2 research outputs found
Light-Emitting Quantum Dot Transistors: Emission at High Charge Carrier Densities
For the application of colloidal
semiconductor quantum dots in optoelectronic devices, for example,
solar cells and light-emitting diodes, it is crucial to understand
and control their charge transport and recombination dynamics at high
carrier densities. Both can be studied in ambipolar, light-emitting
field-effect transistors (LEFETs). Here, we report the first quantum
dot light-emitting transistor. Electrolyte-gated PbS quantum dot LEFETs
exhibit near-infrared electroluminescence from a confined region within
the channel, which proves true ambipolar transport in ligand-exchanged
quantum dot solids. Unexpectedly, the external quantum efficiencies
improve significantly with current density. This effect correlates
with the unusual increase of photoluminescence quantum yield and longer
average lifetimes at higher electron and hole concentrations in PbS
quantum dot thin films. We attribute the initially low emission efficiencies
to nonradiative losses through trap states. At higher carrier densities,
these trap states are deactivated and emission is dominated by trions
Controlled In Situ PbSe Quantum Dot Growth around Single-Walled Carbon Nanotubes: A Noncovalent PbSe-SWNT Hybrid Structure
We developed a simple method of synthesizing
noncovalently linked
hybrids of PbSe quantum dots (QDs) and single-walled carbon nanotubes
(SWNTs). The PbSe QDs grow around the SWNTs without any linker molecule
or chemical modification of the SWNTs. We are able to control the
size and shape of the QDs attached to the SWNTs by varying the synthesis
conditions and elucidate the three-dimensional (3D) morphology and
atomic structure of the half-ring-shaped PbSe QDs bonded to the SWNTs
using scanning transmission electron microscopy (STEM) tomography
and high-resolution transmission electron microscopy (HRTEM). The
PbSe QDs not only assemble on the SWNT bundles, but they actually
grow around them. The growth of the PbSe QDs around SWNT sidewalls
is favored over the growth of spherical particles in solution, probably
due to dipole stabilization by the large π-electron system of
the SWNTs