5 V driving organic non-volatile memory transistors with poly(vinyl alcohol) gate insulator and poly(3-hexylthiophene) channel layers

Nam, Sungho,Seo, Jooyeok,Kim, Hwajeong,Kim, Youngkyoo American Institute of Physics 2015 Applied Physics Letters Vol.107 No.15

Pronounced Side Chain Effects in Triple Bond-Conjugated Polymers Containing Naphthalene Diimides for n-Channel Organic Field-Effect Transistors

Nam, Sungho,Hahm, Suk Gyu,Khim, Dongyoon,Kim, Hwajeong,Sajoto, Tissa,Ree, Moonhor,Marder, Seth R.,Anthopoulos, Thomas D.,Bradley, Donal D. C.,Kim, Youngkyoo American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.15

<P>Three triple bond-conjugated naphthalene diimide (NDI) copolymers, poly{[<I>N</I>,<I>N</I>′-bis(2-R<SUB>1</SUB>)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-<I>alt</I>-[(2,5-bis(2-R<SUB>2</SUB>)-1,4-phenylene)bis(ethyn-2,1-diyl)]} (PNDIR<SUB>1</SUB>-R<SUB>2</SUB>), were synthesized via Sonogashira coupling polymerization with varying alkyl side chains at the nitrogen atoms of the imide ring and 2,5-positions of the 1,4-diethynylbenzene moiety. Considering their identical polymer backbone structures, the side chains were found to have a strong influence on the surface morphology/nanostructure, thus playing a critical role in charge-transporting properties of the three NDI-based copolymers. Among the polymers, the one with an octyldodecyl (OD) chain at the nitrogen atoms of imide ring and a hexadecyloxy (HO) chain at the 2,5-positions of 1,4-diethynylbenzene, P(NDIOD-HO), exhibited the highest electron mobility of 0.016 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, as compared to NDI-based copolymers with an ethylhexyl chain at the 2,5-positions of 1,4-diethynylbenzene. The enhanced charge mobility in the P(NDIOD-HO) layers is attributed to the well-aligned nano-fiber-like surface morphology and highly ordered packing structure with a dominant edge-on orientation, thus enabling efficient in-plane charge transport. Our results on the molecular structure-charge transport property relationship in these materials may provide an insight into novel design of n-type conjugated polymers for applications in the organic electronics of the future.</P> [FIG OMISSION]</BR>

Polyacetylene-based polyelectrolyte as a universal interfacial layer for efficient inverted polymer solar cells

Nam, Sungho,Seo, Jooyeok,Song, Myeonghun,Kim, Hwajeong,Ree, Moonhor,Gal, Yeong-Soon,Bradley, Donal D.C.,Kim, Youngkyoo ELSEVIER 2017 ORGANIC ELECTRONICS Vol.48 No.-

<P><B>Abstract</B></P> <P>Here we report that poly(N-dodecyl-2-ethynylpyridiniumbromide) (PDEPB) interlayers between electron-collecting zinc oxide (ZnO) layers and bulk heterojunction (BHJ) layers act as a universal interfacial layer for improving the performances of inverted-type polymer:fullerene solar cells. Three different BHJ layers, poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C<SUB>61</SUB>-butyric acid methyl ester (PC<SUB>61</SUB>BM), poly[(4,8-bis(2-ethylhexyloxy)-benzo[1,2-b:4,5-b']dithiophene)-2,6-diyl-alt-(N-2-ethylhexylthieno[3,4-<I>c</I>]pyrrole-4,6-dione)-2,6-diyl]] (PBDTTPD):PC<SUB>61</SUB>BM, and poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-<I>b</I>]-thiophenediyl] (PTB7) and [6,6]-phenyl-C<SUB>71</SUB>-butyric acid methyl ester (PC<SUB>71</SUB>BM), were employed so as to prove the role of the PDEPB interlayers. Results showed that the power conversion efficiency (PCE) of polymer:fullerene solar cells with the three different BHJ layers increased in the presence of the PDEPB interlayers prepared from 0.5 mg/ml solutions. The improved PCE was attributed to the conformal coating of the PDEPB layers on the ZnO layers (by atomic force microscopy measurement), lowered work functions of ZnO induced by the PDEPB layers (by Kelvin probe measurement), and reduced interface resistance (by impedance spectroscopy measurement), as supported by the noticeable change in the atom environments of both the ZnO and PDEPB layers (by X-ray photoelectron spectroscopy measurement).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polyacetylene-based polyelectrolyte interlayers improve device performances. </LI> <LI> The polyacetylene interlayers work for various active layer materials. </LI> <LI> The ZnO surface defects can be effectively reduced by the polyacetylene interlayers. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

All-polymer solar cells with bulk heterojunction nanolayers of chemically doped electron-donating and electron-accepting polymers

Nam, Sungho,Shin, Minjung,Park, Soohyeong,Lee, Sooyong,Kim, Hwajeong,Kim, Youngkyoo The Royal Society of Chemistry 2012 Physical chemistry chemical physics Vol.14 No.43

