Browsing by Author "Lin, Jiann T."

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Benzimidazole/Pyridoimidazole-Based Organic Sensitizers for High-Performance Dye-Sensitized Solar Cells
(2017-05-04)
Chaurasia, Sumit
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Li, Chun-Ting
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Desta, Mulu Berhe
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Ni, Jen-Shyang
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Lin, Jiann T.
A new series of benzimidazole (BIm)-based dyes (SC32 and SC33) and pyridoimidazole-(PIm) based dyes (SC35, SC36N and SC36) were synthesized as sensitizers for dye-sensitized solar cells (DSSCs). The N-substituent and C-substituent at the BIm and PIm cores were found to be the dominating factor in determining the electronic properties of the dyes and their DSSCs performance. The efficiency of BIm-based dyes (SC35 and SC36) was found to be higher than that of the PIm-based dyes (SC32 and SC33) due to better light harvesting. The C-substituents in SC36, a 4-hexylloxybenzene and a hexyl chain, are beneficial to dark current suppression, and hence SC36 achieves the best efficiency of 7.38% (approximate to 85% of N719). The two BIm dyes have better cell efficiencies than their congeners with a bithiophene entity between the BIm and the anchor due to better light harvesting of the former.
Dibenzo[f,h]thieno[3,4-b] quinoxaline-fullerene heterojunction bilayer solar cells with complementary spectrum coverage
(2010-10-01)
Kekuda, Dhananjaya
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Huang, Jen-Shien
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Velusamy, Marappan
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Lin, Jiann T.
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Chu, Chih-Wei
In the present article, potential of a bilayer organic solar cell has been investigated. We utilize newly synthesized small molecules, namely dibenzo[f,h]thieno[3,4-b]quinoxaline as electron donors for solar cells in heterojunction bilayer configuration. These small molecules with a narrow absorption band in the range 400-450 nm provide a complementary spectrum for the fullerene C(70), thereby leading to an overall power conversion efficiency of 2.6 +/- 0.2% under 100 mW/cm(2) incident radiation. Thermal annealing seems to impact the charge separation at the donor-acceptor interface, which eventually affects device performance. This work demonstrates that carefully optimized bilayer devices are comparable to the bulk heterojunction counterparts. (C) 2010 Elsevier B.V. All rights reserved.
Dibenzothiophene/oxide and quinoxaline/pyrazine derivatives serving as electron-transport materials
(2006-07-21)
Huang, Tai-Hsiang
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Whang, Wha-Tzong
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Shen, Jiun Yi
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Wen, Yuh-Sheng
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Lin, Jiann T.
A series of 2,8-disubstituted dibenzothiophene and 2,8-disubstituted dibenzothiophene-SS-dioxide derivatives containing quinoxaline and pyrazine moieties are synthesized via three key steps: i) palladium-catalyzed Sonogashira coupling reaction to form dialkynes; ii) conversion of the dialkynes to diones; and iii) condensation of the diones with diamines. Single-crystal characterization of 2,8-di(6,7-dimethyl-3-phenyl-2-quinoxalinyl)-5H-5 lambda(6)-dibenzo[b,d]thiophene-5,5-dione indicates a triclinic crystal structure with space group P1 and a non-coplanar structure. These new materials are amorphous, with glass-transition temperatures ranging from 132 to 194 degrees C. The compounds (Cpd) exhibit high electron mobilities and serve as effective electron-transport materials for organic light-emitting devices. Double-layer devices are fabricated with the structure indium tin oxide (ITO)/Qn/Cpd/LiF/Al, where yellow-emitting 2,3-bis[4-(N-phenyl-9-ethyl-3-carbazolylamino)phenyl]quinoxaline (Qn) serves as the emitting layer. An external quantum efficiency of 1.41 %, a power efficiency of 4.94 lm W-1, and a current efficiency of 1.62 cd A(-1) are achieved at a current density of 100 mA cm(-2).
Electroluminescent main-chain copolymers containing phosphorescent benzimidazole-based iridium complexes as copolymerization backbone units or dopants
(2010-06-01)
Huang, Wei-Sheng
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Wu, Ying-Hsien
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Lin, Hong-Cheu
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Lin, Jiann T.
