A–DA′D–A-Type Pentacyclic Fused-Ring Electron Acceptors for Efficient Organic Solar Cells

Although superior power conversion efficiencies (PCEs)
(>19%) have
been achieved by organic solar cells (OSCs), high materials cost severely
prevents this photovoltaic technology from laboratory to industrial
maturity. Particularly, the prevailing A–DA′D–A-type
heptacyclic fused-ring electron acceptors (FREAs) suffered from arduous
synthesis and extremely low overall synthetic yield. Herein, we report
three A–DA′D–A-type pentacyclic FREAs (BTPT4F-EH,
BTPT4F-BO, and BTPT4F-HD) with varied side chain length for application
in OSCs. Compared with the prevailing heptacyclic FREAs, the pentacyclic
FREAs exhibited much lower synthetic complexity. Single-crystal analysis
unraveled that stair-like two-dimensional molecular stacking mode
was formed in the crystal of BTPT4F-BO due to the existence of strong
π–π interactions and hydrogen bonds, which could
guarantee efficient charge transport in A–DA′D–A-type
pentacyclic FREAs. As a result, a remarkable PCE of 15.0% has been
offered by the OSC based on BTPT4F-BO. The high PCE and low synthetic
complexity further contributed to an unprecedented figure of merit
(FOM = 0.36) for BTPT4F-BO. This work suggests, with respect to heptacyclic
FREAs, A–DA′D–A-type pentacyclic FREAs are more
competitive candidates for the future industrial manufacturing of
OSCs.