Superior Visible Photoelectric Response with Au/Cu2NiSnS4 Core-Shell Nanocrystals.

The incorporation of plasmonic metal nanostructures into semiconducting chalcogenides in the form of core-shell structures provides a promising approach to enhancing the performance of photodetectors. In this study, we combined Au nanoparticles with newly developed copper-based chalcogenides Cu2NiSnS4 (Au/CNTS) to achieve an ultrahigh optoelectronic response in the visible regime. The high-quality Au/CNTS core-shell nanocrystals (NCs) were synthesized by developing a unique colloidal hot-injection method, which allowed for excellent control over sizes, shapes, and elemental compositions. The as-synthesized Au/CNTS hybrid core-shell NCs exhibited enhanced optical absorption, carrier extraction efficiency, and improved photosensing performance owing to the plasmonic-induced resonance energy transfer effect of the Au core. This effect led to a significant increase in the carrier density of the Au/CNTS NCs, resulting in a measured responsivity of 1.2 × 103 AW-1, a specific detectivity of 6.2 × 1011 Jones, and an external quantum efficiency of 3.8 × 105 % at an incident power density of 318.5 µW cm-2. These results enlighten a new era in the development of plasmonic core-shell nanostructure-based visible photodetectors.

Photodetectors with High Responsivity by Thickness Tunable Mixed Halide Perovskite Nanosheets.

Chemical transformation of typically "nonlayered" phases into two-dimensional structures remains a formidable task. Among the thickness tunable CsPbX3 (X = Br, Br/I, I) nanosheets (NSs), CsPbBr1.5I1.5 NSs with a thickness of ∼4.9 nm have structural stability superior to ∼6.8 nm CsPbI3 NSs and better hole mobility than ∼3.7 nm CsPbBr3 NSs. Moving beyond the much-explored CsPbBr3 photodetectors, we demonstrate a sharp improvement of the photodetection of CsPbBr1.5I1.5 NS devices by thickening the NSs to ∼6.1 nm through combining 8-carbon and 18-carbon ligand surfactants. Thereby, the responsivity increases up to one of the highest values of 3313 A W-1 at 1.5 V (and 3946 A W-1 at 2 V) with detectivity of 1.6 × 1011 Jones at 1.5 V, due to the increase in carrier mobility up to 7.9 × 10-4 cm2 V-1 s-1. The better device performance of the NSs than 8.6-13.9 nm nanocubes (NCs) is due to their planarity which facilitates in-plane mobilization of the charge carriers.

Thickness-Attuned CsPbBr3 Nanosheets with Enhanced p-Type Field Effect Mobility.

Since the invention of field effect transistors (FETs) in the mid-20th century, nanosheet (NS) transistors have been considered the future toward fulfilling Moore's law of scaling. Moving beyond conventional semiconductors, thickness tunable orthorhombic CsPbBr3 NSs are achieved by a perfect control in which the lateral dimension can be extended close to 1 µm. While 18-carbon-chain ligands produce ∼4.5 nm thick NSs, the strongly adsorbed less dynamic 8-carbon-chain ligands result in ∼9.2 nm NSs. Equipped with a minimum trap state density, a lower effective mass of charge carriers, and better carrier transport, the NSs enable an order of magnitude increase in the field effect mobility as compared to that of CsPbBr3 nanocubes, thus revealing the efficacy of designing the two-dimensional morphology. The p-type field effect mobility (µFET) of the photoexcited NSs reaches 10-5 cm2 V-1 s-1 at 200 K upon mitigation of the challenges of ionic screening and constrained tunneling probability across organic ligands.

An earth-abundant bimetallic catalyst coated metallic nanowire grown electrode with platinum-like pH-universal hydrogen evolution activity at high current density.

