- Correlation of intermolecular packing distance and crystallinity of D-A polymers according to π-spacer for polymer solar cells
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Donor–acceptor-type polymers, PBDPBT-T, PBDPBT-TT, and PBDPBT-biT, were polymerized via Stille coupling reactions. In the unfavorable mode of DFT calculations, the distance between BDP in the two different polymer main chains showed different distance of repeating unit (Dn) according to the π-spacers type. Especially, PBDPBT-TT caused larger D2 than PBDPBT-T and PBDPBT-biT. The UV–vis absorption spectra of PBDPBT-T and PBDPBT-biT films were red-shifted compared with the solution absorption, whereas that of a PBDPBT-TT film was blue-shifted. PBDPBT-T and PBDPBT-biT had high crystallinity and a tendency of face-on orientation. In contrast, PBDPBT-TT had low crystallinity. Owing to differences in packing formation, the polymers had different JSC values. When a polymer solar cell device was fabricated through a solution process, PBDPBT-biT (in a 1:1.5 ratio with PC70BM) exhibited a PCE of 4.50%, with a JSC value of 8.6?mA/cm2, a VOC value of 0.88?V, and an FF value of 59.4%.
- Lee, Tae Ho,Choi, Min Hee,Jeon, Sung Jae,Moon, Doo Kyung
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- A planar copolymer for high efficiency polymer solar cells
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(Graph Presented) An alternating copolymer, poly(2-(5-(5,6-bis(octyloxy)-4- (thiophen-2-yl)benzo[c][1,2,5] thiadiazol-7-yl)thiophen-2-yl)-9-octyl-9H- carbazole) (HXS-1), was designed, synthesized, and used as the donor material for high efficiency polymer
- Ruiping, Qin,Weiwei, Li,Cuihong, Li,Chun, Du,Veit, Clemens,Schleiermacher, Hans-Frieder,Andersson, Mattias,Zhishan, Bo,Zhengping, Liu,Inganaes, Olle,Wuerfel, Uli,Fengling, Zhang
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- Chain length dependence of the photovoltaic properties of monodisperse donor-acceptor oligomers as model compounds of polydisperse low band gap polymers
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Well-defined conjugated oligomers (Sn) containing from 1 to 8 units of a tricyclic building block involving a dioctyloxybenzothiadiazole unit with two thienyl side rings (S1) are synthesized by a bottom-up approach. UV-Vis absorption data of solutions show that chain extension produces a narrowing of the HOMO-LUMO gap (Δ E) to values slightly smaller than that of the parent polymer (P1). Plots of Δ E and of the band gap of films (E g) versus the reciprocal chain length show that Δ E and Eg converge towards a limit corresponding to an effective conjugation length (ECL) of 7-8 S1 units. UV-Vis absorption and photoluminescence data of solutions and solid films show that chain extension enhances the propensity to inter-chain aggregation. This conclusion is confirmed by GIXD analyses which reveal that the edge-on orientation of short-chain systems evolves toward a face-on orientation as chain length increases while the stacking distance decreases beyond 7 units. The results obtained on solution-processed BHJ solar cells show a progressive improvement of power conversion efficiency (PCE) with chain extension; however, the convergence limit of PCE remains inferior to that obtained with the polymer. These results are discussed with regard to the role of mono/ polydispersity and chain aggregation.
