title: Chemical and Physical Reduction of High Valence Ni States in Mesoporous NiO Film for Solar Cell Application.
abstract: The most common material for dye-sensitized photocathodes is mesoporous NiO. We transformed the usual brownish NiO to be more transparent by reducing high valence Ni impurities. Two pretreatment methods have been used: chemical reduction by NaBH4and thermal reduction by heating. The power conversion efficiency of the cell was increased by 33% through chemical treatment, and an increase in open-circuit voltage from 105 to 225 mV was obtained upon heat treatment. By optical spectroelectrochemistry, we could identify two species with characteristically different spectra assigned to Ni3+and Ni4+. We suggest that the reduction of surface Ni3+and Ni4+to Ni2+decreases the recombination reaction between holes on the NiO surface with the electrolyte. It also keeps the dye firmly on the surface, building a barrier for electrolyte recombination. This causes an increase in open-circuit photovoltage for the treated film.
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, 751 20 Uppsala, Sweden.
authors.forename: Luca
authors.initials: L
authors.lastname: D'Amario
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, 751 20 Uppsala, Sweden.
authors.forename: Roger
authors.initials: R
authors.lastname: Jiang
authors.affiliation: Department of Physics and Astronomy, Ångström Laboratory, Uppsala University , Box 516, 751 20 Uppsala, Sweden.
authors.forename: Ute B
authors.initials: UB
authors.lastname: Cappel
authors.affiliation: School of Chemistry, Newcastle University , Newcastle upon Tyne, NE1 7RU, United Kingdom.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Gibson
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, 751 20 Uppsala, Sweden.|Center of Molecular Devices, Department of Chemistry, Royal Institute of Technology (KTH) , 10044 Stockholm, Sweden.
authors.forename: Gerrit
authors.identifier: http://orcid.org/0000-0002-8249-1469
authors.initials: G
authors.lastname: Boschloo
authors.affiliation: Department of Physics and Astronomy, Ångström Laboratory, Uppsala University , Box 516, 751 20 Uppsala, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Rensmo
authors.affiliation: Center of Molecular Devices, Department of Chemistry, Royal Institute of Technology (KTH) , 10044 Stockholm, Sweden.|Department of Chemistry, Organic Chemistry Royal Institute of Technology (KTH) , 10044 Stockholm, Sweden.
authors.forename: Licheng
authors.identifier: http://orcid.org/0000-0002-4521-2870
authors.initials: L
authors.lastname: Sun
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, 751 20 Uppsala, Sweden.
authors.forename: Leif
authors.initials: L
authors.lastname: Hammarström
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, 751 20 Uppsala, Sweden.|Center of Molecular Devices, Department of Chemistry, Royal Institute of Technology (KTH) , 10044 Stockholm, Sweden.
authors.forename: Haining
authors.initials: H
authors.lastname: Tian
keywords: characterization; dye-sensitized solar cell; hole UV−vis spectrum; p-type; photovoltage; recombination