A new non-fullerene acceptor based on the heptacyclic benzotriazole unit for efficient organic solar cells

Non-fullerene acceptors (NFA) become a promising family of organic photovoltaic materials, and have attracted considerable interest for their great potential in manufacturing large-area flexible solar panels by low cost coating methods. A near-IR non-fullerene electron acceptor (Y9), featuring two 3-undecyl-thieno[2',3':4,5]thieno[3,2-b]pyrrole units and benzotriazole unit to form a fused DA’D type heterocyclic ring was designed and synthesized. Y9 displayed broad and strong absorption in the 600–900 nm, a low optical bandgap of 1.36 eV. The organic solar cell (OSC) device using Y9 as an acceptor blending with PBDB-T donor showed a power conversion efficiency (PCE) of 10.64% in single junction OSC. After the device optimization, the device possessed efficient exciton separation and charge transfer, efficient and balanced charge transport and negligible bimolecular recombination. The optimized device could deliver a high PCE of 13.26%, demonstrating the great potential of NIR non-fullerene acceptor in single junction organic solar cells.