All-small-molecule organic solar cells with 18.1% efficiency and enhanced stability enabled by improving light harvesting and nanoscale microstructure

Achieving a bi-continuous morphology with appropriate and solidified nanoscale domains in the active layers is a challenging task for all-small-molecule organic solar cells (all-SMOSCs), which is the main reason that their power conversion efficiencies (PCEs) and relevant stability indexes still lag those of bulk-heterojunction (BHJ) polymer solar cells (PSCs). In this vein, highly efficient and stable all-SMOSCs were developed based on a ternary BHJ layer of MPhS-C2:L8-BO:L8-S9. The addition of asymmetric acceptor L8-S9 broadens the absorption spectra and enhances the molecular packing of host acceptors while simultaneously modifying the BHJ microstructure and suppressing the non-geminate recombination and morphological evolution of the host blend. Consequently, the optimal ternary blend exhibits a superior PCE of 18.10% compared with the related binary devices. Impressively, the ternary system can maintain 80% of its initial efficiency for up to approximately 1,000 h under one sun operation.