N-Type pyromellitic diimide-benzodithiophene-containing conjugated polymers for all-polymer solar cells with high open-circuit voltage

n-Type conjugated polymers were synthesized by using pyromellitic diimide monomers with two different alkyl side chain substitutions as electron-accepting units and benzodithiophene as electron-donating unit via Stille coupling reaction. The obtained polymers were characterized by UV-vis spectroscopy and cyclic voltammetry. The results illustrate that the substituted alkyl side chains 2-ethylhexyl and 2-octyldodecyl have negligible effect on the optical properties of the resulting polymers. The LUMO levels of the polymers located at -3.5 to -3.6 eV. All-polymer bulk heterojunction solar cell with "P3HT" as p-type polymer in standard architecture were fabricated, the cell based on the polymer with 2-octyldodecyl side chain (P2) shows good photovoltaic performance with power conversion efficiency up to 0.47% and a high open circuit voltage of 0.96 V.