Synthesis and absorption spectra of n-type conjugated polymers based on perylene diimide

Two novel n-type conjugated polymers based on perylene diimide (PDI), poly(PDI-vinylene) (PDIV), and poly(PDI-thienylene) (PDITh), have been designed and synthesized by the Stille coupling reaction. In comparison with the PDI monomer (compound M1), PDIV and PDITh films show a significantly broad absorption band from 380 to 720 nm, and a narrower bandgap of ≈1.71 and 1.74 eV, respectively. Cyclic voltammograms of the two polymers display a couple of reversible reduction/re-oxidation (n-doping/dedoping) peaks. The onset reduction (n-doping) potentials of PDIV and PDITh are at -0.62 V and -0.66 V versus Ag/Ag⁺ respectively, which correspond to the electron affinities (EAs) of 4.09 eV for PDIV and 4.05 eV for PDITh. The EA values of the two polymers are the highest among the n-type conjugated polymers reported to date. The results indicate that PDIV and PDITh could be used as polymer acceptors in all polymer solar cells.