Title | Challenges in MAPbI3 layer production by vapor deposition in Ultra-High-vacuum: insight from real-time Grazing Incidence Fast Atom Diffraction (GIFAD)
Date | Monday, September 2, 2024, at 9:30 a.m. (UTC +2)
Speaker | Abdel Rahman ALLOUCHE, ISMO
Abstract |
In the recent years, hybrid halide perovskites have demonstrated significant advancements. However, persistent challenges remain, in relation to long-term stability and up-scalability for industrial applications. Vapor deposition in vacuum has been proposed as a promising approach to address these issues in addition to offering a better control over the deposition process.
Up to know, vacuum deposition is generally performed in high vacuum, at base pressures between 10-7 and 10-5 mbar, where water vapor is the dominant contamination. Hybrid halide perovskites layers produced in these conditions show extremely poor interface quality, which is detrimental to charge transport. To push further the vacuum deposition approach, we adopted the paradigm of Molecular beam Epitaxy: work in ultra-high vacuum conditions (10-10 mbar) and perform real-time characterization of the growth process using Grazing Incidence Fast Atom Diffraction (GIFAD). This technique monitors the growth mode and the organization dynamics with exclusive surface sensitivity and with submonolayer resolution.
Our findings reveal that under the clean environment of ultra-high vacuum, it is not possible to produce methylammonium lead iodide (MAPbI3) at room temperature, whatever the precursors (MAI and PbI2) are evaporated simultaneously or sequentially. Instead, pure PbI2 layers are systematically formed, and their conversion to perovskites appears unfeasible due to very low sticking coefficient of MAI. These finding point to the critical influence of contaminants, such as water, in high vacuum environment (10-5 – 10-7 mbar).
