Browsing by Author "Lan, Shang-Che"

Now showing 1 - 9 of 9

Benzooxadiazole-based donor/acceptor copolymers imparting bulk-heterojunction solar cells with high open-circuit voltages
(2013-01-08)
Jiang, Jian-Ming
;
Yang, Po-An
;
Lan, Shang-Che
;
Yu, Chia-Ming
;
Wei, Kung-Hwa
In this study we used Suzuki cross-coupling to synthesize three new donor/acceptor copolymers-PFTBO, PAF1130, and PCTBO-featuring soluble alkoxy-modified 2,1,3-benzooxadiazole (BO) moieties as acceptor units and electron-rich building blocks-dialkyl fluorene (F), alkylidene fluorene (AF), and carbazole (C), respectively-as donor units. These polymers, which we characterized using gel permeation chromatography, thermogravimetric analysis, NMR spectroscopy, UV-Vis absorption spectroscopy, and electrochemical cyclic voltammetry, exhibited good solubility, low-lying energy levels for their highest occupied molecular orbitals, excellent thermal stability, and air stability. Using these polymers, we fabricated bulk-heterojunction solar cell devices having the structure indium tin oxide/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/polymer:[6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) (1:1, w/w)/Ca/Al. Under AM 1.5G illumination (100 mW cm(-2)), the solar cell incorporating PFTBO exhibited a high value of V-OC of 1.04 V and that based on PCTBO provided a power conversion efficiency of 4.1% without the need for any post treatment. (C) 2012 Elsevier Ltd. All rights reserved.
Conjugated random copolymers of benzodithiophene-benzooxadiazole-diketopyrrolopyrrole with full visible light absorption for bulk heterojunction solar cells
(2013)
Jiang, Jian-Ming
;
Chen, Hsiu-Cheng
;
Lin, His-Kuei
;
Yu, Chia-Ming
;
Lan, Shang-Che
We have used Stille coupling polymerization to synthesize a series of new donor-acceptor (D-A) conjugated random copolymers-PBDTT-BO-DPP-that comprise electron-rich alkylthienyl-substituted benzodithiophene (BDTT) units in conjugation with electron-deficient 2,1,3-benzooxadiazole (BO) and diketopyrrolopyrrole (DPP) moieties that have complementary light absorption behavior. These polymers exhibited excellent thermal stability with thermal degrading temperatures higher than 340 degrees C. Each of these copolymers exhibited (i) broad visible light absorption from 400 to 900 nm and (ii) a low optical band gap that is smaller than 1.4 eV and a low-lying highest occupied molecular orbital that is deeper than -5.22 eV. As a result, bulk heterojunction photovoltaic devices derived from these polymers and fullerenes provided a high short-circuit current density that is larger than 12 mA cm(-2). In particular, a photovoltaic device prepared from the PBDTT-BO-DPP (molar ratio, 1 : 0.5 : 0.5)/PC71BM (w/w, 1 : 2) blend system with 1-chloronaphthalene (1 volume%) as an additive exhibited excellent photovoltaic performance, with a value of V-oc of 0.73 V, a high short-circuit current density of 17 mA cm(-2), a fill factor of 0.55, and a promising power conversion efficiency of 6.8%, indicating that complementary light-absorption random polymer structures have great potential for increasing the photocurrent in bulk heterojunction photovoltaic devices.
Organic photovoltaics
(2012-12-01)
Su, Yu-Wei
;
Lan, Shang-Che
;
Wei, Kung-Hwa
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In the last ten years, the highest efficiency obtained from organic photovoltaics (OPVs), such as bulk heterojunction polymer: fullerene solar cells, has risen from 2.5 to 11 %. This rapid progress suggests that the commercialization of OPVs should be realized soon if we can solve some technical issues. The advances in the development of OPVs can be attributed to four fronts: (i) a better understanding of the mechanism of photon-to-electron conversion; (ii) new materials with tailored energy levels and solubility; (iii) new processing approaches to induce optimal microstructures in the active layer; and (iv) new device architectures with novel interfacial layers. Herein, we review the materials, the microstructures of the active layers, the device structures, the interfacial layers that have been developed recently for OPVs, and provide future perspectives for this promising technology.
Side chain structure affects the molecular packing and photovoltaic performance of oligothiophene-based solution-processable small molecules
(2015-01-01)
Lan, Shang-Che
;
Chang, Chiao-Kai
;
Lu, Yueh-Hsin
;
Lin, Shu-Wei
;
Jen, Alex K. -Y.
