A novel low band gap conjugated polymer based on N-substituted dithieno[3,2-b:2′,3′-d]pyrrole

Poly{[N-dodecyl-dithieno(3,2-b:2′,3′-d)pyrrole-2,6-diyl]-alt-[2,1,3-benzothiadiazole-4,7-diyl]} (PBTDTP) was successfully prepared via Stille coupling. The new polymer is soluble in common organic solvents such as chloroform (CHCl₃), tetrahydrofuran (THF) and o-dichlorobenzene. Compared with N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole (DTP) homopolymer, the maximum absorption of PBTDTP was red-shifted approximately 40 nm. The optical band gap of the polymer in film state is 1.55 eV calculated from the onset of absorption spectrum. The cyclic voltammetry measurements of the polymer depicted a HOMO energy level of -5.0 eV and a LUMO energy level of -3.3 eV of PBTDTP. This work demonstrates that this newly synthesized polymer is a promising p-type material for application in bulk hetero-junction organic solar cells.