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Kranthiraja, Kakaraparthi,Gunasekar, Kumarasamy,Song, Myungkwan,Gal, Yeong-Soon,Lee, Jae Wook,Jin, Sung-Ho Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.5
We have designed and developed a new ladder type tetrafused ${\pi}$-conjugated building block such as dihydroindolo[3,2-b]indole (DINI) and investigated its role as an electron rich unit. The photovoltaic properties of a new semiconducting ${\pi}$-conjugated polymer, poly[[5,10-bisoctyl-5,10-dihydroindolo[3,2-b]indole-[5,6- bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole]], represented by PDINI-OBTC8 are described. The new polymer PDINI-OBTC8 was synthesized in donor-acceptor (D-A) fashion, where fused ${\pi}$-conjugated tetracyclic DINI, and 5,6-bis(octyloxy)-4,7-di(thiophen-2-yl) benzo[c][1,2,5]thiadiazole (OBTC8) were employed as electron rich (donor) and electron deficient (acceptor) moieties, respectively. The conventional bulk heterojunction (BHJ) device structure ITO/PEDOT:PSS/PDINI-OBTC8:PCB71M/LiF/Al was utilized to fabricate polymer solar cells (PSCs), which comprises the blend of PDINI-OBTC8 and [6,6]-phenyl-$C_{71}$-butyric acid methyl ester ($PC_{71}BM$) in BHJ network. A BHJ PSC that contain PDINI-OBTC8 delivered power conversion efficiency (PCE) value of 1.68% with 1 vol% of 1,8-diidooctane (DIO) under the illumination of A.M 1.5G 100 $mW/cm^2$.
Kranthiraja, Kakaraparthi,Park, Sang Ho,Kim, Hyunji,Gunasekar, Kumarasamy,Han, Gibok,Kim, Bumjoon J.,Kim, Chang Su,Kim, Soohyun,Lee, Hyunjung,Nishikubo, Ryosuke,Saeki, Akinori,Jin, Sung-Ho,Song, Myung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.41
<P>We present an efficient approach to develop a series of multifunctional pi-conjugated polymers (P1-P3) by controlling the degree of fluorination (OF, 2F, and 4F) on the side chain linked to the benzodithiophene unit of the pi-conjugated polymer. The most promising changes were noticed in optical, electrochemical, and morphological properties upon varying the degree of fluorine atoms on the side chain. The properly aligned energy levels with respect to the perovskite and PCBM prompted us to use them in perovskite solar cells (PSCs) as hole-transporting materials (HTMs) and in bulk heterojunction organic solar cells (BHJ OSCs) as photoactive donors. Interestingly, P2 (2F) and P3 (4F) showed an enhanced power conversion efficiency (PCE) of 14.94%, 10.35% compared to PI (OF) (9.80%) in dopant-free PSCs. Similarly, P2 (2F) and P3 (4F) also showed improved PCE of 7.93% and 7.43%, respectively, compared to P1 (OF) (PCE of 4.35%) in BHJ OSCs. The high photvoltaic performance of the P2 and P3 based photovotaic devices over P1 are well correlated with their energy level alignment, charge transporting, morphological and packing properties, and hole transfer yields. In addition, the P1-P3 based dopant-free PSCs and BHJ OSCs showed an excellent ambient stability up to 30 days without a significant drop in their initial performance.</P>
Kranthiraja, Kakaraparthi,Long, Dang Xuan,Sree, Vijaya Gopalan,Cho, Woosum,Cho, Young-Rae,Zaheer, Abbas,Lee, Jong-Cheol,Noh, Yong-Young,Jin, Sung-Ho American Chemical Society 2018 Macromolecules Vol.51 No.15
<P>Improving π-conjugated polymer electron transport and injection efficiency are important to realize high performance n-channel organic field-effect transistors (OFETs). This paper reports a series of naphthalene diimide (NDI-) based n-type π-conjugated polymers, NDI-T-1FP-T, NDI-T-2FP-T, and NDI-T-4FP-T, with varioulis amounts of fluorine atoms (1F, 2F, and 4F) in their backbones. We found notable differences in energy levels, ground and excited state dipole moments (Δμ<SUB>ge</SUB>), exciton lifetimes, dihedral angles, and charge transport properties by varying the fluorine content: Δμ<SUB>ge</SUB> and charge transport properties reduced with increasing fluorine content. Electron mobility of optimized top gate bottom contact OFETs using the n-type π-conjugated polymers were 0.35, 0.18, and 0.16 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, respectively. OFET performances were further improved further by low concentration polyethylenimine (PEI) doping, significantly improving field-effect mobility to (maximum) 0.51, 0.34, and 0.26 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, respectively. Doped NDI-T-4FP-T with 4F in particular showed unipolar n-channel behavior by depletion of the hole current.</P> [FIG OMISSION]</BR>
