Ligand Effect in 1-Octanethiol Passivation of InP/ZnSe/ZnS Quantum Dots-Evidence of Incomplete Surface Passivation during Synthesis.

The lack of anionic carboxylate ligands on the surface of InP/ZnSe/ZnS quantum dots (QDs), where zinc carboxylate ligands can be converted to carboxylic acid or carboxylate ligands via proton transfer by 1-octanethiol, is demonstrated. The as-synthesized QDs initially have an under-coordinated vacancy surface, which is passivated by solvent ligands such as ethanol and acetone. Upon exposure of 1-octanethiol to the QD surface, 1-octanethiol effectively induces the surface binding of anionic carboxylate ligands (derived from zinc carboxylate ligands) by proton transfer, which consequently exchanges ethanol and acetone ligands that bind on the incomplete QD surface. These systematic chemical analyses, such as thermogravimetric analysis-mass spectrometry and proton nuclear magnetic resonance spectroscopy, directly show the interplay of surface ligands, and it associates with QD light-emitting diodes (QD-LEDs). It is believed that this better understanding can lead to industrially feasible QD-LEDs.

CuS nanoplates from ionic liquid precursors-Application in organic photovoltaic cells.

Hexagonal p-type semiconductor CuS nanoplates were synthesized via a hot injection method from bis(trimethylsilyl)sulfide and the ionic liquid precursor bis(N-dodecylpyridinium) tetrachloridocuprate(ii). The particles have a broad size distribution with diameters between 30 and 680 nm and well-developed crystal habits. The nanoplates were successfully incorporated into organic photovoltaic (OPV) cells as hole conduction materials. The power conversion efficiency of OPV cells fabricated with the nanoplates is 16% higher than that of a control device fabricated without the nanoplates.

Multi-layer printing of OLEDs as a tool for the creation of security features.

The combined deposition of structured and homogenous layers for the device setup of OLEDs results in a structured display visible with a gray scale impression. These permanently imprinted structures are only visible during the application of an electrical field and almost invisible in the off state. Most intriguing applications of such devices are security marks, electronic watermarks but also for advertising and design applications the creation of gray scale structures might have interesting applications.

Enhanced Electroluminescence via a Nanohybrid Material Consisting of Aromatic Ligand-Modified InP Quantum Dots and an Electron-Blocking Polymer as the Single Active Layer in Quantum Dot-LEDs.

Electron overcharge causes rapid luminescence quenching in the quantum dot (QD) emission layer in QD light-emitting diodes (QD-LEDs), resulting in low device performance. In this paper we describe the application of different aromatic thiol ligands and their influence on device performance as well as their behavior in combination with an electron blocking material (EBM). The three different ligands, 1-octanethiol (OcSH), thiophenol (TP), and phenylbutan-1-thiol (PBSH), were introduced on to InP/ZnSe/ZnS QDs referred to as QD-OcSH, QD-TP, and QD-PBSH. PBSH is in particular applied as a ligand to improve QD solubility and to enhance the charge transport properties synergistically with EBM probably via π-π interaction. We synthesized poly-[N,N-bis[4-(carbazolyl)phenyl]-4-vinylaniline] (PBCTA) and utilized it as an EBM to alleviate excess electrons in the active layer in QD-LEDs. The comparison of the three QD systems in an inverted device structure without the application of PBCTA as an EBM shows the highest efficiency for QD-PBSH. Moreover, when PBCTA is introduced as an EBM in the active layer in combination with QD-PBSH in a conventional device structure, the current efficiency shows a twofold increase compared to the reference device without EBM. These results strongly confirm the role of PBCTA as an EBM that effectively alleviates excess electrons in the active layer, leading to higher device efficiency.

Metal Sulfide Nanoparticle Synthesis with Ionic Liquids - State of the Art and Future Perspectives.

Metal sulfides are among the most promising materials for a wide variety of technologically relevant applications ranging from energy to environment and beyond. Incidentally, ionic liquids (ILs) have been among the top research subjects for the same applications and also for inorganic materials synthesis. As a result, the exploitation of the peculiar properties of ILs for metal sulfide synthesis could provide attractive new avenues for the generation of new, highly specific metal sulfides for numerous applications. This article therefore describes current developments in metal sulfide nanoparticle synthesis as exemplified by a number of highlight examples. Moreover, the article demonstrates how ILs have been used in metal sulfide synthesis and discusses the benefits of using ILs over more traditional approaches. Finally, the article demonstrates some technological challenges and how ILs could be used to further advance the production and specific property engineering of metal sulfide nanomaterials, again based on a number of selected examples.

Mixed Mercaptocarboxylic Acid Shells Provide Stable Dispersions of InPZnS/ZnSe/ZnS Multishell Quantum Dots in Aqueous Media.

Highly luminescent indium phosphide zinc sulfide (InPZnS) quantum dots (QDs), with zinc selenide/zinc sulfide (ZnSe/ZnS) shells, were synthesized. The QDs were modified via a post-synthetic ligand exchange reaction with 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) in different MPA:MUA ratios, making this study the first investigation into the effects of mixed ligand shells on InPZnS QDs. Moreover, this article also describes an optimized method for the correlation of the QD size vs. optical absorption of the QDs. Upon ligand exchange, the QDs can be dispersed in water. Longer ligands (MUA) provide more stable dispersions than short-chain ligands. Thicker ZnSe/ZnS shells provide a better photoluminescence quantum yield (PLQY) and higher emission stability upon ligand exchange. Both the ligand exchange and the optical properties are highly reproducible between different QD batches. Before dialysis, QDs with a ZnS shell thickness of ~4.9 monolayers (ML), stabilized with a mixed MPA:MUA (mixing ratio of 1:10), showed the highest PLQY, at ~45%. After dialysis, QDs with a ZnS shell thickness of ~4.9 ML, stabilized with a mixed MPA:MUA and a ratio of 1:10 and 1:100, showed the highest PLQYs, of ~41%. The dispersions were stable up to 44 days at ambient conditions and in the dark. After 44 days, QDs with a ZnS shell thickness of ~4.9 ML, stabilized with only MUA, showed the highest PLQY, of ~34%.

Semitransparent quantum dot light-emitting diodes by cadmium-free colloidal quantum dots.

The InP/ZnSe/ZnS multishell colloidal quantum dots (QDs) were prepared by convenient heating-up method for an emission layer of semitransparent quantum dot light-emitting diodes (QD-LEDs). The synthesized InP/ZnSe/ZnS multishell QDs exhibited an emission peak at 545 nm for clear green color with a full-width at half-maximum (FWHM) of 50 nm, and photoluminescent (PL) quantum yield (QY) of 45%. The multishell on the indium phosphide (InP) core helped increasing QY and stability by reducing interfacial defects. Using a Ca/Ag cathode, the whole QD-LEDs were semitransparent throughout the visible wavelengths. The maximum brightness and currernt efficiency of semitransparent QD-LEDs reached 587 cd/m2 and 1.52 cd/A by controlling the thickness of Ca/Ag cathode, which is comparable to the device with opaque LiF/Al cathode (1444 cd/m2 and 1.98 cd/A). The performance of our semitransparent and eco-friendly device is not matched with traditional cadmium (Cd) based QD-LEDs yet, but it shows the great potential for various window-type information displays.