Traditional electron microscopy techniques such as bright-field imaging provide poor contrast for organic films and identification of structures in amorphous material can be problematic, particularly in high-performance organic solar cells. By combining energy-filtered corrected transmission electron microscopy, together with electron energy loss and X-ray energy-dispersive hyperspectral imaging, we have imaged PTB7/PC61BM blended polymer optical photovoltaic films, and were able to identify domains ranging in size from several hundred nanometers to several nanometers in extent. This work verifies that microstructural domains exist in bulk heterojunctions in PTB7/PC61BM polymeric solar cells at multiple length scales and expands our understanding of optimal device performance providing insight for the design of even higher performance cells.

Finding a faster alternative to tilt-series electron tomography is critical for rapidly evolving fields such as the semiconductor industry, where failure analysis could greatly benefit from higher throughput. We present a theoretical and experimental evaluation of scanning confocal electron energy-loss microscopy (SCEELM) using valence-loss signals, which is a promising technique for the reliable reconstruction of materials with sub-10-nm resolution. Such a confocal geometry transfers information from the focused portion of the electron beam and enables rapid three-dimensional (3D) reconstruction by depth sectioning. SCEELM can minimize or eliminate the missing-information cone and the elongation problem that are associated with other depth-sectioning image techniques in a transmission electron microscope. Valence-loss SCEELM data acquisition is an order of magnitude faster and requires little postprocessing compared with tilt-series electron tomography. With postspecimen chromatic aberration (Cc) correction, SCEELM signals can be acquired in parallel in the direction of energy dispersion with the aid of a physical pinhole. This increases the efficiency by 10×–100×, and can provide 3D resolved chemical information for multiple core-loss signals simultaneously.