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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Optical and Atomic Force Microscopy Characterization of PbI2 Quantum Dots

Lead iodide (PbI2) clusters were synthesized from the chemical reaction of NaI (or KI) with Pb(NO3)2 in H2O, D2O, CH3OH, and C3H7OH media. The observation of the absorption features above 350 nm with the help of integrating sphere accessory strongly suggests the quantum dot formation of PbI2 in solution. Spectral comparison between the synthesized PbI2 clusters in solution and PbI2 nanophase by impregnation of PbI2 in four different pore-sized porous silica indicates that the PbI2 cluster size in solution is less than 2.5 nm in lateral dimension. Atomic force microscopy (AFM) measurements show that the PbL clusters deposited onto three different molecularly flat surfaces are single-layered. The measured height is 1.0 - 0.1 nm. The swollen layer thickness can be attributed to the intralayer contraction from the strong lateral interaction among PbI2 molecules, which is supported by ab initio calculation. Raman scattering measurement of LO and TO modes of PbI2 in bulk and in the confined state were also conducted in 50-150 cu cm region. The observed three bands at 74, %, 106 1/cm are assigned to TO2, LO2, and LO, mode, respectively. The relatively small red-shift in LO modes may be caused by the surface phonon polaritons of PbI2 nanophase in the porous silica.

Mu, R.↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one PbI2 sheet oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of six PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of three PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of five PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of seven PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the hexagonal P6_3mc space group. The structure is two-dimensional and consists of two PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the hexagonal P6_3mc space group. The structure is two-dimensional and consists of four PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of six PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms. In the second I1- site, I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of twelve PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of nine PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. There are three shorter (3.28 Å) and three longer (3.29 Å) Pb–I bond lengths. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PbI2 by Materials Project

PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of nine PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.30 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Spin–orbit effects on the electronic and optical properties of lead iodide

Lead iodide (PbI2) has gained much interest due to its direct electronic gap in the visible range and layered crystal structure. It has thereby been considered as a promising material for applications in atomically thin optoelectronic devices. In this work, we present a detailed investigation of the effect of spin–orbit coupling (SOC) that arises from the presence of heavy atoms on the electronic and optical properties of PbI2 using first-principles calculations based on density-functional theory and many-body perturbation theory. We find that SOC not only alters the bandgap but also induces the mixing of orbital characters, resulting in a significant change in the overall band structure and charge carrier effective masses. Moreover, the band orbital mixing caused by SOC results in the dramatic change in optical transition matrix elements and, correspondingly, the absorption spectrum. Our experimentally measured absorption spectra validate the calculation results and demonstrate the importance of SOC in the optical processes of PbI2. Our findings provide insights that are important for the potential use of PbI2 as a material platform for visible optoelectronic devices.

Physics↗
DOE OSTI2025

Orientation-Driven Chirality Funnels in Chiral Low-Dimensional Lead-Halide Perovskite Heterostructures

Chiral hybrid metal-halide perovskites show low-symmetry crystal structures, large Rashba splitting, spin-filtering, and strong chiroptical activity. Circular dichroism and circularly polarized photoluminescence have been investigated in chiral perovskites with increasingly distorted chiral structures. Here, we report the fabrication of chiral (R/S)-EBAPbI3 (EBA = α-ethylbenzylamine) single crystals, which possess highly distorted octahedral structures with a high angle variance value of ∼68 degree2. Using control in the fabrication conditions, we transfer chiral single crystals to thin films and achieve different crystal orientation preferences that induce tunable chiroptical properties to their heterostructures with PbI2 nanodomains, which we characterize with in situ X-ray diffraction and grazing-incidence wide-angle X-ray scattering measurements. Using transient chiroptical spectroscopies, we resolve photoexcited charge carrier dynamics and chirality transfer processes in such heterostructures down to cryogenic temperatures. We observe rapid carrier transfer along the in-plane (002) facets in chiral perovskite phases to PbI2 nanostructures within the initial few picoseconds, while carrier transfer along the out-of-plane (002) facets occurs at a slower rate. This fast transfer process leads to high photoluminescence intensities and large degrees of circular polarization in the emission from PbI2 nanodomains at cryogenic temperatures. Our findings report a multidimensional chiral-achiral heterostructure which takes advantage of controllable chirality transfer and offers new routes for future spintronic and chiroptical applications.

