title: Triphenylamine groups improve blocking behavior of phenoxazine dyes in cobalt-electrolyte-based dye-sensitized solar cells.
abstract: Novel phenoxazine dyes are successfully introduced as sensitizers into dye-sensitized solar cells (DSCs) with cobalt-based electrolyte. In sensitizers with triphenylamine (TPA) groups recombination from electrons in the TiO2 conduction band to the cobalt(III) species is suppressed. The effect of the steric properties of the phenoxazine sensitizers on the overall device performance and on recombination and regeneration processes is compared. Optimized DSCs sensitized with IB2 having two TPA groups in combination with tris(2,2'-bipyridyl) cobalt(II/III) yield efficiencies of 6.3%, similar to that of IB3, which is equipped with mutiple alkoxy groups. TH310 with only one TPA group gives lower efficiency and open circuit voltage, while IB1 without TPA groups performs even worse. These results demonstrate that both TPA groups on the IB2 are needed for an efficient blocking effect. These results reveal a possible new role for TPA units in DSC sensitizer design.
authors.affiliation: Department of Chemistry-Ångström Laboratory, Center of Molecular Devices, Uppsala University, Box 523, 751 20 Uppsala (Sweden).
authors.forename: Yan
authors.initials: Y
authors.lastname: Hao
authors.forename: Haining
authors.initials: H
authors.lastname: Tian
authors.forename: Jiayan
authors.initials: J
authors.lastname: Cong
authors.forename: Wenxing
authors.initials: W
authors.lastname: Yang
authors.forename: Ilkay
authors.initials: I
authors.lastname: Bora
authors.forename: Licheng
authors.initials: L
authors.lastname: Sun
authors.forename: Gerrit
authors.initials: G
authors.lastname: Boschloo
authors.forename: Anders
authors.initials: A
authors.lastname: Hagfeldt
keywords: blocking effect; cobalt redox mediator; dye-sensitized solar cells; phenoxazine dyes; triphenylamine