Recent work on quasi-2D Ruddlesden–Popper phase organolead halide perovskites has shown that they possess many interesting optical and physical properties. Most notably, they are significantly more stable when exposed to moisture when compared to the typical 3D perovskite methylammonium lead iodide (MAPI); direct evidence for the chemical source of this stability remains elusive, however. Here, we present a detailed study of the superior moisture stability of a quasi-2D Ruddlesden–Popper perovskite, n-butylammonium methylammonium lead iodide (nBA-MAPI), compared to that of MAPI, and examine a simple, yet efficient, methodology to improve the stability of MAPI devices through the application of a thin layer of nBA-MAPI to the surface. By employing a variety of analytical techniques (photoluminescence, time-of-flight secondary ion mass spectrometry, cyclic voltammetry, X-ray diffraction) we determine that the improved stability of Ruddlesden–Popper perovskites is a consequence of a unique degradation pathway which produces a passivating surface layer, composed of increasingly stable phases of the 2D perovskite, via disproportionation. Our work establishes that this protective material isolates the bulk of the perovskite from a newly identified hydration layer which is found to accumulate at the C60/perovskite interface of full devices, slowing further hydrolysis reactions that would damage the device. As MAPI devices degrade quickly without any protection, a surface treatment of nBA-MAPI is an efficient way to delay device deterioration by creating an artificial 2D surface layer that similarly inhibits interaction with the hydration layer.
Ruddlesden–Popper phase quasi-2-D organolead halide perovskites like n-butylammonium methylammonium lead iodide (nBA-MAPI) exhibit improved moisture stability over typical 3-D perovskite materials, making them exciting for use in a variety of applications such as photovoltaic (PV) devices. This improved stability is the result of a unique disproportionation-based degradation mechanism that protects the bulk of the nBA-MAPI from extensive damage through the formation of a protective, low-n surface layer. In addition to this surface layer, nBA-MAPI films also exhibit the dynamic growth of micrometer-scale crystallites and cracks at the surface of the film, unique and potentially important byproducts of quasi-2-D perovskite disproportionation. Here, we present a detailed study of these crystallites using several analytical techniques including photoluminescence spectroscopy (PL), confocal fluorescence microscopy (CFM), atomic force microscopy (AFM) combined with time-of-flight-secondary ion mass spectrometry (ToF-SIMS), and others in an effort to better understand the relationship between material disproportionation and crystallite growth. Our results show that the crystallites form after exposure to humid air and confirm that they are composed of low-n phases of nBA-MAPI. The crystallites are found to extend into the interior of the film and exhibit continued growth while exposed to moisture over 72 h. This growth is accompanied by both a decrease in the bulk 2-D phase and an increase in a 3-D-like phase in the surface PL spectra, indicating that the crystallites are likely a product of moisture-driven disproportionation. Importantly, similar crystallites are also observed to form within model PV devices, indicating that such processes must be accounted for when designing future devices containing materials like nBA-MAPI.
The long-term instability of typical organolead halide perovskites has led to increased interest in Ruddlesden–Popper phase (RPP) perovskites. These materials have been shown to possess high stability under a variety of conditions, including humidity, making them interesting candidates for stable perovskite devices. Here, we report the increased moisture stability of a methylammonium lead triiodide-based (MAPI) RPP perovskite containing n-hexylammonium (hexyl-MAPI) as compared to an otherwise-identical material synthesized using n-butylammonium (butyl-MAPI), attributed to decreased halide mobility within the material. Despite only small differences in chemical composition, hexyl-MAPI photovoltaic devices show a significantly lower performance loss compared to butyl-MAPI devices when exposed to 78% RH, using both Au and reactive Ag electrodes. We find evidence that both perovskites develop a passivation layer composed of low-n perovskite phases at the film surface following exposure to humidity, but only butyl-MAPI films exhibit clear spectroscopic evidence of distinct low-n phases. Analysis of full devices using time-of-flight secondary ion mass spectrometry provides additional evidence of the passivation layer and shows hexyl-MAPI leaches less iodide during moisture exposure. Halide mobility measurements further confirm this observation and show that the activation energy of halide mobility in n = 2 hexyl-MAPI (74± 6 kJ/mol) is larger than that in butyl-MAPI (60± 4 kJ/mol). Together, these results show that increasing the barrier to halide mobility in perovskite materials reduces the rate of iodide leaching and indicates that RPP perovskite phases could be used to increase the stability of perovskite photovoltaic devices, regardless of the metal contact.
Ni-P films that are catalytically active for the hydrogen-evolution reaction were electrodeposited onto photoactive Si substrates between 20 °C and 80 °C from an aqueous solution. Ni-P films deposited at...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.