New Benzo[1,2‐ b :4,5‐ b′ ]dithiophene‐Based Small Molecules Containing Alkoxyphenyl Side Chains for High Efficiency Solution‐Processed Organic Solar Cells

A new acceptor–donor–acceptor (A–D–A) small molecule, namely, BDT‐PO‐DPP, based on the alkoxyphenyl (PO)‐substituted benzo[1,2‐ b :4,5‐ b′ ]dithiophene (BDT) derivative and the diketopyrrolopyrrole (DPP) unit was synthesized as an electron donor for solution‐processed small‐molecule organic solar cells (SMOSCs). BDT‐PO‐DPP exhibited good thermal stability, with a 5 % weight‐lost temperature at 401 °C under a nitrogen atmosphere. BDT‐PO‐DPP exhibited a lower HOMO energy level of −5.25 eV and a weaker aggregation ability than alkoxy‐substituted BDT‐O‐DPP. A bulk heterojunction SMOSC device based on BDT‐PO‐DPP and [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester was prepared, and it showed a power conversion efficiency up to 5.63 % with a high open‐circuit voltage of 0.83 V, a short circuit current density of 11.23 mA cm −2 , and a fill factor of 60.37 % by using 1,2‐dichlorobenzene as the co‐solvent after thermal annealing at 110 °C. The results indicate that the alkoxyphenyl‐substituted BDT derivative is a promising electron‐donor building block for constructing highly efficient solution‐processed SMOSCs.