jp6b12327_si_003.pdf (3.08 MB)
Directional Carrier Transfer in Strongly Coupled Binary Nanocrystal Superlattice Films Formed by Assembly and in Situ Ligand Exchange at a Liquid–Air Interface
journal contribution
posted on 2017-02-05, 00:00 authored by Yaoting Wu, Siming Li, Natalie Gogotsi, Tianshuo Zhao, Blaise Fleury, Cherie R. Kagan, Christopher B. Murray, Jason B. BaxterTwo species of monodisperse
nanocrystals (NCs) can self-assemble
into a variety of complex 2D and 3D periodic structures, or binary
NC superlattice (BNSL) films, based on the relative number and size
of the NCs. BNSL films offer great promise for both fundamental scientific
studies and optoelectronic applications; however, the utility of as-assembled
structures has been limited by the insulating ligands that originate
from the synthesis of NCs. Here we report the application of an in situ ligand exchange strategy at a liquid–air
interface to replace the long synthesis ligands with short ligands
while preserving the long-range order of BNSL films. This approach
is demonstrated for BNSL structures consisting of PbSe NCs of different
size combinations and ligands of interest for photovoltaic devices,
infrared detectors, and light-emitting diodes. To confirm enhanced
coupling introduced by ligand exchange, we show ultrafast (∼1
ps) directional carrier transfer across the type-I heterojunction
formed by NCs of different sizes within ligand-exchanged BNSL films.
This approach shows the potential promise of functional BNSL films,
where the local and long-range energy landscape and electronic coupling
can be adjusted by tuning NC composition, size, and interparticle
spacing.