Subphthalocyanine-Diketopyrrolopyrrole Conjugates: 3D Star-Shaped Systems as Non-Fullerene Acceptors in Polymer Solar Cells with High Open-Circuit Voltage

Four star-shaped electron acceptors (C-1-OPh, C-3-OPh, C-1-Cl and C-3-Cl) based on a subphthalocyanine core bearing three diketopyrrolopyrrole wings linked by an acetylene bridge have been synthesized. These derivatives feature two different axial substituents (i. e., 4-tert-butylphenoxy (OPh) or chlorine (Cl)) and for each of them, both the C-1 and the C-3 regioisomers have been investigated. The four compounds exhibit a broad absorption band in the 450-700 nm region, with bandgap values near to 2 eV. These materials were applied in the active layer of inverted bulk-heterojunction polymer solar cells in combination with the donor polymer PBDB-T. Derivatives bearing the OPh axial group showed the best performances, with C-1-OPh being the most promising with a PCE of 3.27 % and a V-oc as high as 1.17 V. Despite presenting the widest absorption range, the photovoltaic results obtained with C-1-Cl turned out to be the lowest (PCE=1.01 %).