Synthesis and photovoltaic behavior of two new alternative donor-acceptor conjugated copolymers containing isoindigo moiety.

Two donor-acceptor copolymers (P1 and P2) containing isoindigo as the acceptor unit and the benzodithiophene and bisthiophene-dithieno[3,2-b:2′,3′-d]-pyrrole as the donor unit have been designed and synthesized by the Pd-catalyzed Stille coupling reaction. The copolymers show broad and flat absorption, exhibit good solubility, and thermal stability, but possess optical bandgaps of 1.62 and 1.42 eV, respectively, and different donor-acceptor distance, of which the former is shorter than the later. The power conversion efficiency of the polymer solar cells based on P2:PC₆₁BM (1:1 wt%) reached 1.86% with open-circuit voltage of 0.54 V and a short-circuit current of 6.36 mA/cm², under the illumination of AM 1.5, 100 mW/cm². Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]