AVS 50th International Symposium
    Thin Films Wednesday Sessions
       Session TF2-WeA

Paper TF2-WeA4
Cu Diffusion from Back Contacts in CdS/CdTe PV Devices

Wednesday, November 5, 2003, 3:00 pm, Room 329

Session: Optical Thin Films and Photovoltaics II
Presenter: S.E. Asher, National Renewable Energy Laboratory
Authors: S.E. Asher, National Renewable Energy Laboratory
T.A. Gessert, National Renewable Energy Laboratory
C. Narayanswamy, National Renewable Energy Laboratory
D. Albin, National Renewable Energy Laboratory
R. Dhere, National Renewable Energy Laboratory
C. Ferekides, University of South Florida
M.R. Young, National Renewable Energy Laboratory
Correspondent: Click to Email
It has been shown that for nearly all polycrystalline CdS/CdTe photovoltaic (PV) devices, the presence of Cu within the back contact is linked to both significant improvements in device performance as well as potential long-term device instability. There have been several studies of Cu distributions in devices performed using secondary ion mass spectrometry (SIMS), and in most depth profiles the Cu appears to segregate to the CdS layer in the device. Taken with the knowledge that grain sizes in the CdS are smaller, this has suggested that Cu is distributed primarily along grain boundaries. However, artifacts in the SIMS measurements may distort the profile and lead to erroneous conclusions if differences in sputter rate and corrections for ion yield are not made. In this study we use ion implanted standards of Cu into CdTe and CdS to quantify the levels of Cu in CdTe/CdS devices before, and after, one of three different back contact processes are applied. Our results show that while Cu does increase in the CdS layer of the device, the level prior to contacting is usually lower than in the CdTe. We also show that the CdCl@sub2@ process typically performed prior to application of the back contact can introduce signicant levels of Cu into the device. Device characteristics are also compared with the SIMS diffusion profiles.