Synthesis and Characterization of a New Phenanthrenequinoxaline-Based Polymer for Organic Solar Cells

Abstract

Two donor-acceptor (D-A) conjugated polymers, PQx and PphQx, composed of alkylthienyl-substituted benzo[1,2-b:4,5-b'] dithiophene (BDTT) as the electron donor and the new electron acceptors quinoxaline (Qx) or phenanthrenequinoxaline (phQx), were synthesized with Stille cross-coupling reactions. The number-averaged molecular weights (M-n) of PQx and PphQx were found to be 25.1 and 23.2 kDa, respectively, with a dispersity of 2.6. The band-gap energies of PQx and PphQx are 1.82 and 1.75 eV, respectively. These results indicate that, because phQx units have highly planar structures, their inclusion in D-A polymers will be a very effective method for increasing the polymers' effective conjugation lengths. The hole mobilities of PQx and PphQx were determined to be 5.0 x 10(-5) and 2.2 x 10(-4) cm(2) V-1 s(-1), respectively. A polymer solar cell device prepared with PphQx as the active layer was found to exhibit a power conversion efficiency (PCE) of 5.03%; thus, the introduction of phQx units enhanced both the short circuit current density and PCE of the device.