- Thieno[3,2-b]thiophene-substituted benzodithiophene in donor-acceptor type semiconducting copolymers: A feasible approach to improve performances of organic photovoltaic cells
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Thieno[3,2-b]thiophene-substituted benzo[1,2-b:4,5-b′]dithiophene donor units (TTBDT) serve as novel promising building blocks for donor-acceptor (D-A) copolymers in organic photovoltaic cells. In this study, a new D-A type copolymer (PTTBDT-TPD) consisting of TTBDT and thieno[3,4-c]pyrrole-4,6-dione (TPD) is synthesized by Stille coupling polymerization. A PTTBDT-TPD analog consisting of TTBDT and alkylthienyl-substituted BDT (PTBDT-TPD) is also synthesized to compare the optical, electrochemical, morphological, and photovoltaic properties of the polymers. Bulk heterojunction photovoltaic devices are fabricated using the polymers as p-type donors and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as the n-type acceptor. The power conversion efficiencies of the devices fabricated using PTTBDT-TPD and PTBDT-TPD are 6.03 and 5.44%, respectively. The difference in efficiency is attributed to the broad UV-visible absorption and high crystallinity of PTTBDT-TPD. The replacement of the alkylthienyl moiety with thieno[3,2-b]thiophene on BDT can yield broad UV-visible absorption due to extended π-conjugation, and enhanced molecular ordering and orientation for organic photovoltaic cells.
- Kim, Ji-Hoon,Kim, Hee Su,Park, Jong Baek,Kang, In-Nam,Hwang, Do-Hoon
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- Thieno[3,2-b]thiophene-substituted benzo[1,2-b:4,5-b ′]dithiophene as a promising building block for low bandgap semiconducting polymers for high-performance single and tandem organic photovoltaic cells
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We designed and synthetized a new poly{4,8-bis((2-ethylhexyl)thieno[3,2-b] thiophene)-benzo[1,2-b:4,5-b′]dithiophene-alt-2-ethylhexyl-4, 6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate} (PTTBDT-FTT) comprising bis(2-ethylhexylthieno[3,2-b]thiophenylbenzo[1,2-b:4,5-b′]dithiophene (TTBDT) and 2-ethylhexyl 3-fluorothieno[3,4-b]thiophene-2-carboxylate (FTT). The optical bandgap of PTTBDT-FTT was 1.55 eV. The energy levels of the highest occupied and lowest unoccupied molecular orbitals of PTTBDT-FTT were -5.31 and -3.73 eV, respectively. Two-dimensional grazing-incidence X-ray scattering measurements showed that the film's PTTBDT-FTT chains are predominantly arranged with a face-on orientation with respect to the substrate, with strong π-π stacking. An organic thin-film transistor fabricated using PTTBDT-FTT as the active semiconductor showed high hole mobility of 2.1 × 10-2 cm2/(V·s). Single-junction bulk heterojunction photovoltaic cells with the configuration ITO/PEDOT:PSS/PTTBDT-FTT:PC71BM/Ca/Al were fabricated, which showed a maximum power conversion efficiency (PCE) of 7.44%. Inverted photovoltaic cells with the structure ITO/PEIE/PTTBDT-FTT: PC71BM/MoO3/Ag were also fabricated, with a maximum PCE of 7.71%. A tandem photovoltaic device comprising the inverted PTTBDT-FTT:PC 71BM cell and a P3HT:ICBA-based cell as the top and bottom cell components, respectively, showed a maximum PCE of 8.66%. This work demonstrated that the newly developed PTTBDT-FTT polymer was very promising for applications in both single and tandem solar cells. Furthermore, this work highlighted the fact that an extended π-system in the electron-donor moiety in low bandgap polymers is crucial for improving polymer solar cells.
- Kim, Ji-Hoon,Song, Chang Eun,Kim, Bongsoo,Kang, In-Nam,Shin, Won Suk,Hwang, Do-Hoon
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- The effect of thieno[3,2-b]thiophene on the absorption, charge mobility and photovoltaic performance of diketopyrrolopyrrole-based low bandgap conjugated polymers
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A series of two-dimensional diketopyrrolopyrrole-based low band gap conjugated polymers were synthesized. Replacing thiophene with thieno[3,2-b]thiophene in the side chain and bridge resulted in significant changes to the optical, electrochemical, and morphological properties of the polymers, as well as the subsequent performance of devices made from these materials. The polymer with thieno[3,2-b]thiophene as a bridge instead of a side chain exhibited an increased absorption coefficient and hole mobility, and resulted in the highest power conversion efficiency (5.34%) in this series of polymers. This finding provides valuable insight for the development of more efficient low band-gap polymers.
- Li, Yongxi,Chang, Chih-Yu,Chen, Yu,Song, Yi,Li, Chang-Zhi,Yip, Hin-Lap,Jen, Alex K.-Y.,Li, Chao
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p. 7526 - 7533
(2013/11/19)
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