Suppressing Deep Traps in PbS Colloidal Quantum Dots via Facile Iodide Substitutional Doping for Solar Cells with Efficiency >10%

Surface passivation of PbS colloidal quantum dots (QDs) with iodide has been used in highly efficient solar cells. Iodide passivation is typically achieved by ligand exchange processes on QD films. Complementary to this approach, herein we present a non-intrusive solution-based strategy for doping QDs with iodide to further optimize solar cell performance. The doping step is applied in-situ at the end of the synthesis of the QDs. The optimum precursor I/Pb ratio is found to be in the 1.5-3% range at which iodide substitutes S without excessively altering the dots´ surface chemistry. This allows for band engineering and decreasing the density of deep trap states of the QDs which taken together lead to PbS QD solar cells with efficiency in excess of 10%.Peer ReviewedPostprint (author's final draft

Efficient dipole-dipole coupling of Mott-Wannier and Frenkel excitons in (Ga,In)N quantum well/polyfluorene semiconductor heterostructures

Journal ArticleWe investigate interactions between Mott-Wannier (MW) and Frenkel excitons in a family of hybrid structures consisting of thin organic (polyfluorene) films placed in close proximity (systematically adjusted by GaN cap layer thickness) to single inorganic [(Ga, In)N/GaN] quantum wells (QWs). Characterization of the QW structures using Rutherford backscattering spectrometry and atomic force microscopy allows direct measurement of the thickness and the morphology of the GaN cap layers. Time-resolved photoluminescence experiments in the 8-75 K temperature range confirm our earlier demonstration that nonradiative energy transfer can occur between inorganic and organic semiconductors. We assign the transfer mechanism to resonant Förster (dipole-dipole) coupling between MW exciton energy donors and Frenkel exciton energy acceptors and at 15 K we find transfer efficiencies of up to 43%. The dependence of the energy transfer rate on the distance R between the inorganic QW donor dipole and organic film acceptor dipole indicates that a plane-plane interaction, characterized by a 1/R2 variation, best describes the situation found in our structures

Optimized production of coal fly ash derived synthetic zeolites for mercury removal from wastewater

Coal fly ash (CFA) derived synthetic zeolites have become popular with recent advances and its ever-expanding range of applications, particularly as an adsorbent for water and gas purification and as a binder or additive in the construction industry and agriculture. Among these applications, perpetual interest has been in utilization of CFA derived synthetic zeolites for removal of heavy metals from wastewater. We herein focus on utilization of locally available CFA for efficient adsorption of mercury from wastewater. To this end, experimental conditions were investigated so that to produce synthetic zeolites from Kazakhstani CFAs with conversion into zeolite up to 78%, which has remarkably high magnetite content. In particular, the effect of synthesis reaction temperature, reaction time, and loading of adsorbent were systematically investigated and optimized. All produced synthetic zeolites and the respective CFAs were characterized using XRD, XRF, PSA and porosimetric instruments to obtain microstructural and mineralogical data. Furthermore, the synthesized zeolites were studied for the removal of mercury from aqueous solutions. A comparison of removal eficiency and its relationship to the physical and chemical properties of the synthetic zeolites were analyzed and interpreted

Zeolite development from fly ASH and utilization in lignite mine-water treatment

The synthetic zeolitic materials were tested comparatively, showing that the more intense the zeolitic presence in the synthetic materials, the greater the uptake rates for certain groups of trace elements

Mineralogical, microstructural and thermal characterization of coal fly ash produced from Kazakhstani power plants

Coal fly ash (CFA) is a waste by-product of coal combustion. Kazakhstan has vast coal deposits and is major consumer of coal and hence produces huge amounts of CFA annually. The government aims to recycle and effectively utilize this waste by-product. Thus, a detailed study of the physical and chemical properties of material is required as the data available in literature is either outdated or not applicable for recently produced CFA samples. The full mineralogical, microstructural and thermal characterization of three types of coal fly ash (CFA) produced in two large Kazakhstani power plants is reported in this work. The properties of CFAs were compared between samples as well as with published values

Manufacturing of ultra-fine particle coal fly ash–A380 aluminum matrix composites with improved mechanical properties by improved ring milling and oscillating microgrid mixing

An experimental study is presented of ultra-fine coal fly ash (CFA) aluminum matrix composites produced by successive high-power ring milling of CFA, oscillating microgrid mixing of the CFA–aluminum melt, gravity casting and rapid cooling. Samples corresponding to different CFA concentrations and particle size distributions (1 μm average, or less) are produced and subjected to microstructural and mechanical characterization, including tensile, compressive, impact, hardness and wear testing. While the usual trade-off between increased strength and hardness and reduced ductility and toughness is observed, the obtained ultra-fine particle composites are confirmed to have overall improved mechanical properties compared to composites with larger size particles previously produced by ball milling

A comparative study on phyllosilicate and tectosilicate mineral structural properties

Natural minerals are widely used in numerous environmental applications, mainly as sorbents in ion exchange and sorption processes. Minerals, such as zeolites and clays, can be found all over the world, but they are mined containing a variety of different impurities; this prevents their accurate characterization. The present study examines various methods used for the characterization of three common natural silicate minerals, one zeolite (clinoptilolite) and two clays (montmorillonite and vermiculite). Their characterization was performed through a series of analytical measurements so as to gather all the information needed regarding their structural properties. Therefore, “similar” minerals such as clinoptilolite vs. heulandite and vermiculite vs. hydrobiotite can be distinguished; revealing important properties when comes to their practical application. The methods used in the present study are X-ray powder diffraction (XRD), X-ray fluorescence, Fourier transform infrared (FTIR) spectroscopy, TG/DTG/DTA and N2-porosimetry (BET). An extensive literature review of the natural silicate minerals has been conducted and the relevant results and methods are comparatively reported. The analytical results enabled the distinguish of the examined minerals. XRD, FTIR, TG/DTG/DTA showed that all three minerals have characteristic bands that can be used to easily distinguish from others