Naphthalene diimide-diketopyrrolopyrrole copolymers as non-fullerene acceptors for use in bulk-heterojunction all-polymer UV-NIR photodetectors

A series of random copolymers containing the two electron-withdrawing units naphthalene diimide (NDI) and diketopyrrolopyrrole (DPP) and a thiophene (T) spacer were designed and synthesized as nonfullerene acceptors for all-polymer photodetectors. Increasing the number of DPP-T segments in the polymer backbone leads to a significant red shift in maximal absorption, bandgap narrowing, better film morphology and lower dark current density. A specific detectivity over 10(12) Jones in a broad spectral region of 340-960 nm under -0.1 V bias was achieved with a photodetector using a blend of a donor polymer based on dithienopyrrole and diketopyrrolopyrrole (PDTP-DPP) and a copolymer (PNDI-DPP10) as an acceptor. In comparison, the device performance was found to be better than for the one based on PDTP-DPP and the PNDI homopolymer.