Synthesis of π-Extended Dithienobenzodithiophene-Containing Medium Bandgap Copolymers and Their Photovoltaic Application

Two medium bandgap alternating conjugated copolymers, namely, poly{5,10-di(2-hexyldecyloxy)dithieno[2,3- d :2′,3′- d ′]benzo[1,2- b :4,5- b ′]dithiophene-2,7-diyl- alt -thiophene-2,5-di-yl} ( P1 ) and poly{5,10-di(2-hexyldecyloxy)dithieno[2,3- d :2′,3′- d ′]benzo[1,2- b :4,5- b ′]dithiophene-2,7-di-yl- alt -thieno[3,2- b ]thiophene-2,5-diyl} ( P2 ), were prepared by the palladium-catalyzed Stille polycondensation and characterized by gel permeation chromatography (GPC), UV-Vis absorption and photoluminescence (PL) spectra, thermal gravimetric analysis (TGA), cyclic voltammetry (CV) etc .

The resultant copolymers show moderate solubility in common organic solvents and enough stabilities for photovoltaic application. And both copolymers absorb the solar light from 300–600 nm, with the optical band gaps () calculated from the onset of absorption in the solid film of ca. 2.1 eV. The highest occupied molecular orbital (HOMO) levels of two copolymers determined by CV were at about −5.35 eV.