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Kim, Min Je,Park, Jae Hoon,Kang, Boseok,Kim, Dongjin,Jung, A-Ra,Yang, Jeehye,Kang, Moon Sung,Lee, Dong Yun,Cho, Kilwon,Kim, Hyunjung,Kim, BongSoo,Cho, Jeong Ho American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.26
<P>The performances of organic thin film transistors (OTFTs) produced by polymer solution casting are tightly correlated with the morphology and chain-ordering of semiconducting polymer layers, which depends on the processing conditions applied. The slow evaporation of a high boiling point (bp) solvent permits sufficient time for the assembly of polymer chains during the process, resulting in improving the film crystallinity and inducing favorable polymer chain orientations for charge transport. The use of high bp solvents, however, often results in dewetting of thin films formed on hydrophobic surfaces, such as the commonly used octadecyltrichlorosilane (ODTS)-treated SiO2 gate dielectric. Dewetting hampers the formation of uniform and highly crystalline semiconducting active channel layers. In this manuscript, we demonstrated the formation of highly crystalline dithienothienyl diketopyrrolopyrrole (TT-DPP)-based polymer films using a flow-coating method to enable the fabrication of ambipolar transistors and inverters. Importantly, unlike conventional spin-coating methods, the flow-coating method allowed us to use high bp solvents, even on a hydrophobic surface, and minimized the polymer solution waste. The crystalline orientations of the TT-DPP-based polymers were tuned depending on the solvent used (four different bp solvents were tested) and the employment of a thermal annealing step. The use of high bp solvents and thermal annealing of the polymer films significantly enhanced the crystalline microstructures in the flow-coated films, resulting in considerable carrier mobility increase in the OTFTs compared to the spin-coated films. Our simple, inexpensive, and scalable flow-coating method, for the first time employed in printing semiconducting polymers, presents a significant step toward optimizing the electrical performances of organic ambipolar transistors through organic semiconducting layer film crystallinity engineering.</P>
Poly(3-hexylthiophene) Nanorods with Aligned Chain Orientation for Organic Photovoltaics
Kim, Jong Soo,Park, Yunmin,Lee, Dong Yun,Lee, Ji Hwang,Park, Jong Hwan,Kim, Jin Kon,Cho, Kilwon WILEY-VCH Verlag 2010 Advanced Functional Materials Vol.20 No.4
<P>A structured polymer solar cell architecture featuring a large interface between donor and acceptor with connecting paths to the respective electrodes is explored. To this end, poly-(3-hexylthiophene) (P3HT) nanorods oriented perpendicularly to indium tin oxide (ITO) glass are fabricated using an anodic aluminum oxide template. It is found that the P3HT chains in bulk films or nanorods are oriented differently; perpendicular or parallel to the ITO substrate, respectively. Such chain alignment of the P3HT nanorods enhanced the electrical conductivity up to tenfold compared with planar P3HT films. Furthermore, the donor/acceptor contact area could be maximised using P3HT nanorods as donor and C60 as acceptor. In a photovoltaic device employing this structure, remarkable photoluminescence quenching (88%) and a seven-fold efficiency increase (relative to a device with a planar bilayer) are achieved.</P> <B>Graphic Abstract</B> <P>The contact area between donor (poly(3-hexylthiophene), P3HT) and acceptor (C60) and the degree of P3HT molecular orientation are increased by use of an anodic aluminum oxide template. The cell consisting of P3HT nanorods and C60 shows much lower levels of photoluminescence emission than does the planar bilayer P3HT/C60 cell, and yields a dramatic increase in photovoltaic performance. <img src='wiley_img/1616301X-2010-20-4-ADFM200901760-content.gif' alt='wiley_img/1616301X-2010-20-4-ADFM200901760-content'> </P>
Kim, Joo-Hyun,Park, Jong Hwan,Lee, Ji Hwang,Kim, Jong Soo,Sim, Myungsun,Shim, Chiyeoung,Cho, Kilwon Royal Society of Chemistry 2010 Journal of materials chemistry Vol.20 No.35
