- A comparative study of the effect of fluorine substitution on the photovoltaic performance of benzothiadiazole-based copolymers
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Two conjugated alternating copolymers to be used as the donor materials of the active layers in polymer solar cells have been designed and synthesized via a Stille coupling reaction. The alternating structure consisted of 4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene (BDT) as the donor unit and benzo[c][1,2,5]thiadiazole (BT) or fluorinated benzo[c][1,2,5]thiadiazole (FBT) as the acceptor unit, along with a thiophene group as the π-bridge between the donor and acceptor units. Since the donor units have attached alkoxy pendant chains, both polymers were soluble in common organic solvents. UV-vis spectra of both copolymers exhibited broad absorption bands in the range of 325-900 and 380-900 nm, respectively, and corresponding low band gaps of 1.82 and 1.80 eV. After fluorination of the BT unit, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the polymer were lowered and estimated to be -5.51 and -3.71 eV, respectively. It was found that substitution of an F atom into the BT units facilitated the intramolecular charge transfer. In comparison with the nonfluorinated polymer, the photovoltaic performance of the fluorinated polymer was significantly improved due to the enhanced Jsc and Voc. Based on the ITO/PEDOT:PSS/polymer:PC61BM/LiF/Al device structure, the optimal device efficiency was obtained from a device with a blend of PBDTFBT and PC61BM at a weight ratio of 1:1. For this blend ratio, the values of Jsc and power conversion efficiency (PCE) obtained at room temperature are 7.98 mA cm-2 and 3.62%, respectively, under the illumination of AM 1.5 (100 mW cm-2).
- Wang, Tzong-Liu,Yang, Chien-Hsin,Chuang, Yao-Yuan
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- Molecular-level architectural design using benzothiadiazole-based polymers for photovoltaic applications
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A series of low band gap, planar conjugated polymers, P1 (PFDTBT), P2 (PFDTDFBT) and P3 (PFDTTBT), based on fluorene and benzothiadiazole, was synthesized. The effect of fluorine substitution and fused aromatic spacers on the optoelectronic and photovoltaic performance was studied. The polymer, derived from dithienylated benzothiodiazole and fluorene, P1, exhibited a highest occupied molecular orbital (HOMO) energy level at -5.48 eV. Density functional theory (DFT) studies as well as experimental measurements suggested that upon substitution of the acceptor with fluorine, both the HOMO and lowest unoccupied molecular orbital (LUMO) energy levels of the resulting polymer, P2, were lowered, leading to a higher open circuit voltage and short circuit current with an overall improvement of more than 110% for the photovoltaic devices. Moreover, a decrease in the torsion angle between the units was also observed for the fluorinated polymer P2 due to the enhanced electrostatic interaction between the fluorine substituents and sulfur atoms, leading to a high hole mobility. The use of a fused π-bridge in polymer P3 for the enhancement of the planarity as compared to the P1 backbone was also studied. This enhanced planarity led to the highest observed mobility among the reported three polymers as well as to an improvement in the device efficiency by more than 40% for P3.
- Viswanathan, Vinila N.,Rao, Arun D.,Pandey, Upendra K.,Kesavan, Arul Varman,Ramamurthy, Praveen C.
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p. 863 - 873
(2017/06/21)
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- 5,6-Difluorobenzothiadiazole and silafluorene based conjugated polymers for organic photovoltaic cells
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To achieve 5,6-difluorobenzothiadiazole and 2,7-linked silafluorene based soluble conjugated polymers, flexible side chains were attached at different positions of the conjugated polymers. Three soluble polymers PSiF-D(OT)DFBT, PSiF-TTDFBT, and PDOSiF-DTDFBT were prepared and used as donor materials for polymer solar cells. PSiF-D(OT)DFBT exhibits a band gap of 2.06 eV with a deep HOMO of -5.64 eV. PSiF-TTDFBT shows a band gap of 1.75 eV with the HOMO of -5.23 eV. PDOSiF-DTDFBT is of a band gap of 1.86 eV with the HOMO level of -5.37 eV. Among these three polymers, PDOSiF-DTDFBT shows the highest field effect transistor (FET) hole mobility up to 3.31 × 10-2 cm2 V-1 s-1, PDOSiF-DTDFBT:PC71BM blend films show the highest SCLC mobility up to 5.10 × 10-4 cm2 V-1 s-1, and polymer solar cells (PSCs) with the blend of PDOSiF-DTDFBT:PC71BM (1:1, by weight) as the active layer gave a power conversion efficiency (PCE) of 4.03% with an open circuit voltage (V oc) of 0.73 V, a short circuit current (Jsc) of 8.55 mA cm-2, and a fill factor (FF) of 0.65. Our studies also reveal the structure-property relationship of 2,7-linked silafluorene and 5,6-difluorobenzothiadiazole based conjugated polymers.
