Preparation of lead iodide films by iodination of chemically deposited lead sulphide films

A method of preparation of PbI₂ films by iodination of chemically deposited PbS films is described. The X-ray characterization of these films show that they are poly-crystalline in nature and the crystallites are preferentially oriented with c-axis perpendicular to the plane of the substrates. The analysis of the diffuse reflectance measurements performed on material scraped off the substrates yielded a forbidden energy gap of 2.34 eV in conformation with the results of pure PbI₂ powder. The transmittance spectra of these films, in the wavelength range 400 to 600 nm, revealed a characteristic strong absorption edge at about 510 nm and a hump at about 490 nm. On the basis of the changes in conductance of PbS film during iodine treatment a mechanism of iodination has been proposed.     

垂直布里奇曼法生长碘化铅单晶体

碘化铅（PbI2）晶体的平均原子序数较高,有较宽的禁带宽度,作为一种新型室温核辐射探测器材料有着广阔前景．以高纯Pb和I2单质为原料,采用两温区气相输运法（TVM）成功合成出单相PbI2多晶原料,并以此为原科,用垂直布里奇曼法（VBM）生长了3种不同颜色的PhI2单晶体．研究表明：晶体生长工艺参数对晶体的质量有重要影响,适当调整温度场和安瓿在生长炉中的位置,可有效地避免或减轻晶体富碘现象,从而生长出优质的黄色PbI2单晶体。     

Ordered nanostructure of PS-b-PEO copolymer by solvent annealing with mixture of benzene/water vapor and its micropattern fabrication

We investigate the effect of water/benzene co-solvent vapor on the ordering of poly(styrene-b-ethylene oxide) (PS-b-PEO) copolymer thin film on silicon substrate upon solvent annealing. In-plane cylindrical PEO microdomains were observed after exposure of benzene vapor. The addition of water vapor dominantly produced the cylindrical PEO domains aligned perpendicular to the substrate. The best ordering of the cylinders was obtained at the water fraction of approximately 0.05. The degree of ordering decreases while the periodicity of haxagonally packed PEO cylinders increases with the amount of water in the vapor mixture. The average center-to-center distance of hexagonally packed cylindrical PEO microdomains increases with the water fraction from approximately 25 nm to 40 nm. As one way of utilizing the dewetting of thin films inevitable during solvent annealing, PS-b-PEO micropatterns prepared by microcontact printing were treated with co-solvent vapor, which allows us to fabricate the controlled dewet structures guided by the micropatterns. Cylinder-to-sphere phase transition of PEO microdomains also occurred upon solvent annealing in the micropatterned PS-b-PEO films.     

Solution-processed planar lead iodide photovoltaic device

PbI₂-based photovoltaic devices having ITO/ZnO (or WO₃) /PbI₂/graphite (or without graphite) /carbon black structure were fabricated by spin coating at ambient conditions. The structures were characterized using AFM, PXRD, and UV–Vis spectroscopy. The best devices yielded 0.32% power conversion efficiency. The short circuit current decreased with increasing the thickness of the PbI₂ film and without the graphite layer. The open circuit voltage decreased when replacing ZnO by WO₃. Selecting better n-type and hole transporting materials as well as improving manufacturing methods will increase PCE of PbI₂ based devices.     

Growth and properties of lead iodide thin films by spin coating

In this study, lead iodide (PbI₂) thin films were deposited on glass substrates by spin coating a solution of 0.2 M PbI₂ dissolved in dimethylformamide, varying the deposition time and the spin speed. The thickness of the thin films decreased with increase in spin speed and deposition time, as examined by profilometry measurements. The structure, morphology, optical and electrical properties of the thin films were analysed using various techniques. X-ray diffraction patterns revealed that the thin films possessed hexagonal structures. The thin films were grown highly oriented to [001] direction of the hexagonal lattice. Raman peaks detected at 96 and 136 cm^?1 were corresponding to the characteristic vibration modes of PbI₂. The X-ray photoelectron spectroscopy detected the presence of Pb and I with core level binding energies corresponding to that in PbI₂. Atomic force microcopy showed smooth and compact morphology of the thin films. From UV–Vis transmittance and reflectance spectral analysis, the bandgap of the thin films ～2.3 eV was evaluated. The dark conductivity of the thin films was computed and the value decreased as the deposition time and spin speed increased.     

Rapid sonochemical preparation of shape-selective lead iodide

Lead iodide (PbI₂) films/crystals with various nano/micro morphologies (e.g., Nanoflake, block and microrod) were rapidly synthesized by taking advantage of a simple sonochemical method. The PbI₂ crystals with uniform nanoflake structures could be fabricated directly on lead foils with the irradiation time as short as 36 s via interfacial reaction between lead foils and elemental iodine in ethanol at ambient temperature. It was found experimentally that the morphologies of the resulting thin films/crystals could be well controlled by the adjustment of several parameters including irradiation time, reaction solvents, iodine concentration, ultrasonic power, and reaction temperature. Most importantly, the resultant PbI₂ films are stable enough to resist rolling under the drastic ultrasound irradiation in a liquid media. This method is believed to be the fastest way for in situ fabrication of morphology-controlled semiconductor films on various metal substrates for subsequent applications related to the other metal iodide or metal sulfide semiconductor films.     

