(262f) Chloride Surface Modified Cadmium Telluride Nanocrystals for Photovoltaics

Semiconductor nanocrystals (NCs) are of great scientific and commercial interest due to their optoelectronic properties. However, improvements in nanocrystals for solar cell applications, specifically cadmium telluride, require the ability to controllably manipulate their surface. Halides are ideal for nanocrystal surface functionalization as their small size provides advantages in passivation, coupling, and processing compared to the ubiquitous long-chained aliphatic surfactants. Here, we present the controlled surface modification of cadmium telluride nanocrystals with chloride while maintaining colloidal stability in organic solvents with a secondary labile ligand. After deposition of NCs from solution, the secondary ligand is easily removed with vacuum leaving behind an entirely organic-free NC film, offering a processing advantage for solution-based semiconductor thin films. X-ray Photoelectron Spectroscopy, Rutherford Backscatter Spectroscopy, and H-NMR supports successful substitution of the native ligand with the halide species while UV-Vis Absorption Spectroscopy and Transmission Electron Microscopy confirm maintenance of particle size, shape and solubility in organic solvents. Furthermore, we investigate the effect of the chloride on thermally treated, or sintered, NCs films. X-Ray Diffraction and Small Angle X-Ray Scattering reveal recrystallization and grain growth while Capacitance-Voltage, Field Effect Transistors, and Time-Resolved Photoluminescence probe enhancements in electrical and optical properties of sintered NC films. Our material system offers a unique method to deposit films from solution with easily removable secondary ligands that tend to contaminate films with electrically insulating materials. This study introduces a nanocrystal system with a quantitative handle on surface manipulations for a broad range of investigations and applications for photovoltaics.