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 [1]. Nevertheless, a challenge remains: how to access these buried interfaces without modifying the initial chemical information. This work addresses this problematic and aims to develop an innovative methodology of coupling two in-depth profile characterizations, to better understand the chemical composition from the surface to the interfaces. For this purpose, 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). The craters resulting from profiling by GD-OES were then chemically studied by XPS in order to determine the chemical composition at different levels of the layer as well as at the interface area. We observed that all the conditions employed for GD-OES profiling led to iodine loss, a systematic reduction or oxidation of lead as well as the degradation of the organic part, 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.

The application of GD-OES and XPS coupling was then tested on a full stack device, where GD-OES was applied for etching the Au electrode and stopped before reaching the interface. Indeed, the live acquisition of the profile enables us to precisely stop before the area of interest, making it possible to preserve the integrity of the chemical information registered through the modified residual overlayer. The in-depth profile was then proceeded by using XPS sputtering inside the crater created by GD-OES. Reduction of lead was detected all along the profile, and a new triiodine species emerged at the interface. The degradation of the organic compounds in perovskite after etching was also noticed, but this behavior was fully studied and understood in previous work [2].

Accordingly, to better understand the origin of the detected species and their behavior after a certain time, this coupling methodology must be first studied on a fresh reference device and then applied on aged solar devices for better comparison. It can also be carried out on tandem solar cells to reach different levels of the device.