A Triphenylamine–Naphthalenediimide–Fullerene Triad: Synthesis, Photoinduced Charge Separation and Solution‐Processable Bulk Heterojunction Solar Cells

Abstract A new naphthalenediimide (NDI) derivative linked to triphenylamine (TPA) and fullerene (TPA–NDI–C 60 triad; S3 ) was designed, synthesized and characterized. Femtosecond laser transient absorption spectral measurements revealed that fast electron transfer from TPA to the singlet‐excited state of NDI occurred to form a charge‐separated state (TPA .+ –NDI .− –C60) with a rate constant of approximately 10 12 s −1 , followed by the charge‐shift reaction from NDI .− to C 60 to produce the charge‐separated state (TPA .+ –NDI–C 60 .− ) that decayed by back electron transfer with a rate constant of 4.4×10 9 s −1 (with a corresponding lifetime of 230 ps). Organic bulk heterojunction solar cells were fabricated using the triad S3 as an n‐type semiconductor along with the conventional donor polymer poly(3‐hexylthiophene). The power conversion efficiency reached 3.03 % before annealing and 4.85 % after annealing in the optimized devices. To rationalize the performance of these organic photovoltaic devices, atomic force microscopy was used to study the morphology of poly(3‐hexylthiophene): S3 blend surfaces, which were found to be well interlaced and free from projections, lumps, or indentations.