Metastable alloying structures in MAPbI3−xClx crystals

Abstract

Chlorine incorporation engineering has been widely used in optoelectronic devices based on methylammonium lead iodide (MAPbI3) perovskites. However, the characteristics of I/Cl alloying structures in MAPbI3−xClx mixed-halide perovskites and their influences on the optoelectronic properties have been issues of a long-standing controversy. Here, we present a detailed study of the I/Cl alloying structures in MAPbI3−xClx (x = 0.0 to 0.3) single crystals. We found that a small amount of Cl can substitute for the iodide of the PbI3 inorganic lattice, leading to a phase transition from the tetragonal to cubic phase and anomalous cation dynamics evolution. Analyses based on time-dependent X-ray diffraction, 207Pb NMR, and 2H NMR indicate that the alloying structures of the MAPbI3−xClx crystals are metastable and decompose over time. In addition, the photocurrent response measurement of MAPbI3−xClx proved a close correlation between the alloying structures and photoelectric properties of the material. This work sheds light on the essential understanding of the I/Cl alloying structure and provides a plausible explanation for the controversy regarding the role of chloride ions in optoelectronic devices.

In-Situ Nano-Auger Probe of Chloride-Ions during CH3NH3PbI3−xClx Perovskite Formation

“…The fine control over optoelectronic properties and ease of synthesis has driven MAPbI 3 to broad applications, including PSCs [ 11 ], solar-water splitting [ 12 ], lasing [ 13 ], and light-emitting diodes [ 14 ]. In addition, the incorporation of a small amount of bromine or chlorine into MAPbI 3 is known to improve device properties [ 15 ]. Since the first report on PSCs using mixed halide MAPb 3−x Cl x as a light absorber, the PCE of the MAPb 3−x Cl x devices has already exceeded 18% [ 16 , 17 ].…”

Illumination-Induced Changes in Methylammonium Lead Bromine Perovskites. An In Situ 2H NMR Study

“…Following the previous work, we applied solid-state 2 H NMR to selectively deuterated MAPbBr 3 samples, in which the methyl groups of the MA cations were fully deuterated. 26,27 The benefits of investigating the behaviors of MA cations are predicated upon the fact that MAPbBr 3 can be considered as a host−guest system. In such a system, the molecular dynamics of the MA cations constrained within the lead halide perovskite cages are very sensitive to dynamic changes in the host lattice.…”

“…In such a system, the molecular dynamics of the MA cations constrained within the lead halide perovskite cages are very sensitive to dynamic changes in the host lattice. 27 Therefore, these changes in the molecular dynamics of MA cations can be used as a molecular probe to monitor subtle changes in the host lattice. 27−29 The results demonstrate that the orientations of MA cations are widely distributed in the tetragonal I phase.…”

“…The present work is committed to addressing the above-discussed issues by applying in situ solid-state 2 H nuclear magnetic resonance (NMR) spectroscopy to probe the illumination-induced structural and dynamic changes of the MA cations in MAPbBr 3 . Following the previous work, we applied solid-state 2 H NMR to selectively deuterated MAPbBr 3 samples, in which the methyl groups of the MA cations were fully deuterated. , The benefits of investigating the behaviors of MA cations are predicated upon the fact that MAPbBr 3 can be considered as a host–guest system. In such a system, the molecular dynamics of the MA cations constrained within the lead halide perovskite cages are very sensitive to dynamic changes in the host lattice .…”

A-Site Mixing to Adjust the Photovoltaic Performance of a Double-Cation Perovskite: It Is Not Always the Simple Way

“…207 Pb NMR spectroscopy shows the intriguing sensitivity to probe changes in the inorganic lattice, particularly within the local Pb environments. , The solid state MAS 207 Pb NMR spectra obtained for the MA 1– x DMA x PbBr 3 samples (0 ≤ x ≤ 0.4) are presented in Figure a. The 207 Pb signal obtained for MAPbBr 3 exhibits a chemical shift of 360 ppm with full width at half-maximum (fwhm) values of ∼130 ppm.…”