<P>Here, we report the preparation of well-controlled nanoscale morphologies in photoactive thin films. The fabrication of bulk heterojunction structures in blend films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C<SUB>61</SUB>-butyric acid methyl ester (PCBM) employed two steps to achieve first the <I>in situ</I> formation of self-organized P3HT nanowires using a marginal solvent, and second, phase separation <I>via</I> mild thermal annealing. Morphological changes in the active layers that had been spin-cast from a marginal solvent, with varying annealing temperatures, were systematically studied and compared to the morphologies of films spin-cast from a good solvent. The interpenetrating nanowire structure yielded power conversion efficiencies as high as 4.07% due to the enhanced charge transport. Hole and electron mobilities increased substantially to 1.6 × 10<SUP>−3</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and 1.4 × 10<SUP>−3</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, respectively, due to the two step process of P3HT crystallization by nanowire formation and subsequent phase separation. Photovoltaic performances improved with increasing film thickness up to 300 nm as a result of the interpenetrating donor/acceptor network structure.</P> <P>Graphic Abstract</P><P>Two separate steps of adding marginal solvent and subsequent thermal annealing provide the well-controlled bulk heterojunction morphology to obtain enhanced photovoltaic performance. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm00666a'> </P>
Kim, Do Hwan,Lee, Bang-Lin,Moon, Hyunsik,Kang, Hee Min,Jeong, Eun Jeong,Park, Jeong-Il,Han, Kuk-Min,Lee, Sangyoon,Yoo, Byung Wook,Koo, Bon Won,Kim, Joo Young,Lee, Wi Hyoung,Cho, Kilwon,Becerril, Hecto American Chemical Society 2009 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.131 No.17
<P>The ability to control the molecular organization of electronically active liquid-crystalline polymer semiconductors on surfaces provides opportunities to develop easy-to-process yet highly ordered supramolecular systems and, in particular, to optimize their electrical and environmental reliability in applications in the field of large-area printed electronics and photovoltaics. Understanding the relationship between liquid-crystalline nanostructure and electrical stability on appropriate molecular surfaces is the key to enhancing the performance of organic field-effect transistors (OFETs) to a degree comparable to that of amorphous silicon (a-Si). Here, we report a novel donor-acceptor type liquid-crystalline semiconducting copolymer, poly(didodecylquaterthiophene-alt-didodecylbithiazole), which contains both electron-donating quaterthiophene and electron-accepting 5,5'-bithiazole units. This copolymer exhibits excellent electrical characteristics such as field-effect mobilities as high as 0.33 cm(2)/V.s and good bias-stress stability comparable to that of amorphous silicon (a-Si). Liquid-crystalline thin films with structural anisotropy form spontaneously through self-organization of individual polymer chains as a result of intermolecular interactions in the liquid-crystalline mesophase. These thin films adopt preferential well-ordered intermolecular pi-pi stacking parallel to the substrate surface. This bottom-up assembly of the liquid-crystalline semiconducting copolymer enables facile fabrication of highly ordered channel layers with remarkable electrical stability.</P>
Kim, Do Hwan,Lee, Jiyoul,Park, Jeong‐,Il,Chung, Jong Won,Lee, Wi Hyoung,Giri, Gaurav,Yoo, Byungwook,Koo, Bonwon,Kim, Joo Young,Jin, Yong Wan,Cho, Kilwon,Lee, Bang‐,Lin,Lee, Sangyoon WILEY‐VCH Verlag 2011 Advanced functional materials Vol.21 No.23
<P><B>Abstract</B></P><P>In order to fabricate polymer field‐effect transistors (PFETs) with high electrical stability under bias‐stress, it is crucial to minimize the density of charge trapping sites caused by the disordered regions. Here we report PFETs with excellent electrical stability comparable to that of single‐crystalline organic semiconductors by specifically controlling the molecular weight (MW) of the donor‐acceptor type copolymer semiconductors, poly (didodecylquaterthiophene‐<I>alt</I>‐didodecylbithiazole). We found that MW‐induced thermally structural transition from liquid‐crystalline to semi‐crystalline phases strongly affects the device performance (charge‐carrier mobility and electrical bias‐stability) as well as the nanostructures such as the molecular ordering and the morphological feature. In particular, for the polymer with a MW of 22 kDa, the transfer curves varied little (Δ<I>V</I><SUB>th</SUB> = 3∼4 V) during a period of prolonged bias stress (about 50 000 s) under ambient conditions. This enhancement of the electrical bias‐stability can be attributed to highly ordered liquid‐crystalline nanostructure of copolymer semiconductors on dielectric surface via the optimization of molecular weights.</P>
