Three pyrido[2,3,4,5-lmn]phenanthridine derivatives and their large band gap copolymers for organic solar cells

Abstract

Three novel pyrido[2,3,4,5-lmn]phenanthridine derivatives of 4,9-dialkylpyrido[2,3,4,5-lmn]phenanthridine-5,10-dione, 10-alkoxy-4-alkylpyrido[2,3,4,5-lmn]phenanthridin-5-one, and 5,10-dialkoxypyrido[2,3,4,5-lmn]phenanthridine were synthesized as building blocks of copolymers Pa, Pb and Pc, giving relatively large band gaps of 2.13, 2.19 and 2.21 eV, respectively. Bulk-heterojunction (BHJ) solar cells were fabricated in a typical device configuration by utilizing the resulting polymers as the donor of the active layer. A power conversion efficiency (PCE) of 3.47% was achieved from the Pa-based device without any additives or thermal annealing. A further improved PCE of 4.54% was achieved in inverted device architecture, and it is hitherto the highest efficiency of BHJ polymer solar cells using a donor polymer with a band gap above 2.1 eV.