Structural, Optical, and Electrical Properties of PbSe Nanocrystal Solids Treated Thermally or with Simple Amines

We describe the structural, optical, and electrical properties of films of spin-cast, oleate-capped PbSe nanocrystals that are treated thermally or chemically in solutions of hydrazine, methylamine, or pyridine to produce electronically coupled nanocrystal solids. Postdeposition heat treatments trig...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2008-05, Vol.130 (18), p.5974-5985
Main Authors: Law, Matt, Luther, Joseph M, Song, Qing, Hughes, Barbara K, Perkins, Craig L, Nozik, Arthur J
Format: Article
Language:English
Subjects:
ACETONITRILE
AMINES
Basic Sciences
ELECTRICAL PROPERTIES
ELECTRON MICROSCOPY
ETHANOL
FIELD EFFECT TRANSISTORS
HEAT TREATMENTS
HYDRAZINE
MATERIALS SCIENCE
METHYLAMINE
NANOSCIENCE AND NANOTECHNOLOGY
PYRIDINE
SCATTERING
SINTERING
SOLAR CELLS
SPECTROSCOPY
TRANSISTORS
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Summary:We describe the structural, optical, and electrical properties of films of spin-cast, oleate-capped PbSe nanocrystals that are treated thermally or chemically in solutions of hydrazine, methylamine, or pyridine to produce electronically coupled nanocrystal solids. Postdeposition heat treatments trigger nanocrystal sintering at ∼200 °C, before a substantial fraction of the oleate capping group evaporates or pyrolyzes. The sintered nanocrystal films have a large hole density and are highly conductive. Most of the amine treatments preserve the size of the nanocrystals and remove much of the oleate, decreasing the separation between nanocrystals and yielding conductive films. X-ray scattering, X-ray photoelectron and optical spectroscopy, electron microscopy, and field-effect transistor electrical measurements are used to compare the impact of these chemical treatments. We find that the concentration of amines adsorbed to the NC films is very low in all cases. Treatments in hydrazine in acetonitrile remove only 2−7% of the oleate yet result in high-mobility n-type transistors. In contrast, ethanol-based hydrazine treatments remove 85−90% of the original oleate load. Treatments in pure ethanol strip 20% of the oleate and create conductive p-type transistors. Methylamine- and pyridine-treated films are also p-type. These chemically treated films oxidize rapidly in air to yield, after short air exposures, highly conductive p-type nanocrystal solids. Our results aid in the rational development of solar cells based on colloidal nanocrystal films.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja800040c