Variation of the Side Chain Branch Position Leads to Vastly Improved Molecular Weight and OPV Performance in 4, 8-dialkoxybenzo[1, 2-b:4, 5-b′]dithiophene/2, 1, 3-benzothiadiazole Copolymers. (9th July 2011)

• Record Type: Journal Article
• Authors: Coffin, Robert C.; MacNeill, Christopher M.; Peterson, Eric D.; Ward, Jeremy W.; Owen, Jack W.; McLellan, Claire A.; Smith, Gregory M.; Noftle, Ronald E.; Jurchescu, Oana D.; Carroll, David L.
• Other Names: López-Sandoval Román Academic Editor.
• Is Part Of: Journal of nanotechnology. Volume 2011(2011)
• Publication Date: 2011-07-09
• Subjects: Nanotechnology -- Periodicals; Nanotechnology; Nanotechnology; Periodicals; Periodicals; 620.5
• DOI: 10.1155/2011/572329
• Languages: English
• ISSNs: 1687-9503

Abstract

Abstract : Through manipulation of the solubilizing side chains, we were able to dramatically improve the molecular weight ( M w ) of 4, 8-dialkoxybenzo[1, 2- b :4, 5- b ′ ]dithiophene (BDT)/2, 1, 3-benzothiadiazole (BT) copolymers. When dodecyl side chains (P1 ) are employed at the 4- and 8-positions of the BDT unit, we obtain a chloroform-soluble copolymer fraction with M w of 6.3 kg/mol. Surprisingly, by moving to the commonly employed 2-ethylhexyl branch (P2 ), M w decreases to 3.4 kg/mol. This is despite numerous reports that this side chain increases solubility and M w . By moving the ethyl branch in one position relative to the polymer backbone (1-ethylhexyl, P3 ), M w is dramatically increased to 68.8 kg/mol. As a result of this M w increase, the shape of the absorption profile is dramatically altered, with λ max = 637 nm compared with 598 nm for P1 and 579 nm for P2 . The hole mobility as determined by thin film transistor (TFT) measurements is improved from ~ 1 × 10 − 6 cm 2 /Vs for P1 and P2 to 7 × 10 − 4 cm 2 /Vs for P3, while solar cell power conversion efficiency in increased to 2.91 % for P3 relative to 0.31 % and 0.19 % for P1 and P2, respectively.