Annealing and Treatment Effects on Se Diffusion in CdTe Photovoltaics

The interdiffusion of CdTe and CdSe at the window layer interface to form alloyed CdSe
x
Te
1−x
(CST) layers has been shown to improve the efficiency of CdTe photovoltaic devices, and there is evidence from the literature that Se passivates defects in these devices, particularly at grain boundaries. This work investigates the importance of the Cl treatment by comparing untreated, air-annealed and Cl treated CST devices to determine whether the Cl treatment is required for CST devices. We show that the Cl treatment increases Se diffusion and is still necessary for efficient CST devices, although it is not clear whether the efficiency gains are due to the effects of greater Se diffusion or the usual benefits of the Cl treatment on CdTe photovoltaics.