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Chakravarthi, Nallan,Gunasekar, Kumarasamy,Cho, Woosum,Long, Dang Xuan,Kim, Yun-Hi,Song, Chang Eun,Lee, Jong-Cheol,Facchetti, Antonio,Song, Myungkwan,Noh, Yong-Young,Jin, Sung-Ho The Royal Society of Chemistry 2016 ENERGY AND ENVIRONMENTAL SCIENCE Vol.9 No.8
<P>Achieving the state-of-the-art performance of solution processable and flexible organic electronics requires efficient, stable, and cost-effective interfacial layers (ILs). Here, we report an alcohol soluble phosphine oxide functionalized 1,3,5-triazine derivative (PO-TAZ) as an IL, which remarkably tailors the work function of conductors including metals, transparent metal oxides and organic materials, making it an ideal candidate for an interfacial material in organic electronics. Consequently, PO-TAZ thin films enable the fabrication of organic and organic-inorganic (perovskite) solar cells with power conversion efficiencies of 10.04% and 16.41%, respectively, and n-channel organic field-effect transistors with an electron mobility of 8 cm(2) V-1 s(-1). Owing to the low-cost processing associated with PO-TAZ and the tremendous improvement in device performances as compared to the devices without PO-TAZ along with ambient stability, PO-TAZ is a good choice for efficient organic electronics in large area printing processes.</P>
Chakravarthi, Nallan,Gunasekar, Kumarasamy,Kim, Chang Su,Kim, Dong-Ho,Song, Myungkwan,Park, Young Geun,Lee, Jin Yong,Shin, Yurim,Kang, In-Nam,Jin, Sung-Ho American Chemical Society 2015 Macromolecules Vol.48 No.8
<P>In all the previously reported 4,8-dithienylbenzo[1,2-b:4,5-b']dithiophene (DTBDT)-based pi-conjugated polymers, the polymerization and two-dimensional (2D) conjugation extension pathways were through the thiophenes fused to the phenyl core of DTBDT and through the thiophenes linked to the benzene core of DTBDT, respectively (BDT-directed DTBDT). Herein, with the aim of discovering another potential way to introduce the DTBDT motif in the donor-acceptor alternating polymer structure, we first report the synthesis of three new p-conjugated polymers, P1, P2, and P3, with a modified DTBDT building block as a donor unit. This modification results in new polymerization and 2D conjugation extension pathways for the polymers through the thiophenes linked to the benzene core of DTBDT and through the thiophenes fused to the phenyl core of the DTBDT, respectively (dithienylbenzene-directed DTBDT). Although these modified polymerization pathways of DTBDT result in less delocalized conjugation along the dithienylbenzene direction, the optical and electrochemical properties reveal that the electron-donating property of dithienylbenzene-directed DTBDT was strong enough to generate strong intramolecular charge transfer (ICT) and maintain low-lying highest occupied molecular orbital (HOMO) energy levels (-5.21 to -5.28 eV) for high air stability. Inverted organic solar cells (IOSCs) were fabricated with the configuration of ITO/ZnO/polymer:PC71BM/PEDOT:PSS/Ag. By systematic optimization of the performance of the IOSCs using polar solvent treatment, the IOSCs based on P1, P2, and P3 displayed promising power conversion efficiencies (PCE) of 6.31, 5.65, and 7.10%, respectively, which compare well with the PCE of already reported BDT-directed DTBDT-based polymers. More importantly, the stability of the IOSCs was demonstrated by their retention of 83% PCE after ambient storage for 30 days. These study results revealed the promising potential of the proposed molecular design strategy for introducing new 2D conjugation extension and polymerization pathways for a DTBDT unit for high performance and stable IOSCs. This strategy can be applied to the judicious molecular design of new polymeric materials for achieving high PCE.</P>
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>
Chakravarthi, Nallan,Gunasekar, Kumarasamy,Kranthiraja, Kakaraparthi,Kim, Taeik,Cho, Woosum,Kim, Chang Su,Kim, Dong-Ho,Song, Myungkwan,Jin, Sung-Ho The Royal Society of Chemistry 2015 Polymer chemistry Vol.6 No.40
<▼1><▼1><P>Bis-tolane as an integrated part of the benzodithiophene donor unit for OSCs.