Non-Fullerene Acceptors Containing Alkylated Large it-Conjugated Building Blocks for Efficient Organic Photovoltaic Cells

A sidechain optimization strategy is widely utilized in organic semiconductor materials to optimize both solubility and solid-state properties. Here, we introduced octyl rather than phenylalkyl groups onto indacenodithienothio-phene (IDTT) to construct three acceptor-donor-acceptor '-donor-acceptor (A-D-A '-D-A)-type acceptors, CNDTBT-C8IDTT-INCN, CNDTBT-C8IDTT-FINCN, and CNDTBT-C8IDTT-ClINCN. Benefiting from the reduced steric bulk of the octyl group, these acceptors show closer pi-pi stacking distances (similar to 3.58 angstrom), which is beneficial for charge transport. A fluorine-substituted acceptor CNDTBT-C8IDTT-FINCN displays excellent performance in solar cells due to efficient suppression of the charge recombination process and good charge transport ability in blend films. A PBDB-T:CNDTBT-C8IDTT-FINCN-based device achieved the highest power conversion efficiency (PCE) of 12.06%, with open -circuit voltage VOC = 0.83 V, JSC = 20.58 mA cm-2, and FF = 70%.