In this study we synthesized a series of solution-processable small molecules comprising 2,2'-bithiophene (BTh), terthiophene (TTh), and thiobarbituric acid (TB) units as the central core, pi-conjugated spacer, and acceptor end-capping moieties, respectively, but with alkyl side-chains of different lengths presented from their central BTh units (TBTThBTh-H, TBTThBTh-C4, TBTThBTh-C8, TBTThBTh-C12). We then investigated the structure-property relationships of these compounds in terms of their packing behaviors and bulk heterojunction (BHJ) photovoltaic properties. And we found that the packing of these molecules in neat films is critically dependent of their side-chain lengths, as evidenced by the variations in their lamellar structures determined with grazing-incidence wide-angle X-ray scattering (GIWAXS). The power conversion efficiencies (PCEs) of the photovoltaic BHJ devices comprising these small molecules and PC61BM exhibited zigzag-shaped variations with respect to the alkyl side-chain lengths, with the PCE of devices incorporating TBTThBTh-H and TBTThBTh-C8 being higher than those of devices incorporating TBTThBTh-C4 and TBTThBTh-C12. Using GIWAXS to probe the molecular packing in the BHJ active layers, we found that the alkyl chain lengths of the small molecules had a large impact on the formation of crystallites in the BHJ films; the molecules with more uniform and shorter alkyl side-chain lengths provide stronger intermolecular interactions, being more favorable for the crystallization of these molecules.
Side Chain Structure Affects the Photovoltaic Performance of Two-Dimensional Conjugated Polymers
(2014-01-14)
Jiang, Jian-Ming
;
Lin, His-Kuei
;
Lin, Yu-Che
;
Chen, Hsiu-Cheng
;
Lan, Shang-Che
We used Stille coupling of electron-rich benzo[1,2-b:4,5-b']dithiophene (BDT) presenting conjugated alkylthiophene (T), alkylphenyl (P), or alkylfuran (F) side chains with electron-deficient alkoxy-modified 2,1,3-benzooxadiazole (BO) moieties to obtain a series of two-dimensional, conjugated, D-pi-A polymers (PBDTTBO, PBDTPBO, and PBDTFBO). The side chains of the BDT units altered the solubility, conformations, and electronic properties of the synthesized conjugated, polymers, allowing tuning of their photovoltaic properties when blended with fullerenes. Density functional theory calculations revealed that the presence of these side chain groups on the BDT donor units affected the torsion angles between the side chain groups and the conjugated main chains but resulted in only slightly different energy levels for the highest occupied molecular orbitals for these polymers, consistent with results obtained experimentally using cyclic voltammetry. These polymers displayed excellent thermal stabilities (5 wt % degradation temperatures: >330 degrees C) and broad spectral absorptions (from 450 to 700 nm). Transmission electron microscopy images revealed that the morphologies of active layers comprising these two-dimensional conjugated polymers and the fullerene derivative PC71BM did, however, vary substantially depending on the structure of the side chains that affects the solubility of the polymers. As a result, the efficiencies of photovoltaic devices incorporating PBDTFBO, PBDTPBO, or PBDTTBO polymers and PC71BM varied greatly, from 3.6 to 5.9%. When using 1-chloronaphthalene (1 vol %) or 1,8-diiodooctane (1 vol %) as an additive for processing the active layer, the power conversion efficiencies (PCEs) of photovoltaic devices incorporating blends of PBDTFBO, PBDTPBO, or PBDTTBO and PC71BM (1:2) improved to 5.4, 6.4, and 7.4%, respectively, due to their optimized morphologies, with the PCE of 7.4% being among the highest values reported for conjugated polymers involving BO moieties. Thus, the photovoltaic properties of these conjugated polymers were highly tunable through slight modifications of their side chain structures.
Side-Chain-Bulk Effects on the Molecular Packing and Photovoltaic Performance of Benzotrithiophene-Benzooxadiazole Conjugated Copolymers
(2015-04-27)
Lan, Shang-Che
;
Chang, Chiao-Kai
;
Wang, Yi-Chien
;
Wei, Kung-Hwa
;
材料科學與工程學系
Two alternating donor-acceptor conjugated polymers, PBTTBO-C13C11 and PBTTBO-C13C8, comprising 5-alkylbenzo[1,2-b:3,4-b:5,6-d]trithiophene (BTT) as the donor and 4,7-bis(4-dodecylthien-2-yl)benzo[1,2,5]oxadiazole (BO) as the acceptor, with different alkyl side-chain architectures on their BTT units are synthesized, and their bulk heterojunction photovoltaic properties when blended with the fullerene PC71BM are characterized. Even a slight change in the length of the alkyl chain of the BTT units influences the steric bulk to such a degree that it substantially affects the molecular packing of the polymers and the performance of their photovoltaic devices. The bulkier side chains of the polymer PBTTBO-C13C11 not only prevent its crystallization, but also suppress its light-absorption coefficient relative to that of PBTTBO-C13C8, as evidenced by X-ray diffraction and UV/Vis absorption studies, presumably because of weakened intermolecular interactions. Moreover, the polymer bearing bulkier side chains, PBTTBO-C13C11, is less miscible with PC71BM than PBTTBO-C13C8, and this characteristic determines the morphology of their annealed blended films, as shown by TEM studies. The best efficiency is obtained with a device containing an annealed PBTTBO-C13C8/PC71BM (1/2 w/w) active layer that was maintained at 120 degrees C for 10 min, which shows a power conversion efficiency of 6.2%, an open-circuit voltage of 0.75 V, a short-circuit current density of 12.6 mAcm(-2), and a fill factor of 66%.
