Innovative Methodology for an Advanced Characterization of Perovskite Systems to Reach Buried Interfaces: In-Depth Profile by Coupling GD-OES and XPS

Interfaces properties in solar cells play a crucial role on the device's performance and stability, hence the importance of investigating the chemical behavior at the buried interfaces in solar devices. This work aims to develop an innovative methodology of coupling two in-depth profile characterizations, to accurately and reliably investigate the chemical composition from the surface to the interfaces. Hence, Glow Discharge Optical Emission Spectroscopy (GD-OES) and X-Ray Photoelectron Spectroscopy (XPS) were applied consecutively on half-cells. First, an optimization of the operating conditions was carried out to minimize the degradation of the perovskite layers. In the case of GD-OES not only the Radio Frequency power and the plasma gas pressure are changed, but also the nature of this gas (Ar, Ar/O). Secondly, the craters resulting from profiling by GD-OES were chemically studied by XPS in order to determine the chemical composition at different level of the layer as well as in the interface area. We observed that all the conditions employed for GD-OES profiling led to a systematic reduction or oxidation of lead as well as the degradation of the organic part and iodine loss, more or less pronounced depending on the plasma gas. A comparison of SEM (Scanning Electron Microscopy) images inside and outside the craters also showed a remarkable change in the surface morphology for a bombarded surface by Ar or Ar/O. Once this coupling optimized, it was applied on a complete solar device as a first step to sputter the Au contact electrode and reach the HTL/Perovskite interface with minimum degradation of the perovskite layer.