Time-resolved morphological study of bulk heterojunction films for efficient organic solar devices

The crucial requirement of device stability in the development of organic electronics was addressed. In particular, the nanoscale morphology of bulk heterojunction organic films for photovoltaic applications was studied by time-resolved energy dispersive X-ray reflectometry in synergy with atomic force microscopy analysis. A reorganization of the organic molecules in the film upon illumination was detected. The occurrence of two distinct processes (characterized by a reorganization of the blend bulk and an increase of its surface roughness, respectively) was revealed. Furthermore, the effect of the morphological instability on the device efficiency over time was quantified. Finally, the effect of thermal annealing treatments and of the choice of different cathodes was verified.