Multi-technique detection of lead iodide hybrid perovskite degradation pathways under varying electric fields

Abstract

Although hybrid perovskite light-emitting diodes have made significant advances in terms of device performance, the lack of long-term stability remains an impediment to widespread implementation. A unified understanding of the complexity describing the degradation in materials such as methylammonium lead iodide (MAPI) is absent. This work uses low-dose in-situ electron microscopes and time-resolved photoluminescence (TRPL) to 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 modelling indicates that the MAPI decomposition process is a simultaneous combination of iodine migration, vacancy formation and organic cation decomposition. The 1H MAS NMR data from as-synthesized MAPI reveals direct evidence of pre-existing 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 demonstrates 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.