Browsing by Author "Jiang, Jian-Ming"

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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.
Complementary solvent additives tune the orientation of polymer lamellae, reduce the sizes of aggregated fullerene domains, and enhance the performance of bulk heterojunction solar cells
(2014-01-01)
Liu, Chih-Ming
;
Su, Yu-Wei
;
Jiang, Jian-Ming
;
Chen, Hsiu-Cheng
;
Lin, Shu-Wei
In this study we employed 1-chloronaphthalene (CN) and 1,8-diiodooctane (DIO) as binary additives exhibiting complementarily preferential solubility for processing the crystalline conjugated polymer poly[bis(dodecyl)thiophene-dodecyl-thieno[3,4-c]pyrrole-4,6-dione] (PBTC12TPD) and the fullerene [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) in chloroform. Using synchrotron grazing-incidence small-/wide-angle X-ray scattering and transmission electron microscopy to analyse the structure of the PBTC12TPD-PC71BM blend films, we found that the binary additives with different volume ratios in the processing solvent allow us to tune the relative population of face-on to edge-on PBTC12TPD lamellae and the size of PC71BM clusters in the blend films; the sizes of the fractal-like PC71BM clusters and the aggregated domains of PC71BM clusters increased and decreased, respectively, upon increasing the amount of DIO, whereas the relative ratio of face-on to edge-on PBTC12TPD lamellae increased upon increasing the amount of CN. When fabricating the photovoltaic devices, the short-circuit current density of the devices with the PBTC12TPD-PC71BM active layer having been processed with the binary additives is higher than that of the device incorporating an active layer processed without any additive. As a result, the power conversion efficiency of a device incorporating an active layer of PBTC12TPD-PC71BM (1 : 1.5, w/w) processed with binary additives of 0.5% DIO and 1% CN in chloroform increased to 6.8% from a value of 4.9%, a relative increase of 40%, for the corresponding device containing the same active layer but processed without any additive.
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.
Crystalline donor-acceptor conjugated polymers for bulk heterojunction photovoltaics
(2013)
Jiang, Jian-Ming
;
Yuan, Mao-Chuan
;
Dinakaran, K.
;
Hariharan, A.
;
Wei, Kung-Hwa
Molecular engineering of conjugated polymers for tuning their energy bands is an important process in the quest for highly efficient bulk heterojunction (BHJ) polymer photovoltaic devices. One effective approach is to construct a conjugated polymer by conjugating two chemical units possessing different electron donating (donor) and accepting (acceptor) capabilities. Conjugated copolymers featuring donor-acceptor (D/A) subunits are promising materials for solar cell applications because of their tunable energy bands and solubility that can be tailored to the performances of the photovoltaic devices. Under proper processing conditions, the conjugated polymers with rigid and planar D/A segments can undergo self-assembly to form crystalline structures that improve charge carrier mobility and provide better resistance to the permeation of water and oxygen compared to amorphous polymers. Conjugated polymers with D/A structure have been investigated thoroughly over the last few years. In this highlight, we present an overview of recent developments in BHJ organic photovoltaics employing D/A crystalline copolymers as active layer materials for photon-to-electron conversion, with particular emphasis on crystalline D/A polymers featuring newly developed acceptor structures, including thieno [3,4-c]pyrrole-4,6-dione, diketo-pyrrole-pyrrole, bithiazole, thiazolothiazole and thieno[3,2-b]thiophene moieties, and conclude with future perspectives.
Crystalline Low-Band Gap Polymers Comprising Thiophene and 2,1,3-Benzooxadiazole Units for Bulk Heterojunction Solar Cells
(2011-12-13)
Jiang, Jian-Ming
;
Yang, Po-An
;
Hsieh, Tsung-Hsuan
;
Wei, Kung-Hwa
;
材料科學與工程學系
We have used Stille coupling polymerization to synthesize a series of new crystalline low band gap conjugated polymers-PTHBO, PBTTBO, and PTTTBO-constituting mainly electron-rich thiophene (TH), 2,2'-bithiophene (BT), and thieno[3,2-b]thiophene (TT) units in conjugation with electron-deficient 2,1,3-benzooxadiazole (BO) moieties. All of these polymers exhibited (i) sufficient energy offsets with respect to those of fullerenes to allow efficient charge transfer and (ii) low-lying highest occupied molecular orbital (HOMO, -5.47 eV). These polymers exhibited excellent thermal stability, high crystallinity, and broad spectral absorptions. As a result, bulk hetero-junction photovoltaic devices derived from these polymers and fullerenes provided open-circuit voltages (V(oc)) as high as 1.02 V. In particular, the photovoltaic device comprising the PTTTBO/PC(61)BM (1:1) blend system and 1,8-diiodooctane (DIO, 0.5 vol %) as an additive exhibited excellent performance, under AM 1.5 G irradiation (100 mW cm(-2)), with a value of V(oc) of 0.85 V, a short-circuit current density (J(sc)) of 11.6 mA cm(-2), a fill factor (FF) of 0.54, and a promising power conversion efficiency (PCE) of 5.3%.
