Multitechnique Detection of Lead Iodide Hybrid Perovskite Degradation Pathways under Varying Electric Fields

Although hybrid perovskite-based devices have made significant advances in terms of device performance, long-term stability remains a major challenge to widespread implementation. A unified understanding of the complexity describing the degradation of these types of materials is absent, and in this work, one common hybrid perovskite material, methylammonium lead iodide (MAPI), is used as a vehicle to show how a unified understanding can be achieved using complementary characterization techniques. This work uses low-dose <i>in situ</i> electron microscopes with electric fields ranging from 2.5 to 5 V/μm in a scanning electron microscope before focusing on the lower fields of 1.25 and 2.5 V/μm, where an electric threshold is identified. The results demonstrate that material loss is initiated at the MAPI grain boundaries near the negative electrode interface, where MA⁺ is reduced. Above the electrochemical threshold, extensive material volatilization and amorphous layer formation were detected, accompanied by significant PL quenching. High-field solid-state MAS NMR and materials modeling indicate that the MAPI decomposition process is a simultaneous combination of iodine migration, vacancy formation, and organic cation decomposition. The ¹H MAS NMR data from the as-synthesized MAPI show direct evidence of preexisting iodine vacancies that induce the formation of CH₃NH₂, forming possible dative coordination to the lead framework positions. Subsequent data from MAPI degraded under exposure to electric fields (1.25 and 2.50 V/μm) directly demonstrate the presence of decomposition products such as NH₄I, CH₃I, and CH₂I₂ through pinhole formation at the electrochemical threshold and more widespread damage induced above this threshold. The methodology presented here can be applied to investigate other hybrid perovskite materials through direct spin coating on the corresponding substrates, deepening our understanding and providing insights for improved device stability.