Energy level modification in lead sulfide quantum dot photovoltaics through ligand exchange

Publication Type:



APS Meeting Abstracts, (2014)




The electronic properties of lead sulfide colloidal quantum dots (PbS QDs) can be controlled through modification of QD size and surface chemistry.
Novel surface passivation techniques involving organic or inorganic
ligands have contributed to a rapid rise in the efficiency of QD
photovoltaics, yet the influence of ligand-induced surface dipoles on PbS
QD energy levels and photovoltaic device operation is not yet completely
understood. Here, the valence band energies of PbS QDs treated with twelve
different ligands are measured using ultraviolet photoelectron
spectroscopy (UPS), and a valence band shift of up to 0.75 eV is observed
between different ligand treatments. Atomistic simulations of ligand
binding to pristine PbS(100) and PbS(111) slabs qualitatively reproduce
the measured energy level shifts. 1,2-benzenedithiol and 1,3-benzendithiol
treatments, which result in valence band energies differing by ~ 0.2 eV,
are employed for PbS QDs in three different solar cell architectures, and
changes in device performance are correlated with the measured energy
level shift. These findings complement the known bandgap-tunability of
colloidal QDs and highlight an additional level of control over the
electronic properties of PbS QDs.