Synthesis of the Copolymer Based on Diketopyrrolopyrrole with Didecyl Chain for OPVs

A new accepter unit, diphenylpyrrolo[3,2-b]pyrrole-2,5-dione with didecyl chain, was prepared and utilized for the synthesis of the conjugated polymer containing electron donor-acceptor pair for OPVs. The iDPP, part of the structure of a natural dye found in lichens, is the regioisomer of the known DPP with switched position of the carbonyl group and nitrogen atom. At the 4-positions of the N-substituted phenyl groups of 1,4-bis(4-butylphenyl)-pyrrolo[3,2-b]-pyrrole-2,5-dione unit in P-butyl, the butyl group was substituted with decyl group to increase solubility. The absorption spectrum of polymer with diphenylpyrrolo[3,2-b]pyrrole-2,5-dione unit exhibit two maximum peaks at about 365 and 542 nm. The spectrum of the P1 as the solid thin film shows absorption band with maximum peaks at 370 and 536 nm, and the absorption onset at 703 nm, corresponding to band gap of 1.76 eV. The oxidation and reduction potential onset of the synthesized polymer were estimated to be 0.84 and ?1.22 V, which correspond to HOMO and LUMO energy levels of ?5.64 and ?3.58 eV, respectively. The devices comprising P1 with PC₆₁BM annealed at 100°C showed a V_OC of 0.79 V, a J_SC of 1.75 mA/cm², and a FF of 0.31, leading to the power conversion efficiency of 0.43% under white light illumination (AM 1.5 G, 100 mW/cm²).