Tuning the optoelectronic properties of dual-acceptor based low-bandgap ambipolar polymers by changing the thiophene-bridge length†
Three very-low-bandgap dual-acceptor based polymers containing diketopyrrolopyrrole (DPP) and a thiadiazoloquinoxaline (TQ) derivative were prepared. Both acceptors in these polymers were separated by one, two and three thiophenes. By only inserting one thiophene between DPP and benzodithiophene condensed TQ, the polymer PDPP-T-TQ shows a very low optical bandgap of 0.60 eV with an electron affinity of −4.23 eV. Optical and electrochemical bandgaps of the polymers were enlarged with increasing the thiophene-bridge length between both acceptors. GIWAXS measurements confirmed that the polymer with three thiophene bridges (PDPP-3T-TQ) showed an ordered arrangement of the crystallites, providing the best ambipolar device performance among these polymers.