Effects of Oxygen Plasma on the Chemical, Light-emitting, and Electrical Transport Properties of Inorganic and Hybrid Lead Bromide Perovskite Nanocrystal Films

We show that oxygen plasma affects in different ways the structural, chemical, optical, and electrical properties of methylammonium and cesium lead bromide nanocrystals. Hybrid organic-inorganic nanocrystals were severely and quickly degraded by oxygen plasma at 50 W. Their photoluminescence was quenched with almost 100% loss of the initial quantum yield, which is linked to decomposition of the nanocrystals. Inorganic nanocrystals were more resistant to oxygen plasma in the same conditions. Despite a moderate loss of photoluminescence and electrical conductivity, oxygen plasma had a positive impact, removing unbound ligands and resulting in more ohmic behavior of the film. This paves the way for the application of oxygen plasma in the development of perovskite-based optoelectronic devices

Role of acid-base equilibria in the size, shape, and phase control of cesium lead bromide nanocrystals

A binary ligand system composed of aliphatic carboxylic acids and primary amines of various chain lengths is commonly employed in diverse synthesis methods for CsPbBr3 nanocrystals (NCs). In this work, we have carried out a systematic study examining how the concentration of ligands (oleylamine and oleic acid) and the resulting acidity (or basicity) affects the hot injection synthesis of CsPbBr3 NCs. We devise a general synthesis scheme for cesium lead bromide NCs which allows control over size, size distribution, shape, and phase (CsPbBr3 or Cs4PbBr6) by combining key insights on the acid base interactions that rule this ligand system. Furthermore, our findings shed light upon the solubility of PbBr2 in this binary ligand system, and plausible mechanisms are suggested in order to understand the ligand-mediated phase control and structural stability of CsPbBr3 NCs

Описание и генерация перестановок, содержащих циклы

Запропоновано загальний підхід до генерації перестановок, що містять цикли, на основі введених конструктивних засобів опису комбінаторних множин. Формулюються та розв’язуються різні задачі генерації перестановок заданого класу. Для опису перестановок, представлених у вигляді добутку заданої кількості циклів, вводиться комбінаторна множина. Для введеної множини будуються комбінаторний вид та відповідний твірний ряд. Наводяться приклади.The paper proposes a general approach to generating permutations that contain cycles, based on constructive tools introduced to describe combinatorial sets. Different generation problems for permutations of definite class are formulated and solved. A combinatorial set is introduced to define permutations represented as the multiplication of a definite number of cycles. For this set, combinatorial species and associated generating series are constructed. Examples are given

Molecular Iodine for a General Synthesis of Binary and Ternary Inorganic and Hybrid Organic-inorganic Iodide Nanocrystals

We report the synthesis of various binary and ternary inorganic and hybrid organic-inorganic iodide nanocrystals starting from molecular iodine (I2). The procedure utilizes a reaction between I2 and oleylamine that yields oleylammonium iodide -the iodide precursor for a subsequent preparation of nanocrystals. The syntheses are facile, carried out under air, in vials heated on a hotplate and deliver nanocrystals with narrow size distributions and, in the case of red and near infrared-emitting lead-based perovskites, with 70-80% photoluminescence quantum yields. The latter were used to fabricate red and infrared bright light-emitting diodes, with external quantum efficiencies (EQE) exceeding 3%

Exploiting the lability of metal halide perovskites for doping semiconductor nanocomposites

Cesium lead halides have intrinsically unstable crystal lattices and easily transform within perovskite and nonperovskite structures. In this work, we explore the conversion of the perovskite CsPbBr into CsPbBr in the presence of PbS at 450 °C to produce doped nanocrystal-based composites with embedded CsPbBr nanoprecipitates. We show that PbBr is extracted from CsPbBr and diffuses into the PbS lattice with a consequent increase in the concentration of free charge carriers. This new doping strategy enables the adjustment of the density of charge carriers between 10 19 and 10 20 cm -3, and it may serve as a general strategy for doping other nanocrystal-based semiconductors

