Riya Bose

Photocatalytic Au–Bi2S3 Heteronanostructures†

Au-Bi2S3 heteronanostructure photocatalysts were designed in which the coupling of a metal plasmon and a semiconductor exciton aids the absorption of solar light, enhances charge separation, and results in improved catalytic activity. Furthermore, these nanostructures show a unique pattern of structural combination, with Au nanoparticles positioned at the center of Bi2S3 nanorods. The chemistry of formation of these nanostructures, their epitaxy at the junction, and their photoconductance were studied, as well as their photoresponse properties.

Mn-Doped Multinary CIZS and AIZS Nanocrystals

Multinary nanocrystals (CuInS2, CIS, and AgInS2, AIS) are widely known for their strong defect state emission. On alloying with Zn (CIZS and AIZS), stable and intense emission tunable in visible and NIR windows has already been achieved. In these nanocrystals, the photogenerated hole efficiently moves to the defect-induced state and recombines with the electron in the conduction band. As a result, the defect state emission is predominantly observed without any band edge excitonic emission. Herein, we report the doping of the transition-metal ion Mn in these nanocrystals, which in certain compositions of the host nanocrystals quenches this strong defect state emission and predominantly shows the spin-flip Mn emission. Though several Mn-doped semiconductor nanocrystals are reported in the literature, these nanocrystals are of its first kind that can be excited in the visible window, do not contain the toxic element Cd, and provide efficient emission. Hence, when Mn emission is required, these multinary nanocrystals can be the ideal versatile materials for widespread technological applications.

Fast Crystallization and Improved Stability of Perovskite Solar Cells with Zn2SnO4 Electron Transporting Layer: Interface Matters

Here we report that mesoporous ternary oxide Zn2SnO4 can significantly promotes the crystallization of hybrid perovskite layers and serves as an efficient electron transporting material in perovskite solar cells. Such devices exhibit an energy conversion efficiency of 13.34%, which is even higher than that achieved with the commonly used TiO2 in the similar experimental conditions (9.1%). Simple one-step spin coating of CH3NH3PbI3-xClx on Zn2SnO4 is found to lead to rapidly crystallized bilayer perovskite structure without any solvent engineering. Furthermore, ultrafast transient absorption measurement reveals efficient charge transfer at the Zn2SnO4/perovskite interface. Most importantly, solar cells with Zn2SnO4 as the electron-transporting material exhibit negligible electrical hysteresis and exceptionally high stability without encapsulation for over one month. Besides underscoring Zn2SnO4 as a highly promising electron transporting material for perovskite solar cells, our results demonstrate the significant role of interfaces on improving the perovskite crystallization and photovoltaic performance.

Multifunctional Doped Semiconductor Nanocrystals

Multifunctional nanomaterials with combined magnetic and optical properties remain one of the most demanded materials in upcoming research. To obtain these materials, we report here several doped semiconductor nanocrystals that simultaneously show tunable emission in a visible and NIR spectral window, above-room-temperature ferromagnetism, and improved conductivity. These nanocrystals are designed by inserting Ni(II) as a dopant in various semiconducting hosts with binary, alloyed, and ternary composition, and the induced multifunctional properties are observed to be stable and reproducible. These semiconducting materials combined with fluorescence and magnetic properties would be useful for a wide range of applications spanning from life science to modern developing device technology.

Heteroepitaxial Junction in Au-ZnSe Nanostructure: Experiment versus First-Principle Simulation

Composing together the experimental as well as the simulated results, we demonstrate here the atomic placements and the electronic structure at the epitaxial junction of a solution-processed heteronanostructure Au-ZnSe. Despite the large lattice mismatch (∼32%) between fcc Au and zinc-blende structured ZnSe, the heterostructures are formed via coincidence site epitaxy, which appears periodically because of the arrangements of their proper unit cell placements at the junction. This reduces the interface energy and drives the formation of such heteronanostructures. Details of the physical processes involved in the formation of these nanostructures have been discussed in this letter, and epitaxy at the heterojunction is strongly supported by HRTEM measurement and DFT calculation. This material has the possibility of plasmon-exciton coupling and therefore might be a futuristic material for utilizations in catalysis, nanoelectronics, and other related applications.

Real-Space Mapping of Surface Trap States in CIGSe Nanocrystals Using 4D Electron Microscopy

Surface trap states in copper indium gallium selenide semiconductor nanocrystals (NCs), which serve as undesirable channels for nonradiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with subpicosecond temporal and nanometer spatial resolutions. Here, we precisely map the collective surface charge carrier dynamics of copper indium gallium selenide NCs as a function of the surface trap states before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, the removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs.

Au–Thiol Interaction Chemistry to Influence the Structural Transformation of Semiconductor Nanocrystals and Formation of Giant Nanostructures

Giant nanostructures which are difficult to design by the classical growth process can be fabricated in a facilitated and well programmed surface ligand removal protocol employing the thiol-gold strong interaction chemistry. When thiol capped small ZnSe seed nanocrystals are treated with amine capped gold particles, gold snatches the thiol ligands from ZnSe and forces them to agglomerate leading to the giant crystalline ZnSe nanostructures.