High-resolution transmission electron microscopy imaging of graphene-encapsulated CH3NH3PbI3 solution

Abstract

Organic−inorganic hybrid perovskites (OIHPs) have emerged as potential candidate materials for photovoltaic devices because of their superior optoelectronic properties. Nonetheless, real-time characterization of their formation and decomposition process inside the liquid phase with atomic-level resolution, which is vital to understand the synthesis mechanism and to further improve the device performance, has not been reported yet. In-situ liquid-phase transmission electron microscope (TEM) enables high-resolution real-time characterization. However, the imaging resolution is limited to a few nanometers by the relatively thick encapsulation layer (e.g., Si₃N_x) and its higher atomic number element. Herein, using high-intactness and high-cleanness suspended graphene membrane to seal liquid, organic solution of methylammonium lead iodide (MAPbI₃), the most representative OIHPs, has been successful encapsulated. The as-prepared graphene liquid cells exhibit high density and wide size distribution range (50–600 ​nm) via precise composition regulation of the solution to encapsulate both nanocrystals and thin films in the liquid. TEM imaging is conducted to visualize the synthesis and decomposition processes of organic-inorganic hybrid perovskites with high spatial (sub-nm) and temporal (sub-second) resolution, revealing the effect of nanocrystal size, bubbles and adjacent nanocrystals. This study not only provides a new routine to real-time observe OIHPs synthesis and decomposition process in liquid state, but also deepens the understanding of liquid reaction at atomic scale.