Synthesis, characterization of bay-substituted perylene diimide based D-A-D type small molecules and their applications as a non-fullerene electron acceptor in polymer solar cells

Abstract

We report a series of bay substituted perylene diimide based donor-acceptor-donor (D-A-D) type small molecule acceptor derivatives such as S-I, S-II, S-III and S-IV for small molecule based organic solar cell (SM-OSC) applications. The electron rich thiophene derivatives such as thiophene, 2-hexylthiophene, 2,2′-bithiophene, and 5-hexyl-2,2′-bithiophene were used as a donor (D), and perylene diimide was used as an acceptor (A). The synthesized small molecules were confirmed by FT-IR, NMR, and HR-MS. The small molecules showed wide and strong absorption in the UV-vis region up to 750 nm, which reduced the optical band gap to <2 eV. The calculated highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were comparable with those of the PC61BM. Scanning electron microscope (SEM) studies confirmed the aggregation of the small molecules, S-I to S-IV. Small molecules showed thermal stability up to 300 °C. In bulk heterojunction organic solar cells (BHJ-OSCs), the S-I based device showed a maximum power conversion efficiency (PCE) of 0.12% with P3HT polymer donor. The PCE was declined with respect to the number of thiophene units and the flexible alkyl chain in the bay position. Keywords: Perylene diimide, Donor–acceptor, Small molecule, Non-fullerene, Suzuki coupling