Analysis of ZnTe:Cu/Ti Contacts for Crystalline CdTe

Recent studies of thin-film CdS/CdTe photovoltaic (PV) devices have suggested that significantly higher device performance will not be achieved unless both the net-acceptor density (N_A) and minority-carrier diffusion length (L_D) in the CdTe are simultaneously increased. Toward this goal, CdTe research at NREL currently includes studies that use either bulk crystalline CdT e or epitaxial CdT e layers to study changes in N_A and L_D during the controlled incorporation of various intrinsic and extrinsic dopants. Unfortunately, for many of these studies, electrical contacts remain a limiting factor. In this paper we describe studies designed to enhance our understanding of the strengths and weaknesses of using the NREL ZnTe:Cu/Ti back-contact process for the analysis of various crystalline CdTe samples. Because this contact has been shown to yield high performance and stability, we believe that understanding its use on crystalline materials could advance our development of alternative contact processes that embody the potential for even higher performance.