April 15, 2015
Speaker: Dr. Mircea Cotlet, Center for Functional Nanomaterials, Brookhaven National Laboratory
Colloidal nanocrystals or quantum dots (QDs) have received increased attention due to their size-dependent optoelectronic properties and their potential utilization in PV, LED or as biological nanotags. QDs like CdSe/ZnS absorbing/emitting in VIS have been intensively studied at the single nanoparticle level, representing thus far a good candidate model system for photovoltaic relevant studies, with thousands of single nanoparticle studies reported so far. Challenges remain when it comes to the detection of optical signals from isolated low bandgap QDs absorbing/emitting in near infrared (NIR) like for example PbS/CdS QDs, where we counted so far only two reports (M.Bawendi and T.Krauss).
In this talk I will present recent results from our group that address photoinduced charge transfer (CT) from isolated core/shell PbS/CdS QDs to acceptor materials like TiO2 and PEDOT:PSS. I will show how single nanocrystal spectroscopy can unravel heterogeneity in (radiative) recombination of electron and hole in the PbS core following optical excitation, and how this heterogeneity is dramatically suppressed in the presence of charge transfer, either electron or hole. I will comment the findings for PbS/CdS QDs in connection with our previous work on charge transfer involving large bandgap CdSe/ZnS QDs, highlighting clear differences that we observed in single particle behavior between PbS and CdSe and that we believe originate from differences in their materials composition, e.g. difference in electron and hole masses.