Pulsed laser deposition of thin films: Hard materials and solar cells.

摘要

This research utilizes a high vacuum pulsed laser ablation/deposition system to create novel thin films and devices. Materials used include titanium carbide, silicon carbide, cadmium telluride, and cadmium sulfide. Using the second harmonic of a Nd:YAG laser, the titanium carbide was deposited directly as well as 90 degrees from the target in two different experiments, employing a static magnetic field for one and a planar electric field for the other. The electric field apparatus is reminiscent of one used in a time-of-flight (TOF) mass spectrometer, with a bottom repeller plate and an extractor plate on top with a mesh-covered hole where the ions are extracted through and deposited on a quartz substrate. Post deposition, X-ray photon spectroscopy (XPS) surface analysis was performed on the deposited thin films to confirm the chemical composition as well as the chemical state of the directly deposited samples. In addition, atomic force microscopy (AFM) images were acquired for the electric field samples to show the difference in surface morphology between the direct and extracted thin films. In a second experiment, a thin film solar cell system was deposited onto an indium tin oxide (ITO) coated glass superstrate. The layers of the device are as follows: Glass/ITO/CdS/CdTe/CdCl₂/Sb ₂Te₃. The cell was annealed in air at 350 degrees Celsius two times, after the CdS layer was deposited and after the CdCl₂ layer was deposited. After all the layers were put down, front and back contacts were affixed using conductive copper tape. The samples were then sent to the National Renewable Energy Laboratory (NREL) in Colorado for device analysis. Suggestions are then made on how each of the processes can be improved in the future.