Functionalization of diketopyrrolopyrrole with dendritic oligothiophenes: Synthesis, photophysical properties, and application in solar cells

Diketopyrrolopyrrole (DPP) is one of the most widely used organic dye moieties in conjugated organic semiconductors for use in organic electronics. To enrich the library of DPP based organic semiconductors and to further understand the structure-property-performance relationship of this type materials, in this paper, the diketopyrrolopyrrole moiety was functionalized with three-dimensional (3D) π-conjugated dendritic oligothiophenes (DOTs), and four diketopyrrolopyrrole compounds decorated with dendritic oligothiophenes (DOT-c-DPPs) were obtained and characterized in detailed. Results show that all these four compounds are monodisperse with defined molecular structure. Spectroscopy and cyclic voltammetry measurement results showed that the introduction of dendritic oligothiophene unit on the DPP unit improves the light absorption ability over 350–500 nm, and decreases the optical band gap slightly, which are in good accordance with theoretical calculation results that the frontier molecular orbitals are mainly located at the central DPP unit. Solution processed organic solar cells using these DOT-c-DPPs as the electron donor were fabricated and tested. Improved device performance was found for the bigger molecule for its less aggregation tendency.