Issue 20, 2016

A feasibility study of unconventional planar ligand spacers in chalcogenide nanocrystals

Abstract

The solar cell efficiency of chalcogenide nanocrystals (quantum dots) has been limited in the past by the insulation between neighboring quantum dots caused by intervening, often long-chain, aliphatic ligands. We have conducted a computationally based feasibility study to investigate the use of ultra-thin, planar, charge-conducting ligands as an alternative to traditional long passive ligands. Not only might these radically unconventional ligands decrease the mean distance between adjacent quantum dots, but, since they are charge-conducting, they have the potential to actively enhance charge migration. Our ab initio studies compare the binding energies, electronic energy gaps, and absorption characteristics for both conventional and unconventional ligands, such as phthalocyanines, porphyrins and coronene. This comparison identified these unconventional ligands with the exception of titanyl phthalocyanine, that bind to themselves more strongly than to the surface of the quantum dot, which is likely to be less desirable for enhancing charge transport. The distribution of finite energy levels of the bound system is sensitive to the ligand’s binding site and the levels correspond to delocalized states. We also observed a trap state localized on a single Pb atom when a sulfur-containing phenyldithiocarbamate (PTC) ligand is attached to a slightly off-stoichiometric dot in a manner that the sulfur of the ligand completes stoichiometry of the bound system. Hence, this is indicative of the source of trap state when thio-based ligands are bound to chalcogenide nanocrystals. We also predict that titanyl phthalocyanine in a mix with chalcogenide dots of diameter ∼1.5 Å can form a donor–acceptor system.

Graphical abstract: A feasibility study of unconventional planar ligand spacers in chalcogenide nanocrystals

Supplementary files

Article information

Article type
Paper
Submitted
07 Dec 2015
Accepted
19 Feb 2016
First published
19 Feb 2016

Phys. Chem. Chem. Phys., 2016,18, 13781-13793

A feasibility study of unconventional planar ligand spacers in chalcogenide nanocrystals

B. Lukose and P. Clancy, Phys. Chem. Chem. Phys., 2016, 18, 13781 DOI: 10.1039/C5CP07521A

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