Organic photovoltaic devices (OPVs) based on organic semiconductor (OSC) materials have recently gained popularity. However, one limitation of such devices is their short lifetime, attributed to chemical and photochemical degradation through multiple pathways. Although many studies have focused on OSC degradation, an understanding of heterogeneity of degradation in active layer materials at the nanoscale has yet to emerge. Although interfaces within OPVs are known to be heterogeneous at this scale, especially at contacts between charge transport layers and the OSC, it is unclear if this heterogeneity leads to differences in degradation rates or pathways. One method for monitoring chemical degradation is Raman microscopy because of its rich molecular information, although spatial resolution of this technique is diffraction limited. To access nanoscale information, we use shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS), based on metallic nanostructures that provide highly distant-dependent electromagnetic field enhancement in the near-surface region. A novel, ultrathin indium tin oxide (ITO) shell coating protects the Au nanoparticle core from unwanted chemical interactions, while maintaining a conductive device-relevant environment necessary to study buried charge transport interfaces in OPV devices. A custom Raman microscope was designed and built in-house to enable spatially localized excitation for SERS for these nanoparticles while reducing far-field contributions. This microscope also contains backscattering dark field capabilities for precise location of individual nanoparticles without losing position on the sample. Using SHINERS with statistical sampling of many individual nanorods across a charge transport interface reveals relationships between the chemical structure of nanoscale defects and the resulting degradation products. Data for a model system at a P3HT-ZnO interface will be presented.

SHINERS for studying nanoscale organic semiconductor interfaces

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