Browsing by Author "Chang, Chiao-Kai"

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Fluorene Conjugated Polymer/Nickel Oxide Nanocomposite Hole Transport Layer Enhances the Efficiency of Organic Photovoltaic Devices
(2017-01-25)
Chiou, Guan-Chiun
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Lin, Ming-Wei
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Lai, Yu-Ling
;
Chang, Chiao-Kai
;
Jiang, Jian-Ming
A nanocomposite layer comprising the conjugated polymer poly[(9,9-bis(3\'(N,N-dimethylamino)propy1)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)fluorene] (PFN) and nickel oxide (NiOx) has been employed as the hole transport layer (HTL) in organic photovoltaics (OPVs) featuring PBDTTBO-C-8 and [6,6] -phenyl -C-71-butyric acid methyl ester (PC71BM) as the active layer. The optimal device incorporating the PFN:NiOx nanocomposite as the HTLs displayed a power conversion efficiency (PCE) to 6.2%, up from 4.5% for the corresponding device incorporating pristine NiOx as the HTL layer: a nearly 40% improvement in PCE. X-ray photoelectron spectroscopy (XPS) was used to determine the types of chemical bonding, ultraviolet photoelectron spectroscopy (UPS) to measure the change in work function, and atomic force microscopy (AFM) to examine the morphology of the composite layers. The growth of nickel trioxide, Ni2O3, in the PFN:NiOx layer played a key role in producing the p-doping effect and in tuning the work function, thereby improving the overall device performance.
Novel fluoride-substituted donor/acceptor polymers containing benzodithiophene and quinoxaline units for use in low-band gap solar cells
(2016-09)
Singh, Ashutosh
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Singh, Ravinder
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Lin, Chein-Min
;
Pola, Murali Krishna
;
Chang, Chiao-Kai
In this study we used Stille polycondensation to synthesize a series of low-band gap fluoride-substituted conjugated polymers containing electron-donating benzodithiophene (BDT) and electron-accepting quinoxaline (Qx) units, with the latter presenting either two or four fluoride atoms. These donor/acceptor polymers exhibited a broad absorption range (from 300 to 750 nm), with band gap energies of less than 1.20 eV (measured using cyclic voltammetry). Because of their strongly electron-donating thiophene units, the donor/acceptor polymers featuring the more highly fluorinated structures possessed the lowest band gaps (as low as 1.14 eV) and, thus, induced the greatest photovoltaic performance among these tested polymers. The highest power conversion efficiency (2.13%) was obtained from the polymer solar cell featuring an active layer of the polymer PTF2 blended with PC70BM (1:1.5, w/w), with a short-circuit current density, open circuit voltage, and fill factor of 8.7 mA cm(-2), 0.72 V, and 0.34, respectively. (C) 2016 Elsevier Ltd. All rights reserved.
Side chain structure affects the molecular packing and photovoltaic performance of oligothiophene-based solution-processable small molecules
(2015-01-01)
Lan, Shang-Che
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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
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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%.