Hybrid perovskite crystals have emerged as an important class of semiconductors because of their remarkable performance in optoelectronics devices. The interface structure and chemistry of these crystals are key determinants of the device’s performance. Unfortunately, little is known about the intrinsic properties of the surfaces of perovskite materials because extrinsic effects, such as complex microstructures, processing conditions, and hydration under ambient conditions, are thought to cause resistive losses and high leakage current in solar cells. We reveal the intrinsic structural and optoelectronic properties of both pristinely cleaved and aged surfaces of single crystals. We identify surface restructuring on the aged surfaces (visualized on the atomic-scale by scanning tunneling microscopy) that lead to compositional and optical bandgap changes as well as degradation of carrier dynamics, photocurrent, and solar cell device performance. The insights reported herein clarify the key variables involved in the performance of perovskite-based solar cells and fabrication of high-quality surface single crystals, thus paving the way toward their future exploitation in highly efficient solar cells.

In an effort to develop nanostructured photocatalysts to achieve high performance in heterogeneous photocatalysis, a novel composite V2O5/BiVO4/TiO2 photocatalyst was successfully synthesized by using a sequentially hydrothermal and adhering method. The structural and optical properties of the as-prepared samples were comparatively characterized. The formed ternary nanojunctions were composed of TiO2 nanobelts and V2O5/BiVO4 nanorods which were self-assembled by smaller V2O5 and BiVO4 nanoparticles. Compared to pure TiO2 nanobelts and V2O5/BiVO4 nanorods, the V2O5/BiVO4/TiO2 composite exhibited higher photocatalytic activity in decomposition of gaseous toluene under visible light irradiation (λ > 400 nm). Electron spin resonance examination confirmed that the photoinduced active species (•OH and O2 •–) were involved in the photocatalytic degradation of toluene. A detailed mechanism accounting for the enhanced photocatalytic activity of the V2O5/BiVO4/TiO2 nanocomposite was proposed in terms of the energy band structures of the components. The rationally designed ternary nanojunctions could effectively enhance the photocatalytic performance by increasing photoinduced charge carriers through the charges separation across their multiple interfaces.

In the fields of photocatalysis and photovoltaics, ultrafast dynamical processes, including carrier trapping and recombination on material surfaces, are among the key factors that determine the overall energy conversion efficiency. A precise knowledge of these dynamical events on the nanometer (nm) and femtosecond (fs) scales was not accessible until recently. The only way to access such fundamental processes fully is to map the surface dynamics selectively in real space and time. In this study, we establish a second generation of four-dimensional scanning ultrafast electron microscopy (4D S-UEM) and demonstrate the ability to record time-resolved images (snapshots) of material surfaces with 650 fs and ∼5 nm temporal and spatial resolutions, respectively. In this method, the surface of a specimen is excited by a clocking optical pulse and imaged using a pulsed primary electron beam as a probe pulse, generating secondary electrons (SEs), which are emitted from the surface of the specimen in a manner that is sensitive to the local electron/hole density. This method provides direct and controllable information regarding surface dynamics. We clearly demonstrate how the surface morphology, grains, defects, and nanostructured features can significantly impact the overall dynamical processes on the surface of photoactive-materials. In addition, the ability to access two regimes of dynamical probing in a single experiment and the energy loss of SEs in semiconductor-nanoscale materials will also be discussed.

We report the observation of the undocumented visible one-photon photoluminescence (PL) of single silver nanorods excited by 532 and 633 nm continuous wave lasers with single-nanoparticle spectroscopy. We attribute the PL of silver nanorods to the intraband transition excited hotelectron radiative decay. The PL of silver nanorods closely resembles the corresponding LSPR scattering spectrum, and both are dependent on their aspect ratio. The good correlation between the quantitative PL intensity and the absorption cross section at the excitation wavelength of each nanorod leads to an aspect ratio independent PL quantum yield. The PL quantum yield of silver nanorods is similar to that of gold nanorods (10 −6 ), indicating an efficient intraband excitation of hot electrons. The understanding of the PL mechanism of Ag nanorods points to the high-energy nature of the hot electrons excited via intraband transition, which has important indications in utilizing hot electrons for energy harvesting and photocatalysis.