Electrical, optical and structural properties of lead iodide

Lead iodide PbI₂ is an excellent and interesting candidate for high efficiency room temperature detectors working in the medium energy range of 1 keV–1 MeV. It can be widely applied in medicine, monitoring ecology, nondestructive defectoscopy and X-ray and gamma spectroscopy. The peculiarities of this material are high resistivity, ability to work in a wide range of temperatures and high chemical stability. The method of preparation was direct synthesis from lead and iodine. The material was further purified by zone melting and grown by Bridgman-Stockbarger method. In this work we have concentrated on the study of the influence of dopants such as lanthanides (Er,Gd, Ho, Tb, Tm, Yb, GdI₃, HoI₃, GdI₃) and elements of other groups, such as Au, Ag, Ge on the physical, electrical and optical properties of the PbI₂. These were evaluated by resistivity and low temperature photoluminescence measurements. The Synchrotron X-ray topography was successfully introduced to study defects. The quality of the material was analyzed after synthesis, zone melting and growth. The dependence on the concentration of dopants was investigated too.     

Metal coordination assists fabrication of multifunctional aerogel

Interfacial design is one of the most promising ways in improving mechanical properties of nanocomposites.In this work,a multifunctional aerogel with excellent mechanical performances,sensing sensitivity,and fire retardancy is fabricated by taking advantage of metal coordination between biopolymer and Fe3+.Montmorillonite (MMT) nanosheets are added to induce a 'brick and mortar' structure.The coordination remarkably reduces structural defects,leading to well-formed lamellas that can effectively distribute stress under sever compression without plastic deformation.The structural merits impart the aerogel highly reversible compressibility even at 99 ％ strain and superior durability.Besides,it demonstrates high sensing performance in wearable health monitoring devices,and shows fire resistance property that can maintain elasticity in a flame.The work offers a facile and effective method to create multifunctional aerogels from various polymers.     

Optical properties of lead iodide between 0.4946 and 6.185 eV

The optical and dielectric constants of PbI₂ thin films have been determined from transmittance and reflectance measurements, for photon energies between 0.4946 and 6.185 eV. The absorption coefficient, bandgap energy, and dielectric constants were determined at room temperature by the normal incidence method. The first three lines of the hydrogenic exciton series associated with the absorption edge are well resolved in reflectivity measurements. The transmittance measurements enable the evaluation of the value of bandgap energy E_g. The bandgap energy of PbI₂ at room temperature was found to be 2.55 eV. A careful analysis of the absorption coefficients indicated the crystalline character of the sample studied; a similar diagnosis was obtained from X-ray evidence. SEM analysis revealed that as the thickness of the films increases the material becomes amorphous.     

生物材料表面微图形化及其研究进展

生物材料表面微图形化是利用微图形技术在生物材料表面构筑具有规则、有序结构的微图形化区域，或进一步改善微图形区域表面的物理化学性质，通过研究材料表面形貌和表面物理化学性质与生物相容性的关系，获得有利于细胞生长的有序化微环境．本文综述了当前研究的材料表面微图形化加工技术、微图形在生物材料中的应用、细胞与微图形的关系等．     

Organic acids on the fabrication of sol-gel lead zirconate titanate fibers

Lead zirconate titanate (PZT, 53/47) fibers are prepared by sol-gel method using organic acids - acrylic and methacrylic acid - to modify the precursors. The macroscopic properties, molecular structure, crystallization behaviour and microstructure of the fibers are investigated as a function of the content and type of acid. Organic acids produce long gel and ceramic fibers, due to the beneficial effect of the long polymeric chains that are generated in the precursor gel. However the longest, strongest, densest and with the highest homogeneity fibers are obtained when acrylic acid is used. The linear shape of the molecular structure of acrylic acid, together with a lower content of organic species to be released, is favourable to the preparation of round and crack free PZT fibers, when acrylic acid is used.     

Influence of solution rate and substrate temperature on the properties of lead iodide films deposited by spray pyrolysis

Polycrystalline lead iodide (PbI₂) thin films have been deposited by spray pyrolysis method using N,N-dimethylformamide (DMF) as solvent as a function of several deposition parameters. DMF is used as an alternative to water due to the larger solubility limit of PbI₂ in this solvent. In this work, the solution rate during the deposition time of 3 h was varied in the range of 0.11 cm³/min up to 0.30 cm³/min. A growth rate varying from 19 Å s^?1 up to 47 Å s^?1 was obtained as a function of solution rate. Dark current as a function of temperature for the final films reveals that for larger solution rates smaller values of electrical resistivity is obtained. For a solution rate of 0.30 cm³/min, an electrical transport activation energy (E _a) of about 0.65 eV was measured for the whole temperature range. On the other hand, for the sample deposited with a solution rate of 0.11 cm³/min, two main transport mechanisms can be observed with an activation energy of about 1.23 eV for temperatures above 50 °C. The effect of substrate temperature is also discussed. Samples were deposited in the temperature range of 170 °C up to 250 °C with a fixed solution rate of 0.16 cm³/min. In addition, the films were exposed to X-ray irradiation in the mammography diagnosis region, using a molybdenum (Mo) anode and a peak tube potential between 26 and 36 kV (equivalent photon energies between 10 keV and 15 keV).     

