Humidity controlled crystallization of thin CH3NH3PbI3 films for high performance perovskite solar cell

Control of crystallization of a solution‐processed perovskite layer is of prime importance for high performance solar cells. In spite of the negative effect of water on perovskite solar energy conversion in several previous works, we observed that humidity plays a critical role to develop a thin uniform, dense perovskite film with preferred crystals, in particular, in a device with architecture of ITO/PEDOT:PSS/CH₃NH₃PbI₃/ PC₇₁BM/LiF/Al fabricated by two‐step sequential spin‐coating process. Humidity controlled spin‐coating of CH₃NH₃I on the pre‐formed PbI₂ layer was the most influential process and systematic structural investigation as a function of humidity revealed that grains of CH₃NH₃PbI₃ perovskite crystals increase in size with their preferred orientation while film surface becomes roughened as the humidity increases. The performance of a device was closely related to the humidity dependent film morphology and in 40% relative humidity, the device exhibited the maximum power conversion efficiency of approximately 12% more than 10 times greater than that of a device fabricated at 20% humidity. The results suggest that our process with controlled humidity can be another efficient route for high performance and reliable perovskite solar cells. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Short-living defects and recombination processes in Li6Gd(BO3)3 crystals

Results of a study of transient optical absorption (TOA) and luminescence of lithium-gadolinium orthoborate Li₆Gd(BO₃)₃ (LGBO) in the visible and ultraviolet spectral regions are presented. As revealed by absorption optical spectroscopy with nanosecond time resolution, the LGBO TOA derives from optical transitions in hole centers, with the optical density relaxation kinetics being mediated by interdefect tunneling recombination involving these centers and neutral lithium atoms acting as electronic Li⁰ centers. At 290 K, the Li⁰ centers are involved in thermally stimulated migration, which is not accompanied by carrier transfer to the conduction or valence band. The slow TOA decay kinetics components, with characteristic times ranging from a few milliseconds to seconds, have been assigned to diffusion-limited annihilation of lithium interstitials with vacancies. The mechanisms responsible for the creation and relaxation of short-living Frenkel defect pairs in the LGBO cation sublattice have been analyzed.     

Transient hole-polaron optical absorption in Li<Subscript>6</Subscript>Gd(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystals

Results of a study of transient optical absorption (TOA) and luminescence of lithium gadolinium orthoborate Li₆Gd(BO₃)₃ (LGBO) in the visible and UV spectral regions are presented. As revealed by absorption optical spectroscopy with nanosecond time resolution, the LGBO TOA derives from optical transitions in hole centers, with the optical density relaxation kinetics being mediated by interdefect tunneling recombination involving these centers and neutral lithium atoms acting as electronic Li⁰ centers. At 290 K, the Li⁰ centers are involved in thermostimulated migration, which is not accompanied by carrier transfer to the conduction or valence band. The slow components of the TOA decay kinetics, with characteristic times ranging from a few milliseconds to seconds, have been assigned to diffusion-limited annihilation of lithium interstitials with vacancies. The mechanisms responsible for the creation and relaxation of short-lived Frenkel defect pairs in the LGBO cation sublattice have been analyzed.     

硅纳米孔柱阵列及其四氧化三铁复合薄膜的湿敏电容特性研究

报道了硅纳米孔柱阵列（Si-NPA），Fe₃O₄复合的Si-NPA（Fe ₃O₄/Si-NPA）两种薄 膜材料的制备方法并对其形貌和结构进行了表征，研究了其电容湿度传感特性.结果表明，S i-NPA，Fe₃O₄/Si-NPA均为微米/纳米结构复合体系.当环境相对湿 度从11％上升到95％ 时，采用100 Hz的信号频率进行测试，以Si-NPA和Fe₃O₄/Si-NPA 为电介质材料制成的湿 敏元件的电容增加值分别为起始值的1500％和5500％；采用1000 Hz的信号频率测试时，则 分别为起始值的800％和12000％，显示出两种材料较高的湿度灵敏性和较强的绝对电容输出 信号强度.同时，在升湿和降湿过程中，Si-NPA，Fe₃O₄/Si-NPA都 具有较快的响应速度 ，其响应时间分别为15 s，5 s和20 s，15 s.文章结合材料的形貌和结构特性对其物理机理 进行了分析.上述结果表明，Si-NPA无论是直接作为湿度薄膜传感材料还是作为复合薄膜湿 度传感材料的衬底都具有很好的前景. 关键词： 硅纳米孔柱阵列 3O₄')" href="#">Fe₃O₄ 湿度电容传感特性     

Sensors for the nitrogen oxides, NO2, NO and N2O, based on In2O3 and WO3 nanowires

Sensing characteristics of ZnO, In₂O₃ and WO₃ nanowires have been investigated for the three nitrogen oxides, NO₂, NO and N₂O. In₂O₃ nanowires of ∼20 nm diameter prepared by using porous alumina membranes are found to have a sensitivity (defined as the ratio of the sensor resistance in the gas concerned to that in air) of about 60 for 10 ppm of all the three gases at a relatively low temperature of 150 °C. The response and recovery times are around 20 s. The sensitivity of these In₂O₃ nanowires is around 40 for 0.1 ppm of NO₂ and N₂O at 150 °C. WO₃ nanowires of 5–15 nm diameter, prepared by the solvothermal process show a sensitivity of 20–25 for 10 ppm of the three nitrogen oxides at 250 °C. The response and recovery times are 10 s and 60 s, respectively. The sensitivity is around 10 for 0.1 ppm of NO₂ at 250 °C. The sensitivity of In₂O₃ and WO₃ nanowires is not affected by humidity even up to 90% relative humidity. The study also reveals that the sensing mechanism for the three nitrogen oxides have a commonality in that the desorption of oxygen is a crucial step in all the cases. PACS 07.07.Df; 85.35.-p; 82.35.Np     

