Alternating D-A1-D-A2 Copolymers Containing Two Electron-Deficient Moieties for Efficient Polymer Solar Cells
Dongfeng Dang a, Wenjun Sun a, Ergang Wang a, Zaifei Ma b, Fengling Zhang b, Renqiang Yang c
a Chalmers University of Technology, Fysikgrand 3, 5121, Gothenburg, 41296, Sweden
b Linköping University Sweden, SE-581 83, Linköping, Sweden
c Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Poster, Ergang Wang, 200
Publication date: 1st March 2014

Polymer solar cells (PSCs) are promising sustainable solar energy converters, which are attracting more and more attention because of their unique advantages of low cost, light weight, and potential use in flexible devices. To further improve the efficiencies of PSCs for practical applications, it is necessary to develop new conjugated polymers with several merits including low band gap, appropriate HOMO and LUMO positions, high mobility, decent solubility. A facial method to design polymers with these merits is to combine electron-rich (donor) and electron-deficient (acceptor) groups as repeating units, forming internal donor-acceptor (D-A) structures.[1]The energy levels and the absorption spectra of the polymers can be tuned by the donor and acceptor units. In this work, we found that when we introduced two electron-deficient units with different absorption behaviors forming a D-A1-D-A2 structure in the repeating unit, the resulting copolymer can benefit from both of the electron-deficient units and thus attain a broader absorption spectrum compared to the polymers containing one electron-deficient unit.[2]Although D-A1-D-A2 polymers have been mentioned in few reports,[3]there is lack of systematic studies on the comparisonbetween D-A1-D-A2 polymers and their constituent parts D-A1 and D-A2 polymers. A new fluorinated D-A1-D-A2 copolymer PTQTI-F was synthesized in this work.[4]Bulk heterojunction solar cells fabricated with this polymer as donor and PC61BM as acceptor realized a PCE of 6.32% with a higher Voc of 0.93 V, an enhanced Jsc of 12.58 mA cm−2 and a FF of 0.54, which is the highest efficiency recorded for a polymer containing two acceptor units. Further modification of the structure can even improve the efficiency to over 7%. The facile concept proposed in this work opens a door for the design of new conjugated polymers with wide absorption spectra for efficient PSCs.

Chemical structures of the D-A1-D-A2 copolymers and the J-V curves of the solar cells
(1) E. G. Wang, Z. Ma, Z. Zhang, K. Vandewal, P. Henriksson, O. Inganäs, F. Zhang, M. R. Andersson, An Easily Accessible Isoindigo–Based Polymer for High–Performance Polymer Solar Cells. J Am Chem Soc 2011, 133, 14244. (2) W. Sun, Z. Ma, D. Dang, W. Zhu, M. R. Andersson, F. Zhang, E. Wang, An alternating D-A1-D-A2 copolymer containing two electron-deficient moieties for efficient polymer solar cells. J Mater Chem A 2013, 1, 11141. (3) S. Subramaniyan, F. S. Kim, G. Q. Ren, H. Y. Li, S. A. Jenekhe, High Mobility Thiazole-Diketopyrrolopyrrole Copolymer Semiconductors for High Performance Field-Effect Transistors and Photovoltaic Devices. Macromolecules 2012, 45, 9029. (4) D. Dang, W. Chen, R. Yang, W. Zhu, W. Mammo, E. Wang, Fluorine substitution enhanced photovoltaic performance of a D–A1–D–A2 copolymer. Chem Commun 2013, 49, 933.
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