Introducing an identical benzodithiophene donor unit for polymer donors and small-molecule acceptors to unveil the relationship between the molecular structure and photovoltaic performance of non-fullerene organic solar cells

The side-chain conjugation strategy is adopted in the synthesis of heptacyclic non-fullerene electron acceptors, ITIC2, ITIC-S, and ITIC-SF, for application in organic solar cells (OSCs). The new ITIC-SF molecule features a BDT-SF building block which is the electron-donating component in the widely used donor PBDB-T-SF. Compared with ITIC-S without fluorine substituents, fluorination weakens the crystallinity of ITIC-SF, while the intermolecular interaction between the PBDB-T-SF donor and ITIC-SF acceptor, containing the same BDT-SF building block, results in the increased crystallinity of the corresponding blend films. The OSC based on PBDB-T-SF:ITIC-SF exhibits a champion power conversion efficiency (PCE) of 12.1%, higher than the PCE of 10.1% for the device based on PBDB-T-SF:ITIC2 and the PCE of 11.6% for the device based on PBDB-T-SF:ITIC-S. The better photovoltaic performance of the OSC based on PBDB-T-SF:ITIC-SF is benefitted from the weaker bimolecular recombination and more efficient charge transfer and extraction of the device. The structure-property relationship of the non-fullerene acceptors revealed in this work will play an important role in instructing the molecular structure design of high performance photovoltaic materials for the development of OSCs.