Lead Iodide Single Crystals Research Articles

Thin MAPb0.5Sn0.5I3 Perovskite Single Crystals for Sensitive Infrared Light Detection.

Metal halide perovskite single-crystal detectors have attracted increasing attention due to the advantages of low noise, high sensitivity, and fast response. However, the narrow photoresponse range of widely investigated lead-based perovskite single crystals limit their application in near-infrared (NIR) detection. In this work, tin (Sn) is incorporated into methylammonium lead iodide (MAPbI3) single crystals to extend the absorption range to around 950 nm. Using a space-confined strategy, MAPb0.5Sn0.5I3 single-crystal thin films with a thickness of 15 μm is obtained, which is applied for sensitive NIR detection. The as-fabricated detectors show a responsivity of 0.514 A/W and a specific detectivity of 1.4974×1011 cmHz1/2/W under 905 nm light illumination and –1V. Moreover, the NIR detectors exhibit good operational stability (∼30000 s), which can be attributed to the low trap density and good stability of perovskite single crystals. This work demonstrates an effective way for sensitive NIR detection.

Low-temperature luminescence in organic-inorganic lead iodide perovskite single crystals

We present a temperature and laser-power dependent photoluminescence (PL) study of methylammonium lead iodide (CH3NH3PbI3) single crystals in the orthorhombic phase. At temperatures below 140 K, we revealed the multi-component PL emission. In addition to a free exciton with an energy of 1.65 eV, we found emission bands with peaks approximately equal to 1.6 eV, 1.52 eV, and 1.48 eV. Analysis of the thermal evolution of the intensities, peak positions, and linewidths of all the PL bands allowed one to determine their origin. We attributed the PL peak with energy of 1.6 eV to a bound exciton, while the free exciton-bound exciton splitting energy is 50–60 meV. The PL emission with an energy of 1.52 eV can be explained by the donor-acceptor pair (DAP) recombination, where donor and acceptor defects have a depth of about 12 meV and 120 meV, respectively. MA (CH3NH3) interstitials (MA) and lead vacancies (V) are the most suitable for the DAP transition to occur in CH3NH3PbI3 crystals. The 1.48 eV PL emission is consistent with the recombination of self-trapped excitons, and interstitial iodine is likely to be an active trap source. We found the variation of the self-trapped depth from 15 meV (at 80 K) to 53 meV (at 80 K) with increasing the temperature. Although the multi-component PL emission in CH3NH3PbI3 single crystals appears at low temperatures, defects and excitonic traps that cause this emission can affect the photophysics of hybrid perovskites at higher temperatures.

Chain-Length Dependence of Thermal Conductivity in 2D Alkylammonium Lead Iodide Single Crystals.

In 2D organic-inorganic hybrid perovskite materials, layers of conducting inorganic material are separated by insulating organic spacers whose length and composition can be tuned. We report the heat capacity and cross-plane thermal conductivity of 2D alkylammonium lead iodide single crystals with increasing chain length, (CnH2n+1NH3)2PbI4 (n = 4-7). The measured thermal conductivities are some of the lowest ever recorded for single crystals, with averages in the range k = 0.099-0.125 W/m K. Although a model based on independent interface resistances between adjacent layers predicts an increase in thermal conductivity with a chain length of more than 30%, experimentally we find that the thermal conductivity is nearly independent of chain length and possibly decreases. We hypothesize that phonons carry an appreciable portion of the heat across the interface coherently, rather than being limited by individual weak interfaces.