- Zhou, Cheng,Liang, Yamin,Liu, Feng,Sun, Chen,Huang, Xuelong,Xie, Zengqi,Huang, Fei,Roncali, Jean,Russell, Thomas P.,Cao, Yong
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- Synthesis and characterization of an anthracene-based low band gap polymer for photovoltaic devices
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We have synthesized an anthracene-based conjugated polymer, poly[(9,10-bis(oct-1-ynyl) anthracene)-alt-(5,6-bis(octyloxy)-4,7-bis(thiophen- 2-yl)benzo-[c][1,2,5]-thiadiazole)] (PANTBT), for application in organic photovoltaic devices. It exhibited a number average molecular weight of 14,300 g/mol and was fairly soluble in ch lilorinated organic solven ts due to flexible octynyl- and octy-loxy side chains on the P a nthracene and benzoth iadiazole moieties. P ANTBT showed absorption covering 300-660 nm. Through the bond alternation betwee ifn the electron-sufficient anthracene (and thiophene) and electron-deficient benzothiadiazole units, a band gap of PANTBT was decreased to 1.89 eV, showing a deep HOMO level of -5.31 eV. As a result, PANTBT exhibited promising photovoltaic properties with a PCE value of 1.90% (Voc = 0.77 V, Jsc = -6.50 mA/cm2, FF = 0.38) upon blending with PC71BM under AM 1.5G. Copyright
- Jung, In Hwan,Kim, Hoyeon,Lee, Wonho,Jung, Byung Jun,Woo, Han Young,Yoo, Seunghyup,Shim, Hong-Ku
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- Improved bulk-heterojunction polymer solar cell performance through optimization of the linker groupin donor-acceptor conjugated polymer
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Two donor-acceptor conjugated polymers PCTBTC8 and PCTTBTC12 have been prepared from Suzuki coupling reactions between the 2,7-carbazole and alkoxy substituted 2,1,3-benzothiadiazole units with two different linker groups thiophene and thieno[3,2-b] thiophene, respectively. The polymer PCTTBTC12 with the thieno thiophene linker group possessed a red-shifted UV-vis absorption spectrum and similar HOMO level in comparison with PCTBTC8. BHJ polymer solar cells were fabricated to investigate the photovoltaic properties of the two polymers and the polymer PCTTBTC12 showed superior device performance than PCTBTC8 with a significantly improved current density. In addition, the hole only devices tests results indicated that the hole mobility of the polymer was increased by replacing the thiophene group with fused thieno thiophene as the linker. The relationships between the device performance with the light absorption, energy levels, BHJ film morphology and hole mobility are discussed in details. And the improved photovoltaic property of the polymer PCTTBTC12 probably can be contributed to the better light absorption spectrum and enhanced hole transporting ability related to the more electron rich nature and planar structure of the thieno[3,2-b] thiophene group.
- Sun, Ying,Lin, Baoping,Yang, Hong,Gong, Xiaohui
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- Synthesis and characterization of highly soluble phenanthro[1,10,9,8-c,d,e,f,g]carbazole-based copolymer: Effects of thermal treatment on crystalline order and charge carrier mobility
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In this study, a novel donor-acceptor type semiconducting polymer was designed and synthesized based on phenanthro[1,10,9,8-c,d,e,f,g]carbazole backbone. The resulting polymer, poly[4-(5-(6-(2-decyltetradecyl)-6H-phenanthro[1,10,9,8-c,d,e,f,g]carbazol-4-yl)thiophen-2-yl)-5,6-bis(octyloxy)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole] (PPTBTT), exhibited high solubility in various solvents which enables facile fabrication of semiconducting devices such as thin-film transistors, and also opens up possibilities for large scale solution processing. Absorption spectra of PPTBTT showed large bathochromic shift when the polymer was prepared as a thin-film, which can be explained by the high solubility and molecular packing of the synthesized polymer. X-ray diffraction measurements showed that the crystalline structure of PPTBTT polymer film is largely influenced by the thermal treatment temperature. Together with the atomic force microscopy data, it was found that the optimal thermal treatment temperature of PPTBTT film is 170 °C. The charge transfer characteristics were confirmed by fabricating PPTBTT thin-film transistor. In accordance with the polycrystalline structure, PPTBTT film transistor showed the highest mobility of 0.0092 cm2 V?1 s?1 and on/off ratio of 104 when the device was annealed at 170 °C.
- Jeong, Nam Yeong,Jang, Min Su,Park, So Min,Chung, Dae Sung,Kim, Yun-Hi,Kwon, Soon-Ki
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- D-π-A-π-D type benzothiadiazole-triphenylamine based small molecules containing cyano on the π-bridge for solution-processed organic solar cells with high open-circuit voltage
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Two novel D-π-A-π-D structured small molecules composed of benzothiadiazole and triphenylamine were designed and synthesized. BDCTBT with cyano on the π-bridge exhibited a deep HOMO energy level, resulting in an impressive VOC of up to 1.04 V with a PCE of 3.85%, while non-cyano substituted BDETBT yielded a VOC of 0.94 V and a PCE of 1.99%.
