Issue 48, 2016

Synthesis, molecular and photovoltaic/transistor properties of heptacyclic ladder-type di(thienobenzo)fluorene-based copolymers

Abstract

We present a facile synthesis method to make a new ladder-type heptacyclic dithienobenzofluorene (DTBF) framework, where the central 2,7-fluorene unit is covalently fastened with two external thiophenes via two C[double bond, length as m-dash]C bridges. A dieneyne-containing precursor undergoes DBU-induced double benzannulation to regiospecifically introduce two solubilizing 2-octyldodecyl side chains at 5,10-positions of DTBF. The rigid and coplanar Br-DTBF monomer with sufficient solubility was copolymerized with 5,6-difluoro-4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (Sn-DTFBT) and 5,10-bis(5-(trimethylstannyl)thiophen-2-yl)naphtho[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (Sn-DTNT) via Stille coupling to furnish two donor–acceptor copolymers, PDTBFFBT and PDTBFNT, respectively. Their thermal, optical, electrochemical, molecular stacking and photovoltaic properties are investigated. PDTBFNT has a higher molecular weight, smaller optical and electrochemical band gaps, and stronger solid-state packing than PDTBFFBT. DFT calculations were carried out to gain insight into the electronic and structural properties of DTBF and its derivatives. Bulk heterojunction solar devices with the ITO/ZnO/polymers:PC71BM/MoO3/Ag configuration were fabricated. By adding 5 vol% diphenyl ether (DPE) as an additive, PDTBFNT:PC71BM and PDTBFFBT:PC71BM devices achieved the power conversion efficiencies of 5.22% and 2.68%, respectively. The superior efficiency of PDTBFNT over PDTBFFBT is attributed to the better LUMO energy alignment between PDTBFNT and PC71BM and the face-on π-stacking of PDTBFNT in the active layer. Moreover, PDTBFNT exhibited a higher field-effect transistor hole mobility of 1.90 × 10−2 cm2 V−1 s−1 than PDTBFFBT with a value of 3.96 × 10−3 cm2 V−1 s−1.

Graphical abstract: Synthesis, molecular and photovoltaic/transistor properties of heptacyclic ladder-type di(thienobenzo)fluorene-based copolymers

Supplementary files

Article information

Article type
Paper
Submitted
04 10 2016
Accepted
18 10 2016
First published
07 11 2016

J. Mater. Chem. C, 2016,4, 11427-11435

Synthesis, molecular and photovoltaic/transistor properties of heptacyclic ladder-type di(thienobenzo)fluorene-based copolymers

C. Lee, Y. Lai, F. Cao, J. Hsu, Z. Lin, U. Jeng, C. Su and Y. Cheng, J. Mater. Chem. C, 2016, 4, 11427 DOI: 10.1039/C6TC04300C

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