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材料科學與工程學系
A series of novel electroluminescent main-chain copolymers containing fluorene-1,4-bis(9-octyl-9H-carbarzol-3yl)-2,5-dioctyloxy-benzene (BCB) segments and phosphorescent benzimidazole-based iridium (Ir) complexes in the backbones were synthesized by Suzuki coupling reaction. The relative intensity of phosphorescence and fluorescence were affected by the energy transfer and back transfer efficiencies between the polymer backbones and the iridium units as evidenced by solid state PL and EL spectra. PLED devices with a configuration of TTO/PEDOT: PSS (70 nm)/Ir-copolymers (P3-P10) or Ir-doped copolymers (P1-P2 doped with Ir-complex 4) (60-80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm) were fabricated, where electroluminescence (EL) efficiencies depended on the chemical constituents and the triplet energies of the copolymers. PLED devices based on Ir-containing copolymer P8 or copolymer P2 doped with 5 mol% Ir-complex 4 exhibited white-light emissions with EL properties of eta(ext,max) = 0.93%, eta(c,max) = 1.88 cd A(-1), and L(max) = 1960 cd m(-2) from the former (P8), and eta(ext,max) = 4.09%, eta(c,max) = 10.94 cd A(-1), and L(max) = 4870 cd m(-2) from the latter (P2 doped with Ir-complex 4), respectively. The CIE coordinates, color-rendering index (CRI) and correlated color temperature (CCT) of the two PLED devices were (0.33, 0.30) at 13 V, 74 and 5966 K for the former, and (0.35, 0.32) at 15 V, 82 and 6147 K for the latter, respectively.
Green phosphorescent iridium dendrimers containing dendronized benzoimidazole-based ligands for OLEDs
(2008-10-01)
Huang, Wei-Sheng
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Lin, Jiann T.
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Lin, Hong-Cheu
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材料科學與工程學系
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Department of Materials Science and Engineering
A series of novel non-conjugated functionalized benzoimidazole-based dendrimers containing peripheral benzyl ether type dendrons have been synthesized and characterized. These compounds undergo cyclometalation with iridium trichloride to form iridium(III) complexes. The emission wavelengths of these dendrimers are in the range from 510 to 530 nm, and the photoluminescence quantum yields (PLQYs) in the range from 0.45 to 0.80. Dendrimers (Gn)(2)Ir(acac) and (Gn)(3)Ir exhibit a reversible one-electron oxidation wave at similar to 0.55 V and similar to 0.37 V (vs. Ag/AgNO3), respectively. With a device configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid)/4, 4'-bis(N-carbarzolyl)biphenyl:(G2)(3)Ir 20 wt% dopant/1,3,5-tris(2-N-phenyl-benzoimidazolyl)benzene/LiF/Al has a maximum external quantum efficiency (EQE) of 17.6% and a maximum current efficiency of 61.5 cd/A. (C) 2008 Elsevier B.V. All rights reserved.
Highly branched green phosphorescent tris-cyclometalated iridium(III) complexes for solution-processed organic light-emitting diodes
(2009-07-01)
Huang, Wei-Sheng
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Lin, Chia-Wei
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Lin, Jiann T.
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Huang, Jen-Hsien
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Chu, Chih-Wei
A series benzoimidazole-based dendritric complexes of iridium dendrimers containing Frechet-type dendrons with peripheral fluorenyl surface groups have been synthesized. These iridium dendrimers are green-emitting with high phosphorescence quantum yield, and can be spin-coated as films of good quality. From cyclic voltammograms (CV), high onset potentials at 1.42-1.58 V due to the peripheral fluorene group were observed. Device from a second generation dendrimer 17 with structure of ITO/PEDOT:PSS/CBP: 20 wt% 17/TPBI/LiF/Al (PEDOT:PSS = poly(ethylene dioxythiophene): polystyrenesulfonate and CBP = bis(N-carbazolyl)biphenyl) has the best performance: maximum external quantum efficiency of 13.58% and maximum current efficiency of 45.7 cd/A. Space-charge-limited current (SCLC) flow technique was used to measure the mobility of charge carriers in the blend films of the compounds in CBP. Blend films of higher generation dendrimers have lower hole mobility, albeit with higher device efficiencies. (C) 2009 Elsevier B.V. All rights reserved.
