Charge Recombination Kinetics at an in Situ Chemical Bath-Deposited CdS/Nanocrystalline TiO2 Interface

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• 作者：Yasuhiro Tachibana ; Kazuya Umekita ; Yasuhide Otsuka ; Susumu Kuwabata
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：April 23, 2009
• 年：2009
• 卷：113
• 期：16
• 页码：6852-6858
• 全文大小：230K
• 年卷期：v.113,no.16(April 23, 2009)
• ISSN：1932-7455

文摘

We have conducted submicrosecond to millisecond transient absorption studies to elucidate the parameters controlling charge recombination kinetics at an in situ chemical bath-deposited CdS/TiO₂ interface. The CdS/TiO₂ nanostructures were prepared by depositing CdS in the TiO₂ nanocrystalline films via the SILAR, successive ionic layer adsorption and reaction, technique. Steady-state absorption spectroscopy and XRD measurements of the films indicated that the CdS amount increases as a function of the CdS deposition cycles. In contrast, the CdS crystallinity size remains constant after reaching approximately 4 nm. Comparison of the transient absorption spectra between CdS/TiO₂ and CdS/Al₂O₃ (Al₂O₃ is employed as an insulator) suggests that an efficient electron injection occurs from CdS to a TiO₂ conduction band. Charge recombination kinetics for the CdS/TiO₂ appears to be multiexponential, being similar to the transient dynamics observed for dye-sensitized TiO₂ films. A detailed analysis of the charge recombination dynamics with nonadiabatic electron transfer theory revealed that the recombination half-lifetime, t_50%, correlates closely with the CdS crystallinity size, resulting in recombination retardation by a factor of 100 with increase in the crystallinity radius from 0.8 to 2.1 nm. This correlation is discussed in relation to the function of CdS quantum dots-sensitized TiO₂ solar cells.