AVS 46th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoP

Paper TF-MoP20
An Alternative Procedure for the Deposition of Close-Spaced Sublimation CdTe/CdS Solar Cells

Monday, October 25, 1999, 5:30 pm, Room 4C

Session: Poster Session
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
C. Ballif, National Renewable Energy Laboratory
L.L. Kazmerski, National Renewable Energy Laboratory
Correspondent: Click to Email
In previous work (JVST 1998 and 1999), we demonstrated that a recrystallization process causes the changes in physical properties of CdTe films heat-treated with CdCl@sub 2@. Using this information, we were able to induce recrystallization in close-spaced sublimation (CSS) CdTe films, depositing these films at temperatures about 200°C lower than usually used in this process. This lower-temperature deposition process is very attractive in the fabrication of solar cells because it implies in energy economy, and also avoids or minimizes the problem with diffusion of impurities from the glass substrate to the active elements in the cell. In the present work, we deposited CSS CdTe films on solar-cell substrate structures using relatively low temperatures and varied deposition parameters, (e.g., deposition temperature and growth rate). We also subjected the films to two different treatments (dipping in CdCl@sub 2@/methanol solution and exposure to CdCl@sub 2@ vapor), and varied many parameters, such as treatment temperature and time, and saturation of the solution. The objective was to optimize the deposition and heat-treatment parameters to obtain high efficiency cells. The structure of the CdTe films was studied using atomic force microscopy, to obtain information on average grain size and surface topography; X-rays diffraction, to obtain information on lattice parameter and phase formation; and X-ray Photoelectron Spectroscopy, to study film composition. We correlated the various deposition and treatment parameters with the performance parameters (quantum efficiency, open-circuit voltage, short-circuit current, fill factor, and efficiency) of completed devices. We showed that, although the solar cells fabricated at higher temperatures still provide the best efficiencies, the low temperature method can produce solar cells with intermediate efficiencies (>10%), which will be more attractive for industrial application, because of the manufacturing and economic advantages.