Modulating Energy Level on an A-D-A′-D-A-Type Unfused Acceptor by a Benzothiadiazole Core Enables Organic Solar Cells with Simple Procedure and High Performance

Unfused-ring acceptors (UFAs) have gained considerable research attention as they offer simple chemical structures through simplified synthesis methods, which would boost the commercialization of organic solar cells (OSCs). Recently, a new small molecule acceptor (SMA) named Y6 was reported, yielding high-performance OSCs. Herein, the Y6-like A-DA′D-A framework is developed to A-D-A′-D-A-type backbone adopted in constructing UFAs. Two new Y6-like UFAs are synthesized within four steps and the effect of noncovalent atoms at the central electron-deficient core on material properties and device performances is studied. It is found that the introduction of fluorine atoms can bring larger red-shift in the absorption spectra and better aggregation of the resulting UFA film states compared with those of oxygen atoms. Interestingly, the variations in the noncovalent interaction atoms induce different intermolecular charge transfer between donors and UFAs. When blended with another economical donor, PTQ10, F substitution at the benzothiadiazole ring is more effective than O substitution, leading to the increased short-circuit current density (J_SC) and higher efficiency of over 12%, among the best performances of UFA-based OSCs. This contribution demonstrates the appropriate introduction of noncovalent interaction is a promising method for tuning energy levels, absorption, and aggregation of UFAs for high-performance OSCs.