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.