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

Paper TF2-WeA3
The Effects of Cu and Cl at the Device Junction on the Performance of CdTe-CdS Photovoltaic Cells

Wednesday, November 5, 2003, 2:40 pm, Room 329

Session: Optical Thin Films and Photovoltaics II
Presenter: T.J. Bukowski, National Renewable Energy Laboratory
Authors: T.J. Bukowski, National Renewable Energy Laboratory
D. Albin, National Renewable Energy Laboratory
J. Pankow, National Renewable Energy Laboratory
S.E. Asher, National Renewable Energy Laboratory
Correspondent: Click to Email
Current CdTe photovoltaic device design utilizes processing steps that incorporate both Cu and Cl into the cell structure. Such treatments produce an enhancement in the initial device efficiencies. However, there has been concern that Cu and Cl at the CdTe-CdS interface may have an effect on the stability of the device. In the unstressed state, CdTe devices are known to have significant amounts of both Cu and Cl at the interface. In addition, Cu placed at the back contact has been proven to diffuse toward the interface as the device is stressed, increasing the amount of Cu at the junction. There is thought to be a correlation between the amounts of Cu diffused to the interface from the back-contact and the resulting observed degradation in performance, the origin of which has yet to be determined. We have begun experiments studying how direct incorporation of Cu and Cl at the interface affects device performance. In this study, we detail the correlation observed between CuCl vapor-deposited at the CdS/CdTe interface prior to CdTe deposition with resulting device performance. X-ray diffraction, x-ray photoelectron spectroscopy, SIMS, Raman spectroscopy and optical absorption techniques are used to characterize the resulting change in the CdS films as a result of incorporating Cu and Cl. It is shown that at treatments below 250°C a CuCl layer forms on the surface of the CdS. Above 250°C, additional compounds begin to appear such as Cu@sub x@S. Absorption data shows that the band edge of the CdS shifts from 2.61eV down to 2.41eV as the CuCl treatment temperature increases. Devices are then made from the treated CdS films and their J-V data compared with data from both untreated controls and degraded devices. Device performance results are then correlated with the amounts of CuCl deposited at the interface.