Search

We show here how differences in surface composition for monolayer (ML)-tethered pyridine (Py)-treated CdSe quantum dots (QDs) affect band edge energetics, as a function of QD diameter. We compare U...

We report the characterization of the frontier orbital energies and interface dipole effects for bare and ligand-capped 3.6 and 6.0 nm diameter CdSe nanocrystals (NC) tethered to smooth gold substrates, using He(I) and He(II) UV photoemission spectroscopy. Changes in the ionization potential (IP) of the NCs and local effective work function of the films were explored as a function of the dipolar nature of the NC capping ligands. The addition of thiol-capping ligands 1-hexanethiol, 1-benzenethiol, and 4-fluorothiophenol to both sizes of NCs produces negligible shifts in energy offset between the high kinetic energy edge of the CdSe NCs and the gold substrate Fermi energy. However, the local vacuum level and IP of the nanocrystal layer are altered by as much as 0.3 eV. We demonstrate the importance of determining both the local vacuum level and the high kinetic energy edge of a tethered NC sample. These studies demonstrate a method that can be used in the future to characterize the frontier orbital energy offsets for modified or unmodified nanocrystalline films, in which the NCs are incorporated into host materials, for applications ranging from photovoltaics to light-emitting diodes.

The heterojunctions formed between different organic dyes (O/O' heterojunctions), organic dyes with contacting oxide or metal electrodes (O/I heterojunctions), and semiconductor nanoparticles with organic host polymers and ligands (SC-NP/ O heterojunctions) must be understood and optimized in order to enhance the energy conversion efficiencies of photovoltaics using these materials as their active components. We have used combinations of UV-photoelectron spectroscopy, and X-ray photoelectron spectroscopy (UPS/XPS) in the characterization of representative heterojunctions, and extrapolate these studies to the optimization of new photovoltaic and photoelectrochemical energy conversion devices.