Organometal halide perovskites have attracted considerable attention because of their striking electrical and optical properties that are desirable for application in solar cells and optoelectronic devices; however, the structure-related dynamics of photogenerated charges are almost always masked by ensemble averaging in conventional spectroscopic methods, making it difficult to clarify the underlying mechanism. Here we investigate the photoluminescence characteristics of CH 3 NH 3 PbBr 3 perovskite nanoparticles using single-particle spectroscopy combined with electron microscopy. The in situ analysis of light and Lewis-base-induced surface passivation revealed that the photoluminescence quenching and blinking phenomena of single CH 3 NH 3 PbBr 3 nanoparticles are most probably caused by charge trapping at surface states, where the number of effective trapping sites was estimated to be 1−4 per particle.O rganometal halide perovskites, mostly methylammonium lead halides (CH 3 NH 3 PbX 3 ; hereafter denoted as MAPbX 3 , where MA = CH 3 NH 3 and X = Cl, Br, or I), have attracted great attention for photovoltaic applications because of their low cost and ability to rapidly increase the power conversion efficiency by up to 20%. 1−4 The high efficiency is explained as the combined advantages of the broad lightabsorption range, high optical-absorption coefficient (∼10 5 cm −1 ), fast charge generation combined with slow recombination, and long-range diffusion length of charge carriers. 3−5 The tunability of the electronic levels of the perovskites by changing metal or halogen ions is a particularly important advantage because it provides an elegant means to adjust their optical absorption properties so that a good overlap with sunlight can be obtained. The same hybrid perovskite structures also offer prospects of promising applications in lasers and light-emitting diodes (LEDs). 6,7 In general, the active MAPbX 3 layer of the high-performance perovskite solar cells has been prepared by sequentially depositing a solution of PbX 2 and a solution of CH 3 NH 3 X (MAX) onto a mesoporous TiO 2 film, followed by removing the solvent to crystallize the perovskite structures with dimensions from tens to hundreds of nanometers. 8 The size and morphology of perovskite grains are definitely important for charge-generation, -transport, and -trapping properties that are essential to photovoltaic and optoelectronic devices; however, the fate of the photogenerated charge carriers on specific structures has remained unclear because almost all spectroscopic measurements have been conducted on bulk samples where the primary particles usually aggregate. Therefore, physicochemical examinations at the single-particle level are urgently required for elucidating the underlying mechanisms of charge dynamics.In this work, we synthesized colloidal MAPbBr 3 nanoparticles (NPs) by employing a ligand-f ree reprecipitation method. Organic ligands are usually essential for synthesis, but they may interact with the surface instead and capture the char...

Hematite (α-Fe2O3) is one of the most promising candidates as a photoanode materials for solar water splitting. Owing to the difficulty in suppressing the significant charge recombination, however, the photoelectrochemical (PEC) conversion efficiency of hematite is still far below the theoretical limit. Here we report thick hematite films (∼1500 nm) constructed by highly ordered and intimately attached hematite mesocrystals (MCs) for highly efficient PEC water oxidation. Due to the formation of abundant interfacial oxygen vacancies yielding a high carrier density of ∼1020 cm−3 and the resulting extremely large proportion of depletion regions with short depletion widths (<10 nm) in hierarchical structures, charge separation and collection efficiencies could be markedly improved. Moreover, it was found that long-lived charges are generated via excitation by shorter wavelength light (below ∼500 nm), thus enabling long-range hole transfer through the MC network to drive high efficiency of light-to-energy conversion under back illumination.

Organolead halide perovskites MAPbX (MA = CHNH, X = Cl, Br, or I) are known to undergo reversible halide exchange reactions, enabling bandgap tuning over the visible light region. Using single-particle photoluminescence (PL) imaging for in situ observation, we have studied the structure-dependent charge dynamics during halide exchange with iodide ions on an MAPbBr crystal. In particular, we optically detected nanometer-scale iodide-rich domains (i.e., MAPbBrI) and found that their lifetimes of several tens of milliseconds are limited by reaction with diffusing vacancies. Furthermore, it was discovered that these domains effectively collect the charge carriers from the bulk crystal, thus resulting in amplified spontaneous emission (ASE) under continuous-wave laser irradiation. Our findings will provide direction for development of perovskite heterostructures with enhanced charge utilization.

Controlled fabrication of semiconductor nanostructures with unique physicochemical properties is vital for future technologies. In this study, transformation from red‐emitting metal halide perovskite CH3NH3PbI3 nanocrystals (NCs) to green‐emitting CH3NH3PbBr3 NCs was achieved without significant morphological changes and loss of photoluminescence (PL) efficiency via a controlled halide exchange reaction. In situ single‐particle PL imaging along with detailed structural and elemental characterizations revealed that sudden cooperative transitions between two light‐emitting states via intermediate dark states with >100 s durations during halide exchange originate from two distinct defect‐mediated reconstruction processes with different activation energies (0.072 and 0.40 eV), leading to an isokinetic temperature of ca. 314 K, across a solid‐state miscibility gap between the I‐ and Br‐rich phases inside a single NC.

Metal halide perovskites have attracted considerable attention in applications such as photovoltaic cells and light‐emitting diodes. The performance and durability of perovskite devices are significantly dependent on the nature of structural defects, but the underlying mechanisms of structure‐related photochemical reactions are not yet fully elucidated. This study demonstrates that the photoluminescence (PL) from individual perovskite nanoparticles (NPs) can be utilized to resolve the different trapping pathways of the photogenerated charges, and hence, obtain a correlation between the pathways. PL deactivation and activation were observed and mainly attributed to nonradiative Auger recombination by the trapped charges and the passivation of surface traps by oxygen, respectively. Single‐particle spectroelectrochemical techniques were further employed to explore the possible origin of the effective charge trap states and the reversibility of redox events under electrical bias. Consequently, this study unravels the complex effects of the structural defects on the charge carrier dynamics in perovskites.