Reversible Photoinduced Phase Segregation and Origin of Long Carrier Lifetime in Mixed‐Halide Perovskite Films

Abstract

Mixed-halide hybrid perovskite semiconductors have attracted tremendous attention as a promising candidate for efficient photovoltaic and lightemitting devices. However, these perovskite materials may undergo phase segregation under light illumination, thus affecting their optoelectronic properties. Here, photoexcitation induced phase segregation in triplecation mixed-halide perovskite films that yields to red-shift in the photoluminescence response is reported. It is demonstrated that photo excitation induced halide migration leads to the formation of smaller bandgap iodide-rich and larger bandgap bromide-rich domains in the perovskite film, where the phase segregation rate is found to follow the excitation power-density as a power law. Results confirm that charge carrier lifetime increases due to the trapping of photoexcited carriers in the segregated smaller bandgap iodide-rich domains. Interestingly, these photoinduced changes are fully reversible and thermally activated when the excitation power is turned off. A significant difference in activation energies for halide ion migration is observed during phase segregation and recovery process. Additionally, the emission linewidth broadening is investigated as a function of temperature which is governed by the exciton-optical phonon coupling. The mechanism of photoinduced phase segregation is interpreted based on exciton-phonon coupling strength in both mixed and demixed (segregated) states of perovskite films.

Multifunctional Conjugated Ligand Engineering for Stable and Efficient Perovskite Solar Cells

“…The time‐dependent PL images of pristine CsFAMA film exhibit evolution of heterogeneity upon light illumination, indicating the formation of narrow band‐gap domains that serve as a trap for electron and hole and cause PL quenching. [ 42 ] The homogenized PL images from CsFAMA‐MCL film implies uniformity across the whole film. In addition, charge–discharge experiments also reveal faster discharge processes in CsFAMA‐MCL solar cells, further verifying the reduced ion migration in the CsFAMA‐MCL film (Figure S17, Supporting Information).…”

Photoinduced Halide Segregation in Ruddlesden–Popper 2D Mixed Halide Perovskite Films

“…On the other hand, long-lived charge carriers also allow trapping of charge carriers at the defect sites. [48] For example, the capture of holes by halide ions (e.g., I − ) makes them mobile as the oxidized halide (I • ) is expelled from the lattice. [49] The iodide defects further assist in the movement of halide ions.…”

Roles of MACl in Sequentially Deposited Bromine‐Free Perovskite Absorbers for Efficient Solar Cells

“…[5,17] Besides, it has been demonstrated that mixed halide perovskites suffered from phase segregation under continuous light illumination. [18,19] Han et al spun cast MACl atop FAPbI 3 to vertically recrystallize perovskites upon a small amount of MA into the crystal lattice without compromising the absorption onset. [20] However, a recent work by Yang et al showed that barely using MACl as stabilizer could maintain the α phase of FAPbI 3 .…”