The photovoltaic characteristics of an amorphous polymer containing EDOT and fluorene units were investigated. In particular, the effects of the terminal structure, residual amount of Pd, and molecular weight were systematically investigated. Direct arylation polycondensation of EDOT followed by an established purification method readily afforded polymers with different terminal structures, Pd contents, and molecular weights. Of these factors, the terminal structure of the polymer was a crucial factor affecting the photovoltaic characteristics. For example, the polymer with a Br terminal had a PCE of 2.9% in bulk-heterojunction organic photovoltaics (BHJ OPVs) with a fullerene derivative, whereas the polymer without a Br terminal had a PCE of 4.6% in the same cell configuration. The decreased Pd residues and high molecular weights of the polymers increased the long-term stability of the devices. Moreover, BHJ OPVs containing the high-molecular-weight polymer could be fabricated with an environmentally friendly nonhalogenated solvent.

Conjugated polymers containing phenyl-, pyridyl-, and thiazolyl-flanked diketopyrrolopyrrole (DPP) were synthesized by direct arylation polycondensation of 3,4-ethylenedioxythiophene derivatives and dibrominated DPP-based monomers, in order to probe the effects of the aromatic groups in the DPP units on the absorption property, energy level, and crystallinity. A polymer possessing thiazolyl-flanked DPP units was found to display long-wavelength absorption properties and higher crystallinity than the polymers bearing phenyl-and pyridyl-flanked DPP units. These features of the thiazolyl-based polymer were afforded by its coplanar structure of the main chain. The synthesized polymers showed semiconducting properties in organic field effect transistors and organic photovoltaics. Direct arylation polycondensation is an efficient synthetic method that affords a series of DPP-based polymers in a simple fashion and, thus, helping in a comprehensive understanding on the relationship between the aromatic groups in DPP units and their physical properties.

The Pd-catalyzed polycondensation of 4-octylaniline with various dibromoarylenes was carried out under microwave heating. Microwave heating led to a decrease in the reaction time and an increase in the molecular weight of the polymers as compared to conventional heating. Microwave heating also allowed the catalyst loading to be reduced to 1 mol %, yielding polymerization results that were comparable to those under conventional heating and 5 mol % catalyst. Investigations regarding field-effect transistors and organic photovoltaic cells using the obtained poly(arylamine) with azo-benzene units revealed that increasing the molecular weight of the polymer led to improved device performance, including hole mobility and power conversion efficiency. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 536-542 EXPERIMENTAL Materials 4-Octylaniline, 4,4 0 -dibromobiphenyl, 4,4 0 -dibromostilbene, 2,7 0 -dibromo-9-fluorenone, 1,6 0 -dibromopyrene, tris(dibenzylideneacetone)dipalladium (Pd 2 (dba) 3 ), tri-tert-butylphosphonium tetrafluoroborate (P(t-Bu) 3 ÁHBF 4 ), and NaOt-Bu were received from commercial suppliers and used without further purification. Anhydrous toluene was purchased from Kanto Chemical and used as a dry solvent. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS, CLEVIOS P VP AI 4083) was purchased from Heraeus. PC 70 BM (purity 99%) Additional Supporting Information may be found in the online version of this article.