Revealing the Self‐Degradation Mechanisms in Methylammonium Lead Iodide Perovskites in Dark and Vacuum

Abstract

Organic-inorganic lead halide perovskite phases segregate (and their structures degrade) under illumination, exhibiting a poor stability with hysteresis and producing halide accumulation at the surface.In this work, we observed structural and interfacial dissociation in methylammonium lead iodide (CH NH PbI ) perovskites even under dark and vacuum conditions. Here, we investigate the origin and consequences of self-degradation in CH NH PbI perovskites stored in the dark under vacuum. Diffraction and photoelectron spectroscopic studies reveal the structural dissociation of perovskites into PbI , which further dissociates into metallic lead (Pb ) and I ions, collectively degrading the perovskite stability. Using TOF-SIMS analysis, AuI formation was directly observed, and it was found that an interplay between CH NH , I , and mobile I ions continuously regenerates more I ions, which diffuse to the surface even in the absence of light. Besides, halide diffusion causes a concentration gradient between Pb and I and creates other ionic traps (PbI , PbI ) that segregate as clusters at the perovskite/gold interface. A shift of the onset of the absorption band edge towards shorter wavelengths was also observed by absorption spectroscopy, indicating the formation of defect species upon aging in the dark under vacuum.

Vacuum-Induced Degradation of 2D Perovskites

“…We propose that upon exposure to vacuum, the 2D perovskites are first degraded into PbI 2 , which further decomposes into metallic lead and volatile I − 2 ions. It is noteworthy that similar formation of metallic lead was also observed for 3D perovskites when exposed to vacuum conditions (Gunasekaran et al, 2018).…”

“…In particular, it has been shown that methylammonium iodide sublimes in vacuum, leading to the formation of lead iodide (Deretzis et al, 2015;Juarez-Perez et al, 2018;Alberti et al, 2019). Exposure to vacuum has also been shown to lead to the formation of metallic lead in 3D perovskites (Gunasekaran et al, 2018) and to the reduction of photoluminescence (Fang et al, 2016;Tang et al, 2016). To date, the effect of vacuum on 2D perovskites remained unexplored.…”

Toward Efficient and Stable Perovskite Solar Cells: Choosing Appropriate Passivator to Specific Defects

“…[ 114,143,144 ] Under some aging stresses, such as light irradiation, [ 4 ] moisture, [ 145 ] and thermal stress, [ 108 ] the perovskite material is prone to degradation to generate PbI 2 and other fragments because of its low dissociation energy. [ 146 ] Qin et al first illuminated the trap‐induced degradation mechanism of PSCs. A large number of hole traps were found in the PSC degraded by continuous illumination, and Pb 0 defects have the potential to form hole traps.…”

A new approach to predict the formation of 3D hybrid organic‐inorganic perovskites

“…Perovskite refers to a three‐dimensional (3D) structure for a class of materials with chemical formula ABX 3 (A and B are the cations and X is oxygen or halide) . Perovskites that form with the organic and inorganic constituents are known as hybrid organic‐inorganic perovskites (HOIPs) . Due to extraordinary optical properties, for example, emission, absorption, and tunable optical band gap (visible to infrared), the HOIPs materials are mostly used for photovoltaic applications .…”

“…Due to extraordinary optical properties, for example, emission, absorption, and tunable optical band gap (visible to infrared), the HOIPs materials are mostly used for photovoltaic applications . The properties of perovskite materials can be varied by replacing A, B, or X sites with a suitable protonated organic molecule, divalent metal cations, and halogens, respectively . A representative structure of HOIPs is shown in Figure .…”