Liu, Shangpu↗
NASA NTRS2019

Vapor Growth of Indium Monoiodide

Indium (I) iodide, InI, is part of a group of heavy metal iodides that can be used as room temperature radiation detectors. Other examples are HgI2, PbI2, BiI3, or TlPbI3. InI has several advantages, such as low toxicity, no solid phase transition (such as in HgI2), and no tendency to form polytypes (PbI2, BiI3 ). All binary iodides have layered structures and are quite soft, but InI is also the mechanically most stable compound of the binary compounds. Table 1 shows the main properties of InI in comparison with the other iodides and the most common room temperature radiation detector material, (Cd, Zn)Te. InI is typically grown by the unseeded Bridgman method using a nucleation tip, but Czochralski (CZ) growth has also been demonstrated. The resulting crystals have been used successfully for radiation detection, but both resistivity and mobility are usually well below theoretically predicted values. Physical vapor transport (PVT), although much slower than melt growth, is an alternative method and has been used to grow e.g. HgI2, PbI2, BiI3, CdTe. PVT growth should eliminate or reduce inclusions and impurities since it is based on sublimation, reduce intrinsic defects due to the lower growth temperature, and reduce dislocation densities due to reduced thermal and mechanical stress. As an example, PVT-grown CdTe showed a much improved structural quality compared to Bridgman- or THM-grown material.

Cröll, Arne↗
NASA NTRS1998

Purification and Crystal Growth of Lead Iodide by Physical Vapor Transport Method

Lead iodide (PbI2) is a layered compound semiconductor being developed as room temperature x- and gamma-ray detector. Compared to the more studied material, mercuric iodide, PbI2 has a higher melting temperature and no phase transition until liquid phase which are indications of better mechanical properties. In this study, the source material was purified by the zone-refining process, and the purest section was extracted from center of the the zone-refined ingot to be grown by physical vapor transport (PVT) method. The zone-refined material and as-grown crystals were characterized by optical microscopy and differential scanning calorimetry (DSC) to reveal the surface morphology, purity and stoichiometry. The results shows that both materials are near-stoichiometric composition, with the purity of the as-grown crystals higher than zone-refined materials. The resistivity of the as-grown crystal (10" Omega-cm) was derived from current-voltage (I-V) measurement, and is 10 times higher than the zone-refined materials. Detail results will be presented and discussed.

Wright, G. W.↗
DOE OSTI2021

Perovskite Photovoltaic Devices with Carbon-Based Electrodes Withstanding Reverse-Bias Voltages up to –9 V and Surpassing IEC 61215:2016 International Standard

One of the key challenges of perovskite photovoltaics (PV) is the long-term stability. Although efforts are made to improve the lifetime of perovskite PV devices, their degradation under reverse-bias conditions is barely addressed. Herein, perovskite solar cells with carbon-based electrodes are presented which demonstrate superior resilience against reverse-bias-induced degradation. Although their breakdown voltage is identified to be at approximately -3.6 V, cells do not degrade until the applied reverse-bias exceeds -9 V. Two main degradation mechanisms are identified: 1) iodine loss due to hole tunneling into perovskite, which takes place even at low reverse-bias but decomposes the perovskite only after long time durations; and 2) rapid heating at large reverse-bias leading to formation of PbI2, which starts at shunts and then follows the path of the least resistance for the cell current, which is primarily influenced by the electrode sheet resistances. Finally, perovskite solar modules with carbon-based electrodes are demonstrated, which are subjected to a "hotspot" test described in the IEC 61215:2016 international standard at an accredited module testing laboratory. Passing this accelerated test for the first time confirms the superior stability of perovskite PV devices with carbon-based electrodes and highlights their large industrialization potential.

14 SOLAR ENERGY↗