Distribution of Crystalline Polymer and Fullerene Clusters in Both Horizontal and Vertical Directions of High-Efficiency Bulk Heterojunction Solar Cells
(2013-06-26)
Liu, Chih-Ming
;
Su, Ming-Shin
;
Jiang, Jian-Ming
;
Su, Yu-Wei
;
Su, Chun-Jen
In this study, we used (i) synchrotron grazing-incidence small-/wide-angle X-ray scattering to elucidate the crystallinity of the polymer PBTC12TPD and the sizes of the clusters of the fullerenes PC61BM and ThC61BM and (ii) transmission electron microscopy/electron energy loss spectroscopy to decipher both horizontal and vertical distributions of fullerenes in PBTC12TPD/fullerene films processed with chloroform, chlorobenzene and dichlorobezene. We found that the crystallinity of the polymer and the sizes along with the distributions of the fullerene clusters were critically dependent on the solubility of the polymer in the processing solvent when the solubility of fullerenes is much higher than that of the polymer in the solvent. In particular, with chloroform (CF) as the processing solvent, the polymer and fullerene units in the PBTC12TPD/ThC61BM layer not only give rise to higher crystallinity and a more uniform and finer fullerene cluster dispersion but also formed nanometer scale interpenetrating network structures and presented a gradient in the distribution of the fullerene clusters and polymer, with a higher polymer density near the anode and a higher fullerene density near the cathode. As a result of combined contributions from the enhanced polymer crystallinity, finer and more uniform fullerene dispersion and gradient distributions, both the short current density and the fill factor for the device incorporating the CF-processed active layer increase substantially over that of the device incorporating a dichlorobenzene-processed active layer; the resulting power conversion efficiency of the device incorporating the CF-processed active layer was enhanced by 46% relative to that of the device incorporating a dichlorobenzene-processed active layer.
Fluorene Conjugated Polymer/Nickel Oxide Nanocomposite Hole Transport Layer Enhances the Efficiency of Organic Photovoltaic Devices
(2017-01-25)
Chiou, Guan-Chiun
;
Lin, Ming-Wei
;
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.
Linear solubilizing side chain substituents enhance the photovoltaic properties of two-dimensional conjugated benzodithiophene-based polymers
(2015-11-19)
Jiang, Jian-Ming
;
Raghunath, Putikam
;
Lin, Yu-Che
;
Lin, Hsi-Kuei
;
Ko, Chen-Lin
In this study we synthesized medium-band gap, two-dimensional (2-D) conjugated polymers comprising electron-rich benzo[1,2-b:4,5-b\'] dithiophene (BDT) units presenting conjugated thiophene (T) side chains and electron-deficient alkoxy-modified 2,1,3-benzooxadiazole (BO) moieties. We introduced various solubilizing substituents-linear alkyl, alkoxy, and alkythio units-on the thiophene side chains to obtain a series of 2-D conjugated D-pi-A polymers: PBDTT-C-BO, PBDTT-O-BO, and PBDTT-S-BO. The solubilizing substituents of the BDT units altered the solubility, conformations, and electronic properties of the synthesized conjugated polymers, allowing tuning of the photovoltaic properties when blended with fullerenes. We investigated the effects of the different linear solubilizing substituents of the BDT units on the structural, optical, and electronic properties (e.g., band gap energies) of the resulting 2-D conjugated polymers, as determined from quantum-chemical calculations, UV-Vis absorption spectra, and grazing-incidence X-ray diffraction. Atomic force microscopy and transmission electron microscopy images revealed the morphologies of active layers comprising these 2-D conjugated polymers and the fullerene derivative [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM). Through rational structural modifications of the solubilizing substituents in the 2-D conjugated polymers with alkoxy, alkythio or alkyl units, the resulting PCEs varied from 5.4 to 7.5%. A polymer solar cell based on a blend of PBDTT-C-BO and PC71BM exhibited the best photovoltaic performance among our three studied systems, with a high short-circuit current density (J(sc)) of 15.7 mA cm(-2) and a power conversion efficiency of 7.5%, without the need for any processing additives or post-treatment processes, highlighting the importance of careful selection of appropriate solubilizing substituent that attached to the donor segments when designing efficient D-pi-A polymers for use in solar cells. (C) 2015 Elsevier Ltd. All rights reserved.
