Charge and Energy Transport in Single Quantum Dot/Organic Hybrid Nanostructures

Hybrid quantum dot /organic semiconductor systems are of great interest in optoelectronic and photovoltaic applications, because they combine the robust and tunable optical properties of inorganic semiconductors with the processability of organic thin films. In particular, cadmium selenide (CdSe) quantum dots coordinated with oligo-(phenylene vinylene) ligands have displayed a number of hybrid optical properties that make them particularly well-suited to these applications. When probed on an individual particle level, these so-called CdSe-OPV nanostructures display a number of surprising photophysical characteristics, including strong quenching of fluorescence from coordinating ligands, enhanced emission from the CdSe quantum dot core, suppression of fluorescence intermittency, and photon antibunching, all of which make them attractive in the applications described above. By correlating fluorescence properties with atomic force microscopy, the effects of ligands on quantum dot luminescence are elucidated. In addition, recent studies on individual CdSe-OPV nanostructures have revealed a strong electronic coupling between the coordinating ligands and the nanocrystal core. These studies have shown that excitations in the organic ligands can strongly affect the electronic properties of the quantum dot, leading to linearly polarized optical transitions (both in absorption and emission) and polarization-modulated shifts in band edge emission frequency. These polarization effects suggest exciting new uses for these nanostructures in applications that demand the robust optical properties of quantum dots combined with polarization-switchable control of photon emission