Giant Molecule Acceptor Enables Highly Efficient Organic Solar Cells Processed Using Non‐halogenated Solvent

Abstract High efficiency organic solar cells (OSCs) based on A‐DA′D‐A type small molecule acceptors (SMAs) were mostly fabricated by toxic halogenated solvent processing, and power conversion efficiency (PCE) of the non‐halogenated solvent processed OSCs is mainly restricted by the excessive aggregation of the SMAs. To address this issue, we developed two vinyl π‐spacer linking‐site isomerized giant molecule acceptors (GMAs) with the π‐spacer linking on the inner carbon (EV‐i) or out carbon (EV‐o) of benzene end group of the SMA with longer alkyl side chains (ECOD) for the capability of non‐halogenated solvent‐processing. Interestingly, EV‐i possesses a twisted molecular structure but enhanced conjugation, while EV‐o shows a better planar molecular structure but weakened conjugation. The OSC with EV‐i as acceptor processed by the non‐halogenated solvent o ‐xylene ( o ‐XY) demonstrated a higher PCE of 18.27 % than that of the devices based on the acceptor of ECOD (16.40 %) or EV‐o (2.50 %). 18.27 % is one of the highest PCEs among the OSCs fabricated from non‐halogenated solvents so far, benefitted from the suitable twisted structure, stronger absorbance and high charge carrier mobility of EV‐i. The results indicate that the GMAs with suitable linking site would be the excellent candidates for fabricating high performance OSCs processed by non‐halogenated solvents.