A 3D nonfullerene electron acceptor with a 9,9′-bicarbazole backbone for high-efficiency organic solar cells.

One-dimensional ladder-type nonfullerene electron acceptors (NFAs) with large fused ring cores have been widely used in highly efficient organic solar cells (OSCs). Recent studies have demonstrated that small molecule acceptors with three-dimensional (3D) structures may exhibit low energy loss, and hence can lead to improved OSC performance. In this study, a new 3D NFA (99CZ-8F) with a 9,9′-bicarbazole backbone was designed, synthesized, and characterized, where two linear A-D-A architectures were linked by a single N–N bond. 99CZ-8F showed strong absorption in the range of 500–800 nm in the solid state, which is complementary to the absorption of the donor material PM6. After regulating the morphology of the active layer via binary solvent mixture, the optimized device exhibited a maximum power conversion efficiency (PCE) of 6.6 ± 0.1%, which is among the best reported values for 3D nonfullerene electron acceptor based OSCs. A 3D NFA 99CZ-8F exhibited a PCE of 6.6% via binary solvent regulation. Image 1 • A novel 3D nonfullerene electron acceptor was applied for high-efficiency organic solar cells. • The morphology of active layer is controlled by the drying time and the solubility. • The 3D acceptor can be dispersed in PM6 to form a homogeneous thin film. • The authors report no conflict of interest. The authors are responsible for the content and writing of the paper. [ABSTRACT FROM AUTHOR]