In Situ TEM Monitoring of Phase-Segregation in Inorganic Mixed Halide Perovskite

Abstract

Photoinduced phase separation, which limits the available band gap energies for photovoltaic applications, was reported for a range of mixed-halide perovskites. A microscopic understanding of the phase separation mechanism is still lacking but may be beneficial to rationalize limitations as well as enable the design of phase-stable perovskite semiconductors. In this letter, electron-beam-induced phase separations and transformations were investigated in a small crystallite of CsPb(Br 0.8 I 0.2 ) 3 by means of in situ high-resolution imaging in a transmission electron microscope. The acquired time series was evaluated using principal and independent component analysis to classify the structural change during the illumination by the electron beam. A more iodine-rich phase with the approximate composition of CsPb(Br 0.6 I 0.4 ) 3 was found to form at the edges of the particle, while a ternary pure bromide phase of CsPbBr 3 remained at its center. These results provide an atomistic picture of in-grain phase segregation into iodide-rich phases at grain boundaries and bromide-rich phases in the interior of the grain.

Kinetic Study on the Adsorption of 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane on Ag Nanoparticles in Chloroform: Implications for the Charge Transfer Complex of Ag–F4TCNQ

“…The Ag NP patterns are compared to high-resolution TEM data obtained from an isolated particle (see Figure f). The hexagonal patterns obtained from Fourier transform (FT) diffractogram analysis of this image (see Figure g–i) serve as the confirmation of the observed Ag NP NBED patterns (Figure b,c). We associate the more complicated patterns (Figure d,e) with the diffraction of the formed Ag–F 4 TCNQ complex, which has been confirmed by the optical absorption and EELS analysis.…”

“…These data were compared to characteristic isolated Ag NP patterns obtained by Fourier transform (FT) diffractogram analysis of highresolution TEM using a home-developed software. 49 ■ ASSOCIATED CONTENT * sı Supporting Information…”

Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility

“…We have recently reported such behavior in perovskite nanocrystals between 6–10 nm in size 24 . While the size of I-rich domains in segregated mixed halide films has been reported to grow to similar scales 8 , 10 , 25 , even upon direct photoexcitation of these domains (Fig. 1 g) our THz spectra demonstrate an absence of strong carrier localisation.…”

“…On the one hand, lattice anharmonicity can be a cause of segregation, given that such lattice distortions in the photoexcited state facilitate ionic displacements. The funnelling of charge carriers to regions where phonon anharmonicity is stronger agrees with the preferential formation of segregated domains at surfaces, grain boundaries, or defective regions that experience a softening of the lattice potential and are more likely to allow halide segregation 25 , 40 . On the other hand, the formation of boundaries and lattice distortions can be a consequence of halide demixing.…”

Thermodynamic stability screening of IR-photonic processed multication halide perovskite thin films

“…However, photoinduced phase segregation is a complex phenomenon, which requires further experimental investigations to be fully understood. 33,[38][39][40] During crystal growth, vacancy and interstitial point defects, among others, create sub-band gap states and deep traps which act as recombination centers and enable ion migration. 41,42 Reducing the density of these defects will improve the stability.…”