Uniform Thin Films of CdSe and CdSe(ZnS) Core(Shell) Quantum Dots by Sol鈥揋el Assembly: Enabling Photoelectrochemical Characterization and Electronic Applications

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• 作者：Lasantha Korala ; Zhijie Wang ; Yi Liu ; Stephen Maldonado ; Stephanie L. Brock
• 刊名：ACS Nano
• 出版年：2013
• 出版时间：February 26, 2013
• 年：2013
• 卷：7
• 期：2
• 页码：1215-1223
• 全文大小：579K
• 年卷期：v.7,no.2(February 26, 2013)
• ISSN：1936-086X

文摘

Optoelectronic properties of quantum dot (QD) films are limited by (1) poor interfacial chemistry and (2) nonradiative recombination due to surface traps. To address these performance issues, sol鈥揼el methods are applied to fabricate thin films of CdSe and core(shell) CdSe(ZnS) QDs. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging with chemical analysis confirms that the surface of the QDs in the sol鈥揼el thin films are chalcogen-rich, consistent with an oxidative-induced gelation mechanism in which connectivity is achieved by formation of dichalcogenide covalent linkages between particles. The ligand removal and assembly process is probed by thermogravimetric, spectroscopic, and microscopic studies. Further enhancement of interparticle coupling via mild thermal annealing, which removes residual ligands and reinforces QD connectivity, results in QD sol鈥揼el thin films with superior charge transport properties, as shown by a dramatic enhancement of electrochemical photocurrent under white light illumination relative to thin films composed of ligand-capped QDs. A more than 2-fold enhancement in photocurrent, and a further increase in photovoltage can be achieved by passivation of surface defects via overcoating with a thin ZnS shell. The ability to tune interfacial and surface characteristics for the optimization of photophysical properties suggests that the sol鈥揼el approach may enable formation of QD thin films suitable for a range of optoelectronic applications.

Keywords:

quantum dots; sol鈭抔el methods; photocurrent; surface passivation; ligand exchange