"This image is a topographical Atomic Force Microscopy image of the surface of an organic bulk heterojunction solar cell after solvent vapor annealing the top active layer in chloroform for five minutes. The active layer is composed of a blend of electron donor material, DTS(FBTTh2)2, and electron acceptor material, PC71BM. The active layer was solvent vapor annealed by placing the device inertly in a container filled with chloroform vapor.
From an initially pitted surface, the solvent vapor annealing drives the molecules in the active layer to self-reorganize. The stunning swirls in the image are created by the crystallization of the active layer through molecular self-reorganization. This incredible morphological transformation is being studied as a means of improving the efficiency of organic solar cells."