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Visualizing Morphological Principles for Efficient Photocurrent Generation in Organic Non-Fullerene Acceptor Blends

: Köntges, W.; Perkhun, P.; Kammerer, J.; Alkarsifi, R.; Würfel, U.; Margeat, O.; Videlot-Ackermann, C.; Simon, J.-J.; Schröder, R.R.; Ackermann, J.; Pfannmöller, M.


Energy & environmental science 13 (2020), Nr.4, S.1259-1268
ISSN: 1754-5692
ISSN: 1754-5706
Fraunhofer ISE ()
Photovoltaik; Neuartige Photovoltaik-Technologien; organische Solarzelle

The efficiency of organic solar cells with donor polymers and non-fullerene acceptors depends on a complex morphology. Similar chemical and electronic structures impede generating in-depth insights in morphological details. We visualise molecular arrangements and the nanomorphology in PBDB-T:ITIC blends by correlating transmission electron micrographs and material distribution maps. Material phases are identified by machine learning on hyperspectral data from electron spectroscopic imaging. We observe a specific polymorph of ITIC after thermal annealing. During annealing, enhanced by the presence of additives, PBDB-T acts as nucleation site for ITIC due to strong π–π-interactions of the electron withdrawing groups of both molecules. This leads to efficient charge transport paths in ITIC phases with direct π–π-contact to PBDB-T at the interface. We conclude that π–π-stacking between donor and acceptor molecules facilitates charge carrier generation within mixed interface regions.