TPA‐PPEs – New alternating donor copolymers for potential application in photovoltaic devices

A series of phenyleneethynylene copolymers with triphenylamine units as hole-transporting moieties (TPA-PPEs) were synthesized by the palladium-catalyzed cross-coupling polycondensation of diethynyltriphenylamines and selected dihalogen comonomers, for instance substituted benzene, thiophene, benzothiadiazole, or anthracene. Incorporation of the electron-rich amino group into the PPE backbone does not interrupt the main chain conjugation. Furthermore, it has a decreasing effect on the oxidation potential, thus makes these polymers interesting as hole-injection/hole-transporting materials. The chemical structure of the new alternating copolymers was confirmed by 1H and 13C NMR spectroscopy and elemental analysis and gel-permeation chromatography (GPC; THF, Mn ≈ 15,000–30,000 g/mol) was conducted. Furthermore, their optical properties were investigated by UV/vis spectroscopy. The TPA-PPEs exhibit absorption maxima at around 400 nm (π-π*), except anthracene containing copolymer 3f (λmax = 514 nm in THF) and benzothiadiazole containing one 3g (λmax = 503 nm in THF). The TPA copolymers have oxidation potentials about 1.1 V (Ag/AgCl). They are good photoconducting materials (3a: IPhoto = 4 × 10−10 A at 425 nm (400 V), 3g: IPhoto = 1.3 × 10−11 A at λmax = 500 nm (20 V)) and show emission after excitation at around 450 nm (560 nm 3f). Their application in nonoptimized polymer solar cells (bulk heterojunction) led to power conversion efficiencies of around 1–1.8% after illumination with 100 mW/cm2 of AM1.5. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009