Morphological and Mechanical Stability of Non-Fullerene Organic Solar Cells
Harald Ade a
a North Carolina State University, Partners Way, 911, Raleigh, United States
Materials for Sustainable Development Conference (MATSUS)
Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)
#STAPOS - Stability of perovskite and organic solar cells
Barcelona, Spain, 2022 October 24th - 28th
Organizers: Carsten Deibel and Qiong Wang
Invited Speaker, Harald Ade, presentation 107
DOI: https://doi.org/10.29363/nanoge.nfm.2022.107
Publication date: 11th July 2022

Organic solar cells (OSCs) are one of the most promising cost-effective options for utilizing solar energy in high energy-per-weight or semi-transparent applications. Recently, the OSC field has been revolutionized through synthesis and processing advances, primarily through the development of numerous novel non-fullerene small molecular acceptors (NFA) with efficiencies now reaching >19% when paired with suitable donor polymers. The device stability and mechanical durability of these  non-fullerene OSCs have received less attention and developing devices with high performance, long-term morphological stability, and mechanical robustness remains challenging, particularly if the material choice is restricted by roll-to-roll and benign solvent processing requirements and desirable ductility requirements. Yet, morphological and mechanical stability is a prerequisite for OSC commercialization. Here, we discuss our current understanding of the phase behavior of OSC donor:acceptor mixtures and the relation of phase behavior and the underlying hetero- and homo-molecule interactions to performance, processing needs (e.g., kinetic quenches), and morphological and mechanical stability. Characterization methods range from SIMS and DSC measurements to delineate phase diagrams and miscibility to x-ray scattering to determine critical morphology parameters and molecule packing and dynamic mechanical analysis (DMA) to assess specifically the hetero-interactions. The results presented and its ongoing evolution are intended to uncover fundamental molecular structure-function relationships that would allow predictive guidance on how desired properties can be targeted by specific chemical design. Comparative studies show that the molecular hetero-interactions between the donor and NFA are not always the geometric mean of the homo-interactions. This underscores the limited success often encountered when Hanson Solubility Parameters and surface energies are used to estimate molecular interactions.

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