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 non-fullerene 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 1012 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.