Investigating the Tetragonal‐to‐Orthorhombic Phase Transition of Methylammonium Lead Iodide Single Crystals by Detailed Photoluminescence Analysis

AbstractHere, the phase‐transition from tetragonal to orthorhombic crystal structure of the halide perovskite methylammonium lead iodide single crystal is investigated. Temperature dependent photoluminescence (PL) measurements in the temperature range between 165 and 100 K show complex PL spectra where in total five different PL peaks can be identified. All observed PL features can be assigned to different optical effects from the two crystal phases using detailed PL analyses. This allows to quantify the fraction of tetragonal phase that still occurs below the phase transition temperature. It is found that at 150 K, 0.015% tetragonal phase remain, and PL signatures are observed from quantum confined tetragonal domains, suggesting their size to be about 7–15 nm down to 120 K. The tetragonal inclusions also exhibit an increased Urbach Energy, implying a high degree of structural disorder. The results first illustrate how a careful analysis of the PL can serve to deduce structural information, and second, how structural deviations in halide perovskites have a significant impact on the optoelectronic properties of this promising class of semiconductors.

(Invited) Perovskite Single Crystals with Free-Hole Trapping Centers for Photodetector and Solar Cell Applications

The methylammonium lead iodide (MAPbI3) single crystals show extremely low trap-state density, high charge carrier diffusion length, long radiative carrier lifetime and high charge carrier mobility, making them outstanding candidates for a variety of potential applications including solar cells and photodetectors. However, these single crystals whatever the structure compositions still severely suffer from the presence of impurity traces such as triiodide that formed during their growth at high temperature. These traces can act as electron and hole quenching centers on the surface and at the device interface, hindering the further development of the performance of the solar cells and photodetectors based on these crystals. They also suffer from ions migrauion, vacancies, interstitials, and surface resturcturing and degradation especially under environmental conditions. Here, we will first show tremendous impact of the presence of excess triiodide on the charge carrier lifetime, carrier mobility and the performance of their solar cell and photodetector devices. We will also show the significant impact of the structure of organic cations on halogen migration, vacancies, and interstitials, carrier lifetimes as well as surface degradation of these single crystal perovskites using a combination of experimental and theoretical investigations. Finally, the unprecedented photo-response and photo-conversion efficiency after the chemical treatment of these single crystals will be presented and discussed.

Self-Powered X-Ray Photodetector Based on Ultrathin PbI2Single Crystal

Lead iodide (PbI2) single crystals have been extensively investigated due to their potential applications in nuclear radiation detectors at room temperature. In this letter, the properties of ultrathin PbI2 single crystals were obtained and investigated by X-ray diffraction, ultraviolet-visible diffuse reflection spectroscopy, and field emission scanning electron microscopy. The X-ray photodetector based on ultrathin PbI2 single crystal with a Schottky configuration of Au/PbI2/Mo was also fabricated through a facile method. Especially, the X-ray photodetector exhibits good stability and reproducibility. A large sensitivity of ${0}.{12} \times {10}^{{4}} \mu \text{C}$ /Gyair/cm2 was obtained for X-ray photodetector based on PbI2 single crystal at zero bias under a low radiation dose rate (0.19 mGy/h), which is sixty times higher than that of currently $\alpha $ -Se X-ray detectors at high bias. Moreover, we have further illustrated the working principles of the photodetector at zero, positive and negative bias with and without X-ray illumination. Our investigation substantiates the potential of the self-powered X-ray photodetector based on ultrathin PbI2 single crystal as a candidate device in optoelectronic applications.

Assessing Temperature Dependence of Drift Mobility in Methylammonium Lead Iodide Perovskite Single Crystals

Hybrid organic–inorganic perovskites have emerged as cost-effective and high-performance semiconductors for optoelectronic applications. Precise knowledge of charge carrier mobility and especially the temperature dependence of mobility is therefore of utmost relevance for advancing high-performance materials. Here, the charge carrier mobility in methylammonium lead iodide single crystals is investigated with time of flight technique from 290 to 100 K. A nondispersive transport with an electron mobility of 135 (±20) cm2/V s and a hole mobility of 90 (±20) cm2/V s is obtained at room temperature. A power-law temperature dependence of mobility, μ ∝ Tm, with an exponent m = −2.8 and −2.0, is measured for electrons and holes in the tetragonal phase. The highest electron and hole mobilities measured are 635 (±70) and 415 (±20) cm2/V s, respectively. Our results indicate that the scattering of charge carriers with phonons is the limiting factor for carrier mobilities at room temperature.

