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Kini, Gururaj P.,Choi, Jun Young,Jeon, Sung Jae,Suh, Il Soon,Moon, Doo Kyung Elsevier 2018 Polymer Vol.148 No.-
<P><B>Abstract</B></P> <P>We present a series of three terpolymers involving benzo [1,2-c:4,5-c']dithiophene-4,8-dione (BDD) and benzothiadiazole (BT) as acceptor units, and oligothiophene as the donor unit (PBDD-TnFBT terpolymers). We optimized the structures of these terpolymers by varying the number of fluorine (F) atoms on the BT unit and studied its effects on photovoltaic performance (<B>P1</B> (BT), <B>P2</B> (FBT), and <B>P3</B> (2FBT)). Density functional theory analysis, optical-electrochemical analysis, and X-ray diffraction study revealed that the fluorination of BT significantly decreased frontier energy levels, enhanced both intermolecular interactions and planarization of polymer backbone in the resulted polymers. As a result, <B>P3,</B> having two F substituents on BT, exhibited stronger intermolecular interactions, predominant face-on orientation with a shorter π-π stacking distance of 3.51 Å, high hole mobility, and optimal nanoscale morphology compared to single F substituent (<B>P2</B>) and zero F substituent (<B>P1</B>) counterparts. Consequently, polymer solar cells based on <B>P3</B> demonstrated higher power conversion efficiency (PCE) of 6.2% than those based on <B>P1</B> and <B>P2</B> (1.4 and 1.7% respectively). This study illustrates the interrelation between the degree of fluorination and photovoltaic performance and effectively contributes to the design of high-PCE polymer donors for photovoltaic application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Three terpolymers involving BDD and BT with the different number of fluorine (F) atoms were introduced. </LI> <LI> The interrelation between the degree of fluorination with charge transport behavior and polymer performance in PSC were investigated. </LI> <LI> Fluorination of BT significantly decreased frontier energy levels and enhanced intermolecular interactions in polymers. </LI> <LI> The PCE of PSCs was greatly improved from P1 (BT) 1.4% to 6.2 % P3 (2FBT) by the addition of F-atoms. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kini, Gururaj P.,Choi, Jun Young,Jeon, Sung Jae,Suh, Il Soon,Moon, Doo Kyung Applied Science Publishers 2019 Dyes and pigments Vol.164 No.-
<P><B>Abstract</B></P> <P>Structural modification of benzo[c]-1,2,5-thiadiazole (BT) has been proved to be the prominent way to fine-tune the frontier energy levels and the intermolecular and intramolecular interactions in organic conjugated materials. In this study, a new acceptor unit, alkyl benzo[c][1,2,5]thiadiazole-5-carboxylate (BT-Est), was designed and synthesized by drafting mono alkoxy-carboxylate substituent on 5-position of BT core. Its compatibility in the conjugated system was investigated by co-polymerizing BT-Est with well-known benzo[1,2-<I>b</I>:4,5-<I>b</I>']dithiophene monomers containing either 2-(2-ethylhexyl)thienyl or 2-((2-ethylhexyl)thio)thienyl side chains to form two new polymers, <B>P1</B> and <B>P2</B>, respectively. The BT-Est yielded polymers with good solubility, medium bandgap (∼1.71 eV), and deep highest occupied molecular orbital energy levels (−5.48 to −5.54 eV). Among the polymers, <B>P1</B> exhibited broader absorption, compact molecular packing, high charge carrier mobility, and effective exciton dissociation, despite of the torsion angle caused by the free rotation of the carboxylate group in the polymer backbone. Consequently, the best power-conversion efficiency of 6.9%, with a <I>J</I> <SUB>SC</SUB> of 14.6 mA cm<SUP>−2</SUP>, <I>V</I> <SUB>OC</SUB> of 0.9 V, and FF of 52.5% were obtained for <B>P1-</B>based devices with the well-known non-fullerene acceptor ITIC. We systematically expounded the structure-property relationship of the BT-Est polymers using diverse characterization methods. Our results demonstrated that the mono carboxylate-substitution on the BT core can be used as the alternate strategy to modulate the optoelectronic properties and control the aggregation in the conjugated polymers. Thus, BT-Est has the potential to produce new donor–acceptor conjugated polymers and small molecules for application in organic electronics.</P>
Kini, Gururaj P.,Oh, Sora,Abbas, Zaheer,Rasool, Shafket,Jahandar, Muhammad,Song, Chang Eun,Lee, Sang Kyu,Shin, Won Suk,So, Won-Wook,Lee, Jong-Cheol American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.14
