Size Quantization
Effects on Interfacial Electron
Transfer Dynamics in Ru(II)–Polypyridyl Complex Sensitized
ZnO QDs
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Abstract
Quantum-size confinement in semiconductor
material offers size
based tunability of interband gap energy as well as intraband sublevels.
In this work, size quantization of wide bandgap ZnO quantum dots has
been explored in the study of interfacial charge separation reaction
using a catechol functionalized Ru(II)–polypyridyl complex
as a photosensitizer molecule. Femtosecond time-resolved transient
absorption studies have revealed multiple electron injection events
based on discrete conduction band states of ZnO QDs. The electron
injection rates have been rationalized for quantum confinement effects
owing to different sizes of ZnO QDs. Furthermore, the size dependency
of the intrinsic lifetime of electrons injected into discrete energy
levels of ZnO QDs has been revealed in charge recombination reaction
with the Ru(III)–polypyridyl complex cation. The charge recombination
dynamics reveals a competing trend of carrier confinement and carrier
leak upon reducing particle size. This study shows the optimization
of finite size effects in achieving better interfacial charge separation
at the dye/semiconductor interface