Precise Facet Engineering of Perovskite Single Crystals by Ligand-Mediated Strategy

Inorganic–organic hybrid perovskite single crystals are potential materials for the application of high performance optoelectronic devices. The exposed surface of single crystals can dramatically affect the measured properties. Facet-dependent behaviors are also speculated. However, impeded by the lack of facile facet engineering strategy for inorganic–organic hybrid perovskites, the relationship between different facets and respective performance remains elusive. In this work, we present a simple approach of ligand-mediated crystal growth to control the shape and the exposed facets of methylammonium lead iodide single crystals. The addition of oleylamine ligand can trigger the continuous morphological transition from dodecahedral-shaped single crystal enclosed by (100)T and (112)T to cubic-shaped single crystal enclosed by (110)T and (002)T while maintaining the material composition and crystalline phase. We fabricated single crystal based photodetectors and carried out the first unambiguous study on the...

Growth of lead iodide single crystals used for nuclear radiation detection of Gamma‐rays

PbI2 single crystals have been fabricated by vertical Bridgeman (VB) method and vertical gradient freezing (VGF) method. The crystal grown by the VGF method exhibited high quality with no stress cracks and high infrared transmission rate compared with the one grown by VB method. A transparent orange PbI2 single crystal with size of Φ20 mm×80 mm was obtained by the improved parameters. Electrical resistivity of the crystal was as large as 1.4×1011Ωcm, and the infrared transmission rate was as high as 53% in the wave‐numbers from 4000 to 400 cm−1. The wafer was deposited with graphite explode, and the photopeak was very sharp with the shaping time of 2.7 μs to detect 241Am@59.5 keV γ‐rays.

The In-Gap Electronic State Spectrum of Methylammonium Lead Iodide Single-Crystal Perovskites.

The density of trap states within the bandgap of methylammonium lead iodide single crystals is investigated. Defect states close to both the conduction and valence bands are probed. Additionally, a comprehensive electronic characterization of crystals is carried out, including measurements of the electron and hole mobility, and the energy landscape (band diagram) at the surface.

Removal of oxidic impurities for the growth of high purity lead iodide single crystals

It could be shown that the hydrogen (H2) treatment of lead iodide (PbI2) is capable to effectively reduce oxidic impurities contained in the source material used for single crystal growth. Comparative experiments of melting PbI2 in H2 and Ar atmosphere as well as thermal analysis (DTA, DSC/TG) of contaminated PbI2 were carried out to characterise the influence of the H2 treatment on the resulting material purity. At the same time, a hygroscopic nature of PbI2 could be disproved, and new results on the controversially discussed thermal behaviour of solid, oxide-polluted PbI2 are presented. Effective measures for the avoidance of oxidic impurities during source material processing could be derived. Finally, the effectiveness of an H2 treatment is confirmed by single crystal growth experiments using the Czochralski technique. PbI2 crystals with improved structural properties and, for the first time, a reproducible predetermination of crystallographic orientation are shown.

Growth and Study of Single Crystals of Lead iodide

Growth and Study of Single Crystals of Lead iodide

Impurity induced structural phase transformations in melt grown single crystals of lead iodide

AbstractLead iodide is a wide‐band gap and highly resistive semiconductor considered to be a promising room temperature nuclear detector. The phenomenon of polytypism is posing interesting problems of phase transformations among its polytypic modifications and formation of polytypic admixture during growth due to native impurities. Transformations have also been observed even when the material is stored for few months that causes deterioration in functioning of the PbI2 devices. Lead iodide has been purified and single crystals were grown using zone‐refining system. The observed phase transformations during growth and storage have been explained in the light of distortion of [PbI6]4‐ octahedron due to impurities present in the material and the known crystal structures of PbI2. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Czochralski growth of lead iodide single crystals: Investigations and comparison with the Bridgman method

