A Soluble Diketopyrrolopyrrole Derivative and Its Applications for Organic Phototransistors

A small molecular diketopyrrolopyrrole (DPP) derivative containing 2,4-difluorinated phenyl groups, 3,6-bis(5-((E)-2,4-difluorostyryl)thiophen-2-yl)-2,5-bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (EHD2FV), was synthesized by a cross-coupling reaction with 90% yield. The solid EHD2FV film exhibited a broad optical absorption up to 1000 nm, it featured a deep-lying LUMO energy (4.49 eV). EHD2FV was employed as an electron acceptor (n-type) for bulk heterojunction (BHJ) layers, which act as a sensing channel layer in organic phototransistors (OPTRs), while poly(3-hexylthiophene) (P3HT) was introduced as an electron donor (p-type). The OPTRs with the P3HT : EHD2FV BHJ layers were capable of sensing a deep red light (700 nm). The results showed that the best photosensing performance (photoresponsivity=337.1 mA/W) was achieved at the EHD2FV molar ratio of 0.05.