A self-supported and flexible current collector solely made of earth-abundant elements, NiCo layered double hydroxide (LDH) wrapped around Cu nanowires (Cu-Ws) grown on top of commercially available Cu mesh (Cu-m), outperforms the benchmark 40 wt% Pt/C in catalyzing the electrochemical hydrogen evolution reaction (HER). The Cu-m/Cu-W/NiCo-LDH cathode operates both in acidic and alkaline media exhibiting high turnover frequencies (TOF) at 30 mV (0.3 H2 s-1 in 1 M KOH and 0.32 H2 s-1 in 0.5 M H2SO4, respectively) and minimal overpotentials of 15 ± 6 mV in 1 M KOH and 27 ± 2 mV in 0.5 M H2SO4 at -10 mA cm-2. Cu-m/Cu-W/NiCo-LDH outperforms the activity of 40 wt% Pt/C that needs overpotentials of 22 and 18 mV in 1 M KOH and 0.5 M H2SO4, respectively. With a tremendous advantage over Pt/C in triggering proton reduction with fast kinetics, similar mass activity and pH-universality, the current collector demonstrates outstanding operational durability even at above -1 A cm-2. The high density of electronic states near the Fermi energy level of Cu-Ws is found to be a pivotal factor for efficient electron transfer to the NiCo-LDH catalyst. This class of self-supported electrodes is expected to trigger rapid progress in developing high performance energy conversion and storage devices.

Core/Shell Nanocrystal Tailored Carrier Dynamics in Hysteresisless Perovskite Solar Cells with ∼20% Efficiency and Long Operational Stability.

The ambient stability, hysteresis, and trap states in organo-halide perovskite solar cells (PSCs) are correlated to the influence of interlayer interfaces and grain boundaries. Astute incorporation of Cu2ZnSnS4 (CZTS) and Au/CZTS core/shell nanocrystals (NCs) can realize the goal of simultaneously achieving better performance and ambient stability of the PSCs. With optimized Au/CZTS NC size and concentration in the photoactive layer, power conversion efficiency can be increased up to 19.97 ± 0.6% with ambient air stability >800 h, as compared to 14.46 ± 1.02% for the unmodified devices. Through efficient carrier generation by CZTS and perovskite, accompanied by the plasmonic effect of Au, carrier density is sufficiently increased as validated by transient absorption spectroscopy. NCs facilitate the interfacial charge transfer by suitable band alignment and removal of recombination centers such as metallic Pb0, surface defects, or impurity sites. NC embedding also increases the perovskite grain size and assists in pinhole filling, reducing the trap state density.

Attuning the Electronic Properties of Two-Dimensional Co-Fe-O for Accelerating Water Electrolysis and Photolysis.

Two-dimensional (2D) materials such as layered double hydroxides (LDH) are promising electrocatalysts, especially for water oxidation, owing to their unique physical and electronic properties besides having adequate surface area and availability of unsaturated active metal centers. Herein, we illustrate the high-temperature transformation of bimetallic LDH to semicrystalline 2D metal oxide nanoplates that can maneuver their electronic properties and thereby accelerate the water dissociation reactions. The nanoplates prepared at 300 °C require only 280 ± 13 and 177 ± 7 mV overpotentials for oxygen/hydrogen evolution reactions (OER and HER) to achieve a current density of ±10 mA cm-2 in 1 M KOH, respectively. In a two-electrode water splitting cell, while this bifunctional catalyst needs 1.69 V to deliver a current density of 10 mA cm-2, the LDH precursor demands a cell voltage of 1.93 V. However, both the catalysts demonstrate excellent durability for more than 200 h. When the bifunctional metal oxide electrolyzer is connected to perovskite solar cells for unassisted solar-driven water splitting, impressively, such an integrated photovoltaic-electrolyzer can achieve a solar-to-hydrogen (STH) efficiency of 9.3%. The predominantly superior catalytic activity of the nanoplates is due to the abundance of unsaturated oxygen which decreases the free energy of adsorption of the intermediates.

Correction: Solution-processed Cu2XSnS4 (X = Fe, Co, Ni) photo-electrochemical and thin film solar cells on vertically grown ZnO nanorod arrays.

[This corrects the article DOI: 10.1039/C6RA24149B.].

A new family of wurtzite-phase Cu2ZnAS4-x and CuZn2AS4 (A = Al, Ga, In) nanocrystals for solar energy conversion applications.

A new family of quaternary semiconductors Cu2ZnAS4-x and CuZn2AS4 (A = Al, Ga, In) has been synthesized in the form of wurtzite phase nanocrystals for the first time. The nanocrystals can be converted to the stannite phase via thermal annealing under a N2 atmosphere. A direct band gap in the visible wavelength region combined with a high absorption cross-section makes these materials promising for solar energy conversion applications.