Influence of surface composition on back-contact performance in CdTe/CdS PV devices

The atomic composition of the surface of the CdTe layer in a CdTe/CdS photo voltaic (PV) device has a significant influence on the quality of the elect rical contact to this layer. This paper reports the results of a systemic s tudy that correlates the composition of the back surface as measured with X -ray photoelectron spectroscopy (XPS) with pre-contact processing and devic e performance. We found that certain processing steps produce an oxide laye r that degrades performance by producing a metal-oxide-semiconductor (MOS) contact, rather than the intended metal-semiconductor, Scottky barrier cont act. We also found that the asdeposited CdTe film is cadmium-rich for sever al hundred angostroms at the back surface. This n-type layer may impede cur rent flow for majority holes, degrading device performance. Published in 20 00 by John Wiley & Sons, Ltd.