Importance of air ambient during CdCl2 treatment of thin film CdTe solar cells studied through temperature dependent admittance spectroscopy

CdCl₂ treatment is a crucial step in the production of high efficiency CdTe solar cells. Thin-film CdS/CdTe solar cells have been prepared by ANTEC GmbH (Germany) both in vacuum and in air ambient. We compared these series of samples using the admittance spectroscopy (AS) technique. The presence of air increases remarkably the shallow acceptor concentration in the CdTe, confirming earlier studies. A broad band of deep defects is still found in all samples (independent of the activation). We also illustrate how the presence of a Schottky back contact to the CdTe solar cells introduces a capacitance step in the AS measurements, enabling the determination of the barrier height.