In situ energy dispersive x-ray reflectometry measurements on organic solar cells upon working

The change in the morphology of plastic solar cells was studied by means of time-resolved energy dispersive x-ray reflectivity (XRR). This unconventional application of the XRR technique allowed the follow up of in situ morphological evolution of an organic photovoltaic device upon working. The study consisted of three steps: A preliminary set of XRR measurements on various samples representing the intermediate stages of cell construction, which provided accurate data regarding the electronic densities of the different layers; the verification of the morphological stability of the device under ambient condition; a real-time collection of XRR patterns, both in the dark and during $15\mathrm{h}$ in artificial light conditions which allowed the changes in the system morphology at the electrode-active layer interface to be monitored. In this way, a progressive thickening of this interface, responsible for a reduction in the performances of the device, was observed directly.