AVS 45th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoA

Paper TF-MoA10
Investigation of Induced Recrystallization and Stress in Close-Spaced Sublimation CdTe Thin Films

Monday, November 2, 1998, 5:00 pm, Room 310

Session: Mechanical Properties of Thin Films
Presenter: H.R. Moutinho, National Renewable Energy Laboratory
Authors: H.R. Moutinho, National Renewable Energy Laboratory
R.G. Dhere, National Renewable Energy Laboratory
M.M. Al-Jassim, National Renewable Energy Laboratory
P. Sheldon, National Renewable Energy Laboratory
B.T. Mayo, Southern University
L.L. Kazmerski, National Renewable Energy Laboratory
Correspondent: Click to Email
Close-spaced-sublimation (CSS) CdTe has produced the best CdS/CdTe thin-film solar cells reported to date. In all CdTe cell deposition options, a post-deposition treatment with CdCl@sub 2@/methanol solution at elevated temperature is a mandatory step for maximizing the device efficiency. We have previously reported that these large-grain CSS films do not recrystallize and that the initial in-plane stress is not completely relieved during the treatment, in contrast to films deposited by other methods (e.g. physical vapor deposition). In this work, we deposited CSS CdTe films at lower temperatures and higher deposition rates to force lower-grain-size layers, which are more susceptible to recrystallization. The objective was to induce recrystallization from the chemical/heat treatment to realize films with substantially less stress and, consequently, better device quality. The CdTe films were deposited on normal CdS/SnO@sub 2@/glass structures and chemically treated at various temperatures and times to optimize the recrystallization process. The topography and grain size of the films were determined by atomic-force microscopy, X-ray diffraction, and transmission electron microscopy, and the minority-carrier lifetime by time-resolved photoluminescence. The CdCl@sub 2@ treatment temperature was varied from 300 to 400° and the treatment time from 1 to 30 minutes. The stress in the films was investigated using X-ray techniques, and significant reduction in the stress was observed concurrent with the recrystallization/recovery process. We investigated the evolution of stress in the early stages of the treatment to establish the mechanisms through which recrystallization starts in these films. CdTe films deposited by physical vapor deposition were also analyzed, and the results were compared with the ones for the CSS films. Finally, the efficiencies of cells prepared from conventional CSS CdTe were compared to these lower stress thin-film devices.