The interesting aspect of the nanoparticle approach for photovoltaic applications is that for certain nanoparticle packing structures that can, in principle, be deﬁned by nanoparticle size, there exist extended, continuous, conducting paths for electrons. Measurements of polarization- and time-resolved photoluminescence from P3HT nanoparticles have revealed an interesting dependence on particle size and internal structure. Time evolution of polarization contrast indicates an interesting size/structure-dependent polarization dephasing. Power law analysis of the long-time PL decay suggests a signiﬁcantly larger mean electronhole radius for smaller nanoparticles, which may facilitate higher charge harvesting effciencies in a nanoparticle-based organic photovoltaic architecture. These assemblies of conducting polymer nanoparticles could offer a route to higher efficiency in organic photovoltaic systems
CdSe Nanocomposite Systems
The optical properties of CdSe-oligo(phenylene vinylene) composite nanostructures (pictured) are vastly modified from those of either the CdSe and organic consituents. Recent experiments in our group have shown a reduction in fluorescence intermittency (aka “blinking”), near-unity ligand-to-nanocrystal energy transfer, and a strongly one-dimensional transition dipole moment in CdSe-OPV (shown at left), all of which arise only in the presence of these semiconducting ligands, which we probe utilizing single molecule polarization anisotropy and wide-field defocused imaging. This change in transition dipole moment, which appears as a degenerate 2D transition orthogonal to the crystalline axis in non-functionalized nanocrystals, allows control of nanostructure emission by tuning the polarization of the excitation field, making these nanostructures promising as optoelectronic components.
Near-field Scanning Optical Microscopy
Near-field scanning optical microscopy offers the opportunity to resolve structures beyond the diffraction limit.
Charged CdSe Systems
The distinct response of colloidal QDstoanappliedexternal ﬁeld not only makes them attractive
candidates for light-emitting diodes (QD-LEDs), but also presents a promising prospect for biological imaging. The spectral properties of CdSe quantum dots on ITO surfaces are being explored. These studies provide new insight into the role of electronic perturbations of QD luminescence by excess charges.
Single Molecule Chiroptical Measurements
The focus of single molecule chiroptical studies is to understand how different isolated molecules interact with chiral light. The desire is to understand the physical cause of why single molecules (if they do) vary from ensemble measurements. By understanding the variation from molecule to molecule, we in a way learn about the trees that make up the forest instead of just the forest. Properties we are trying to understand are how environment, orientation, conformation, among other factors affect chiroptical response.