In situ transmission electron microscopy study of electron beam-induced transformations in colloidal cesium lead halide perovskite nanocrystals

An increasing number of studies have recently reported the rapid degradation of hybrid and all-inorganic lead halide perovskite nanocrystals under electron beam irradiation in the transmission electron microscope, with the formation of nanometer size, high contrast particles. The nature of these nanoparticles and the involved transformations in the perovskite nanocrystals are still a matter of debate. Herein, we have studied the effects of high energy (80/200 keV) electron irradiation on colloidal cesium lead bromide (CsPbBr3) nanocrystals with different shapes and sizes, especially 3 nm thick nanosheets, a morphology that facilitated the analysis of the various ongoing processes. Our results show that the CsPbBr3 nanocrystals undergo a radiolysis process, with electron stimulated desorption of a fraction of bromine atoms and the reduction of a fraction of Pb2+ ions to Pb0. Subsequently Pb0 atoms diffuse and aggregate, giving rise to the high contrast particles, as previously reported by various groups. The diffusion is facilitated by both high temperature and electron beam irradiation. The early stage Pb nanoparticles are epitaxially bound to the parent CsPbBr3 lattice, and evolve into nonepitaxially bound Pb crystals upon further irradiation, leading to local amorphization and consequent dismantling of the CsPbBr3 lattice. The comparison among CsPbBr3 nanocrystals with various shapes and sizes evidences that the damage is particularly pronounced at the corners and edges of the surface, due to a lower diffusion barrier for Pb0 on the surface than inside the crystal and the presence of a larger fraction of under-coordinated atoms

Ultrafast THz probe of photo-induced polarons in lead-halide perovskites

We study the nature of photo-excited charge carriers in CsPbBr3 nanocrystal thin films by ultrafast optical pump - THz probe spectroscopy. We observe a deviation from a pure Drude dispersion of the THz dielectric response that is ascribed to the polaronic nature of carriers; a transient blueshift of observed phonon frequencies is indicative of the coupling between photogenerated charges and stretching-bending modes of the deformed inorganic sublattice, as confirmed by DFT calculations

Exploiting the Lability of Metal Halide Perovskites for Doping Semiconductor Nanocomposites

Cesium lead halides have intrinsically unstable crystal lattices and easily transform within perovskite and nonperovskite structures. In this work, we explore the conversion of the perovskite CsPbBr3 into Cs4PbBr6 in the presence of PbS at 450 °C to produce doped nanocrystal-based composites with embedded Cs4PbBr6 nanoprecipitates. We show that PbBr2 is extracted from CsPbBr3 and diffuses into the PbS lattice with a consequent increase in the concentration of free charge carriers. This new doping strategy enables the adjustment of the density of charge carriers between 1019 and 1020 cm-3, and it may serve as a general strategy for doping other nanocrystal-based semiconductors.M.C. has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 665385. ICN2 acknowledges funding from Generalitat de Catalunya 2017 SGR 327. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 823717 – ESTEEM3. M.V.K. acknowledges the support by the European Research Council under the Horizon 2020 Framework Program (ERC Consolidator Grant SCALE-HALO Grant Agreement No. 819740) and by FET-OPEN project no. 862656 (DROP-IT)

Lead Halide Perovskite Nanocrystals: A New Age of Semiconductive Nanocrystals

This thesis will mainly focus on the synthesis and characterization of colloidal lead halide perovskite (LHP) nanocrystals (NCs). It will also shed light on many synthetic aspects of these NCs, such as their size, shape and compositional control, as well as on how to increase their stability and processability, allowing the use of LHP NCs in devices. Furthermore, this thesis will present several nano-scaled reactions using lead halide NCs, which result in so-called \u201cnanocrystal transformations\u201d. To bridge the gap between the fundamental synthetic work and the application of these NCs, several proof-of-principle devices have been made with LHP NCs, including solar cells and LEDs and will all be demonstrated herein. Finally, several new halide based NCs have been synthesized and will be discusses, broadening the scope of this work not only to LHP NCs, but also to halide based NCs in general