Pulsed laser annealing and rapid thermal annealing of copper-indium-gallium-diselenide-based thin film solar cells

Effects of Pulsed Laser Annealing (PLA) treatment on the film properties and the performance of CIGS solar cells have been studied under various annealing conditions. This technique has been used for the first time to modify near-surface defects and related junction properties in Cu(In,Ga)Se2 (CIGS) solar cells.; CIGS films deposited on Mo/glass substrates were annealed using a 25 ns pulsed laser beam (248 nm wavelength) and a 250 ns pulsed laser beam (308 nm wavelength) with a larger beam size at selected laser energy densities in the range of 20 to 110 mJ/cm2 and pulse number in the range of 5 to 20 pulses. The narrowing of X-Ray Diffraction (XRD) peak, new shoulders of Grazing Incidence X-ray Diffraction (GIXD) and the increase of Scanning Electron Microscopy (SEM) surface feature size suggest near surface structure changes. The Dual-Beam Optical Modulation (DBOM) and Hall-effect measurements indicate PLA treatment increases the effective carrier lifetime and mobility as well as the sheet resistance. In addition, several annealed CdS/CIGS films processed by PLA were fabricated into solar cells and characterized by Photo- and Dark- J-V and Quantum Efficiency (Q-E) measurements. Significant improvement was observed in the overall cell performance, diode quality, and spectral response when compared to pre-annealed cells. Deep-Level Transient Spectroscopy (DLTS) results showed a 50% reduction of the density of shallow defect trap after low-power PLA treatments. The energy density of the laser beam and the pulse number were found to play key roles in modifying the optical and electrical properties of the CIGS films and hence the cell performance. Results suggest that the optimal PLA energy density and pulse number are around 30 mJ/cm 2 and 5 pulses, respectively.; A comprehensive study of the effects of Rapid Thermal Annealing (RTA) on the film properties and the performance of CIGS solar cells has been carried out in this dissertation. CIGS samples and devices were characterized by using XRD, GIXD, SEM, Hall effect, Photo- and Dark- J-V and Q-E measurements before and after RTA treatment under various ramp up and down rates, peak temperatures, holding times, and ambient conditions. Results show that progressive RTA treatments could significantly improve the overall uniformity and performance of large-area CIGS solar cells. Under low RTA temperatures, the surface composition and morphology remain unchanged. The simple RTA treatment on CIGS cells shows an increase of quantum efficiency and some improvement of cell performance. The estimated optimal annealing temperature should be between 200 and 300°C with a holding time of 1-minute or less. (Abstract shortened by UMI.)...