<br/>The rise of new low-bandgap donors and non-fullerene acceptors led organic solar cells (OSC) to surpass the 18% efficiency mark. Despite this, the vast majority of state-of-the-art devices are fabricated from halogenated solvent inks via spincoating under inert conditions. Replacing toxic halogenated solvents in the processing of OSCs is a requirement to comply with Occupational Safety and Health standards for large scale procesing and commercialization. Previous attempts have used Hansen Solubility Parameters (HSP) to assess the viability of alternative solvents based on their favorable fitting within solubility spheres limits. However, formulations with low toxicity high-boiling point borderline-solubility solvents are often overlooked as their drying kinetics and poor donor solubility is unfavorable for spincoating.<br/>Here, we design monoterpene green solvent formulations to fabricate PM6:BTP-EC9 devices via bladecoating with power conversion efficiencies of up to 15% and reduced toxicity (&gt;2800 mg/kg) , resembling that of table salt and baking soda. We determine the HSP spheres of the donor and acceptor, identify a wide range of lower toxicity nonhalogenated solvents that fall within the limits and at the outskirts of spheres, and formulate binary solvent compositions based on the linear additive behavior of HSP values. We analyze the effects of the evaporation, alongside HSP affinity and solubility dynamics of 4 different monorerpene inks on the formation of the bulk heterjuntion via in-situ absorbance measurements and in-depth optoelectronic characterization, and optimize drying conditions for bladecoating in air to maximize performance. Eucalyptol-based devices demonstrate only a 20% loss in performance after 2 months, resembling the stability of devices fabricated with chloroform. Lastly, we fabricatee large area devices (2cm<sup>2</sup>) with efficiencies of 13.5%, showcasing the applicability of monoterpene solvents for large-scale processing.

Fresh breath for organic solar cells: Photoactive ink formulation based on monoterpene food additive and fragrance green solvents

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.