Interpretation of beneficial annealing of CIGSe cell buffured with co-evaporated In2S3

The present contribution aims at better understanding the origin of the beneficial effect of the annealing of CIGSe-based solar cell buffered with co-evaporated (PVD)In₂S₃. For long, most of the works dealing with such alternatives to chemical bath deposited (CBD)CdS buffer layer have been focused on the CIGSe/buffer interface, where the pn junction is formed. Herein, we show that as already suggested by Nguyen et al. [1] in the case of (CBD)In₂S₃ buffer, the annealing post-treatment most probably improves the Voc and FF of the devices because it changes the nature and/or the density of defects at the In₂S₃/r-ZnO interface. Such a conclusion is motivated by our observation that rinsing the CIGSe/(PVD)In₂S₃ structures with water before the window deposition induces the same effect as the annealing, then such treated samples are less improved by annealing. In addition, the X-ray photoelectron spectroscopy analyses performed on the CIGSe/(PVD)In₂S₃ structure before and after the water treatment show that Na carbonates are removed from the surface by the water. This latter observation suggests that the main impact of the annealing of the cells buffered with co-evaporated In₂S₃ would be the destruction or the out migration of the Na-based compounds at the buffer/r-ZnO interface.