Effects of band gap illumination on surface layers of lead iodide

Thin films of lead iodide (PbI₂) decompose under band gap illumination, giving rise to iodine desorption and the formation of lead aggregates. We report on mass spectrometry, conductivity and photoconductivity measurements made in order to define the desorbing species and to elucidate the dissociation mechanism. The desorption rates of atomic and molecular iodine, together with the dark conductivity and the photoconductivity, were measured as functions of the PbI₂ film temperature in the range 300–500 K. The molecular desorption in particular seems to undergo a transition from a diffusion-controlled process (which governs the dark conductivity and the atomic iodine desorption) to a process dominated by the concentration of photoholes at temperatures above 400 K. At these temperatures a striking resemblance appears between the variations in the molecular iodine desorption and the photoconductivity with temperature. This leads us to suggest a model in which the iodine molecules are primarily evolved at special surface sites, e.g. grain boundaries, which also dominate the photoconductivity.     

Polyaniline micropattern onto flexible substrate by vapor deposition polymerization-mediated inkjet printing

An approach to pattern a conducting polymer on various flexible substrates using vapor deposition polymerization-mediated inkjet printing method was demonstrated. Complex patterns of doped emeraldine salt polyaniline were obtained via chemical oxidation polymerization of vaporized aniline monomer on inkjet-printed oxidant patterns. The features of pattern were precisely controlled by inkjet printing with a micrometer-scale resolution. Fourier transformed infrared attenuated total reflection analysis was conducted in order to confirm the polymerization of aniline monomer and UV-visible spectroscopy analysis was used to investigate the oxidation state of obtained polyaniline. The minimum width of patterned line was ca. 80 μm. The sheet resistance of patterned polyaniline films was 3.8 × 10³ Ω/□ for an average patterned film thickness of ca. 450 nm.     

Low temperature preparation of polycrystalline lead-tin tellurides in a lead iodide flux

Lead-tin telluride was prepared as a polycrystalline powder by heating a mixture of the component elements in a lead iodide flux at about 650°C. The powder, as prepared, can be used as raw material for single crystal growth or epitaxial film preparation.     

Advances in cesium lead iodide perovskite solar cells: Processing science matters

The prevailing perovskite solar cells (PSCs) employ hybrid organic–inorganic halide perovskites as light absorbers, but these materials exhibit relatively poor environmental stability, which potentially hinders the practical deployment of PSCs. One important strategy to address this issue is replacing the volatile and hygroscopic organic cations with inorganic cesium cations in the crystal structure, forming all-inorganic halide perovskites. In this context, CsPbI₃ perovskite is drawing phenomenal attention, primarily because it exhibits an ideal bandgap of 1.7 eV for the use in tandem solar cells, and it shows significantly enhanced thermal stability that is the key to the long-term device operation. Within only half a decade, the power conversion efficiency (PCE) of CsPbI₃ PSCs has ramped beyond 20%, which has been driven by inventions of numerous processing methods for high-quality CsPbI₃ perovskite thin films. These methods are broadly classified into three categories: vapor deposition, nanocrystals assembly, and solution deposition. Herein we present a systematic review on these methods and related materials sciences. In particular, we comprehensively discuss the dimethylammonium-additive-based solution deposition, which has resulted into the best-performing CsPbI₃ PSCs. We also present the challenges and prospects on future research towards the realization of the full potential of CsPbI₃ PSCs.     

Structural,optical, and electrical properties of phase-controlled cesium lead iodide nanowires

Cesium lead iodide (CsPbI3),in its black perovskite phase,has a suitable bandgap and high quantum efficiency for photovoltaic applications.However,CsPbI3 tends to crystalize into a yellow non-perovskite phase,which has poor optoelectronic properties,at room temperature.Therefore,controlling the phase transition in CsPbI3 is critical for practical application of this material.Here we report a systematic study of the phase transition of one-dimensional CsPbI3 nanowires and their corresponding structural,optical,and electrical properties.We show the formation of perovskite black phase CsPbI3 nanowires from the non-perovskite yellow phase through rapid thermal quenching.Post-transformed black phase CsPbI3 nanowires exhibit increased photoluminescence emission intensity with a shrinking of the bandgap from 2.78 to 1.76 eV.The perovskite nanowires were photoconductive and showed a fast photoresponse and excellent stability at room temperature.These promising optical and electrical properties make the perovskite CsPbI3 nanowires attractive for a variety of nanoscale optoelectronic devices.