Pyridine-bridged diketopyrrolopyrrole conjugated polymers for field-effect transistors and polymer solar cells

Five wide or medium band gap diketopyrrolopyrrole (DPP)-based conjugated polymers with pyridine as bridges were developed for organic field-effect transistors (OFETs) and polymer solar cells (PSCs). By introducing copolymerized aromatic building blocks from strong electron-donating units to electron-deficient units into the conjugated backbone, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the DPP polymers were tailored to the low-lying position. Therefore, the polarity of charge transport in OFETs can be switched from p-type to n-type. The DPP polymer with a low-lying LUMO of -3.80 eV provides a hole-only mobility of 2.95 x 10(-2) cm(2) V-1 s(-1), while an electron-only mobility of 1.24 x 10(-3) cm(2) V-1 s(-1) is found in the DPP polymer with a LUMO of -4.22 eV. Further investigation of photovoltaic cells based on these DPP polymers shows a modest power conversion efficiency (PCE) of around 2%. Our results demonstrate that wide band gap pyridine-bridged DPP polymers have potential application in OFETs and OSCs by adjusting their energy level with alternated units on the conjugated backbone.