Real-Time Characterization of the Nanostructure of a Metal Electrode on an Organic Thin Film: An In Situ X-Ray Scattering Study

We measured the real-time variations in the nanostructure of organic (P3HT:PCBM) films and the interfacial structure between the electrode and an organic layer during thermal annealing using in-situ X-ray scattering measurements. An in-situ annealing system is valuable for investigating the nanostructures of organic thin films by simultaneously measuring the X-ray reflectivity and the grazing incidence wide-angle X-ray scattering profile. The interface between a Ca electrode and a P3HT:PCBM film began to degrade at 90 degrees C; however, thermal degradation could be prevented by a pre-annealing process prior to the metal deposition step. Device performance measurements revealed that the interface degradation could explain why organic photovoltaic devices with Ca electrodes performed poorly after an annealing process.