Organolead halide perovskites MAPbX3 (MA = CH3NH3+, 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 MAPbBr3 crystal. In particular, we optically detected nanometer-scale iodide-rich domains (i.e., MAPbBrI2) 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.

AbstractThe higher-order structures of semiconductor-based photocatalysts play crucial roles in their physicochemical properties for efficient light-to-energy conversion. A novel perovskite SrTiO3 mesocrystal superstructure with well-defined orientation of assembled cubic nanocrystals was synthesized by topotactic epitaxy from TiO2 mesocrystals through a facile hydrothermal treatment. The SrTiO3 mesocrystal exhibits three times the efficiency for the hydrogen evolution of conventional disordered systems in alkaline aqueous solution. It also exhibits a high quantum yield of 6.7 % at 360 nm in overall water splitting and even good durability up to 1 day. Temporal and spatial spectroscopic observations revealed that the synergy of the efficient electron flow along the internal nanocube network and efficient collection at the larger external cubes produces remarkably long-lived charges for enhanced photocatalysis.

The performance of semiconductor materials in solar water splitting and other applications is strongly influenced by the structure-related dynamics of charge carriers in these materials. In this study, we assessed the trapping, recombination, and surface reactions of photogenerated and electrically injected charges on specific facets of the promising visible active photocatalyst BiVO4 by using single-particle photoluminescence (PL) spectroscopy. Evaluation of the electric-potential-induced PL properties and the PL response to charge scavengers revealed that the visible PL bands observed during visible laser irradiation originate from radiative recombination between holes trapped at the intraband states above the valence band and mobile (free or shallowly trapped) electrons. Furthermore, the trapped holes are preferentially located on the lateral {110} facets of the BiVO4 crystal, while the electrons are uniformly distributed over the crystal. The methodology described in this study thus provides us with a unique opportunity to explore whether or not the crystal faces affect the charge carrier dynamics in the photocatalysis and the photoelectrocatalysis.Keywords: bismuth vanadate; electrochemistry; interfacial charge transfer; photocatalysis; photoluminescence; single-particle spectroscopy; surface reaction

Ti3+ self-doped TiO2 nanocrystals (TNCs) confined with controllable atomic layer deposition (ALD) amorphous layers were developed to provide a novel model of metal–insulator–semiconductor (MIS) photocatalysts for hydrogen generation in the ultraviolet to near-infrared region. Photoexcitation of optimized MIS nanostructures consisting of a metal cocatalyst (Pt), electron tunneling layer (ALD TiO2), and photoactive nonstoichiometric core (Ti3+-doped TNC) exhibited efficient hydrogen generation (52 μmol h–1·g–1), good reusability (16 h), and long-term stability (>7 d). The charge-transfer dynamics were examined using transient absorption spectroscopy to clarify the relationship between the photocatalytic activity and the tunneling effect. Our strategies highlight defect engineering in fabricating MIS photocatalysts with improved charge separation and tailored solar energy conversion properties.

Here we demonstrated that 3D architectures of TiO2 mesocrystals uniformly packed with a chemically exfoliated MoS2 shell exhibit promising reactive efficiency and good stability in synergetic hydrogen evolution. The efficient interfacial electron transfer from the excited TiO2 moieties to the decorated ultrathin MoS2 shell was effectively monitored.

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 CH3NH3PbBr3 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 CH3NH3PbBr3 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.

Pt-modified Au nanorods (NRs) synthesized by anisotropic overgrowth were used for producing H2 under visible and near-infrared light irradiation. The Pt-tipped sample exhibited much higher activity compared with fully covered samples. Using single-particle spectroscopies combined with transmission electron microscopy, we observed obvious quenching phenomena for photoluminescence and light scattering from individual Pt-tipped NRs. The analysis of energy relaxation of plasmon-generated hot electrons indicates the electron transfer from the excited Au to Pt.

Here we demonstrated that 3D architectures of TiO2 mesocrystals uniformly packed with a chemically exfoliated MoS2 shell exhibit promising reactive efficiency and good stability in synergetic hydrogen evolution. The efficient interfacial electron transfer from the excited TiO2 moieties to the decorated ultrathin MoS2 shell was effectively monitored.