Engineering topics
Kubie, Lenore
Publications and source records attributed to Kubie, Lenore.
Atomically Thin Metal Sulfides
We developed a method to colloidally synthesize atomically thin metal sulfides (ATMS). Unlike conventional 2D systems such as MoS 2 and graphene, none of the systems developed here are inherently layered compounds nor have known layered polymorphs in their bulk forms. The synthesis proceeds via a cation-exchange reaction starting from single- and multi-layer Ag 2 S and going to various metal sulfides. The synthesized ATMS retain their size and shape during the cation-exchange reaction and are either single-layer or a few-layer, depending on the starting Ag 2 S samples. They have lateral dimensions on the order of 5-10 nm and are colloidally stabilized by Z- and L-type ligands. Here, we demonstrate the synthesis of single-layer and a few-layer ZnS, CdS, CoS 2 , and PbS. We find that the optical properties of these ATMS are quite distinct from the platelet or quantum-dot versions of the same metal sulfides.
Chapter 3: Thin-Film Colloidal Quantum Dot Solar Cells
In under a decade, progress in quantum dot (QD) solar cell design and fabrication have increased PbS QD solar cell efficiencies from 3% to 11.3%. Such solar cells based on colloidal quantum dots offer the potential for a higher limiting power conversion efficiency through the enhancement of multiple exciton generation (MEG). In the MEG process, one photon produces two or more excitons that can contribute to power generation when the photon energy exceeds the semiconductor bandgap. The efficiency of the MEG process has also increased through the design and fabrication of new nanostructures. The fast pace at which QD devices are improving and the potential for a higher limiting efficiency - as MEG can increase the limiting power conversion efficiency (PCE) for a single-junction solar cell from 33% to ~ 45% - demonstrate the large potential of these systems.
Optically Generated Free-Carrier Collection from an All Single-Walled Carbon Nanotube Active Layer
Semiconducting single-walled carbon nanotubes' (SWCNTs) broad absorption range and all-carbon composition make them attractive materials for light harvesting. We report photoinduced charge transfer from both multichiral and single-chirality SWCNT films into atomically flat SnO 2 and TiO 2 crystals. Higher-energy second excitonic SWCNT transitions produce more photocurrent, demonstrating carrier injection rates are competitive with fast hot-exciton relaxation processes. A logarithmic relationship exists between photoinduced electron-transfer driving force and photocarrier collection efficiency, becoming more efficient with smaller diameter SWCNTs. Photocurrents are generated from both conventional sensitization and in the opposite direction with the semiconductor under accumulation and acting as an ohmic contact with only the p-type nanotubes. Finally, we demonstrate that SWCNT surfactant choice and concentration play a large role in photon conversion efficiency and present methods of maximizing photocurrent yields.