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 spectroscopy because of its rich molecular information. Here 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, to access nanoscale information. SHINERS is typically performed using Au nanoparticles coated in a silica shell. Here, however, the desire to study buried interfaces in conductive OPVs requires the ability maintain conductivity and use of a shell material that is device-relevant. Toward this end, a coating procedure was developed to indium tin oxide (ITO)-coated Au nanorods for SHINERS. These Au@ITO nanorods are sparsely dispersed between two relevant device layers for study.  A modified Raman microscope has been designed and built in-house to enable spatially localized excitation for SERS at these nanoparticles while reducing far-field contributions. This microscope is used to perform SHINERS experiments that demonstrate the ability of Au@ITO nanorods to act as nanoscale, interface-selective Raman probes. SHINERS results from degradation studies involving interfaces between charge transport and active layer materials will be presented.

SHINERS for study of organic semiconductor interfaces at the nanoscale

ACS Spring 2022

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