</P></▼1><▼2><P>With the goal of discovering a new and plausible approach to utilizing the conjugated side chains (CSCs), other than for the previously reported purpose of two-dimensional (2D) π-conjugation extension in π-conjugated polymers, we report, for the first time, the impact of with/without interactions induced <I>via</I> resonance in CSCs on the molecular weight (<I>M</I>w) and photovoltaic performance of polymers. For this, we designed two donor (D)–acceptor (A) polymers, represented as PBDTBPA(H)-DPP and PBDTBPA(F)-DPP, containing alkoxy-BPA(H) and alkoxy-BPA(F) [BPA = biphenylethynyl] on the benzodithiophene (BDT) unit as novel CSCs, respectively. The introduction of these CSCs generated bis-tolane as an integrated part of the BDT unit, which allowed us to address the difference in the polymerization, photophysical, and photovoltaic properties of PBDTBPA(H)-DPP and PBDTBPA(F)-DPP, as a function of the structural variation of CSCs, which has never been investigated in organic solar cells (OSCs). In contrast to the weak electron-donating nature of BPA(H), BPA(F) exhibited a strong electron-donating ability due to the interaction of the lone pair electrons of the fluorine atom with the triple bond <I>via</I> resonance, which decreased the rigidity of the triple bond, whereas in PBDTBPA(H)-DPP the rigidity of the triple bond was retained with no such interaction. The striking differences in the rigidity and different electron-withdrawing tendencies of the CSCs were well correlated with <I>M</I>w and with the highest occupied molecular orbital (HOMO) energy levels of the polymers. As a result, the inverted OSCs based on PBDTBPA(H)-DPP achieved an open-circuit voltage (<I>V</I>oc) of 0.74 V, and power conversion efficiency (PCE) of 5.58%, which was 38% higher than that of PBDTBPA(F)-DPP-based inverted OSCs. More significantly, the inverted OSC devices were highly stable, retaining 80% of their original PCE after 60-day storage in air, even without encapsulation. To the best of our knowledge, this 5.58% is the highest PCE reported to date for the arylethynyl-substituted BDT donor-based OSCs. These results reveal that bis-tolane [BDTBPA(H)] as an integrated part of the new BDT unit is a promising donor building block for high <I>M</I>w donor polymers in addition to 2D extended π-conjugation for high performance bulk heterojunction (BHJ) OSCs.</P></▼2></▼1>
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 $mW/cm^2$.
Nagamani, Selvakumaran,Kumarasamy, Gunasekar,Song, Myungkwan,Kim, Chang Su,Kim, Dong-Ho,Ryu, Seung Yoon,Kang, Jae-Wook,Jin, Sung-Ho Elsevier 2016 Synthetic metals Vol.217 No.-
<P><B>Abstract</B></P> <P>The effects of the gold nanoparticles (Au NPs) on performance of organic solar cells (OSCs) are systematically investigated based on blend of the low band gap polymer and fullerene. The localized surface plasmon resonance (LSPR) induced by the Au NPs enhance the light absorption in the active layer and the photoluminescence spectra showed a significant enhancement in their intensity which mainly contribute to increased light absorption of active layer induced by LSPR. The impedance spectroscopy study revealed that the introduction of Au NPs as interfacial layer decreases the sheet and charge-transport resistance between ITO/PEDOT:PSS or PEDOT:PSS/active layer. From the results, the introduction of Au NPs increased the rate of exciton generation and the probability of exciton dissociation, thus enhancing the short-circuit current density and the fill factor The optimized OSCs incorporated with Au NPs were found to have power conversion efficiency of 5.40% compared to control device (4.65%), measured by using an AM 1.5G solar simulator at 100mW/cm<SUP>2</SUP> light illumination intensity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of gold nanoparticles (Au NPs) at the interfaces of organic solar cells (OSCs) was studied. </LI> <LI> The device using Au NPs at the interfaces of OSCs has a better efficiency due to localized surface plasmon resonance effect. </LI> <LI> The device with Au NPs at the interfaces showed 16.1% enhancement in efficiency. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Incorporation of gold nanoparticles (Au NPs) at the interfaces of organic solar cells enhance the light absorption in the active layer and the photoluminescence spectra showed a significant enhancement in their intensity which mainly contributes to the increased light absorption of active layer induced by localized surface plasmon resonance. The device with Au NPs at the interfaces showed 16.1% enhancement in efficiency.</P> <P>[DISPLAY OMISSION]</P>
Kim, Taeik,Chakravarthi, Nallan,Kumarasamy, Gunasekar,Jin, Sung-Ho Taylor & Francis Inc. 2016 Molecular Crystals and Liquid Crystals Vol.635 No.1
<P>Two donor-acceptor low band gap polymers P1 (octyl as solubilizing group) and P2 (ethylhexyl as solubilizing group) containing fluorenylthiophene-substituted benzoditihiophene as an electron-rich unit and 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione as an electron-deficient unit are designed and synthesized for polymer solar cells application. Compared with P2 based on ethyl hexyl group, P1 with octyl group displays well resolved vibronic shoulder peak in absorption spectra, stronger intermolecular interactions, and higher hole mobility. Polymer solar cells based on P1 and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) exhibit a maximum power conversion efficiency of 1.78% under AM 1.5G illumination (100mW/cm(2)).</P>