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Nearly monodisperse colloidal superstructures of cadmium chalcogenide quantum dots (QDs) are reported. The superstructures, which we named as supra quantum dot (SQD), are typically composed of hundreds of a-few-nanometer-sized QDs three-dimensionally (3D) assembled by oriented attachment. The synthesis route for SQD is quite universal and can be extended to CdS, CdSe, CdTe, and CdSeTe alloy. The size of SQD can be tuned from tens of nanometers to over a hundred nanometers. In the case of CdSe SQD, zinc-blende seeds (primary QDs) act as the building block for the formation of the 3D assembled structures, SQDs, with discrete intermediates nanostructures. Primary seeds, 4 nm tetrahedral shaped QDs, assembled into a large tetrahedron of 20 nm. The 20 nm tetrahedrons, in turn, self-assembled into a larger tetrahedron of 40 nm. The discrete-in-size and sequential assemblies were followed by conventional growth from the remaining precursors and ripening within the particles to result in spheroidal SQDs. SQDs all...

Solid solutions have been widely investigated for solar energy conversion because of the ease to control properties (e.g., band edge positions, charge carrier transport, and chemical stability). In this study, we introduce a new method to investigate intrinsic solar energy conversion properties of solid solutions through fabricating high-quality single-crystalline solid solution films by pulsed laser deposition. This method rules out external factors, such as morphology, crystalline grain size, orientation, density and distribution, surface area, and particle–particle or particle–conducting layer connection, that have plagued previous studies on solid solution photoelectrodes. Perovskite BiFeO3 (BFO) and SrTiO3 (STO) were chosen as “end” members of the solid solutions (i.e., (BFO)x(STO)1–x (0 ≤ x ≤ 1)). Optical and photoelectrochemical (PEC) properties of the solid solutions significantly varied with changing compositions. Among the six studied compositions, BFO:STO (3:1 molar ratio) exhibited the highest...

We report a designed strategy for a synthesis of highly luminescent and photostable composites by incorporating quantum dots (QDs) into layered double hydroxide (LDH) matrices without deterioration of a photoluminescence (PL) efficiency of the fluorophores during the entire processes of composite formations. The QDs synthesized in an organic solvent are encapsulated by polymers, poly(maleic acid-alt-octadecene) to transfer them into water without altering the initial surface ligands. The polymer-encapsulated QDs with negative zeta potentials (−29.5 ± 2.2 mV) were electrostatically assembled with positively charged (24.9 ± 0.6 mV) LDH nanosheets to form QD-polymer-LDH composites (PL quantum yield: 74.1%). QD-polymer-LDH composite films are fabricated by a drop-casting of the solution on substrates. The PL properties of the films preserve those of the organic QD solutions. We also demonstrate that the formation of the QD-polymer-LDH composites affords enhanced photostabilities through multiple protections o...

Although cadmium chalcogenide quantum dot-sensitized photoanode can utilize the whole visible region of the solar spectrum, its poor photochemical stability owing to hole-induced anodic corrosion remains a major problem for the application in photoelectrochemical hydrogen generation systems. Here, modification with IrOx·nH2O, a well-known water-oxidation catalyst substantially improves the photochemical stability of the quantum dot-sensitized photoanode. Moreover, it induces an increased photocurrent and a cathodic shift of the onset potential. This is the first example that an oxygen-evolution catalyst is employed on a quantum dot-sensitized electrode system, and it shows 13.9 mA cm–2 (at 0.6 V) and −0.277 V vs the reversible hydrogen electrode (RHE), which are the highest photocurrent density and the lowest onset potential attained with a ZnO-based electrode, respectively. An average hydrogen evolution rate of 240 μmol h–1 cm–2 at 0.6 V vs RHE has been achieved on a IrOx·nH2O modified electrode, with al...