Terpolymer approach for high performance in OFETs and OPVs

Abstract

We report on the design, synthesis, and characterization of a series of new random terpolymers (PDPP-Thiophene-Selenophene) consisting diketopyrrolopyrrole (DPP) as electron-deficient unit and thiophene and selenophene as electron-rich units with various thiophene/selenophene ratio in conjugated backbone. The optical and structural properties of these random terpolymers can be easily controlled by tuning the ratio between thiophene and selenophene. The absorption onset and the maximum absorption peaks were observed with a gradual red-shift with higher selenophene content in the chain. In polymer solar cells (PSCs), the best power conversion efficiency (PCE) value of 7.2% was obtained from the terpolymer which has 10 mol% of selenophene to thiophene, and unprecedentedly high hole-mobility $(3.28 cm^2 V^{-1} s^{-1})$ was also observed in organic field-effect transistors (OFETs). To understand these trends, the ordering of terpolymers and nano-morphology of terpolymers:PC71BM blends were carefully investigated by grazing-incidence X-ray scattering (GIXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The findings suggested that introduction of selenophene unit in the main backbone significantly influence the lamellar stacking and formation of fibrillar structures.