Proceedings of NFA-Based Organic Solar Cells: Materials, Morphology and Fundamentals (NFASC)
DOI: https://doi.org/10.29363/nanoge.nfasc.2021.010
Publication date: 25th January 2021
Significant breakthroughs with unprecedented power conversion efficiencies (PCEs) exceeding 18% have been achieved for polymer:NFA organic solar cell (OSC) blends recently. Among systems that are able to achieve remarkable efficiencies is the PM6:Y6 bulk-heterojunction (BHJ) blend, which can successfully reach PCEs of up to 15.7%. The PM6:Y6 system can achieve high open circuit voltages (VOC) while maintaining exceptional fill-factor (FF) and short-circuit current (JSC) values. With a low energetic offset, the blend system was found to exhibit radiative and non-radiative recombination losses that are among the lower reported values in the literature. Recombination and extraction dynamic studies revealed that the device shows moderate non-geminate recombination coupled with exceptional extraction throughout the relevant operating conditions. Several surface and bulk characterization techniques including GIWAXS, photo-conductive atomic force microscopy (pc-AFM), and NMR spectroscopy were employed to understand the phase separation, long-range ordering, as well as donor:acceptor (D:A) inter- and intramolecular interactions at an atomic-level resolution. The synergy of multifaceted characterization and device physics was used to uncover key insights on the structure-property relationships of this high performing BHJ blend. Detailed information about D:A interactions and molecular packing revealed that the high performance of over 15% efficiency in this blend can be correlated to a beneficial morphology that allows high JSC and FF to be retained despite the low energetic offset.