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Issue 29, 2011
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New low band gap thieno[3,4-b]thiophene-based polymers with deep HOMO levels for organic solar cells

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Abstract

Two new soluble alternating alkyl-substituted benzo[1,2-b:4,5-b′]dithiophene and ketone-substituted thieno[3,4-b]thiophene copolymers were synthesized and characterized. We found that grafting 3-butyloctyl side chains to the benzo[1,2-b:4,5-b′]dithiophene unit at C4 and C8 afforded the resulting polymer (P1) a high hole mobility (∼10−2 cm2Vs−1) and a low-lying HOMO energy level (5.22 eV). Preliminary experiments in bulk heterojunction solar cells using P1 as the electron donor demonstrated a high power conversion efficiency of 4.8% even with PC61BM as the electron acceptor. The introduction of an electron-withdrawing fluorine atom into the thieno[3,4-b]thiophene unit at the C3 position (P2) lowers the HOMO energy level and consequently improves the open circuit voltage from 0.78 to 0.86 V. These values are about 0.1 V higher than those reported for their analogues based on alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene. This work demonstrates that the replacement of the alkoxy chains on the benzo[1,2-b:4,5-b′]dithiophene unit with less electron-donating alkyl chains is able to lower the HOMO energy levels of this class of polymers without increasing their band gap energy.

Graphical abstract: New low band gap thieno[3,4-b]thiophene-based polymers with deep HOMO levels for organic solar cells

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Publication details

The article was received on 22 Mar 2011, accepted on 03 May 2011 and first published on 17 Jun 2011


Article type: Paper
DOI: 10.1039/C1JM11229E
Citation: J. Mater. Chem., 2011,21, 10920-10928
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    New low band gap thieno[3,4-b]thiophene-based polymers with deep HOMO levels for organic solar cells

    S. Wakim, S. Alem, Z. Li, Y. Zhang, S. Tse, J. Lu, J. Ding and Y. Tao, J. Mater. Chem., 2011, 21, 10920
    DOI: 10.1039/C1JM11229E

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