Synthesis and Photovoltaic Properties of a New Low-Bandgap Polymer Consisting of Benzodithiophene and Fluorinated Benzoselenadiazole Units

Abstract

A donor-acceptor-type conjugated alternating copolymer (PBDT-DFBSe) consisting of benzodithiophene (BDT) and a fluorinated 2,1,3-benzoselenadiazole derivative (DFBSe) is synthesized using Stille cross-coupling. The optical, electrochemical, and photovoltaic properties of PBDT-DFBSe are compared with those of its non-fluorinated analog, PBDT-BSe, which is composed of BDT and 2,1,3-benzoselenadiazole (BSe). The optical bandgap energies of PBDT-BSe and PBDT-DFBSe are determined from their absorption onsets to be 1.64 and 1.60 eV, respectively. Fluorine-containing PBDT-DFBSe shows a deeper highest occupied molecular orbital (HOMO) energy level and higher hole mobility than PBDT-BSe. The device incorporating PBDT-DFBSe has a higher open-circuit voltage (V-oc), short-circuit current density (J(sc)), and power conversion efficiency (PCE) than the device incorporating PBDT-BSe.