A Nanoscale Study on The Morphology and Conductivity of Biosourced Chlorophyll

The increasing demand for electronics causes increasingly worrying environmental issues. For instance, only about 20% of e-waste is formally collected and recycled in an environmentally sound manner, at the global level [1]. Further, the growth of the electronics industry causes the shortage of certain chemical elements (critical and strategic) [2]. This brings us to look for alternatives, e.g. based on abundant bio-sourced and biodegradable organic electronic materials.<br/><br/>As the pigments most used in nature for light absorption, as well as energy and electron transfer [3], chlorophylls are ideal candidates for organic optoelectronic devices. In this work, we initially performed morphological and structural studies on chlorophyll extracted from spinach, deposited on substrates of technological interest. Our extraction protocol is an Ultrasound-Assisted Extraction (UAE), consisting of sonication, centrifugation, filtration, and evaporation steps to obtain a powder that can be then suspended in green solvents (DI water, ethanol, acetone, methanol) [4]. The suspensions were both spin-coated and drop-casted onto SiO₂/Si, to compare the deposition method's impact on coverage and supramolecular aggregation, keeping in mind structures reported in the literature, such as tubular or stacked aggregates [5]. We performed preliminary electrical response studies using e-beam lithography-patterned interdigitated Au electrodes with 400 nm inter-electrode distance. Downsizing the inter-electrode distance is meant to advance the discovery of charge carrier transport mechanisms within individual aggregates, a piece of knowledge required to rationally design biodegradable electronic devices utilizing chlorophyll’s (photo)conductive properties [4].<br/><br/>[1] C. P. Baldé, R. Kuehr, T. Yamamoto, R. McDonald, E. D’Angelo, S. Althaf, G. Bel, O. Deubzer, E. Fernandez-Cubillo, V. Forti, V. Gray, S. Herat, S. Honda, G. Iattoni, V. L. di Cortemiglia, Y. Lobuntsova, I. Nnorom, N. Pralat, and M. Wagner, “THE GLOBAL E WASTE MONITOR 2024,” 2024.<br/><br/>[2] “Element Scarcity - EuChemS Periodic Table.” [Online]. Available: https://www.euchems.eu/euchems-periodic-table/<br/><br/>[3] G. Buscemi, D. Vona, M. Trotta, F. Milano, and G. M. Farinola, “Chlorophylls as Molecular Semiconductors: Introduction and State of Art,” Advanced Materials Technologies, vol. 7, no. 2, p.2100245, 2022, _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/admt.202100245. [Online]. Available: https://onlinelibrary.wiley.com/doi/abs/10.1002/admt.202100245\<br/><br/>[4] “12 Principles of Green Chemistry,” American Chemical Society. Accessed: Jun. 23, 2024. [Online]. Available: https://www.acs.org/greenchemistry/principles/12-principles-of-green-chemistry.html<br/><br/>[5] O. I. Koifman, P. A. Stuzhin, V. V. Travkin, et G. L. Pakhomov, « Chlorophylls in thin-film photovoltaic cells, a critical review », RSC Adv., vol. 11, n^o 25, p. 15131-15152, avr. 2021, doi: 10.1039/D1RA01508G.