Interfacial Electron Transfer in TiO2 Surfaces Sensitized with Ru(II)−Polypyridine Complexes

详细信息    查看全文

• 作者：Elena Jakubikova ; Robert C. Snoeberger III ; Victor S. Batista ; Richard L. Martin ; Enrique R. Batista
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：November 12, 2009
• 年：2009
• 卷：113
• 期：45
• 页码：12532-12540
• 全文大小：445K
• 年卷期：v.113,no.45(November 12, 2009)
• ISSN：1520-5215

文摘

Studies of interfacial electron transfer (IET) in TiO₂ surfaces functionalized with (1) pyridine-4-phosphonic acid, (2) [Ru(tpy)(tpy(PO₃H₂))]²⁺, and (3) [Ru(tpy)(bpy)(H₂O)−Ru(tpy)(tpy(PO₃H₂))]⁴⁺ (tpy = 2,2′:6,2′′-terpyridine; bpy = 2,2′-bipyridine) are reported. We characterize the electronic excitations, electron injection time scales, and interfacial electron transfer (IET) mechanisms through phosphonate anchoring groups. These are promising alternatives to the classic carboxylates of conventional dye-sensitized solar cells since they bind more strongly to TiO₂ surfaces and form stable covalent bonds that are unaffected by humidity. Density functional theory calculations and quantum dynamics simulations of IET indicate that electron injection in 1−TiO₂ can be up to 1 order of magnitude faster when 1 is attached to TiO₂ in a bidentate mode (τ 60 fs) than when attached in a monodentate motif (τ 460 fs). The IET time scale also depends strongly on the properties of the sensitizer as well as on the nature of the electronic excitation initially localized in the adsorbate molecule. We show that IET triggered by the visible light excitation of 2−TiO₂ takes 1−10 ps when 2 is attached in a bidentate mode, a time comparable to the lifetime of the excited electronic state. IET due to visible-light photoexcitation of 3−TiO₂ is slower, since the resulting electronic excitation remains localized in the tpy−tpy bridge that is weakly coupled to the electronic states of the conduction band of TiO₂. These results are particularly valuable to elucidate the possible origin of IET efficiency drops during photoconversion in solar cells based on Ru(II)−polypyridine complexes covalently attached to TiO₂ thin films with phosphonate linkers.