Measuring Optical Absorption in Organic Photovoltaics Using Monochromated Electron Energy-Loss Spectroscopy

The electronic properties of the materials utilized in organic photovoltaics (OPVs) play a key role in the performance of the device. Furthermore, the electronic structure at the interface between the donor and acceptor materials within the photoactive layer influences the ability of exciton charges to separate and, therefore, influences the current generation within the OPV device. Transmission electron microscopy can potentially provide information on the donor/acceptor interface but collecting spatially-resolved electronic information for organic materials has previously proven difficult, as these materials are extremely electron beam sensitive. In this contribution, we demonstrate how such electronic structure information, including the optical absorption spectrum, can be collected reliably and with nanometer scale spatial resolution for OPV materials using electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM).