Energy level modification in lead sulfide quantum dot thin films through ligand exchange

Publication Type:

Journal Article


ACS Nano, ACS Publications, Volume 8, Issue 6, p.5863-5872 (2014)






The electronic properties of colloidal quantum dots (QDs) are critically dependent on both QD size and surface chemistry. Modification of quantum
confinement provides control of the QD bandgap, while ligand-induced
surface dipoles present a hitherto underutilized means of control over the
absolute energy levels of QDs within electronic devices. Here, we show
that the energy levels of lead sulfide QDs, measured by ultraviolet
photoelectron spectroscopy, shift by up to 0.9 eV between different
chemical ligand treatments. The directions of these energy shifts match
the results of atomistic density functional theory simulations and scale
with the ligand dipole moment. Trends in the performance of photovoltaic
devices employing ligand-modified QD films are consistent with the
measured energy level shifts. These results identify
surface-chemistry-mediated energy level shifts as a means of predictably
controlling the electronic properties of colloidal QD films and as a
versatile adjustable parameter in the performance optimization of QD
optoelectronic devices.