Kranthiraja, Kakaraparthi,Aryal, Um Kanta,Sree, Vijaya Gopalan,Gunasekar, Kumarasamy,Lee, Changyeon,Kim, Minseok,Kim, Bumjoon J.,Song, Myungkwan,Jin, Sung-Ho American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.16
<P>The ternary-blend approach has the potential to enhance the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) by providing complementary absorption and efficient charge generation. Unfortunately, most PSCs are processed with toxic halogenated solvents, which are harmful to human health and the environment. Herein, we report the addition of a nonfullerene electron acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-<I>d</I>:2′,3′-<I>d</I>′]-<I>s</I>-indaceno[1,2-<I>b</I>:5,6-<I>b</I>′]dithiophene (ITIC) to a binary blend (poly[4,8-bis(2-(4-(2-ethylhexyloxy)3-fluorophenyl)-5-thienyl)benzo[1,2-<I>b</I>:4,5-<I>b</I>′]dithiophene-<I>alt</I>-1,3-bis(4-octylthien-2-yl)-5-(2-ethylhexyl)thieno[3,4-<I>c</I>]pyrrole-4,6-dione] (P1):[6,6]-phenyl-C<SUB>71</SUB>-butyric acid methyl ester (PC<SUB>71</SUB>BM), PCE = 8.07%) to produce an efficient nonhalogenated green solvent-processed ternary PSC system with a high PCE of 10.11%. The estimated wetting coefficient value (0.086) for the ternary blend suggests that ITIC could be located at the P1:PC<SUB>71</SUB>BM interface, resulting in efficient charge generation and charge transport. In addition, the improved current density, sustained open-circuit voltage and PCE of the optimized ternary PSCs were highly correlated with their better external quantum efficiency response and flat-band potential value obtained from the Mott-Schottky analysis. In addition, the ternary PSCs also showed excellent ambient stability over 720 h. Therefore, our results demonstrate the combination of fullerene and nonfullerene acceptors in ternary blend as an efficient approach to improve the performance of eco-friendly solvent-processed PSCs with long-term stability.</P> [FIG OMISSION]</BR>
Kranthiraja, Kakaraparthi,Gunasekar, Kumarasamy,Cho, Woosum,Song, Myungkwan,Park, Young Geun,Lee, Jin Yong,Shin, Yurim,Kang, In-Nam,Kim, Ajeong,Kim, Hyunjung,Kim, BongSoo,Jin, Sung-Ho American Chemical Society 2014 Macromolecules Vol.47 No.20
<P>Two donor–acceptor (D–A) medium band gap polymers, <B>P1</B> and <B>P2</B>, alkoxyphenylthiophene (APTh) linked benzodithiophene (BDT) as an electron-rich unit and 1,3-di(2′-bromothien-5′-yl)-5-(2-ethylhexyl)thieno[3,4-<I>c</I>]pyrrole-4,6-dione (TPD) (<B>A1</B>) or [5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[<I>c</I>][1,2,5]thiadiazole] (BT) (<B>A2</B>) as an electron-deficient unit, have successfully been synthesized via microwave-assisted Stille polymerization and utilized for bulk heterojunction (BHJ) polymer solar cells (PSCs). <B>P1</B> shows a well-distinguished absorption shoulder between 590 and 620 nm attributed to the π–π stacking of a polymer backbone; such kind of absorption shoulder is not observed in <B>P2</B>, indicating that the <B>P1</B> has more planar structure than that of <B>P2</B>. This is due to the fact that the sulfur atom of thiophene spacer and the oxygen atom of carbonyl groups in TPD have more pronounced intramolecular noncovalent interactions (INCI) in <B>P1</B> than that of the sulfur atom of thiophene spacer and the oxygen atom of alkoxy groups of BT in <B>P2</B>. The bulk heterojunction polymer solar cells (BHJ PSCs) were fabricated with the configuration of ITO/PEDOT:PSS/polymer (<B>P1</B> or <B>P2</B>):PC<SUB>71</SUB>BM/LiF/Al. The <B>P1</B> device shows better photovoltaic performance with open-circuit voltage (<I>V</I><SUB>oc</SUB>) of 0.91 V and the