Exploring the 3D organisation of high-performance organic solar cells

In high performance organic solar cells, the photoactive layer consists of a blend of electron donor and electron accepter constituents, a so-called bulk heterojunction. The requirements for the morphology of an efficient photoactive layer are nanoscale phase separation, which provides a large interface area for exciton dissociation, and the existence of continuous pathways for transport of free charge carriers to the appropriate electrodes. In this context, research is now focused on a better understanding of the influence of morphology (particularly, the nanoscale organisation of the phase segregated constituents) on the physical properties of the active layer [1–3]. Because the active layer is deposited from solution, several parameters determine the morphology formation, such as the blending ratio, the solvent used and its evaporation rate, post treatments like annealing, etc.