Dithienocoronene diimide based conjugated polymers as electron acceptors for all-polymer solar cells

A series of n-type copolymers based on dithienocoronene diimide with different number of thiophene units have been designed and synthesized by Pd-catalyzed Stille coupling polymerization. The soluble polymers P1–P3 exhibit good thermal stability with decomposition temperatures of 340−390 °C. The absorption spectra (400–700 nm) red shift, and optical band gap (1.7–1.9 eV) decreases with increasing thiophene number in the copolymers. The estimated LUMOs for these polymers (ca. −3.5 eV) are relatively insensitive to thiophene number, while the HOMOs (−6.0 to −5.7 eV) up shift with increasing thiophene number. Solution processed bulk heterojunction all-polymer solar cells are fabricated using polymers P1–P3 as acceptor and polythiophene derivative PT5TPA as donor. Power conversion efficiencies (upto 0.84%) increase with increasing thiophene number in the polymer acceptors.