Challenges and Opportunities in the Use of Iron Photosensitizers for Dye-Sensitized Solar Cells and Photoelectrosynthetic Cells Applications

Novel renewable alternatives to meet the needs of our current energy landscape are highly sought after. Photovoltaic solar cells (PV) are considered leading candidates for carbon neutrality due to their numerous benefits and good solar-to-energy conversion efficiency. However, the need is no longer solely focused on electric current generation but also on strategies to store that energy. This led, amongst other technologies, to the development of dye-sensitized photoelectrosynthesis cells (DSPECs), the successor of dye-sensitized solar cells (DSSCs). However, these cost-effective solar cells mostly use photosensitizers based on scarce metals such as ruthenium. Iron-based photosensitizers represent the holy grail due to their low toxicity, greater abundance, and versatile chemistry. However, they still suffer from drastic limitations: their photochemistry and extremely fast excited-state deactivation processes lead to inefficient charge injection and/or fast charge recombination. This review gathers examples of iron-based photosensitizers that have been successfully immobilized on metal oxide surfaces. A critical comparison of Fe-based photosensitizers is made based on their photophysical properties, electrochemistry, and photovoltaic performances.