Design and synthesis of a new fluorinated wide bandgap polymer for efficient non-fullerene solar cells

( Gururaj Kini ),박희선,전성재,문두경 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

Introduction of the Fluorine (F) in conjugated polymer is regarded as smart choice for decreasing energy levels without disturbing the planarity of the polymer backbone. Based on the same approach, we designed new fluorinated wide band polymers with different optical and electronic properties. We effects of these structural modification on the molecular interactions and performances by analyzing and comparing optical-electrochemical analysis, molecular ordering and photovoltaic properties of the resulting polymers. Among polymers, optimized PSCs based on P1 demonstrated a high-power convergence efficiency up to 8.2%. This study provides important insights to the design of donor polymers for non-fullerene organic solar cells.

Effect of mono alkoxy-carboxylate-functionalized benzothiadiazole-based donor polymers for non-fullerene solar cells

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>

Effects on Photovoltaic Performance of Dialkyloxy-benzothiadiazole Copolymers by Varying the Thienoacene Donor

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>

Achieving a solar power conversion efficiency exceeding 9% by modifying the structure of a simple, inexpensive and highly scalable polymer

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>

Controlling the interchain packing and photovoltaic properties via fluorine substitution in terpolymers based on benzo[1,2-c:4,5-c']dithiophene-4,8-dione and benzothiadiazole units

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>

New alkoxy-carboxylate-functionalized donor-acceptor polymers for use in non-fullerene solar cells

( gururaj kini ),최준영,전성재 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.1

Medium Bandgap Donor Polymers incorporating a Novel Ester-Substituted Acceptor for Efficient Non-Fullerene Solar Cells

( Gururaj Kini ),최준영,전성재,문두경 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

Two novel Donor-Acceptor (D-A) copolymers P1 and P2 incorporating novel ester substituted acceptor and benzo[1,2-b:4,5-b′]dithiophene (BDT) units have been synthesized and characterized. The new polymers featured complementary absorption and favorable energy levels to match the non-fullerene acceptor ITIC. The incorporation of carboxylate unit on the acceptor leads to lower lying highest occupied molecular orbital (HOMO) energy levels and easy tuning of solubility in the resulted polymers. In the preliminary studies, photovoltaic devices of polymers P1 and P2 blended with ITIC acceptor demonstrated power conversion efficiency (PCE) of 6.4% and 5.5%, respectively. Further studies are currently underway to optimize the solar cell performance.

Effect of mono alkoxy-carboxylate-functionalized benzothiadiazolebased donor polymers for non-fullerene solar cells

( Gururaj Kini ),이형석,전성재,문두경 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

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-b:4,5-b']dithiophene monomers with different alkyl chains to form polymers, P1 and P2, respectively The BT-Est yielded polymers with good solubility, medium bandgap and deep HOMO energy levels (upto -5.54 eV). Among the polymers, P1 exhibited broader absorption, compact molecular packing and high charge carrier mobility. Consequently, the best power-conversion efficiency of 6.9% were obtained for P1-based devices with non-fullerene acceptor ITIC. 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.

Molecular design of pyrazine based wide bandgap donor polymers for non-fullerene solar cells

( Gururaj Kini ),전성재,문두경 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

Over the years, donor polymers based on electron-deficient nitrogen heterocycles (N-heterocycles) for PSCs have been relatively less explored. In this report, we synthesized two new polymers P1 and P2 having alternate benzodithiophene donor unit and pyrazine acceptor unit with different side chains for use in non-fullerene PSCs. These polymers demonstrated deep frontier energy levels and wide bandgaps (∼2.05 eV). We studied the structure property relationship between these polymers via various characterization techniques. The optimized PSCs obtained by blending P1 and P2 with an NF acceptor, ITIC exhibited impressive efficiencies of 7.6 and 8.1%, respectively. Our findings advance the understanding of the influence of incorporated pyrazine on the optoelectronic properties of polymer donors.

Effects of the fluorination on the inter-chain packing and photovoltaic properties of the A1-D-A2 terpolymers based on benzo [1,2-c:4,5-c′]-dithiophene-4,8-dione and benzothiadiazole units

( Gururaj Kini ),최준영,전성재,문두경 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

We present a series of three new A1-D-A2 based terpolymers, involving benzo[1,2-c:4,5-c']dithiophene-4,8-dione (BDD) and benzothiadiazole (BT). We optimized the structures of these terpolymers by varying number of fluorine atoms (F) on the BT unit and studied their effects on photovoltaic performances (P1 (BT), P2 (FBT) and P3 (2FBT). The fluorination of BT significantly decreased frontier energy levels, enhanced intermolecular interactions and planarization of polymer backbone in the resulted polymers. As a result, P3 having two F-substituents on the BT displayed stronger intermolecular interactions, predominant face-on orientation and optimal nanoscale morphology compared to P1 and P2. Thus, polymer solar cells based on P3 demonstrated higher power conversion efficiency (PCE) of 6.2% compared to P1 and P2. It would contribute to design high-efficiency polymer donors for photovoltaic application.