Efficient Organic Solar Cells Based on Non-Fullerene Acceptors with Two Planar Thiophene-Fused Perylene Diimide Units.

We designed and synthesized two non-fullerene acceptors (CDT-TFP and C8X-TFP), which comprise a central 4H-cyclopenta[2,1-b:3,4-b']dithiophene (CDT) as the bridge and two thiophene-fused perylene diimide (TFP) units. The bulky side chains, such as the 4-hexylphenyl side chains, on the CDT bridge can effectively prevent the acceptor molecules from forming large aggregates, and the π-π stacking of the terminal planar TFP units can form effective electron transport pathways when blending with the donor polymers. These non-fullerene acceptors are used to fabricate organic solar cells (OSCs) by blending with the regioregular middle bandgap polymer reg-PThE. The as-cast devices based on reg-PThE:CDT-TFP show the best power conversion efficiency (PCE) of 8.36% with a Voc of 1.10 V, Jsc of 12.43 mA cm-2, and an FF of 61.4%, whereas the analogue perylene diimide (PDI) dimers (CDT-PDI) that comprise two PDI units bridged with a CDT unit show only a 2.59% PCE with a Voc of 0.92 V, Jsc of 6.82 mA cm-2, and an FF of 41.5%. Our results have demonstrated that the non-fullerene acceptors comprising planar PDI units can achieve excellent photovoltaic performance and provide meaningful guidelines for the design of PDI-based non-fullerene electron acceptors for efficient OSCs.