Multiple Fused Ring-Based Near-Infrared Nonfullerene Acceptors with an Interpenetrated Charge-Transfer Network

Two small molecule acceptors with chlorinated IC as end groups and 10-ring- and 12-ring-fused cores as central units, named R10-4Cl and R12-4Cl, were designed and synthesized, which exhibit low optical band gaps of 1.43 and 1.35 eV, respectively. X-ray crystallographic analysis of R10-4Cl shows that the end groups of adjacent molecules are parallel and partially overlap with a short π–π distance of 3.32 Å, which is helpful for electron transport in this direction. At the same time, there is another type of molecular orientation that lies in these two molecules with an angle about 64.7° because of the close contact of S···O with a distance of 3.15 Å. The two types of molecular arrangements result in an interpenetrated network structure in R10-4Cl films, which is helpful for the rapid charge transfer either along the horizontal direction or the sloping direction. After blending with a PBDB-T polymer donor, the R10-4Cl-based device shows wide photocurrent response from the visible to near-infrared regions, resulting in the better usage of the sunlight source. Benefited from this comprehensive solar energy absorption and the interpenetrated charge transfer, the R10-4Cl-based devices show a power conversion up to 10.7% with an improved J_SC of 18.9 mA cm^–2.