Efficient Organic Solar Cells from Molecular Orientation Control of M-Series Acceptors

A face-on'' molecular orientation is essential for photovoltaic materials with efficient vertical carrier transport, but understanding how themolecular structures control their orientations remains challenging. Based on a ladder-type fused-ring core without sp(3)-hybridized bridging atoms, novel acceptor-donor-acceptor (A-D-A or ADA)-type nonfullerene acceptors (M3 and M32) are developed, and their molecular orientation behaviors are successfully controlled by the neighboring side chains. With linear n-cetyl chains on the nitrogen atoms, the acceptor (M32) tends to adopt an ``edge-on'' molecular orientation, whereas with bulky branched 2-hexyldecyl chains, the acceptor (M3) has a preferred ``face-on'' orientation. Blended with a donor polymer of PM6, M3 shows optimal phase separation and dramatically improved electron transport, consequently leading to a much higher device performance than M32. Further optimization of the M3-based devices yields an outstanding efficiency of 16.66%. The strategy of molecular orientation control proposed here will inspire many other innovative designs and syntheses of high-performance nonfullerene acceptors.

Automated summary

Controlling the molecular orientation of nonfullerene acceptors by adjusting side chains leads to improved device performance, with M3 showing higher efficiency compared to M32 when blended with a donor polymer such as PM6.