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A difluorobenzothiadiazole-based conjugated polymer with alkylthiophene as the side chains for efficient, additive-free and thick-film polymer solar cells

Abstract

Two donor-acceptor (D-A) conjugated polymers with alkylthiophene as side chains, i.e., poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′′′-di(2-(2- decyltetradecyl)thiophene-5-yl)-2,2′;5′,2′′;5′′,2′′′-quaterthiophene-5,5′′′-diyl)] (P-2T) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(2,5-bis(3-(2- decyltetradecyl)thiophene-5-yl)thiophen-2-yl)thieno[3,2-b]thiophene)] (P-TT), are designed and synthesized. Both polymers exhibit temperature-sensitive aggregation in solution. Polymer solar cells (PSCs) based on them are fabricated with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor material. The devices based on P-TT deliver power conversion efficiency (PCE) up to 9.96% while no additive is used. Moreover, the photovoltaic performance of P-TT is insensitive to polymer:PC71BM ratio and active layer thickness, and PCEs are all above 9% with the donor:acceptor (D:A) of 1:1-1:1.8 (wt:wt) and film thickness of 200 - 360 nm. The high photovoltaic performance of P-TT is ascribed to the high and balanced charge carrier mobilities (4.51×10-3 and 3.44×10-3 cm2V-1s-1 for holes and electrons, respectively), owing to the favorable face-on packing of the conjugated backbones as well as the desired morphology of the blend films. Our study demonstrates that alkylthiophenes are one kind of promising synthon of oligothiophene based D-A conjugated polymers, which can serve as side chains for tuning the aggregation of the polymer in solution and the packing mode of the conjugated backbones in film state.

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Publication details

The article was received on 19 Jul 2017, accepted on 05 Sep 2017 and first published on 05 Sep 2017


Article type: Paper
DOI: 10.1039/C7TA06332F
Citation: J. Mater. Chem. A, 2017, Accepted Manuscript
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    A difluorobenzothiadiazole-based conjugated polymer with alkylthiophene as the side chains for efficient, additive-free and thick-film polymer solar cells

    M. He, M. Li, X. Dong, H. Tian, H. Tong, J. Liu, Z. Xie, Y. Geng and F. Wang, J. Mater. Chem. A, 2017, Accepted Manuscript , DOI: 10.1039/C7TA06332F

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