title: Engendering Long-Term Air and Light Stability of a TiO2-Supported Porphyrinic Dye via Atomic Layer Deposition.
abstract: Organic and porphyrin-based chromophores are prevalent in liquid-junction photovoltaic and photocatalytic solar-cell chemistry; however, their long-term air and light instability may limit their practicality in real world technologies. Here, we describe the protection of a zinc porphyrin dye, adsorbed on nanoparticulate TiO2, from air and light degradation by a protective coating of alumina grown with a previously developed post-treatment atomic layer deposition (ALD) technique. The protective Al2O3ALD layer is deposited using dimethylaluminum isopropoxide as an Al source; in contrast to the ubiquitous ALD precursor trimethylaluminum, dimethylaluminum isopropoxide does not degrade the zinc porphyrin dye, as confirmed by UV-vis measurements. The growth of this protective ALD layer around the dye can be monitored by an in-reactor quartz crystal microbalance (QCM). Furthermore, greater than 80% of porphyrin light absorption is retained over ∼1 month of exposure to air and light when the protective coating is present, whereas almost complete loss of porphyrin absorption is observed in less than 2 days in the absence of the ALD protective layer. Applying the Al2O3post-treatment technique to the TiO2-adsorbed dye allows the dye to remain in electronic contact with both the semiconductor surface and a surrounding electrolyte solution, the combination of which makes this technique promising for numerous other electrochemical photovoltaic and photocatalytic applications, especially those involving the dye-sensitized evolution of oxygen.
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: William L
authors.identifier: http://orcid.org/0000-0003-2257-4331
authors.initials: WL
authors.lastname: Hoffeditz
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Ho-Jin
authors.initials: HJ
authors.lastname: Son
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.|Material Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Pellin
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.|Department of Chemistry, Faculty of Science, King Abdulaziz University , Jeddah 21589, Saudi Arabia.
authors.forename: Omar K
authors.identifier: http://orcid.org/0000-0002-9904-9845
authors.initials: OK
authors.lastname: Farha
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.|Material Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Hupp
keywords: atomic layer deposition; dimethylaluminum isopropoxide; dye enshroudment; increased dye stability; porphyrin dye; protective coating