bis(thiophen-2-yl)benzene unit (D). Intra- and/or interchain noncovalent Coulombic interactions were also incorporated into the polymer backbone to promote planarity and crystalline intermolecular packing. The resulting optical band gap and the valence level were tuned to 1.93-2.15 eV and −5.37 to −5.67 eV, respectively, and strong interchain organization was observed by differential scanning calorimetry, high-resolution transmission electron microscopy and grazing incidence X-ray scattering measurements. The number of fluorine atoms and their position significantly influenced the photophysical, morphological and optoelectronic properties of bulk heterojunctions (BHJs) with these polymers. BHJ photovoltaic devices showed a high power conversion efficiency (PCE) of up to 9.8% with an open-circuit voltage of 0.94-1.03 V. To our knowledge, this PCE is one of the highest values for fullerene-based single BHJ devices with WBG polymers having a band gap of over 1.90 eV. A tandem solar cell was also demonstrated successfully to show a PCE of 10.3% by combining a diketopyrrolopyrrole-based low band gap polymer.</P>
Song, Miyeon,Kwon, Illoong,Cha, Seyeong,Min, Naon Public Management Research Association 2017 JOURNAL OF PUBLIC ADMINISTRATION RESEARCH AND THEO Vol.27 No.1
<P>Despite growing reliance on indirect market-based policy instruments under the New Public Management reforms, bureaucrats often prefer direct regulatory instruments. Thus, for successful implementation of indirect policy instruments, it is important to understand the underlying motives for bureaucrats’ preferences. This article shows that based on unique survey data from Korea, bureaucrats with higher public service motivation have a stronger preference for direct policy instruments. This pattern is strong for bureaucrats at lower job levels and for those who report greater willingness for self-sacrifice, but not necessarily for those who show strong commitment for the public interest. These results contradict a view that bureaucrats prefer direct policy instruments out of self-interest to maintain private benefits. Rather, direct policy instruments may require more work and even more unpleasant direct interactions with the clientele being served, but allow the bureaucrats to stay in control of and feel more responsible for the services provided.</P>
A New Dithienopyridine-Based Polymer for an Organic Electronics
Sun, Cheng,Song, Seyeong,Song, Hyeng Gun,Park, So Min,Kim, Jin-Young,Kim, Yun-Hi,Kwon, Soon-Ki American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.8
<P>A new dithienopyridine-based copolymer (PDT-TBT) was designed and synthesized. The copolymer showed good solubility in chloroform, chlorobenzene, and dichlorobenzene. The thermogravimetric analysis curve showed that the copolymer had good thermal stability with weight loss of less than 5% at 341 degrees C. The UV absorption maximum of the polymer appeared at 550 nm in solution and 600 nm in the film. The HOMO and LUMO of the copolymer were -5.50 eV and -3.63 eV, respectively. The copolymer exhibited the best performance when the PC61BM ratio was 1: 2 (w/w %), with a J(SC) of 3.56 mA/cm(2), a VOC of 0.45 V, an FF of 0.27%, and a PCE of 0.43%. A thin film transistor with PDT-TBT as the active layer showed mobility of 5.02x10(-3) cm(2)/Vs, an on/off ratio of 1.19x10(5) and a threshold voltage of -22.75 V.</P>
Lee, Kyu Cheol,Song, Seyeong,Lee, Junghoon,Kim, Dong Suk,Kim, Jin Young,Yang, Changduk WILEY‐VCH Verlag 2015 ChemPhysChem Vol.16 No.6
<P>To be meaningful to guide the rational design of novel high-performance conjugated semiconductors, we prepared three benzo[1,2-b:4,5-b]dithiophene (BDT)-based polymers by systematically moving the branching point of the alkyl chain. The effect of side-chain engineering was thoroughly investigated by a range of techniques. We demonstrate that a subtle change in the branching position in the BDT core can have a critical impact on polymer packing and preferential backbone orientation in thin films; copolymers made from BDT and thieno[3,4-c]pyrrole-4,6-dione units (TPD) adopt more of a face-on orientation as the branching point is shifted closer to the backbone, which can be correlated with a dramatic difference in solar-cells performance. The high short-circuit current density (11.6 mAcm(-2)) for the copolymer with one carbon atom between the alkoxylated oxygen atom and the branching point results from its predominantly face-on orientation and smoother surface in thin films, which results in power conversion efficiencies as high as 4.56%.</P>
Kang, Hyojin,An, Su Yeon,Walker, Bright,Song, Seyeong,Kim, Taehyo,Kim, Jin Young,Yang, Changduk The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.18
<▼1><P>A series of small molecule semiconductors based on the recently conceived thienoisoindigo (TIIG) moiety and three end-capping moieties with varied electron-donating strength and conformations has been synthesized and utilized for organic photovoltaics (OPVs).</P></▼1><▼2><P>In this contribution, a series of small molecule semiconductors based on the recently conceived thienoisoindigo (TIIG) and three different end-capping moieties (benzene (Bz), naphthalene (Np), and benzofuran (Bf)) with varied electron-donating strength and conformations has been synthesized by Suzuki coupling and utilized for organic photovoltaics (OPVs). Incorporation of different end-capping blocks onto the TIIG core facilitated the tuning of optical properties and the electronic structure (HOMO/LUMO energy levels), solid-state morphology and performance in OPVs. It is apparent that the bandgaps within this series (TIIG-Bz, TIIG-Np, and TIIG-Bf) were progressively red-shifted and the absorption coefficients were enhanced by increasing the conjugation length and/or the donor ability of the end-capping units. In addition, HOMO and LUMO levels were shown to simultaneously follow changes made to the end-capping moieties. The best performing OPVs using TIIG-Np : PC71BM exhibited a power conversion efficiency (PCE) of 1.81% with <I>J</I>sc = 7.15 mA cm<SUP>−2</SUP>, FF = 0.39, and <I>V</I>oc = 0.66 V. With the aim of exploring underlying structure–property relationships for this new class of molecular systems, we have quantitatively investigated various morphological structures in both the pristine small molecule films and small molecule/PC71BM blend films using a combination of grazing incidence wide angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM). In this study, a correlation between the molecular structure, thin film morphology, and photovoltaic properties of these conjugated small molecules was established that provides guidance for the molecular design of new photovoltaic semiconductors based on TIIG units.</P></▼2>