We have developed a procedure to grow lead iodide (PbI2, 2H type) crystals using the Czochralski method applying an Ar counter pressure inside a fused silica chamber. The resulting crystal has a length of 3cm and is free of cracks. Electron backscatter diffraction (EBSD) measurements demonstrate that the crystal grew along [112¯0] direction (c-axis perpendicular to growth direction), which was defined by the PbI2 seed. This means that a better control of the growth direction is possible using the Czochralski method. The EBSD patterns suggest a simplified preparation method of the very soft crystals using samples with a surface orientation perpendicular to (0001). Rocking curves measured by high resolution X-ray diffraction (HRXRD) indicate that the structural quality of the approximately 80% single crystalline material is comparable to Bridgman–Stockbarger-grown crystals.

Growth of ultra‐high purity PbI2 single crystal: (1) Preparation of high purity PbI2

AbstractIn order to prepare high purity lead iodide (PbI2) single crystals, the starting material‐iodine (I) has been purified by the sublimation method, and the PbI2 polycrystalline by the normal freezing method. The purification effect of these methods has been confirmed by evaluating the impurity concentration in ingot by glow discharge mass spectrometry (GDMS) analysis. By comparing the purity of three different starting materials, non‐purified iodine+6N‐Pb, purified iodine+6N‐Pb and commercial 6N‐PbI2, PbI2 synthesized by purified iodine in the present experiment has the highest purity. This indicates that these purification methods are suitable. The present research results are expected to prepare high‐resistivity PbI2 used in radiation detector. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of doping on the surface feature and formation of PbI2 polytypes

AbstractA study of phase transformation at elevated temperature has been undertaken on single crystals of lead iodide grown in gel. The crystals of the polytype 2H, which is known to be the common modification of PbI2 at room temperature, have been found to transform into well‐ordered crystals of the polytype 12R after heating for nearly 8 h at 150°C. During the intermediate period of heating the crystals show features of disorder, viz. streaking, arcing, or both, on their x‐ray diffraction photographs. On the other hand, the higher polytypes do not show any change in cell dimensions even after prolonged heating. In addition, it was found that if silver iodide is added in extremely minute quantities as an impurity during crystallization the process of phase transformation in the as‐grown crystals appreciably accelerates. Inspection by optical microscopy of these crystals has revealed the existence of a wide variety of growth features on their basal surfaces. The results have been discussed in detail. Copyright © 2004 John Wiley & Sons, Ltd.

Studies on Growth and Microstructure of Lead Iodide Single Crystals

Single crystals of lead iodide have been grown by gel method. The results of detailed studies made on the growth and microstructures have been described.

Morphology of PbI2 Crystals Grown by Gel Method

The single crystals of Lead Iodide have been grown by gel method. X-ray diffraction studies on these crystals shows that the lattice parameters of grown crystals are almost matching with reported values. The results of detailed studies made on the microstructures of Lead Iodide crystals, have been described. The observations of the faces of these crystals revealed that they have grown by layer as well as spiral mechanisms. The probable role of these parameters is explained along with the surface microstructures on these various shaped crystals.

Nanomechanical properties of lead iodide (PbI 2) layered crystals

Lead iodide is a layered crystal whose layers are binding by van der Waals weak forces. Layered crystals have slip systems at the basal or layer plane. The slip system of lead iodide is composed by the (0001) plane and 〈11 2 ̄ 0〉 direction. Single crystals of lead iodide, produced by ionic exchange reaction, were deposited on glass substrate. The mechanical properties were analyzed by nanoindentation technique. The indentations were made in same direction of the c axis of the crystal, with a Berkovich indenter. Pop-in excursions of the indenter in the loading curve were observed. The origin of these excursions is discussed considering the breakage of layers and their intercalation into the existing ones. The pile-up around indentation impression was observed through scanning electron microscopy. Hardness anisotropy was found and the hardness variation with tip orientation can be explained by the effective resolved shear stress model (ERSS).

Van-Der Waals epitaxial growth mechanism in Bi-doped single crystals of lead iodide

Bi-doped single crystals have been grown using vapour method and chracterised by X-ray diffraction and related phenomena.