1,1,4,4-Tetracyanobuta-1,3-diene Substituted Diketopyrrolopyrroles: An Acceptor for Solution Processable Organic Bulk Heterojunction Solar Cells

Two small molecules composed of 1,1,4,4-tetracyanobuta-1,3-diene substituted diketopyrrolopyrroles (DPPs) denoted as DPPS and DPP6 were synthesized and their photophysical and electrochemical properties were investigated. The frontier molecular orbitals based on empirical relation between cyclic voltammetry redox potentials, experimental IP, and EA energies indicate that these two small molecules can be used as an electron acceptor for the polymer bulk heterojunction solar cells. The BIT solar cells combined with a low band gap D-A copolymer P as an electron donor exhibits promising power conversion efficiency of 3.90% and 4.95%, with DPPS and DPP6, respectively, after the optimization of active layers, indicating that these small molecules based on DPPs can be the alternative as an electron acceptor to replace fullerene, leading to the low-cost solution-processed polymer solar cells.