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 Orga

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• 作者：Ji-Hoon Kim ; Chang Eun Song ; BongSoo Kim ; In-Nam Kang ; Won Suk Shin ; Do-Hoon Hwang
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：January 28, 2014
• 年：2014
• 卷：26
• 期：2
• 页码：1234-1242
• 全文大小：508K
• ISSN：1520-5002

文摘

We designed and synthetized a new poly{4,8-bis((2-ethylhexyl)thieno[3,2-b]thiophene)-benzo[1,2-b:4,5-b鈥瞉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鈥瞉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 鈭?.31 and 鈭?.73 eV, respectively. Two-dimensional grazing-incidence X-ray scattering measurements showed that the film鈥檚 PTTBDT-FTT chains are predominantly arranged with a face-on orientation with respect to the substrate, with strong 蟺鈥撓€ stacking. An organic thin-film transistor fabricated using PTTBDT-FTT as the active semiconductor showed high hole mobility of 2.1 脳 10^鈥? cm²/(V路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:PC₇₁BM 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 蟺-system in the electron-donor moiety in low bandgap polymers is crucial for improving polymer solar cells.