Search results for "Halide"
showing 10 items of 324 documents
Efficient wide band gap double cation – double halide perovskite solar cells
2017
In this work we study the band gap variation and properties of the perovskite compound Cs0.15FA0.85Pb(BrxI1−x)3 as a function of the halide composition, with the aim of developing an efficient complementary absorber for MAPbI3 in all-perovskite tandem devices. We have found the perovskite stoichiometry Cs0.15FA0.85Pb(Br0.7I0.3)3 to be a promising candidate, thanks to its band gap of approximately 2 eV. Single junction devices using this perovskite absorber lead to a maximum PCE of 11.5%, among the highest reported for solar cells using perovskites with a band gap wider than 1.8 eV.
Charge Transport Layers Limiting the Efficiency of Perovskite Solar Cells: How To Optimize Conductivity, Doping, and Thickness
2019
Perovskite solar cells (PSCs) are one of the main research topics of the photovoltaic community; with efficiencies now reaching up to 24%, PSCs are on the way to catching up with classical inorganic solar cells. However, PSCs have not yet reached their full potential. In fact, their efficiency is still limited by nonradiative recombination, mainly via trap-states and by losses due to the poor transport properties of the commonly used transport layers (TLs). Indeed, state-of-the-art TLs (especially if organic) suffer from rather low mobilities, typically within 10(-5) and 10(-2) cm(-2) V-1 s(-1), when compared to the high mobilities, 1-10 cm(-2) V-1 s(-1), measured for perovskites. This work…
Large area perovskite light-emitting diodes by gas-assisted crystallization:
2019
Halide perovskites have been gaining considerable attention recently for use in light-emitting applications, due to their bandgap tunability, color purity and low cost fabrication methods. However, current fabrication techniques limit the processing to small-area devices. Here, we show that a facile N 2 gas-quenching technique can be used to make methylammonium lead bromide-based perovskite light-emitting diodes (PeLEDs) with a peak luminance of 6600 cd m −2 and a current efficiency of 7.0 cd A −1 . We use this strategy to upscale PeLEDs to large-area substrates (230 cm 2 ) by developing a protocol for slot-die coating combined with gas-quenching. The resulting large area devices (9 device…
Single-Source Vacuum Deposition of Mechanosynthesized Inorganic Halide Perovskites
2018
Fully inorganic cesium lead halide perovskite thin films were prepared by an easy, fast and dry process based on single-source vacuum deposition. We investigated the structural and optical characteristics of the so-formed films as a function of chemical composition (chloride, bromide and iodide films were formed), post-deposition thermal annealing, as well as previous mechanosynthesis of perovskite powders. We found out that the CsPbX3 perovskite was preferentially formed for the smaller halides and favored by previous ball-milling of CsX and PbX2 precursors. When bigger halides were used and/or CsX and PbX2 precursors were simply mixed without previous mechanosynthesis, PbX2-rich compounds…
Cut-edge corrosion of a Zn–55Al-coated steel: A comparison between sulphate and chloride solutions
2011
Abstract Ex situ observations and in situ measurements of current and pH distributions over cut-edge coated steels revealed that Zn–55Al coatings are sacrificial only in chloride solutions, because of an activation of both Zn- and Al-rich phases present in the coating. In sulphate solutions, an efficient cathodic protection occurs only for short times of immersion, because only Zn-rich phases are active in this medium. The low solubility and strong acidification induced by Al(OH)SO4 allows only short distance cathodic protection, but cannot prevent red rust precipitation on the steel surface.
Colloids of naked CH 3 NH 3 PbBr 3 Perovskite Nanoparticles: Synthesis, Ssability, and thin solid film deposition
2018
A novel preparation of lead halide, CH3NH3PbBr3, perovskite nanoparticle solid films from colloidal "naked" nanoparticles, that is, dispersible nanoparticles without any surfactant, is reported. The colloids are obtained by simply adding potassium ions, whose counterions are both more lipophilic and less coordinating than bromide ions, to the perovskite precursor solutions (CH3NH3Br/PbBr2 in dimethylformamide) following the reprecipitation strategy. The naked nanoparticles exhibit a low tendency to aggregate in solution, and they effectively self-assembled on a substrate by centrifugation of the colloid, leading to homogeneous nanoparticle solid films with arbitrary thickness. These results…
Metallization of the Na 14 Cl 13 Cluster
1994
The structure and energetics of multiple-excess-electron alkali halide clusters Na14Cl14-n, (1 ≤ n ≤ 6) is studied by ab initio calculations using norm-conserving pseudopotentials and local-spin-density-functional theory. Analysis of various electronic properties (Kohn-Sham one-electron eigenvalue spectra, ionization potentials, participation ratios of Kohn-Sham orbitals), as well as multiple F-center formation energies, suggests that these clusters can be characterized as Nan(NaCl)14-n having a "phase-separated" metallic part NaI. The Na14Cl9 (or Na14Cl9+) cluster exhibits a face (surface) segregated metallic Na5 (Na5+) overlayer, the stability of which is demonstrated by a molecular-dynam…
First-principles comparative study of perfect and defective CsPbX3 (X = Br, I) crystals
2020
We thank R. Merkle for numerous fruitful discussions and G. Siegle for experimental assistance. This study was partly supported by the M-ERA-NET project SunToChem (EK). Calculations were performed using computational facilities of St. Petersburg State University and Max Planck Institute for Solid State Research. Open Access funding provided by the Max Planck Society.
Quantifying the Composition of Methylammonium Lead Iodide Perovskite Thin Films with Infrared Spectroscopy
2019
Lead halide perovskites (ABX3) are generally formed from a reaction of the lead halide salt (BX2) with the halide salt of the A cation (AX). The effects of varying film compositions as result of non-stoichiometric precursor ratios on electronic properties of halide perovskites are currently under debate. It is imperative, but experimentally challenging, to determine the chemical composition of thin films as a function of precursor ratio for a full understanding of the effect. Herein we report a precise quantification of the methylammonium (MA) content in differently fabricated films of MAPbI3 via infrared (IR) spectroscopy. We compare the thin film data to the first high quality dielectric …
The role of halide ions in the anisotropic growth of gold nanoparticles: a microscopic, atomistic perspective
2016
We provide a microscopic view of the role of halides in controlling the anisotropic growth of gold nanorods through a combined computational and experimental study. Atomistic molecular dynamics simulations unveil that Br− adsorption is not only responsible for surface passivation, but also acts as the driving force for CTAB micelle adsorption and stabilization on the gold surface in a facet-dependent way. The partial replacement of Br− by Cl− decreases the difference between facets and the surfactant density. Finally, in the CTAC solution, no halides or micellar structures protect the gold surface and further gold reduction should be uniformly possible. Experimentally observed nanoparticle'…