title: Solution-deposited F:SnO₂/TiO₂ as a base-stable protective layer and antireflective coating for microtextured buried-junction H₂-evolving Si photocathodes.
abstract: Protecting Si photocathodes from corrosion is important for developing tandem water-splitting devices operating in basic media. We show that textured commercial Si-pn(+) photovoltaics protected by solution-processed semiconducting/conducting oxides (plausibly suitable for scalable manufacturing) and coupled to thin layers of Ir yield high-performance H2-evolving photocathodes in base. They also serve as excellent test structures to understand corrosion mechanisms and optimize interfacial electrical contacts between various functional layers. Solution-deposited TiO2 protects Si-pn(+) junctions from corrosion for ∼24 h in base, whereas junctions protected by F:SnO2 fail after only 1 h of electrochemical cycling. Interface layers consisting of Ti metal and/or the highly doped F:SnO2 between the Si and TiO2 reduce Si-emitter/oxide/catalyst contact resistance and thus increase fill factor and efficiency. Controlling the oxide thickness led to record photocurrents near 35 mA cm(-2) at 0 V vs RHE and photocathode efficiencies up to 10.9% in the best cells. Degradation, however, was not completely suppressed. We demonstrate that performance degrades by two mechanisms, (1) deposition of impurities onto the thin catalyst layers, even from high-purity base, and (2) catastrophic failure via pinholes in the oxide layers after several days of operation. These results provide insight into the design of hydrogen-evolving photoelectrodes in basic conditions, and highlight challenges.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oregon , Eugene, Oregon 97403, United States.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Kast
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Enman
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Gurnon
authors.forename: Athavan
authors.initials: A
authors.lastname: Nadarajah
authors.forename: Shannon W
authors.initials: SW
authors.lastname: Boettcher
keywords: alkaline electrolyte; failure mechanism; hydrogen; photocathode; protective layer; solar