Philip Schulz
Institut Photovoltaique d’Ile de France (IPVF), CNRS

Hybrid organic inorganic metal halide perovskites (MHPs) denote a family of compound semiconductors, which established a novel class of optoelectronics, most prominently known for the perovskite solar cell. While the power conversion efficiency of these photovoltaic devices saw a steep rise in the past decade, tailoring the interfaces between the MHP film and charge transport layer became the major control lever to enhance performance and stability. Eventually, the formation of a stable interface between the perovskite film and adjacent functional layers is critical to enable unperturbed device operation. [1,2]

The use of photoemission spectroscopy to analyze the chemical and electronic properties of these interfaces has been challenging due to many possible chemical reactions at the buried interfaces. [3] Here, I will discuss the use of synchrotron- and lab-based X-ray photoelectron spectroscopy (XPS) experiments to address the particular chemistry of MHP interfaces to adjacent oxide charge transport and pre-encapsulation layers (CTL). At the example of SnO2 and NiO layers grown by atomic layer deposition (ALD) on top of a double cation mixed halide perovskite film investigated by hard X-ray photoelectron spectroscopy (HAXPES), we find evidence for the formation of new chemical species and changes in the energy level alignment at the interface detrimental to cell performance. [4]

I will conclude with a general discussion on the use of PES methods for the analysis of MHP layers and in particular the effect of irradiation-induced damage via synchrotron and lab-based X-ray sources, [5] which we also use to track unique physicochemical phenomena such as stimulated self-healing in formamidinium lead bromide. [6]

References:

1. J. Christians, et al. Nature Energy 2018, 3, 68
2. P. Schulz, D. Cahen, A. Kahn, Chem. Rev. 2019, 119, 3349
3. S. Béchu, et al. Adv. Energy Mater. 2020, 201904007
4. N. Mallik, et al. Nano Energy 2024, 126, 109582
5. M. Ralaiarisoa et al. Small Methods 2023, 202300458
6. V. Milotti, et al. Small Methods 2023, 2300222