Pyrazine-incorporating panchromatic sensitizers for dye sensitized solar cells under one sun and dimlight
(2018-07-28)
Desta, Mulu Berhe
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Vinh, Nguyen Son
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Kumar, Ch. Pavan
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Chaurasia, Sumit
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Wu, Wei-Ti
New D-A--A type (D = electron donor, A = auxiliary acceptor, = -conjugated bridge, and A = electron acceptor/anchor) sensitizers with two bis(alkoxy)phenyl substituents incorporating thieno[3,4-b]pyrazines (TP) or a benzo[3,4-b]pyrazine (BP) entity as the auxiliary acceptor have been synthesized for application in dye-sensitized solar cells (DSSCs). Under 1 sun illumination, the DSSCs fabricated from the two BP dyes with a co-adsorbent have efficiencies of 8.39% and 9.03%, respectively. The latter surpasses that of the standard N719 dye (8.87%). Under dim light conditions MD7 exhibited a power conversion efficiency of 18.95% and 27.17% under 300 lux and 6000 lux irradiance, respectively.
Reversed Y-shape di-anchoring sensitizers for dye sensitized solar cells based on benzimidazole core
(2017-05-01)
Desta, Mulu Berhe
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Chaurasia, Sumit
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Lin, Jiann T.
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應用化學系
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Department of Applied Chemistry
Three new Y-shaped D-(pi-A)(2) di-anchoring organic dyes comprising an arylamine as the electron donor, 2-cyanoacrylic acid as electron acceptors and various 2,4,7-trisubstituted benzimidazole entity as theirlinkers/spacers, have been synthesized for dye-sensitized solar cells. The new dyes MD2 and MD3 show red-shifted absorption in solution spectra when compared with their congeners (8b and 9b) without electron-donating hexyloxy substituents. The N-alkyl at the benzimidazble, though helps with improved solubility, apparently results in serious twist between the benzimidazole core and the neighboring thienyl rings in the conjugated segment connected to the acceptor facing the N-alkyl or the phenyl ring connected to the arylamine donor. Photophysical and electrochemical measurements as well as theoretical computations were carried out on the new dyes. In addition to current voltage scan and incident photon to electron conversion efficiency (IPCE), electrochemical impedance spectroscopic (EIS) studies were also conducted. The dye MD3 exhibited the highest light-to-electric energy conversion efficiencies of 6.45% and 6.69%, respectively, for DSSCs without and with CDCA co-adsorbent. Better cell performance of MD3 than 9b can be attributed to better light harvesting and better dark current suppression of the former. (C) 2017 Elsevier Ltd. All rights reserved.
Synthesis, characterization, and photophysics of electroluminescent fluorene/dibenzothiophene- and fluorene/dibenzothiophene-S,S-dioxide-based main-chain copolymers bearing benzimidazole-based iridium complexes as backbones or dopants
(2009-11-27)
Huang, Wei-Sheng
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Wu, Ying-Hsien
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Hsu, Ying-Chan
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Lin, Hong-Cheu
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Lin, Jiann T.
A series of electroluminescent copolymers containing fluorene-2,8-disubstituted dibenzothiophene (PFD), fluorene-2,8-disubstituted dibenzothiophene-SS-dioxide (PFDo) and phosphorescent benzimidazole-based iridium (Ir) complexes in the backbones were synthesized by the Suzuki coupling reaction. The thermal stabilities, HOMO/LUMO levels and triplet energy gap (ET) values were enhanced with increasing contents of dibenzothiophene ( D) or dibenzothiophene-S,S-dioxide (Do) segments in the copolymers. The relative intensities of phosphorescence and fluorescence were affected by the energy transfer and back transfer efficiencies between the polymer backbones and iridium units as evidenced by solid state PL and EL spectra. PLED devices with a configuration of ITO/PEDOT:PSS (50 nm)/metal-free copolymers (P1-P5), Ir-copolymers (P7-P13) and Ir-doped copolymers (P3 doped with Ir-complexes 6 and 8) (60-80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm) were fabricated, and the electroluminescence (EL) efficiencies depended on the chemical constituents and triplet energies of the copolymers. The space-charge-limited current (SCLC) flow technique was used to measure the charge carrier mobilities of these copolymers, where both hole and electron mobilities were in the following order: the metal-free copolymers (P2, P3 and P5) > Ir-doped copolymers (P3+3 or 10 mol% Ir-complex 6) > Ir-copolymers (P7, P8, P12 and P13). (C) 2009 Elsevier Ltd. All rights reserved.