Influence of material migration on the mechanical integrity of inverted organic solar cells

We have identified modifications of material distributions in inverted organic solar cell structures during accelerated aging processes that are potentially linked to the loss of the mechanical integrity of the devices. Non-encapsulated devices were treated with ISOS-D-3 ageing (the so called damp heat exposure at 85 degrees C/85% room humidity in the dark). After performing pull-off tests, the exposed surfaces were analyzed by X-ray photo-emission spectroscopy and atomic force microscopy. For fresh devices, the results revealed that mechanical failure occurs close to the PEDOT:PSS/P3HT:PCBM interface, in agreement with the literature. However, after a short exposure to damp heat, XPS investigations indicate an enrichment of PCBM at the PEDOT:PSS/P3HT:PCBM interface and a change in the PEDOT:PSS surface composition. Both phenomena may explain the rapid drop in device performances and the increased tendency towards delamination.