Are PM6:Y6 Bulk Heterojunction Photoactive Films Cytocompatible and Electrically Stable in Biological Environments?

Organic photovoltaics show great potential for wireless bioelectronics, offering the ability to convert visible-to-near-infrared light into electrical energy. This study investigates the stability and biocompatibility of PM6:Y6 bulk heterojunction layers, chosen for their efficient charge separation and absorption profile compatible with the optical transparency of skin tissue, under simulated physiological conditions. Biocompatibility is validated using the chicken chorioallantoic membrane and cytotoxicity assays with primary neurons, showing no adverse effects on cell viability or morphology. The layers demonstrated stable photoinduced charge separation over 28 days in electrolytic environments with a significant voltage increase of approximate to 40 mV after one day. The addition of a PM6 overlayer improved voltage responses and reduced swelling, possibly acting as a selective barrier, however, leading to a decrease in the achievable peak current densities over time. Atomic force microscopy and transient absorption spectroscopy confirmed the structural and functional stability of the films, with almost unaffected charge generation and recombination rates in aqueous environments. The PM6 layer slowed charge formation due to increased diffusion lengths. These findings underscore the PM6:Y6 blend's potential for use in bioelectronics. Future studies should examine PM6:Y6 performance in vivo conditions and focus on an improved understanding of interaction mechanisms with biological systems.