Solution-processed bi-layer polythiophene–fullerene organic solar cells

An ionic polymer based on a polythiophene backbone with appended imidazolium moieties was successfully implemented as a donor material in fully solution-processed efficient bi-layer solar cells prepared by the low impact meniscus coating technique. High fill factors and device reproducibility were obtained, even for ultrathin polymer layers, indicating excellent film formation properties and good compatibility with solution processing techniques. The possibility of smooth counter ion exchange, allowing solubility modification and efficiency tuning, enables exploration of new functionalities and other device architectures.