Knocking the Stability of Solar Cells with Fluorescent Protein Donors upon Rationalizing Design, Integration, and Mechanism

Though photon-induced electron donor features of fluorescent proteins (FPs) in solution suggest them as excellent photosensitizers, their poor stability upon device fabrication/operation is the today's frontier. This relates to their immediate denaturation in water-free/less environments: inorganic/organic device interfaces and/or organic solvent surroundings. This study provides a fresh solution with a family of hybrid FPs, in which the peripheral carboxylic groups of archetypal FPs -superfolder green fluorescent protein (sfGFP) and mCherry- are transformed into alkoxysilane groups, enabling a straightforward integration with surprising stabilities over months in devices - arbitrary n/p-type semiconducting metal oxide/FP/organic-solvent electrolyte interfaces - attributed to the formation of an ion-silica shell around the FP. This further allowed to understand the charge injection mechanism applying steady-state/time-resolved spectroscopy on different FP-variants with key single-point aromatic amino acid mutations at the chromophore nearest, revealing the electron-donor hopping pathway via the initial loop of the strand beta 7. Finally, devices with state-of-the-art solar-to-energy conversion efficiencies that are stable >2,000 h under operation nicely outperform the prior-art stability of a few seconds/minutes in FP-based solar cells. Hence, this work solves the integration/stability issues which blocking the application of FP-based sensitizer, as well provides a solid understanding of their photo-induced electron transfer mechanism.