Liquid crystalline D-A conjugated oligomers capable of forming well-defined nanostructured films for high performance single-molecular organic solar cells

The nanostructured films with electron-donor (D) and electron-acceptor (A) bicontinuous phases interspaced in nanometer-scale are highly desirable for preparation of high performance oragnic solar cells. Monodisperse conjugated oligomers are characterized by an uniform chemical structure as well as tunable molecular length around 10 nm, and therefore are ideal scaffolds for well-defined nanostructures with a length scale equal to or less than the exciton diffusion length of organic semiconductors. We design and synthesize D-A cooligomers with different molecular lengths for illustrating this concept. These cooligomers can form highly ordered films comprising alternating D-A lamellar nanostructures with the period depending on the molecular length. As a result, single-molecular organic solar cells with an external quantum efficiency up to 46% and a power conversion efficiency (PCE) up to 1.50% have been demonstrated. These results represent the best performance for single-molecular solar cells to date.