Kim, Joo-Hyun,Sin, Dong Hun,Kim, Haena,Jo, Sae Byeok,Lee, Hansol,Han, Joong Tark,Cho, Kilwon American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.22
<P>Size-selected graphene oxide (GO) nanosheets were used to modify the bulk heterojunction (BHJ) morphology and electrical properties of organic photovoltaic (OPV) devices. The GO nanosheets were prepared with sizes ranging from several hundreds of nanometers to micrometers by using a physical sonication process and were then incorporated into PTB7:PC<SUB>71</SUB>BM photoactive layers. Different GO sizes provide varied portions of the basal plane where aromatic sp<SUP>2</SUP>-hybridized regions are dominant and edges where oxygenated functional groups are located; thus, GO size distributions affect the GO dispersion stability and morphological aggregation of the BHJ layer. Electron delocalization by sp<SUP>2</SUP>-hybridization and the electron-withdrawing characteristics of functional groups p-dope the photoactive layer, giving rise to increasing carrier mobilities. Hole and electron mobilities are maximized at GO sizes of several hundreds of nanometers. Consequently, non-geminate recombination is significantly reduced by these facilitated hole and electron transports. The addition of GO nanosheets decreases the recombination order of non-geminate recombination and increases the generated carrier density. This reduction in the non-geminate recombination contributes to an increased power conversion efficiency of PTB7:PC<SUB>71</SUB>BM OPV devices as high as 9.21%, particularly, by increasing the fill factor to 70.5% in normal devices and 69.4% in inverted devices.</P> [FIG OMISSION]</BR>
Kim, Hyun Ho,Kang, Boseok,Suk, Ji Won,Li, Nannan,Kim, Kwang S.,Ruoff, Rodney S.,Lee, Wi Hyoung,Cho, Kilwon American Chemical Society 2015 ACS NANO Vol.9 No.5
<P>Pentacene (C<SUB>22</SUB>H<SUB>14</SUB>), a polycyclic aromatic hydrocarbon, was used as both supporting and sacrificing layers for the clean and doping-free graphene transfer. After successful transfer of graphene to a target substrate, the pentacene layer was physically removed from the graphene surface by using intercalating organic solvent. This solvent-mediated removal of pentacene from graphene surface was investigated by both theoretical calculation and experimental studies with various solvents. The uses of pentacene and appropriate intercalation solvent enabled graphene transfer without forming a residue from the supporting layer. Such residues tend to cause charged impurity scattering and unintentional graphene doping effects. As a result, this clean graphene exhibited extremely homogeneous surface potential profiles over a large area. A field-effect transistor fabricated using this graphene displayed a high hole (electron) mobility of 8050 cm<SUP>2</SUP>/V·s (9940 cm<SUP>2</SUP>/V·s) with a nearly zero Dirac point voltage.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-5/nn5066556/production/images/medium/nn-2014-066556_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5066556'>ACS Electronic Supporting Info</A></P>
High-Efficiency Organic Solar Cells Based on End-Functional-Group-Modified Poly(3-hexylthiophene)
Kim, Jong Soo,Lee, Youngmin,Lee, Ji Hwang,Park, Jong Hwan,Kim, Jin Kon,Cho, Kilwon WILEY-VCH Verlag 2010 Advanced Materials Vol.22 No.12
<P>Photovoltaic devices of end-functional-group-modified poly 3-(hexylthiophene)/ [6,6]-phenyl-C(61) butyric acid methyl ester (P3HT:PCBM; see figure) are fabricated with thermal annealing. The surface energies between donor and acceptor were matched by varying the end group, which can be used to control vertical and horizontal phase separation in the active layer, leading mixed nanomorphology with optimized phase separation, low series resistance, and high performance for solar cell devices.</P>