New copolymers with fluorinated and non-fluorinated benzothiadiazole units for efficient single layer near infra-red photodiodes with fast time response

Abstract

We describe the synthesis and photodetecting properties of new, low band-gap copolymers: P1 with 5,6-difluoro-2,1,3-benzothiadiazole and P2 with 2,1,3-benzothiadiazole, both containing diketopyrrolopyrrole acceptor units. These compounds have been used for fabrication of single layer, solution processed photodetectors. For this purpose, two blends with fullerene derivative (6,6)-phenyl-C61-butyric acid methyl ester ([60]PCBM): P1:[60]PCBM and P2:[60]PCBM, were prepared and applied as active layers in bulk-heterojunction photodiodes. For near infrared light (810 nm), these photodetectors, in spite of single layer structure, display competitive performance, showing specific detectivity up to 5·1011 Jones, responsivity up to 0.3 A/W and rise and fall times of the transient signals below 10 μs.