Three-Step Synthesis Toward Fluorene-Based Non-Fused-Ring Acceptors for Organic Solar Cells

Non-fused-ring electron acceptors have recently gathered substantial interest for the application in organic solar cells because of their competitive photovoltaic properties and other advantages, including easy synthesis and high yields, facilitating the production of cost-efficient devices. In this work, a pair of fluorene-based acceptors, FHM-Cl and FHM-F, respectively featuring a chlorinated and a fluorinated 1,1-dicyanomethylene-3-indanone end group, π-bridged through alkyl-substituted thiophene units to a fluorene core, were synthesized through a three-step synthesis from commercially available precursors. Organic solar cells utilizing these acceptor molecules were subsequently fabricated and optimized with various donor materials. Notably, the combinations D18:FHM-Cl and D18:FHM-F achieved power conversion efficiencies of 10.7% and 7.6%, respectively. A comprehensive study involving optical and electrical characterization, along with morphological analysis, demonstrated that the FHM-Cl-based solar cells exhibited superior light absorption, enhanced solid-state packing and reduced trap-assisted recombination. Moreover, the shelf and thermal stability of the devices further highlight the potential of these acceptors in the design of low-cost and efficient organic solar cells.