Feb 15, 2018 4:00 pm - Nielsen Hall 170 - Colloquium
Matt Beard - NREL
Quantum Confined Semiconductors for Solar Photon Energy Conversion

Semiconductor nanostructures, where at least one dimension is small enough to produce quantum confinement effects, provide new pathways for controlling energy flow and therefore have the potential to increase the efficiency of the primary photon-to-free energy conversion step. In this discussion, I will present the current status of research efforts towards utilizing the unique properties of colloidal quantum dots (NCs confined in three dimensions) in prototype solar cells and photoelectrodes and demonstrate that these unique systems have the potential to bypass the Shockley-Queisser single-junction limit for solar photon conversion. The solar cells and photoelectrodes are constructed using a low temperature solution based deposition of PbS or PbSe QDs as the absorber layer. Different chemical treatments of the QD layer are employed in order to obtain good electrical communication while maintaining the quantum-confined properties of the individual QDs. A unique aspect of our devices is that the QDs exhibit multiple exciton generation (MEG) with an efficiency that is ~ 2 to 3 times greater than the parental bulk semiconductor. The efficiency of the MEG process can be further increased by increasing the complexity of the nanostructures.  We have synthesized Janus-like nanocrystals that are spherical in shape yet asymmetric in composition.  These nano-heterostructures demonstrate an enhanced MEG efficiency relative to the spherical single-phase quantum dots.