Energy architecture of nanocrystal assemblies
Collaborators:    Prof. Ron Naaman, www.weizmann.ac.il/chemphys/cinaaman/home.html
                         Prof.  David N. Beratan, www.chem.duke.edu/~beratan/
 
 
Group Members:  Brian Bloom
 
 
Solar energy is the most promising sustainable energy source for meeting mankind’s future needs. Our current research explores how to utilize light harvesting nanoparticle assemblies to provide high efficiency light-to-electrical energy conversion. A specific focus of our current work is to understand how the composition and assembly of semiconductor nanoparticles must be prescribed to create particular energy architectures that best drive charge separation. We are using photoemission and electrochemical studies of nanoparticles immobilized on a gold electrode(Figure 1), through an organic linker, to quantify the assembly’s energetics. In a recent study(Figure 2) we showed that CdSe nanoparticles, when attached to gold by a dithiol linker, have their HOMO energy Fermi level pinned so that the LUMO energy of the nanoparticle shifts as the bandgap (or size) of the nanoparticle is changed. Through the utilization of this and other developments we are constructing a framework for the creation of efficient nanoparticle based solar cells. 

Figure 2: Change in HOMO (squares) and LUMO (circles) energies of CdSe nanoparticles as a function of size. The red symbols represent energies measured by photocurrent and the open symbols represent energies measured by voltammetry. The energy zero is the vacuum level.
Figure 1:  A layer of semiconductor nanocrystals linked to an Au working electrode through a self-assembled alkanethiol monolayer bridge.