Isomeric Effects of Solution Processed Ladder-Type Non-Fullerene Electron Acceptors

The role of electronic structure and thin film morphology is investigated in determining charge transfer and electron coupling due to orbital interactions in two isomeric non-fullerene acceptors with the structure of acceptor-donoracceptor. Differences are found in the distribution of electron density of the highest occupied molecular and lowest unoccupied molecular orbitals, whose bonding interactions result in improved intermolecular interactions and hence, molecular stacking. When combined with a large band gap polymer donor, solution-processed organic photovoltaic cells are demonstrated with power conversion efficiencies as high as 10.5 +/- 0.4%, and with absorption extending to wavelengths of 800 nm. Due to strong internal organization driven by the planar molecular structure and strong intermolecular interactions, no post-deposition processing such as solvent vapor or thermal annealing is required. To our knowledge, these are the highest efficiencies for as-cast solution-based devices employing non-fullerene acceptors.