XRM2024 - Thu01A - "Chasing ion migration with soft and hard x-rays: Vapor deposited metal halide Perovskite films under electrical stress"

Degradation of performance under operating conditions of organic inorganic halide perovskite solar cells is being actively investigated by researchers around the globe. These studies are aimed at harvesting the full potential of these devices over a wide range of environmental stress conditions and over an extended period of time. Various synthesis pathways are accompanied by a variety of characterization techniques that explore the structural and chemical properties of these materials. In this work we present the synthesis and characterization of vapor deposited CH3NH3PbI3 (MAPbI3)1-3 by soft and hard x-ray techniques. These materials were deposited on custom fabricated chips and sample holders especially adapted to the experimental stations. Electrical biasing from 2.5V to 15V were applied, for different time intervals, to the electrodes. Using soft x-ray STXM (scanning transmission X-ray microscopy) we observed the migration of iodine, carbon and nitrogen ions at iodine M-edge, Carbon and Nitrogen K-edge respectively (Figure 1b). Changes in XAS (X-ray absorption spectrum) were also followed at these edges presenting a direct evidence of chemical changes that accompany these degradations. A similar degradation/migration was also observed using hard x-ray nano-XRF (X-ray fluorescence) investigation where in a strong Iodine migration was observed from the cathode to the anode under electrical biasing (Figure 1c). Finally, these results along with EIS (electrical impedance spectroscopy) investigations allows us to propose a mechanism of electrical field degradation in MAPbI3. These studies were also accompanied by x-ray damage studies, especially in the hard x-ray regime. References : [1] Jun, H., et al. (2023) Journal of Electron Spectroscopy and Related Phenomena., 266: art.n° 147358. [2] Dindault, C., et al. (2022) RSC Advances., 12(39): 25570-25577. [3] Jun, H., et al. (2022) Scientific Reports., 12: art.n° 4520