<P>We report the improved performance of all-polymer solar cells with bulk heterojunction nanolayers of an electron-donating polymer (poly(3-hexylthiophene) (P3HT)) and an electron-accepting polymer (poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT)), which were both doped with 4-ethylbenzenesulfonic acid (EBSA). To choose the doping ratio of P3HT for all-polymer solar cells, various EBSA doping ratios (0, 1, 3, 5, 10, 20 wt%) were tested by employing optical absorption spectroscopy, photoluminescence spectroscopy, photoelectron yield spectroscopy, and space-charge-limited current (SCLC) mobility measurement. The doping reaction of P3HT with EBSA was followed by observing the colour change in solutions. The final doping ratio for P3HT was chosen as 1 wt% from the best hole mobility measured in the thickness direction, while that for F8BT was fixed as 10 wt% (F8BT-EBSA). The polymer:polymer solar cells with bulk heterojunction nanolayers of P3HT-EBSA (EBSA-doped P3HT) and F8BT-EBSA (EBSA-doped F8BT) showed greatly improved short circuit current density (<I>J</I><SUB>SC</SUB>) and open circuit voltage (<I>V</I><SUB>OC</SUB>), compared to the undoped solar cells. As a result, the power conversion efficiency (PCE) was enhanced by <I>ca.</I> 300% for the 6 : 4 (P3HT-EBSA : F8BT-EBSA) composition and <I>ca.</I> 400% for the 8 : 2 composition. The synchrotron-radiation grazing incidence angle X-ray diffraction (GIXD) measurement revealed that the crystallinity of the doped nanolayers significantly increased by EBSA doping owing to the formation of advanced phase segregation morphology, as supported by the surface morphology change measured by atomic force microscopy. Thus the improved PCE can be attributed to the enhanced charge transport by the formation of permanent charges and better charge percolation paths by EBSA doping.</P> <P>Graphic Abstract</P><P>The performance of all-polymer solar cells was remarkably improved by chemical doping of both electron-donating polymer and electron-accepting polymer due to the enhanced charge transport in the double doped bulk heterojunction nanolayers. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cp43002a'> </P>

Interfacial Engineering for High-Efficiency Polymer:Fullerene Solar Cells with Improved Stability

Sungho NAM,Jooyeok SEO,Hyemi HAN,Hwajeong KIM,Moonhor REE,Yeong-Soon GAL,Youngkyoo KIM 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

Doping Effect of OrganosulfonicAcid in Poly(3-hexylthiophene)Films for Organic Field-Effect Transistors

Nam, Sungho,Kim, Joonhyeon,Lee, Hyena,Kim, Hwajeong,Ha, Chang-Sik,Kim, Youngkyoo AmericanChemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.3

<P>We attempted to dope poly(3-hexylthiophene) (P3HT) with 2-ethylbenzenesulfonic acid (EBSA), which has good solubility in organic solvents, in order to improve the performance of organic field effect transistors (OFET). The EBSA doping ratio was varied up to 1.0 wt % because the semiconducting property of P3HT could be lost by higher level doping. The doping reaction was confirmed by the emerged absorption peak at the wavelength of similar to 970 nm and the shifted S2p peak (X-ray photoelectron spectroscopy), while the ionization potential and nanostructure of P3HT films was slightly affected by the EBSA doping. Interestingly, the EBSA doping delivered significantly improved hole mobility because of the greatly enhanced drain current of OFETs by the presence of the permanently charged parts in the P3HT chains. The hole mobility after the EBSA doping was increased by the factor of 55-86 times depending on the regioregularity at the expense of low on/off ratio in the case of unoptimized devices, while the optimized devices showed, similar to 10 times increased hole mobility by the 1.0 wt % EBSA doping with the greatly improved on/off ratio even though the source and drain electrodes were made using relatively cheaper silver instead of gold.</P>

Improved Performance of Polymer:Polymer Solar Cells by Doping Electron‐Accepting Polymers with an Organosulfonic Acid

Nam, Sungho,Shin, Minjung,Kim, Hwajeong,Ha, Chang‐,Sik,Ree, Moonhor,Kim, Youngkyoo WILEY‐VCH Verlag 2011 Advanced functional materials Vol.21 No.23

<P><B>Abstract</B></P><P>The performance of polymer:polymer solar cells that are made using blend films of poly(3‐hexylthiophene) (P3HT) and poly(9,9‐dioctylfluorene‐co‐ benzothiadiazole (F8BT) is improved by doping the F8BT polymer with an organosulfonic acid [4‐ethylbezenesulfonic acid (EBSA)]. The EBSA doping of F8BT, to form F8BT‐EBSA, is performed by means of a two‐stage reaction at room temperature and 60°C with various EBSA weight ratios. The X‐ray photoelectron spectroscopy measurement reveals that both sulfur and nitrogen atoms in the F8BT polymer are affected by the EBSA doping. The F8BT‐EBSA films exhibit huge photoluminescence quenching, ionization potential shift toward lower energy, and greatly enhanced electron mobility. The short‐circuit current density of solar cells is improved by ca. twofold (10 wt.% EBSA doping), while the open‐circuit voltage increases by ca. 0.4 V. Consequently, the power conversion efficiency was improved by ca. threefold, even though the optical density of the P3HT:F8BT‐EBSA blend film is reduced by 10 wt.% EBSA doping due to the nanostructure and surface morphology change.</P>