Symmetry and Coplanarity of Organic Molecules Affect their Packing and Photovoltaic Properties in Solution-Processed Solar Cells
(2014-06-25)
Lan, Shang-Che
;
Raghunath, Putikam
;
Lu, Yueh-Hsin
;
Wang, Yi-Chien
;
Lin, Shu-Wei
In this study we synthesized three acceptor donor acceptor (A-D-A) organic molecules, TB3t-BT, TB3t-BTT, and TB3t-BDT, comprising 2,2\'-bithiophene (BT), benzo[1,2-b:3,4-b\':5,6-d \'\']trithiophene (BTT), and benzo[ 1,2-b;4,5-b\']dithiophene (BDT) units, respectively, as central cores (donors), terthiophene (3t) as pi-conjugated spacers, and thiobarbituric acid (TB) units as acceptors. These molecules display different degrees of coplanarity as evidenced by the differences in dihedral angles calculated from density functional theory. By using differential scanning calorimetry and X-ray diffractions for probing their crystallization characteristics and molecular packing in active layers, we found that the symmetry and coplanarity of molecules would significantly affect the melting/crystallization behavior and the formation of crystalline domains in the blend film with fullerene, PC61BM. TB3t-BT and TB3t-BDT, which each possess an inversion center and display high crystallinity in their pristine state, but they have different driving forces in crystallization, presumably because of different degrees of coplanarity. On the other hand, the asymmetrical TB3t-BTT behaved as an amorphous material even though it possesses a coplanar structure. Among our tested systems, the device comprising as-spun TB3t-BDT/PC61BM (6:4, w/w) active layer featured crystalline domains and displayed the highest power conversion efficiency (PCE) of 4.1%. In contrast, the as-spun TB3t-BT/PC61BM (6:4, w/w) active layer showed well-mixed morphology and with a device PCE of 0.2%; it increased to 3.9% after annealing the active layer at 150 degrees C for 15 min. As for TB3t-BTT, it required a higher content of fullerene in the TB3t-BTT/PC61BM (4:6, w/w) active layer to optimize its device PCE to 1.6%.
Synthesis and Characterization of a Narrow-Bandgap Polymer Containing Alternating Cyclopentadithiophene and Diketo-Pyrrolo-Pyrrole Units for Solar Cell Applications
(2010-04-01)
Chen, Guan-Yu
;
Chiang, Chien-Ming
;
Kekuda, Dhananjay
;
Lan, Shang-Che
;
Chu, Chih-Wei
We have synthesized a narrow-bandgap conjugated polymer (PCTDPP) containing alternating cyclopentadithiophene (CT) and diketo-pyrrolo-pyrrole (DPP) units by Suzuki coupling. This PCTDPP exhibits a low band gap of 1.31 eV and a broad absorption band from 350 to 1000 nm, which allows it to absorb more available photons from sunlight. A bulk hetero-junction polymer solar cell incorporating PCTDPP and C(70) at a blend ratio of 1:3 exhibited a high short-circuit current of 10.87 mA/cm(2) and a power conversion efficiency of 2.27%. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1669-1675,2010
Thiophene spacers impart crystallinity and enhance the efficiency of benzotrithiophene-based conjugated polymers for bulk heterojunction photovoltaics
(2013)
Lan, Shang-Che
;
Yang, Po-An
;
Zhu, Meng-Jie
;
Yu, Chia-Min
;
Jiang, Jian-Ming
In this study we synthesized the donor-acceptor conjugated copolymers PBTT4BT and PBTT4BO featuring benzotrithiophene (BTT) units as donors and benzothiadiazole (BT) and benzoxadiazole (BO) units, respectively, as acceptors, linked through 4-dodecylthiophene spacers. The presence of the spacer units enhanced not only the solubility of the synthesized polymers but also their molecular packing in the solid state; both of these polymers exhibited good crystallinity, as evidenced by a d-spacing of 23.8 angstrom in the (100) plane in their X-ray diffraction curves. When we used these synthesized polymers in bulk heterojunction photovoltaic device applications, the optimal device incorporating PBTT4BO/PC61BM as the active layer exhibited a low efficiency of 3.2%, due to the poor solubility of PBTT4BO, whereas the optimal device incorporating the more-soluble PBTT4BT and PC71BM displayed an efficiency of 4.4%, which is substantially 1.5% higher than that for the PBTTBT/PC71BM device, where PBTTBT was formed by copolymerizing BTT and BT units without any spacer. After thermal annealing, the efficiency of the PBTT4BT/PC71BM device improved further to 5.6%, with a V-OC value of 0.72 V, a J(SC) value of 11.58 mA cm(-2) and a fill factor of 67%. The annealed PBTT4BT/PC71BM active layer possessed a nanoscaled network-like morphology with rod-like PBTT4BT domains that were beneficial for charge separation and transport; accordingly, the power conversion efficiency of the annealed PBTT4BT/PC71BM photovoltaic device was enhanced greatly over that of the as-cast PBTT4BT/PC71BM device.