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. – We will also present a vignette detailing some work at NCSU regarding the integration of OPV into greenhouses [1-4]. 

[1] “Achieving net zero energy greenhouses by integrating semitransparent organic solar cells”, E Ravishankar, RE Booth, C Saravitz, H Sederoff, HW Ade, BT O’Connor, Joule 4, 490-506 (2020)

[2] “Balancing crop production and energy harvesting in organic solar-powered greenhouses”, E Ravishankar, M Charles, Y Xiong, R Henry, J Swift, J Rech, J Calero, et al. Cell Reports Physical Science 2, 100381 (2021)

[3] “Organic solar powered greenhouse performance optimization and global economic opportunity”, E Ravishankar, RE Booth, JA Hollingsworth, H Ade, H Sederoff, et al. Energy & Environmental Science 15, 1659-1671(2021)

[4] “Beyond energy balance in agrivoltaic food production: Emergent crop traits from color selective solar cells”, M Charles, B Edwards, E Ravishankar, J Calero, R Henry, J Rech, et al, bioRxiv (2022) doi: https://doi.org/10.1101/2022.03.10.482833