power conversion efficiency (PCE) of 4.19% than the <B>P2</B> device (<I>V</I><SUB>oc</SUB>: 0.71 V; PCE: 1.88%) in neat blend films under the illumination of AM 1.5G (100 mW/cm<SUP>2</SUP>). Upon treating the active layers containing <B>P1</B> and <B>P2</B> with methanol, the PCE of the <B>P1</B> device is increased from 4.19 to 7.14%. In contrast, the PCE of the <B>P2</B> device is decreased from 1.88 to 1.82%. Space charge limited current mobility, atomic force microscopy, transmission electron microscopy, time-of-flight secondary ion mass spectrometry, and impedance spectroscopy studies strongly support the enhanced PCE for the <B>P1</B> device is attributed to the increased mobility, nanoscale morphology, and reduced resistance upon methanol treatment; these favorable properties for the <B>P1</B> polymer are highly correlated with the planarity of the backbone.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2014/mamobx.2014.47.issue-20/ma5010875/production/images/medium/ma-2014-010875_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma5010875'>ACS Electronic Supporting Info</A></P>
Kranthiraja, Kakaraparthi,Park, Ho-Yeol,Gunasekar, Kumarasamy,Park, Won-Tae,Noh, Yong-Young,Gal, Yeong-Soon,Moon, Jong Hun,Lee, Jin Yong,Jin, Sung-Ho The Polymer Society of Korea 2018 Macromolecular Research Vol.26 No.6
We report a new series of low band gap (LBG) polymers (P1-P4), in which para or meta- alkoxyphenylthiophene (APTh) substituted benzodithiophene and 2,5-ethylhexyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione or 2-ethylhexyl-4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate are key repeating units. All the polymers showed broad absorption profiles over 900 nm with reduced optical band gaps (<TEX>$E_g{^{opt}}$</TEX>). Interestingly, the straightforward modification (exchanging the topology of alkoxy side chain on phenyl group of APTh in donor unit) brought considerable changes in photophysical and photovoltaic properties of new polymers. In particular, meta-substituted polymers (P2, P4) showed reduced <TEX>$E_g{^{opt}}$</TEX> (1.26, 1.41 eV), deep highest occupied molecular orbitals (HOMOs) (-5.23, -5.28 eV) than para-substituted polymers P1, P3 (<TEX>$E_g{^{opt}}=1.33$</TEX>, 1.44 eV; HOMOs=-5.19, -5.20 eV). Furthermore, the optimized P2 and P4 based devices delivered an enhanced power conversion efficiency (PCE) of 4.39 and 4.33%, with open-circuit voltage (<TEX>$V_{oc}$</TEX>) of 0.71 and 0.79 V, respectively, which are higher than P1 (PCE of 2.95 with <TEX>$V_{oc}$</TEX> of 0.65) and P3 (PCE of 2.33% with <TEX>$V_{oc}$</TEX> of 0.69 V) based devices.
Kranthiraja, K.,Park, S. H.,Cho, W.,Park, W. T.,Noh, Y. Y.,Jin, S. H.,Lee, J. W. Springer 2016 Polymer bulletin Vol. No.
<P>In order to explore the effect of bulky side chain substituted benzodithiophene (BDT) based polymers on optoelectronic properties, here we have designed and synthesized two new 2D conjugated donor-acceptor (D-A) copolymers P1 and P2 via Stille coupling of 2,3-bis(4-(2-ethylhexyloxy)phenyl)thiophene (BAPT) substituted BDT as (D) unit and 1,3-di(2-bromothien-5-yl)-5-(2-ethylhexyl)thieno[3,4-c]pyrrole-4,6-dione (TPD) or 2,5-ethylhexyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (DPP) as (A) units. The new polymers P1 and P2 showed broad absorption windows with vibronic shoulders indicate pi-pi stacking of polymer backbones. In addition P1 and P2 showed deep highest occupied molecular orbital (HOMO) energy levels of -5.50, -5.35 eV, respectively which allow delivering high open-circuit voltages (V (oc)) in bulk heterojunction polymer solar cells (BHJ PSCs). The donor photon energy loss (E (g)-eV (oc)) of P1 and P2 are 0.87 and 0.57 which is comparable to the previous reports. BHJ PSCs were fabricated with P1 and P2, and they displayed high V (oc) of 0.99 and 0.78 V, respectively, with maximum power conversion efficiency of 2.05 and 0.96 % in additive free BHJ PSCs. The polymer field effect transistor mobilities of P1 and P2 are 8.0 x 10(-3), 9.2 x 10(-5) cm(2)/V s, respectively.</P>