Fluorescence super-resolution microscopy showed correlated fluctuations of photoluminescence intensity and spatial localization of individual perovskite (CH3NH3PbI3) nanocrystals of size ∼200 × 30 × 30 nm(3). The photoluminescence blinking amplitude caused by a single quencher was a hundred thousand times larger than that of a typical dye molecule at the same excitation power density. The quencher is proposed to be a chemical or structural defect that traps free charges leading to nonradiative recombination. These trapping sites can be activated and deactivated by light.

Photoluminescence (PL) of organo-metal halide perovskite semiconductors can be enhanced by several orders of magnitude by exposure to visible light. We applied PL microscopy and super-resolution optical imaging to investigate this phenomenon with spatial resolution better than 10 nm using films of CH3NH3PbI3 prepared by the equimolar solution-deposition method, resulting in crystals of different sizes. We found that PL of ∼100 nm crystals enhances much faster than that of larger, micrometer-sized ones. This crystal-size dependence of the photochemical light passivation of charge traps responsible for PL quenching allowed us to conclude that traps are present in the entire crystal volume rather than at the surface only. Because of this effect, "dark" micrometer-sized perovskite crystals can be converted into highly luminescent smaller ones just by mechanical grinding. Super-resolution optical imaging shows spatial inhomogeneity of the PL intensity within perovskite crystals and the existence of <100 nm-sized localized emitting sites. The possible origin of these sites is discussed.

Organo-metal halide perovskites are some of the most promising materials for the new generation of low-cost photovoltaic and light-emitting devices. Their solution processability is a beneficial trait, although it leads to a spatial inhomogeneity of perovskite films with a variation of the trap state density at the nanoscale. Comprehending their properties using traditional spectroscopy therefore becomes difficult, calling for a combination with microscopy in order to see beyond the ensemble-averaged response. We studied photoluminescence (PL) blinking of micrometer-sized individual methylammonium lead iodide (MAPbI) perovskite polycrystals, as well as monocrystalline microrods up to 10 μm long. We correlated their PL dynamics with structure employing scanning electron and optical super-resolution microscopy. Combining super-resolution localization imaging and super-resolution optical fluctuation imaging (SOFI), we could detect and quantify preferential emitting regions in polycrystals exhibiting different types of blinking. We propose that blinking in MAPbI occurs by the activation/passivation of a "supertrap" which presumably is a donor-acceptor pair able to trap both electrons and holes. As such, nonradiative recombination via supertraps, in spite being present at a rather low concentrations (10-10 cm), is much more efficient than via all other defect states present in the material at higher concentrations (10-10 cm). We speculate that activation/deactivation of a supertrap occurs by its temporary dissociation into free donor and acceptor impurities. We found that supertraps are most efficient in structurally homogeneous and large MAPbI crystals where carrier diffusion is efficient, which may therefore pose limitations on the efficiency of perovskite-based devices.

Photoinduced degradation of individual methylammonium lead triiodide (MAPbI3) perovskite nanocrystals was studied using super-resolution luminescence microspectroscopy under intense light excitation. The photoluminescence (PL) intensity decrease and blue-shift of the PL spectrum up to 60 nm together with spatial shifts in the emission localization position up to a few hundred nanometers were visualized in real time. PL blinking was found to temporarily suspend the degradation process, indicating that the degradation needs a high concentration of mobile photogenerated charges to occur. We propose that the mechanistic process of degradation occurs as the three-dimensional MAPbI3 crystal structure smoothly collapses to the two-dimensional layered PbI2 structure. The degradation starts locally and then spreads over the whole crystal. The structural collapse is primarily due to migration of methylammonium ions (MA+), which distorts the lattice structure causing alterations to the Pb–I–Pb bond angle and in turn changes the effective band gap.

Halide perovskites are emerging as revolutionary materials for optoelectronics. Their ionic nature and the presence of mobile ionic defects within the crystal structure have a dramatic influence on the operation of thin‐film devices such as solar cells, light‐emitting diodes, and transistors. Thin films are often polycrystalline and it is still under debate how grain boundaries affect the migration of ions and corresponding ionic defects. Laser excitation during photoluminescence (PL) microscopy experiments leads to formation and subsequent migration of ionic defects, which affects the dynamics of charge carrier recombination. From the microscopic observation of lateral PL distribution, the change in the distribution of ionic defects over time can be inferred. Resolving the PL dynamics in time and space of single crystals and thin films with different grain sizes thus, provides crucial information about the influence of grain boundaries on the ionic defect movement. In conjunction with experimental observations, atomistic simulations show that defects are trapped at the grain boundaries, thus inhibiting their diffusion. Hence, with this study, a comprehensive picture highlighting a fundamental property of the material is provided while also setting a theoretical framework in which the interaction between grain boundaries and ionic defect migration can be understood.