In Situ Observation of Light Illumination-Induced Degradation in Organometal Mixed-Halide Perovskite Films

Abstract

Organometal mixed-halide perovskite materials hold great promise for next-generation solar cells, light-emitting diodes, lasers, and photodetectors. Except for the rapid progress in the efficiency of perovskite-based devices, the stability issue over prolonged light illumination has severely hindered their practical application. The deterioration mechanism of organometal halide perovskite materials under light illumination has seldom been conducted to date, which is indispensable to the understanding and optimization of photon-harvesting process inside perovskite-based optoelectronic devices. Here, explicit degradation pathways and comprehensive microscopic understandings of white-light-induced degradation have been put forward for two organometal mixed-halide perovskite materials (e.g., MAPbICl and MAPbBrCl) under high vacuum conditions. In situ compositional analysis and real-time film characterizations reveal that the decomposition of both mixed-halide perovskites starts at the grain boundaries, leading to the formation of hydrocarbons and ammonia gas with the residuals of PbI(Cl), Pb, or PbClBr in the films. The degradation has been correlated to the localized trap states that induce strong coupling between photoexcited carriers and the crystal lattice.

Exploring Red, Green, and Blue Light‐Activated Degradation of Perovskite Films and Solar Cells for Near Space Applications

“…For blue light illumination, we note that there are additional peaks at 31.25° and 36.26° emerging that represent the (111) and (002) peaks of metallic Pb, pointing to a decomposition from PbI 2 to Pb, consistent with the XPS results. The photodecomposition processes of the perovskite films in vacuum follow the degradation mechanisms as our previous reports, which are closely related with the numerous defects existing on the perovskite film surface, e.g., impurities, vacancies, and dangling bonds. During light illumination, these large defect trap states capture the photoexcited charge carriers, perturbing the crystal systems and promoting the coupling between the charge carriers and the crystal lattices …”

Surface CH3NH3+ to CH3+ Ratio Impacts the Work Function of Solution‐Processed and Vacuum‐Sublimed CH3NH3PbI3 Thin Films

“…Even for weak interfacial coupling, poor structural order in the organic layer can induce gap states and band‐bending‐like behavior, which can be detrimental to the preferred ELA for excellent device performance. However, the effects of surface composition variation,[17,24a] especially the organic cations, on the work function and subsequent impacts on energy‐level alignment with other charge transport layers are less addressed …”

Recent Advances in Energetics and Stability of Metal Halide Perovskites for Optoelectronic Applications

“…It was also shown that such an energetic degradation was irreversible in dark and independent of perovskite composition. As confirmed by in situ XPS analysis, metallic Pb appeared in all MAPbI 3− x Cl x , MAPbBr 3− x Cl x , and MAPbI 3− x Br x under white light illumination, which would induce the strong E F pinning and quenching of the surface voltage . It has been noted that the compositional engineering, especially the appropriate substitution of A‐site cations with FA and Cs, could notably improve the photostability of perovskites.…”

“…It has been concluded that the presence of metallic Pb can induce strong E F pining close to the perovskite CBM, which thus quenches the surface photovoltage. Recently, Xu et al demonstrated that white light illumination of 2 h would increase the WF due to the presence of surface photovoltage, while the prolonged illumination up to 24 h would cause the decrease in WF and the VBM shift away from E F (Figure d) . It was also shown that such an energetic degradation was irreversible in dark and independent of perovskite composition.…”

“…a–c) Reproduced with permission . d) UPS spectra of perovskite films for a prolonged illumination time up to 24 h. Reproduced with permission . Copyright 2018, American Chemical Society.…”