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Improved Efficiency of Ternary-Blended Films in Organic Solar Cell
Eunhee Lim 한국진공학회(ASCT) 2021 Applied Science and Convergence Technology Vol.30 No.1
Organic solar cells (OSCs) have attracted great interest as next-generation energy sources. In this study, a diketopyrrolopyrrole (DPP)-based electron-rich small-molecule donor, α-DPP-DT, was incorporated into a P3HT:PCBM binary film to fabricate ternary-blended OSCs. The OSCs were fabricated with the conventional configuration of ITO/PEDOT:PSS/active layer/LiF/Al and exhibited a power conversion efficiency of 2.12 %, which was greater than those of the two corresponding binary-blended devices. Both the open-circuit voltage and short-circuit current density values of the ternary films were lay between the corresponding values of the two binary films. The proposed working mechanism of the ternary-blended films is based on an alloy structure of two donors rather than on a cascade structure.
Doping effect of solution-processed thin-film transistors based on polyfluorene
Lim, Eunhee,Jung, Byung-Jun,Chikamatsu, Masayuki,Azumi, Reiko,Yoshida, Yuji,Yase, Kiyoshi,Do, Lee-Mi,Shim, Hong-Ku Royal Society of Chemistry 2007 Journal of materials chemistry Vol.17 No.14
<P>We report the fabrication of solution-processable organic thin-film transistors (OTFTs) based on poly(9,9′-dioctylfluorene-<I>alt</I>-bithiophene) (F8T2) doped with an electron-acceptor, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F<SUB>4</SUB>TCNQ). The 8% doping of the F8T2 film was found to result in an increased hole mobility, up to 0.01 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, and in an improved on/off ratio, as well as in a low off-current, of the order of 10<SUP>−11</SUP> A. The doped F8T2 device was also found to exhibit a better threshold voltage and reduced hysteresis behavior. These improvements in performance are attributed to the formation of the F8T2-F<SUB>4</SUB>TCNQ complex, which results in better hole injection and improved device stability.</P> <P>Graphic Abstract</P><P>Solution-processable organic thin-film transistors based on polyfluorene doped with an electron-acceptor (F<SUB>4</SUB>TCNQ) showed improved device performance by the formation of a charge-transfer complex. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b615720c'> </P>
Lim, Eunhee,Jung, Byung-Jun,Kim, Sung Min,Kim, Bong Ok,Shim, Hong-Ku The Chemical Society of Japan 2008 Chemistry letters Vol.37 No.7
<P>A series of ter(9,9-dialkylfluorene)s (TFs) containing cyclohexyl and hexyl side groups has been synthesized via the Suzuki coupling reaction. Their chemical structures were characterized by <SUP>1</SUP>H NMR and <SUP>13</SUP>C NMR. All TFs were soluble in common organic solvents and showed good thermal stability up to 400 °C. In particular, T(CHC)F composed of two 9,9-bis(cyclohexylmethyl)fluorenes and one dihexylfluorene showed improved thermal stability over T(HHH)F and was found to be amorphous, unlikely with T(CCC)F. A light-emitting diode device fabricated with an ITO/2-TNATA/NPB/TFs/Alq<SUB>3</SUB>/Liq/Al configuration exhibited blue light emission with EL maxima at 450 nm and EL efficiency of 1.1 cd/A.</P>
Lim, Young Rok,Ko, Yunseok,Park, Jeunghee,Cho, Won Il,Lim, Soo A,Cha, EunHee The Korean Electrochemical Society 2019 Journal of electrochemical science and technology Vol.10 No.1
As a promising candidate for anode materials in lithium ion battery (LIB), tungsten trioxide ($WO_3$) and tungsten disulfide ($WS_2$) nanocrystals were synthesized, and their electrochemical properties were comprehensibly studied using a half cell. One-dimensional $WO_3$ nanowires with uniform diameter of 10 nm were synthesized by hydrothermal method, and two-dimensional (2D) $WS_2$ nanosheets by unique gas phase sulfurization of $WO_3$ using $H_2S$. $WS_2$ nanosheets exhibits uniformly 10 nm thickness. The $WO_3$ nanowires and $WS_2$ nanosheets showed maximum capacities of 552 and $633mA\;h\;g^{-1}$, respectively, after 100 cycles. Especially, the capacity of $WS_2$ is significantly larger than the theoretical capacity ($433mA\;h\;g^{-1}$). We also examined the cycling performance using a larger size $WO_3$ and $WS_2$ nanocrystals, showing that the smaller size plays an important role in enhancing the capacity of LIBs. The larger capacity of $WS_2$ nanosheets than the theoretical value is ascribed to the lower charge transfer resistance of 2D nanostructures.