<P>A series of four donor acceptor alternating copolymers based on dialkyloxy-benzothiadiazole (ROBT) as an acceptor and thienoacenes as donor units were synthesized and tested for polymer solar cells (PSCs). These new polymers had different donor units with varied electron-donating ability (thieno[3,2-b]thiophene (TT), dithieno[3,2-b:2',3'-d]thiophene (DTT), benzo[1,2-b:4,5-b'] dithiophene (BDT), and naphtha[1,2-b:5,6-b']dithiophene (NDT)) in the polymer backbone. To understand the effect of these thienoacenes on the optoelectronic and photovoltaic properties of the copolymers, we systematically analyzed and compared the energy levels, crystallinity, morphology, charge recombination, and charge carrier mobility in the resulting polymers. In this series, optimized photovoltaic cells yielded power conversion efficiency (PCE) values of 6.25% (TT), 9.02% (DTT), 6.34% (BDT), and 2.29% (NDT) with different thienoacene donors. The introduction of DTT into the thienoacene ROBT polymer enabled the generation of well-ordered molecular packings with pi-pi stacking distance of 3.72 angstrom, high charge mobilities, and an interconnected nanofibrillar morphology in blend films. As a result, the PSC employing the polymer with DTT exhibited the highest PCE of 9.02%. Thus, our structure property relationship studies of thienoacene ROBT-based polymers emphasize that the molecular design of the polymers must be carefully optimized, to develop high efficient PSCs. These findings will help us to understand the impact of the donor thienoacene on the optoelectronic and photovoltaic performance of polymers.</P>
Kini, Gururaj P.,Lee, Sang Kyu,Shin, Won Suk,Moon, Sang-Jin,Song, Chang Eun,Lee, Jong-Cheol The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.47
<P>We report a systematic study of the role of introduced alkyl chains in the easily synthesized conjugated PDTT-ROBT copolymers, which consist of dithieno[3,2-<I>b</I>:2′,3′-<I>d</I>]thiophene (DTT) and alkoxy substituted benzothiadiazole (ROBT) subunits. We synthesized new conjugated polymers PDTT-BOBT and PDTT-HDBT, which have molecular structures similar to those of the previously reported PDTTDABT polymer, but have modified alkyl chains in the polymer backbone. The modifications of the alkyl chains from linear (PDTTDABT) to branched (PDTT-BOBT and PDTT-HDBT) had prominent effects on the solubility, crystallinity, molecular orientation and morphology of the co-polymers. Solar cell devices containing the new PDTT-BOBT and PDTT-HDBT polymers exhibited power conversion efficiency (PCE) values of 9.2% and 6.2%, respectively, considerably greater than the 2.2% PCE of the previously reported PDTTDABT polymer, and the 9.2% PCE is in fact the highest to date for donor-acceptor polymers containing the BTOR acceptor. This high PCE may be explained by the well-aligned energy levels, optimum film morphology with bicontinuous interpenetrating networks, enhanced charge carrier mobility and decreased amount of charge recombination that we observed for PDTT-BOBT, in contrast to those exhibited by PDTTDABT and PDTT-HDBT. Considering the potential of PDTT-BOBT for industrial application, we tested the scalability, large-area devices (6600 mm<SUP>2</SUP>) and stability of PDTT-BOBT. As a result, the PDTT-BOBT polymer with its easily synthesized structure and high efficiency has considerable potential for being synthesized on a large scale and for use in printable electronic applications.</P>
Song, Chang Eun,Kim, Yu Jin,Suranagi, Sanjaykumar R.,Kini, Gururaj P.,Park, Sangheon,Lee, Sang Kyu,Shin, Won Suk,Moon, Sang-Jin,Kang, In-Nam,Park, Chan Eon,Lee, Jong-Cheol American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.20
<P>A series of small compound materials based on benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) with three different alkyl side chains were synthesized and used for organic photovoltaics. These small compounds had different alkyl branches (i.e., 2-ethylhexyl (EH), 2-butyloctyl (BO), and 2-hexyldecyl (HD)) attached to DPP units. Thin films made of these compounds were characterized and their solar cell parameters were measured in order to systematically analyze influences of the different side chains of compounds on the film microstructure, molecular packing, and hence, charge-transport and recombination properties. The relatively shorter side chains in the small molecules enabled more ordered packing structures with higher crystallinities, which resulted in higher carrier mobilities and less recombination factors; the small molecule with the EH branches exhibited the best semiconducting properties with a power conversion efficiency of up to 5.54% in solar cell devices. Our study suggested that tuning the alkyl chain length of semiconducting molecules is a powerful strategy for achieving high performance of organic photovoltaics.</P>