- Li, Guangwu,Kang, Chong,Gong, Xue,Zhang, Jicheng,Li, Weiwei,Li, Cuihong,Dong, Huanli,Hu, Wenping,Bo, Zhishan
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p. 5116 - 5123
(2014/07/07)
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- Structural variation of donor-acceptor copolymers containing benzodithiophene with bithienyl substituents to achieve high open circuit voltage in bulk heterojunction solar cells
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Three new donor-acceptor copolymers P1, P2, and P3 were synthesized with benzodithiophene with bithienyl substituents as the donor and 5,6-difluorobenzo[c][1,2,5]thiadiazole, 4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole, and 5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole as the acceptors, respectively. The insertion of thiophene spacer between the donor and the acceptor broadened the absorption of the polymers P2 and P3 and resulted in a red shift of ～30 nm as compared to that of the polymer P1. However, the inclusion of fluorine atoms on the polymer had detrimental effects on the photovoltaic properties of the polymers. The synthesized donor-acceptor polymers were tested in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) acceptor. Polymer P2 gave a PCE of 3.52% with PC71BM in which the active layer was prepared in chloroform with 3% v/v 1,8-diiodooctane (DIO) additive. The effect of fluorine substitution and thiophene group insertion on the UV/Vis absorbance, photovoltaic performances, morphology, and charge carrier mobilities for the polymers are discussed.
- Kularatne, Ruvini S.,Taenzler, Ferdinand J.,Magurudeniya, Harsha D.,Du, Jia,Murphy, John W.,Sheina, Elena E.,Gnade, Bruce E.,Biewer, Michael C.,Stefan, Mihaela C.
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p. 15535 - 15543
(2013/12/04)
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- Facile synthesis of fluorine-substituted benzothiadiazole-based organic semiconductors and their use in solution-processed small-molecule organic solar cells
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A facile new protocol for the synthesis of iodinated derivatives of fluorinated benzothiadiazoles is demonstrated for the production of p-type semiconducting materials. The newly synthesized small-molecule compounds bis[TPA-diTh]-MonoF-BT and bis[TPA-diTh]-DiF-BT exhibited a power conversion efficiency of 2.95 % and a high open-circuit voltage of 0.85 V in solution-processed small-molecule organic solar cells. A facile new protocol was developed for synthesis of iodinated derivatives of fluorinated benzothiadiazoles as precursors for fluorine-substituted benzothiadiazole-based organic semiconductors 2 and 3, which exhibit enhanced intramolecular charge transfer compared to unfluorinated analogue 1 and hence improved photovoltaic performance in small-molecule organic solar cells (see figure). Copyright
- Cho, Nara,Ko, Jaejung,Song, Kihyung,Lee, Jae Kwan
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p. 11433 - 11439,7
(2012/12/12)
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- Facile synthesis of fluorine-substituted benzothiadiazole-based organic semiconductors and their use in solution-processed small-molecule organic solar cells
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A facile new protocol for the synthesis of iodinated derivatives of fluorinated benzothiadiazoles is demonstrated for the production of p-type semiconducting materials. The newly synthesized small-molecule compounds bis[TPA-diTh]-MonoF-BT and bis[TPA-diTh]-DiF-BT exhibited a power conversion efficiency of 2.95 % and a high open-circuit voltage of 0.85 V in solution-processed small-molecule organic solar cells. A facile new protocol was developed for synthesis of iodinated derivatives of fluorinated benzothiadiazoles as precursors for fluorine-substituted benzothiadiazole-based organic semiconductors 2 and 3, which exhibit enhanced intramolecular charge transfer compared to unfluorinated analogue 1 and hence improved photovoltaic performance in small-molecule organic solar cells (see figure). Copyright
- Cho, Nara,Song, Kihyung,Lee, Jae Kwan,Ko, Jaejung
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p. 11433 - 11439
(2013/01/14)
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- FLUORINATED MONOMERS, OLIGOMERS AND POLYMERS FOR USE IN ORGANIC ELECTRONIC DEVICES
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Compounds of Formula (I): (formula (I)) where: X1 and X2 are the same or different and each is independently Cl, Br, I, a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group; and, Y is O, S, Se,
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