Influence of CN Substitution on DPP-furan-based Small-molecule Acceptors for Polymer Solar Cells
Eunhee Lim(임은희) 한국고분자학회 2020 폴리머 Vol.44 No.3
본 연구에서는, 스즈키 짝지음 반응을 이용하여 p- 및 o-DPP-F-PhCN의 두 단분자를 합성하여 고분자 태양전지의 비풀러렌계 어셉터로 사용하였다. 치환기의 위치 및 퓨란 효과에 따른 단분자의 물리적 특성 변화를 살펴보았다. 퓨란 그룹의 도입으로 단분자는 더 높은 상전이 온도와 HOMO 및 LUMO 준위를 나타내었다. o-치환 역시 분자의 에너지 준위를 높게 함으로써, o-DPP-F-PhCN의 에너지 준위가 가장 높게 나타났다. 상대적으로 강하고 장파장 이동된 UV-vis 흡수는 o-DPP-F-PhCN의 강한 분자 응집을 나타낸다. P3HT와 DPP-F-PhCN들을 각각 고분자 도너와 비풀러렌계 어셉터로 사용한 고분자 태양전지를 제작하였고, 두 DPP-F-PhCN이 유사한 효율을 나타내었다. o-DPP-F-PhCN의 강한 응집 거동은 외부양자효율에 유리하였으나, 향상된 오비탈 상호작용에 따른 안정화된 LUMO준위로 인해 상대적으로 낮은 개방전압 값을 나타내었다. In this study, two small-molecules, p- and o-DPP-F-PhCN, were synthesized via a Suzuki coupling reaction and used as nonfullerene acceptors (NFAs) for poly(3-hexylthiophene) (P3HT)-based polymer solar cells (PSCs). The physical properties of the molecules were examined in terms of the substituent position and the effect of the furan moiety. The introduction of a furan moiety resulted in higher phase-transition temperatures and higher-lying molecular orbital energy levels of the molecules. Substitution at the ortho position also elevated the energy levels of the molecules, resulting in the highest-lying values for o-DPP-F-PhCN. A relatively enhanced and red-shifted UV–vis absorption of o-DPP-FPhCN indicated its stronger molecular aggregation. PSCs based on two DPP-F-PhCNs exhibited similar device efficiencies. The stronger aggregation behavior of o-DPP-F-PhCN led to a device with a better external quantum efficiency profile; however, the enhanced orbital interactions and resulting stabilized the lowest unoccupied molecular orbital level of o-DPP-F-PhCN led to a relatively low open-circuit voltage.
Synthesis and photovoltaic properties of a new thiophene-cyclopentadiene-based conjugated polymer.
Lim, Eunhee,Lee, Sungkoo,Lee, Kyeong K American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.5
<P>A new low-band gap polymer containing thiophene and cyclopentadiene, poly(5,2,2'-dioctyldithio-phenylcyclopentadiene) (PDTCP), has been synthesized via the FeCl3 oxidative polymerization. PDTCP showed a broad absorption band and a low energy band gap of 1.82 eV. The photoluminescence (PL) of PDTCP is completely quenched upon addition of PCBM indicative of efficient charge transfer. Bulk heterojunction organic photovoltaic cells (OPVs) fabricated from PDTCP as an electron donor showed an open-circuit voltage (V(OC)) of 0.50 V, a short-circuit current (J(SC)) of 1.24 mA/cm2, and the power conversion efficiency of up to 0.20% under AM 1.5 (100 mW/cm2).</P>