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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,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>
Triazine-based Polyelectrolyte as an Efficient Cathode Interfacial Material for Polymer Solar Cells
Chakravarthi, Nallan,Aryal, Um Kanta,Gunasekar, Kumarasamy,Park, Ho-Yeol,Gal, Yeong-Soon,Cho, Young-Rae,Yoo, Seong Il,Song, Myungkwan,Jin, Sung-Ho American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.29
<P>A novel polyelectrolyte containing triazine (TAZ) and benzodithiophene (BDT) scaffolds with polar phosphine oxide (P=O) and quaternary ammonium ions as pendant groups, respectively, in the polymer backbone (PBTAZPOBr) was synthesized to use it as a cathode interfacial layer (CIL) for polymer solar cell (PSC) application. Owing to the high electron affinity of the TAZ unit and P=O group, PBTAZPOBr could behave as an effective electron transport material. Due to the polar quaternary ammonium and P=O groups, the interfacial dipole moment created by PBTAZPOBr substantially reduced the work function of the metal cathode to afford better energy alignment in the device, thus enabling electron extraction and reducing recombination of excitons at the photoactive layer/cathode interface. Consequently, the PSC devices based on the poly[4,8-bis(2-ethylhexyloxyl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-ethylhexyl-3-fluorothithieno[3,4-b]thiophene-2-carboxylate-4,6-diyl]:[6,6]-phenyl-C71-butyric acid methyl ester (PTB7:PC71BM) system with PBTAZPOBr as CIL displayed simultaneously enhanced open-circuit voltage, short-circuit current density, and fill factor, whereas the power conversion efficiency increased from 5.42% to 8.04% compared to that of the pristine Al device. The outstanding performance of PBTAZPOBr is attributed not only to the polar pendant groups of BDT unit but also to the TAZ unit linked with the P=O group of PBTAZPOBr, demonstrating that functionalized TAZ building blocks are very promising cathode interfacial materials (CIMs). The design strategy proposed in this work will be helpful to develop more efficient CIMs for high performance PSCs in the future.</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>
김용갑,( Chakravarthi Nallan ),전병철,이원주 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0
플라스틱의 용도가 건축용, 자동차용, 전기제품, 항공기, 선박 등으로 광범위하게 확대됨에 따라, 화재 발생시 안전을 고려한 난연화 필요성이 지속적으로 증대되고 있다. 최근에는 높은 난연성과 함께 환경에 적합한 재료의 개발이 강하게 요망되고 있으며, 이에 난연제의 비할로겐화에 대한 개발 요구가 크게 대두되고 있다. 본 연구에서는 폴리우레탄 혹은 에폭시 접착제 적용시 난연 특성을 향상시킬 수 있는 반응형 인계 다이올( 및 올리고머)을 합성 하였다. 또한 후가교성을 부여하기 위해 다이올( 및 올리고머)에 Vinyl기를 도입하였다. 합성된 다이올의 화학적 구조와 열적 특성은 NMR, TGA, DSC를 사용하여 측정하였고 인 함량에 따른 난연 특성을 관찰하였다.
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>