Heterogeneous Nanoscale Morphology in Cross-Sections of Bulk Heterojunction Polymer Solar Cells Visualized by Analytical Electron Microscopy

Using analytical transmission electron microscopy, we investigated spectral images of blends of poly (3- hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). We applied low energy loss spectroscopic imaging and statistical data analysis to create chemical contrast on ultrathin sections of a pristine and an annealed photoactive layer. P3HT and PCBM domains as well as composite phases were identified at nanometer resolution across the section. This allowed for the visualization of the development of domain sizes and compositions from a pristine to an annealed, more efficient morphology in vertical and lateral directions. By using these data, we could deduce high-resolution cross-sectional concentration profiles and compared them with profiles generated by an established method, secondary ion mass spectrometry.