Polymer side-chain substituents elucidate thermochromism of benzodithiophene–dithiophenylacrylonitrile copolymers – polymer solubility correlation of thermochromism and photovoltaic performance. Issue 24 (6th June 2017)

• Record Type: Journal Article
• Authors: Chen, Hung-Yang; Lin, Chiao-Wen; Chen, Chin-Ti; Chen, Chao-Tsen; Golder, Jan; Lan, Yu-Bing; Wang, Juen-Kai
• Is Part Of: Polymer chemistry. Volume 8:Issue 24(2017)
• Page Start: 3689
• Page End: 3701
• Publication Date: 2017-06-06
• Subjects: Polymers -- Periodicals; Macromolecules -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1039/c7py00338b
• Languages: English
• ISSNs: 1759-9954

Abstract

Abstract : pBCN x polymers with different side-chain substituents for thermochromism and photovoltaic studies. Abstract : NinepBCN x polymers based on a donor–π-acceptor benzo[1, 2- b :4, 5- b ′]dithiophene-( E )-2, 3-di(thiophen-2-yl)acrylonitrile main-chain structure and n -octyl/2-ethylhexyl as the side-chain substituents have been designed and synthesized. The thermochromism of thepBCN x polymers has been carefully examined in both solution and the thin-film state. With additional evidences from Raman spectroscopy and AFM microscopy, we have deciphered the varied colours of ninepBCN x polymers in solution and the pronounced thin-film thermochromism only observed for certainpBCN x polymers, i.e., pBCN4, pBCN5, pBCN6, andpBCN8 . The alkyl side-chain, and hence the solubility or aggregation ofpBCN x polymers, is a main factor of the varied colour in solution and the varied thermochromism in the thin film. We have identified that a stronger main-chain and main-chain interaction are present on the ( E )-2, 3-di(thiophen-2-yl)acrylonitrile moiety, whereas the poor to moderate solubilitypBCN3, pBCN5′, andpBCN7 exhibit pronounced thermochromism in solution, andpBCN4, pBCN5, pBCN6, andpBCN8 are four polymers which have good solubility in solution and show thermochromism in the thin-film state. We took navy bluepBCN3 (poor solubility), magentapBCN4 (good solubility), and reddish purplepBCN5′ (moderate solubility) for the fabrication of bulk heterojunction organic photovoltaics (OPVs). With a solvent annealing treatment, the power conversion efficiency of the OPVs has been improved significantly from 4.7% to 6.2% for the good solubilitypBCN4, but there is little and no improvement for the moderate solubilitypBCN5′ and poor solubilitypBCN3, respectively. Our study verifies that the good OPV performance of thepBCN x polymers can be correlated to the pronounced thin-film thermochromism. A good solubility of the polymer is a common characteristic of a material with significant thin-film thermochromism and good OPV performance.