Nonylbisoxazole-based donor–acceptor copolymers for polymer solar cells

Abstract

A new 4,4′-dinonyl-2,2′-bisoxazole (NBO)-based polymer, namely poly{4,8-bis(2-ethylhexoxy)-benzo[1,2-b;3,4-b′]difunan-2,6-diyl-alt-(4, 4′-dinonyl-2,2′-bisoxazole)} (PBDFNBO), was synthesized by a Stille coupling polymerization reaction. The copolymer was found to be soluble in common organic solvents, such as chloroform, tetrahydrofuran and chlorobenzene with excellent film forming properties. The thermal, optical, electrochemical, and photovoltaic properties of PBDFNBO were investigated in detail. Thermo gravimetric analysis (TGA) results indicate that the copolymer possesses good thermal stability. The PBDFNBO film exhibits a narrow absorption band around 300–598 nm (with an optical bandgap of 2.07 eV). The maximum power conversion efficiency (PCE) of the polymer solar cells (PSCs) based on PBDFNBO/PC₇₁BM (1 : 2, w/w) reaches 5.0% with a short circuit current density (J_sc) of 9.9 mA cm⁻², an open circuit voltage (V_oc) of 0.93 V, and a fill factor (FF) of 0.53 under AM 1.5G, 100 mW cm⁻² illumination.