Formation Dynamics of CH3NH3PbI3 Perovskite Following Two-Step Layer Deposition

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• 作者：Jay B. Patel ; Rebecca L. Milot ; Adam D. Wright ; Laura M. Herz ; Michael B. Johnston
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：January 7, 2016
• 年：2016
• 卷：7
• 期：1
• 页码：96-102
• 全文大小：436K
• ISSN：1948-7185

文摘

Hybrid metal-halide perovskites have emerged as a leading class of semiconductors for optoelectronic devices because of their desirable material properties and versatile fabrication methods. However, little is known about the chemical transformations that occur in the initial stages of perovskite crystal formation. Here we follow the real-time formation dynamics of MAPbI₃ from a bilayer of lead iodide (PbI₂) and methylammonium iodide (MAI) deposited through a two-step thermal evaporation process. By lowering the substrate temperature during deposition, we are able to initially inhibit intermixing of the two layers. We subsequently use infrared and visible light transmission, X-ray diffraction, and photoluminescence lifetime measurements to reveal the room-temperature transformations that occur in vacuum and ambient air, as MAI diffuses into the PbI₂ lattice to form MAPbI₃. In vacuum, the transformation to MAPbI₃ is incomplete as unreacted MAI is retained in the film. However, exposure to moist air allows for conversion of the unreacted MAI to MAPbI₃, demonstrating that moisture is essential in making MAI more mobile and thus aiding perovskite crystallization. These dynamic processes are reflected in the observed charge-carrier lifetimes, which strongly fluctuate during periods of large ion migration but steadily increase with improving crystallinity.