Neutron Scattering Elucidates the Structure of Organic Photovoltaic Active Layers

1. Neutron Scattering Elucidates the Structure of Organic Photovoltaic Active Layers Mark D. Dadmun, University of Tennessee Knoxville, DMR 1005987 Organic Photovoltaics (OPVs) are attractive as a lightweight, low-cost and easy to process replacement for inorganic solar cells. The morphology of the OPV active layer is crucial to its performance. The experimental determination of the morphology of OPV active layers is difficult due to the limited contrast between the C60 fullereneand the carbon based polymer with electron microscopy and x-rays. The results of recent neutron scattering experiments1 provide previously unknown detail concerning the miscibility, interfacial structure and morphology of P3HT:PCBM bulk heterojunctions. The results indicate that the perceived optimum morphology of an OPV active layer is incorrect. Interpretation of these results provides a model for an ideal bulk heterojunction morphology that is dramatically different than the current picture. As such, it provides a true paradigm shift in the image of the optimal structure of these materials. (1) W. Yin, M.D. Dadmun “A New Model for the Morphology of P3HT/PCBM Organic Photovoltaics from Small Angle Neutron Scattering: Rivers and Streams.” ACSNano, 5, 4756–4768 (2011) Neutron scattering results show that conjugated polymers and fullerenes are much more miscible than previously assumed, which is inconsistent with the morphology that is commonly presented for optimal organic photovoltaic bulk heterojunctions. A novel ‘rivers and streams’ morphology is proposed and illustrated above, which is consistent with these scattering results and previously reported photovoltaic functionality.