Synthesis and simultaneously enhanced photovoltaic property of poly[4,4,9,9-tetra(4-octyloxyphenyl)-2,7-indaceno[1,2-b:5,6-b′]dithiophene-alt-2,5-thieno[3,2-b]thiophene]

An alternating conjugated polymer derived from 4,4,9,9-tetra(4-octyloxyphenyl)indaceno[1,2-b:5,6-b′]dithiophene and thieno[3,2-b]thiophene was synthesized by Stille coupling reaction. The copolymer shows extensive absorption from 360 nm to 590 nm with optical band gap of 2.12 eV. The highest occupied molecular orbit (HOMO) and the lowest unoccupied molecular orbit (LUMO) energy levels of the copolymer, determined by cyclic voltammetry (CV), are about −5.29 eV and −3.01 eV, respectively. A field-effect hole mobility of 8.1 × 10−4 cm2/(V s) and an on/off ratio of 2.0 × 103 are obtained in the field-effect transistors based on the copolymer. The Jsc, Voc and FF of the polymer photovoltaic cells (PVCs) based on the copolymer were enhanced simultaneously via the inserting of alcohol soluble conjugated polymer interlayer between active layer and metal cathode, and the maximal power conversion efficiency of 4.19% was achieved in the modified devices under an AM 1.5 simulator (100 mWcm−2).