Synthesis and Characterization of Low Band-Gap Polymer based on Fluorinated Quinoxalines for Photovoltaic Application

Abstract

A series of low-band gap fluorinated quinoxaline based donor--acceptor conjugated polymer of PBDT-Qx, PBDT-QxF, PBDT-FQx, and PBDT-FQxF, have been successfully synthesized via Stille coupling reaction. The polymers composed by electron-donating dialkoxy-substituted benzodithiophene (BDT) and electron-withdrawing 2,3-diphenylquinoxaline (DPQ) through a thiophene bridge. To understand the impact of fluorine (F) as strong electron-withdrawing moieties, the polymers have been substituted by F atoms in various number and at divers positions on the DPQ units such as the 6,7-positions, the para-positions of the phenyl substituent on the 2,3-positions, and both locations, and compared to non-fluorinated counterpart. Overall performances present a gradual enhancement of power conversion efficiencies (PCEs) due to favorable effect of F atoms. An optimize device of inverted-type polymer solar cells (PSCs) with structure of ITO/ZnO/polymers:PC71BM/MoO3/Al showed that PBDT-FQxF, with four fluorine atoms on the 6,7-positions and the para-positions of the phenyl substituent on 2,3-positions of DPQ, exhibits the highest PCE of 6.60% with an open-circuit voltage (Voc) of 0.91 V, a short-circuit current density (Jsc) of 10.15 mA/cm-2, and a fill factor (FF) of 71.50%.