Location and Number of Selenium Atoms in Two-Dimensional Conjugated Polymers Affect Their Band-Gap Energies and Photovoltaic Performance
(2014-10-28)
Jiang, Jian-Ming
;
Raghunath, Putikam
;
Lin, Hsi-Kuei
;
Lin, Yu-Che
;
Lin, M. C.
We synthesized and characterized a series of novel two-dimensional Se-atom-substituted donor (D)-p-acceptor (A) conjugated polymersPBDTTTBO, PBDTTTBS, PBDTTSBO, PBDTSTBO, PBDTTSBS, PBDTSTBS, PBDTSSBO, and PBDTSSBSfeaturing benzodithiophene (BDT) as the donor, thiophene (T) as the p-bridge, and 2,1,3-benzooxadiazole (BO) as the acceptor with different number of Se atoms at different p-conjugated locations, including the pi-bridge, side chain, and electron-withdrawing units. We then systematically investigated the effect of different locations and the number of Se atoms in these two-dimensional conjugated polymers on the structural, optical, and electronics such as band-gap energies of the resulting polymers, as determined through quantum-chemical calculations, UVvis absorption spectra, and grazing-incidence X-ray diffraction. We found that through the rational structural modification of the 2-D conjugated Se-substituted polymers the resulting PCEs could vary over 3-fold (from 2.4 to 7.6%), highlighting the importance of careful selection of appropriate chemical structures such as the location of Se atoms when designing efficient D-p-A polymers for use in solar cells. Among these tested BO-containing polymers, PBDTSTBO that has moderate band gaps and good open-circuit voltages (up to 0.86 V) when mixed with PC71BM (1:2, w/w) provided the highest power conversion efficiency (7.6%) in a single-junction polymer solar cell, suggesting that these polymers have potential applicability as donor materials in the bulk heterojunction polymer solar cells.
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.
Solution-Processed Zinc Oxide/Polyethylenimine Nanocomposites as Tunable Electron Transport Layers for Highly Efficient Bulk Heterojunction Polymer Solar Cells
(2015-03-25)
Chen, Hsiu-Cheng
;
Lin, Shu-Wei
;
Jiang, Jian-Ming
;
Su, Yu-Wei
;
Wei, Kung-Hwa
In this study, we employed polyethylenimine-doped sol-gel-processed zinc oxide composites (ZnO:PEI) as efficient electron transport layers (ETL) for facilitating electron extraction in inverted polymer solar cells. Using ultraviolet photoelectron spectroscopy, synchrotron grazing-incidence small-angle X-ray scattering and transmission electron microscopy, we observed that ZnO:PEI composite films\' energy bands could be tuned considerably by varying the content of PEI up to 7 wt %-the conduction band ranged from 4.32 to 4.0 eV-and the structural order of ZnO in the ZnO:PEI thin films would be enhanced to align perpendicular to the ITO electrode, particularly at 7 wt % PEI, facilitating electron transport vertically. We then prepared two types of bulk heterojunction systems-based on poly(3-hexylthiophene) (P3HT):phenyl-C-61-butryric acid methyl ester (PC61BM) and benzo[1,2-b:4,5-b]dithiophene-thiophene-2,1,3-benzooxadiazole (PBDTTBO):phenyl-C-71-butryric acid methyl ester (PC71BM)-that incorporated the ZnO:PEI composite layers. When using a composite of ZnO:PEI (93:7, w/w) as the ETL, the power conversion efficiency (PCE) of the P3HT:PC61BM (1:1, w/w) device improved to 4.6% from a value of 3.7% for the corresponding device that incorporated pristine ZnO as the ETL-a relative increase of 24%. For the PBDTTBO:PC71BM (1:2, w/w) device featuring the same amount of PEI blended in the ETL, the PCE improved to 8.7% from a value of 7.3% for the corresponding device that featured pure ZnO as its ETL-a relative increase of 20%. Accordingly, ZnO:PEI composites can be effective ETLs within organic photovoltaics.
