Novel organic photovoltaic polymer blends: A rapid, 3-dimensional morphology analysis using backscattered electron imaging in the scanning electron microscope

- Imaging morphology of PffBT4T-2OD:PC70BM blend in 3-dimensions.
- Backscattered electron imaging technique in the scanning electron microscope.
- Technique enables rapid morphology analysis, minimal sample preparation.
- PffBT4T-2OD:PC70BM shown to demonstrate strong domain stacking through film.
- Explains impressive performance as a solar cell active layer.

Finding the optimal morphology of novel organic photovoltaic (OPV) polymer blends is a major obstacle slowing the development of more efficient OPV devices. With a focus on accelerating the systematic morphology optimisation process, we demonstrate a technique offering rapid high-resolution, 3-dimensional blend morphology analysis in the scanning electron microscope. This backscattered electron imaging technique is used to investigate the morphological features and length-scales defining the promising PffBT4T-2OD:PC70BM blend system and show how its photovoltaic performance is related to the nature of its phase separation. Low-voltage backscattered electron imaging can be used to probe for structure and domain stacking through the thickness of the film, as well as imaging surface morphology with highly competitive spatial resolution. For reference, we compare our results with equivalent images of the widely studied P3HT:PC60BM blend system. Our results also demonstrate that backscattered electron imaging offers significant advantages over conventional cross-sectional imaging techniques, and show that it enables a fast, systematic approach to control 3-dimensional active layer morphology in polymer:fullerene blends.