- Zeng, Shaohang,Yin, Lunxiang,Ji, Changyan,Jiang, Xueying,Li, Kechang,Li, Yanqin,Wang, Yue
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p. 10627 - 10629
(2012/11/07)
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- Effects of π-conjugated bridges on photovoltaic properties of donor-π-acceptor conjugated copolymers
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A series of conjugated donor (D)-π-acceptor (A) copolymers, P(BDT-F-BT), P(BDT-T-BT), and P(BDT-TT-BT), based on benzodithiophene (BDT) donor unit and benzothiadiazole (BT) acceptor unit with different π-bridges, were designed and synthesized via a Pd-catalyzed Stille-coupling method. The π-bridges between the BDT donor unit and BT acceptor unit are furan (F) in P(BDT-F-BT), thiophene (T) in P(BDT-T-BT) and thieno[3,2-b]thiophene (TT) in P(BDT-TT-BT). It was found that the π-bridges significantly affect the molecular architecture and optoelectronic properties of the copolymers. With the π-bridge varied from furan to thiophene, then to thieno[3,2-b]thiophene, the shape of the molecular chains changed from z-shaped to almost straight line gradually. Band gaps of P(BDT-F-BT), P(BDT-T-BT) and P(BDT-TT-BT) were tuned from 1.96 to 1.82 to 1.78 eV with HOMO levels up-shifted from -5.44 to -5.35 to -5.21 eV, respectively. Bulk heterojunction solar cells with the polymers as donor and PC71BM as acceptor demonstrated power conversion efficiency varied from 2.81% for P(BDT-F-BT) to 3.72% for P(BDT-T-BT) and to 4.93% for P(BDT-TT-BT). Compared to furan and thiophene, thieno[3,2-b]thiophene π-bridge in the copolymers shows superior photovoltaic performance. The results indicate that the photovoltaic performance of some high efficiency D-A copolymers reported in literatures could be improved further by inserting suitable π-bridges.
- Wang, Xiaochen,Sun, Yeping,Chen, Song,Guo, Xia,Zhang, Maojie,Li, Xiaoyu,Li, Yongfang,Wang, Haiqiao
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p. 1208 - 1216
(2012/06/30)
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- Controlling blend film morphology by varying alkyl side chain in highly coplanar donor-acceptor copolymers for photovoltaic application
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A series of varied length alkyl substituted donor-acceptor (D-A) conjugated copolymers with benzo[1,2-b:4,5-b′]dithiophene (BDT) as donor and thiophene rings attached to both sides of the benzothiadiazole (TBT) moieties as acceptors were designed and synthesized. The optical and electrochemical properties showed that the absorption spectrum, the band gaps, and the energy levels of the copolymers were not affected by the varied substituted alkyls, and all these copolymers showed low band gaps around 1.75 eV. In addition, the morphologies of the blend film between copolymers and PCBM can be fine-tuned by increasing the length of substituted alkyl of the copolymers, changing from pea-like aggregation to interpenetrating network to grain-like aggregation. Bulk heterojunction photovoltaic devices were fabricated by using the copolymers as donors and (6,6)-phenyl C61-butyric acid methyl ester (PC 61BM) or (6,6)-phenyl C71-butyric acid methyl ester (PC71BM) as acceptors. The optimized photovoltaic performances showed the stable open-circuit voltage (Voc) in the range of 0.68 to 0.74 eV, and dramatically increasing short circuit current density (Jsc) by optimizing the blending morphologies of copolymer and PCBM films. The optimized photovoltaic performance with a Voc of 0.70 V, J sc of 7.19 mA/cm2, a fill factor (FF) of 0.52, and a power conversion efficiency (PCE) of 2.88%, was obtained by the copolymer PBDT-TBT-C8 (PBDT-TBT-C8:PC61BM, 1:3 w/w, in CB solution). This is due to its low band gap and interpenetrating network morphology of PBDT-TBT-C8:PC 61BM blend film. The photovoltaic device based on PBDT-TBT-C8:PC 71BM showed a Jsc of 8.6 mA/cm2 and a PCE of 3.15%.
- Li, Yaowen,Chen, Yujin,Liu, Xing,Wang, Zhong,Yang, Xiaoming,Tu, Yingfeng,Zhu, Xiulin
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p. 6370 - 6381
(2012/06/18)
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