Biosourced Sepia Melanin as a Potential Donor Material for Low Environmental Footprint Solar Cells

With the global rise in environmental awareness, countries are now transitioning to decarbonized power production while promoting economic prosperity. Sustainable energy conversion technologies must be developed to meet the increasing electricity demand: among them are solar cells.<br/><br/>Unfortunately, solar cell production and end-of-life have serious environmental and societal impacts. [1] For instance, there is no clear solution for the waste that silicon solar cells will generate in the years to come, after arriving at the end of their 25-year expected lifetime. [2]<br/>To mitigate these negative impacts, new materials, processes and end-of-life scenarios should be considered. Biosourced organic, potentially solution-processable and biodegradable materials, represent a potential alternative to synthetic ones used in organic photovoltaics. [3] Even if nature “takes care” of their production, one must identify sustainable extraction protocols from the biosource.<br/><br/>The melanin biopigment has been studied for its electronic and optical properties as potential biosourced organic material for sustainable electronics. [4] In this work, Sepia melanin was extracted from cuttlefish ink using an environmentally benign protocol based on deionized water. [5] The absorption coefficient of the extracted Sepia melanin showed a broadband feature in the visible and ultra-violet regions of the spectrum, which is suitable for solar energy conversion. Devices were then prepared via a solution process technique using the extracted melanin powder. Atomic force microscopy images were collected to characterize the morphology, and the electric properties of the devices were measured with a semiconductor analyzer. Values of the conductivity in the range of 10^-3 S/cm were obtained. Photoconductivity measurements show an increase in the electrical current of more than 1% upon illumination under simulated solar light.<br/><br/>These results demonstrate the potential for Sepia melanin to be used in organic optoelectronics, e.g. solar cells, which could lead to the design of an energy conversion device with a low environmental footprint (biodegradable, among others). Further work to probe the electronic levels of this biosourced material will be conducted by the local density of states measurement with a scanning tunnelling microscope. [6] This information will permit to identify a suitable materials like metal electrodes for contacts of acceptor for a bulk heterojunction solar cell to continue the development toward sustainable electronics.<br/><br/>1. Cellura, M., et al., <i>A review on life cycle environmental impacts of emerging solar cells.</i> Science of The Total Environment, 2024. <b>908</b>: p. 168019.<br/>2. Cornelis P. Baldé, R.K., Tales Yamamoto, Rosie McDonald, Elena D’Angelo, Shahana, et al., <i>THE GLOBAL E-WASTE MONITOR 2024.</i> United Nations Institute for Training and Research, 2024.<br/>3. Uva, A., et al., <i>Bioderived and degradable polymers for transient electronics.</i> Journal of Chemical Technology & Biotechnology, 2022. <b>97</b>(4): p. 801-809.<br/>4. Camus, A., et al., <i>High conductivity Sepia melanin ink films for environmentally benign printed electronics.</i> Proceedings of the National Academy of Sciences, 2022. <b>119</b>(32): p. e2200058119.<br/>5. Eom, T., et al., <i>Nanoarchitecturing of Natural Melanin Nanospheres by Layer-by-Layer Assembly: Macroscale Anti-inflammatory Conductive Coatings with Optoelectronic Tunability.</i> Biomacromolecules, 2017. <b>18</b>(6): p. 1908-1917.<br/>6. Mansurov, V., et al., <i>STM/STS Study of the Density of States and Contrast Behavior at the Boundary between (7 × 7)N and (8 × 8) Structures in the SiN/Si(111) System.</i> Crystals, 2022. <b>12</b>(12): p. 1707.