XPS and UPS Studies of Thin Film PV Materials Modified by Reactions in Liquids

Water-based processing steps are ubiquitous in the semiconductor industry, and the field of photovoltaics (PV) is no exception. During chemical bath deposition (CBD) of CdS, complex chemical reactions occurring at surfaces and in solution are poorly understood, yet have been shown to have powerful effects on the performance in terms of reliability and efficiency of finished PV devices. In the past, electron spectroscopic studies of these reactions have been hampered by the conflicting requirements of ultra-high vacuum and exposure of samples to liquid water. In this paper we present initial results from a new tool at NREL that allows one to conduct atmospheric pressure, liquid phase chemical processes on thin film PV materials and subsequent examination via core and valence level electron spectroscopies without exposing samples to air contamination.