Synthesis of a soluble fulleropyrrolidine derivative for use as an electron acceptor in bulk-heterojunction polymer solar cells

A new phenothiazine-containing fulleropyrrolidine derivative, C60-fused N-methyl-[10-(2-ethylhexyl)-10H-phenothiazin-2yl]-pyrrolidine (C60-PTZP), was synthesized via the 1,3-dipolar cycloaddition reaction of an azomethine ylide intermediate, and used as an electron acceptor for organic photovoltaics (OPVs). The new fulleropyrrolidine derivative was characterized by 1H NMR, 13C NMR, FT-IR and FAB-MS. The C60-PTZP showed good solubility in common organic solvents such as chloroform and chlorobenzene. The optical and electrochemical properties of C60-PTZP were compared with those of the parent [60] fullerene. C60-PTZP showed improved solubility and a higher LUMO energy level than the parent [60] fullerene. Photovoltaic devices with the configuration of ITO/PEDOT:PSS/active layer/LiF/Al were fabricated. To optimize the device fabrication conditions, we varied the weight ratios of the electron donor to the acceptor in the active layer and also changed the post-annealing temperature. The highest power conversion efficiency (PCE) of the fabricated devices was observed to be 1.42% when the weight ratio of P3HT:C60-PTZP was 1:0.5 and annealing was carried out at 100 °C for 30 min.