Bias-dependent photocurrent response in protein nanolayer-embedded solid state planar diode devices

Nam, Sungho,Kim, Hwajeong,Kim, Youngkyoo Royal Society of Chemistry 2010 Nanoscale Vol.2 No.5

<P>A bias-dependent superlinear photocurrent response under white light illumination was measured in the planar diodes with a protein nanolayer of horseradish peroxidase (HRP) that is a key material for sensing hydrogen peroxide in biological systems.</P> <P>Graphic Abstract</P><P>A planar diode device having protein nanolayers exhibited bias-dependent photocurrent behaviors featuring slow discharging characteristics. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b9nr00365g'> </P>

Pronounced Cosolvent Effects in Polymer:Polymer Bulk Heterojunction Solar Cells with Sulfur-Rich Electron-Donating and Imide-Containing Electron-Accepting Polymers

Nam, Sungho,Woo, Sungho,Seo, Jooyeok,Kim, Wook Hyun,Kim, Hwajeong,McNeill, Christopher R.,Shin, Tae Joo,Bradley, Donal D. C.,Kim, Youngkyoo American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.29

<P>The performance of solar cells with a polymer:polymer bulk heterojunction (BHJ) structure, consisting 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) donor and poly[[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)] (P(NDI2OD-T2)) acceptor polymers, was investigated as a function of cosolvent (p-xylene:chlorobenzene (pXL:CB)) composition ratio. A remarkable efficiency improvement (similar to 38%) was achieved by spin-coating the photoactive blend layer from pXL:CB = 80:20 (volume) rather than pXL alone, but the efficiency then decreased when the CB content increased further to pXL:CB = 60:40. The improved efficiency was correlated with a particular PTB7-Th:P(NDI2OD-T2) donor-acceptor blend nanostructure, evidenced by a fiber-like surface morphology, a red-shifted optical absorption, and enhanced PL quenching. Further device optimization for pXL:CB = 80:20 films yielded a power conversion efficiency of similar to 5.4%. However, these devices showed very poor stability (similar to 15 min for a 50% reduction in initial efficiency), owing specifically to degradation of the PTB7-Th donor-component. Replacing PTB7-Th with a more stable donor polymer will be essential for any application potential to be realized.</P>

Hybrid Phototransistors Based on Bulk Heterojunction Films of Poly(3-hexylthiophene) and Zinc Oxide Nanoparticle

Nam, Sungho,Seo, Jooyeok,Park, Soohyeong,Lee, Sooyong,Jeong, Jaehoon,Lee, Hyena,Kim, Hwajeong,Kim, Youngkyoo American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.4

<P>Hybrid phototransistors (HPTRs) were fabricated on glass substrates using organic/inorganic hybrid bulk heterojunction films of p-type poly(3-hexylthiophene) (P3HT) and n-type zinc oxide nanoparticles (ZnO<SUB><I>NP</I></SUB>). The content of ZnO<SUB><I>NP</I></SUB> was varied up to 50 wt % in order to understand the composition effect of ZnO<SUB><I>NP</I></SUB> on the performance of HPTRs. The morphology and nanostructure of the P3HT:ZnO<SUB><I>NP</I></SUB> films was examined by employing high resolution electron microscopes and synchrotron radiation grazing angle X-ray diffraction system. The incident light intensity (<I>P</I><SUB>IN</SUB>) was varied up to 43.6 μW/cm<SUP>2</SUP>, whereas three major wavelengths (525 nm, 555 nm, 605 nm) corresponded to the optical absorption of P3HT were applied. Results showed that the present HPTRs showed typical p-type transistor performance even though the n-type ZnO<SUB><I>NP</I></SUB> content increased up to 50 wt %. The highest transistor performance was obtained at 50 wt %, whereas the lowest performance was measured at 23 wt % because of the immature bulk heterojunction morphology. The drain current (<I>I</I><SUB>D</SUB>) was proportionally increased with <I>P</I><SUB>IN</SUB> due to the photocurrent generation in addition to the field-effect current. The highest apparent and corrected responsivities (<I>R</I><SUB>A</SUB> = 4.7 A/W and <I>R</I><SUB>C</SUB> = 2.07 A/W) were achieved for the HPTR with the P3HT:ZnO<SUB><I>NP</I></SUB> film (50 wt % ZnO<SUB><I>NP</I></SUB>) at <I>P</I><SUB>IN</SUB> = 0.27 μW/cm<SUP>2</SUP> (555 nm).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-4/am302765a/production/images/medium/am-2012-02765a_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am302765a'>ACS Electronic Supporting Info</A></P>