Structural Evolution of Crystalline Conjugated Polymer/Fullerene Domains from Solution to the Solid State in the Presence and Absence of an Additive
(2015-02-12)
Su, Yu-Wei
;
Liu, Chih-Ming
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Jiang, Jian-Ming
;
Tsao, Cheng-Si
;
Cha, Hou-Chin
The power conversion efficiencies of polymer/fullerene solar cells are critically dependent on the nanometer-scale morphologies of their active layers, which are typically processed from solution. Using synchrotron wide- and small-angle X-ray scattering, we have elucidated the intricate mechanism of the structural transitions from solutions to solid films of the crystalline polymer poly[bis(dodecyl)thiophene-thieno[3,4-c]pyrrole-4,6-dione] (PBTTPD) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM), including the effect of the solvent additive 1,6-diiodohexane (DIH). We found that the local assembly of rigid-rod PBTTPD segments that formed in solution instantly and then relaxed within several hundred seconds upon cooling to room temperature from 90 degrees C could re-emerge and develop into seeds for subsequent crystallization of the polymer in the solid films. At room temperature (25 degrees C), the presence of DIH in chlorobenzene slightly enhanced the formation of local assembly PBTTPD segments in the supersaturated PBTTPD in PBTTPD/PC71BM blend solution. Two cases of films were subsequently developed from these blend solutions with drop-casted and spin-coated methods. For spin-coated thin films (90 nm thick), which evolve quickly, polymers crystallinity and the fullerene packing in the solid-state thin films were enhanced in the case of involving DIH. Regarding the effect of DIH for processing the drop-casted thick films (2.5 mu m thick), which evolve slowly, DIH has no observable effect on PBTTPD/PC71BM structure. Our results provide some understanding of the mechanism behind the structural development of polymer/fullerene blends upon their transitions from solution to the solid state, as well as the key functions of the additive.
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, characterization, and photovoltaic properties of a low-bandgap copolymer based on 2,1,3-benzooxadiazole
(2011-01-01)
Jiang, Jian-Ming
;
Yang, Po-An
;
Chen, Hsiu-Cheng
;
Wei, Kung-Hwa
;
材料科學與工程學系
PBDTBO, a conjugated polymer comprising benzo[1,2-b:4,5-b']dithiophene (BDT) and 5,6-bis(octyloxy) benzo[c][1,2,5]-oxadiazole (BO) units, exhibits a deep HOMO energy level of -5.27 eV and excellent solubility. A device incorporating PBDTBO and [6,6]-phenyl-C(61)-butyric acid methyl ester (1 : 1, w/w) exhibited a power conversion efficiency of 5.7%.
Synthesis, characterization, and photovoltaic properties of a low-bandgap copolymer based on 2,1,3-benzooxadiazole
(2011-01-01)
Jiang, Jian-Ming
;
Yang, Po-An
;
Chen, Hsiu-Cheng
;
Wei, Kung-Hwa
;
材料科學與工程學系
PBDTBO, a conjugated polymer comprising benzo[1,2-b:4,5-b']dithiophene (BDT) and 5,6-bis(octyloxy) benzo[c][1,2,5]-oxadiazole (BO) units, exhibits a deep HOMO energy level of -5.27 eV and excellent solubility. A device incorporating PBDTBO and [6,6]-phenyl-C(61)-butyric acid methyl ester (1 : 1, w/w) exhibited a power conversion efficiency of 5.7%.
The new low-band gap polymers comprising C-, Si-, or N-bridged dithiophene and alkoxy-modified 2,1,3-benzooxadiazole units for bulk heterojunction solar cells
(2012-10-01)
Jiang, Jian-Ming
;
Yang, Po-An
;
Yu, Chia-Ming
;
Lin, His-Kuei
;
Huang, Kuei-Chun
In this study, we used Stille coupling polymerization to synthesize a series of new low-band gap-conjugated polymersPCyTBO, PCySiTBO, and PCyNTBOcomprising mainly electron-rich C-, Si-, and N-bridged dithiophene units in conjugation with electron-deficient alkoxy-modified 2,1,3-benzooxadiazole moieties. The highest occupied molecular orbital energy levels of these polymers become higher as the electron-donating ability of C-, Si-, or N-bridged dithiophene units increases. These polymers also displayed excellent thermal stability and broad spectral absorptions, with PCySiTBO revealing some crystallinity. As a result, the photovoltaic device incorporating the PCySiTBO/PC71BM (1:1) blend system and 1,8-diiodooctane (2 vol %) as an additive exhibited excellent performance, under AM 1.5 G irradiation (100 mW cm-2), with a value of Voc of 0.64 V, a short-circuit current density of 13.8 mA cm-2, a fill factor of 0.57, and a promising power conversion efficiency of 5.0%. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
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.