Surface conduction mechanisms and the electrical properties of Al2O3 humidity sensor

The electrical properties of Al₂O₃ humidity sensor are governed by the variations in the surface conductivity of a porous anodic Al₂O₃ film with humidity. We propose a two-carrier mechanism to describe charge transport on porous alumina. At low humidities, a phonon-induced electron tunneling is postulated between donor water sites; at high humidities protonic conduction dominates. A physical model of surface conduction is developed using energy-band concepts. Based on this model, theoretical expressions are presented for the surface conductivity. The model predicts a log-normal distribution of surface conductivity amongst the pores which conforms to the observed electrical properties of the sensor. The experimental plot of log σ versus T^-1 shows that the activation energy varies on transition from the liquid-water state to electron tunneling on the hydroxylated surface. The model also prescribes the Al₂O₃ film-growth parameters for low-and high-humidity sensors which will be useful for fabricating devices of desired response characteristics.     

Sm doped BiFeO3 nanofibers for improved photovoltaic devices

Interdigital electrodes, BiFeO₃ and Sm doped BiFeO₃ nanofibers and corresponding photovoltaic devices were obtained by semiconductor technology and electrostatic spinning method. The interdigital electrodes have prefect structure and the nanofibers have uniform morphology both before and after annealing process examined by SEM and AFM, respectively. The ferroelectric and piezoelectric properties of the BiFeO₃ and Sm doped BiFeO₃ nanofibers were demonstrated by PFM. After Sm doping, the BiFeO₃ nanofibers have improved ferroelectricity. Compared with BiFeO₃ nanofiber photovoltaic device, Sm doped BiFeO₃ nanofiber photovoltaic device has improved photovoltaic performance with increased photocurrent and energy conversion efficiency is improved to 1.65 times. The BiFeO₃-based nanofibers are very promising ferroelectric photovoltaic materials for high performance photovoltaic devices.     

Stacked and nanolaminated Al2O3/TiO2 for surface passivation and encapsulation of silicon

Silicon solar cells passivated with Al₂O₃ require a capping layer that protects the passivation layer from humidity because of sensitivity of Al₂O₃ to moisture. Al₂O₃/TiO₂ stacks obtained by atomic layer deposition have been known to provide a high level of passivation layers because of their excellent field‐effect passivation. In this work, degradation of this Al₂O₃/TiO₂ stack, when exposed to humidity, is examined, and an attempt is made for a humidity‐resistant encapsulation layer by adding Al₂O₃/TiO₂ nanolaminates that can be deposited in‐situ without breaking vacuum. Placing the nanolaminate on top of the TiO₂ and Al₂O₃ stack is found to lead to almost no degradation even after 10 days of humidity exposure. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

硅衬底的SrTiO3淀积膜的湿敏特性与机理研究

对无定形多孔SrTiO₃膜电导率随相对湿度的变化进行了理论模型分析.该模型也适用于其他多孔半导体陶瓷材料.实验样品用氩离子束镀膜技术在SiO₂/Si衬底上淀积SrTiO₃膜并制成平面型电阻结构.结果表明，在室温下，当相对湿度从12%变化至53%时，电流缓慢下降；而当相对湿度从53%变化至92%时，电流又显著上升，即在高湿度条件下具有良好的湿敏特性.电流及其在高湿条件下的上升率随测试频率而增大.吸附响应时间明显长于脱附时间. 关键词：     

Study of diffusive transformations by high energy X-ray diffraction

High energy X-ray diffraction is a powerful tool, able to follow phase transformations during complex thermal or thermo-mechanical treatments. High energy allows one to study volumic specimens of a few mm³ and get successive data within a few seconds or less. The technique is described with different experimental setups (heating devices, detectors for diverse acquisition times) allowing diverse ranges for heating and cooling rates. Three examples are considered to illustrate the results obtained by using high energy X-ray diffraction. The first one corresponds to a simple diffusive phase transformation during an isothermal thermal path for the α–β transformation in a titanium alloy, highlighting the diffusive character considering the cell parameter evolutions of the parent phase. The second one illustrates the precipitation sequences observed during ageing of a β-metastable phase in a titanium alloy that was not obtained by TEM. The last example illustrates the phase evolutions during ageing of a martensitic steel showing the complexity of cell parameters evolution and some evolutions of the stress state.     

Phantom and in vivo study of the look–locher T1 mapping method

This paper describes and tests the LL-EPI method for obtaining quantitative T₁ estimates in a few seconds thereby allowing dynamic T₁ studies. It is shown that the method works even when there is an inflow into the imaged volume, e.g., in a vessel. No calibration is needed. The method has been tested in a phantom study with several different scan parameter set-ups, with and without inflow. The method shows robustness and individual scan parameters and inflow rates do not influence the ability to calculate the Gd-DTPA concentration. Linearity prevail between the measured 1/T₁ and the Gd-DTPA concentration in the range 150 < T₁ < 2500 ms. In a dynamic Gd-DTPA phantom study, it was shown that the dynamic LL-EPI T₁ mapping technique was three times more sensitive than the signal from a T^*₂-weighted EPI sequence. In an in vivo study, dynamic T₁ mapping of the Gd-DTPA uptake in a meningioma was performed. Inspection of the uptake curves indicates that the method is feasible in clinical perfusion studies.     

Preparation of sol-gel method P2O5-Al2O3-SiO2 glasses and their characterization

Nanostructures P₂O₅-Al₂O₃-SiO₂ glasses were prepared by sol-gel method. The glasses were characterized by XRD, FTIR and TG/DTA methods. The average pore size of the glass was less than 3 nm as measured by N₂ adsorption — desorption method. The thermal stability was measured as a function of decomposition temperature and weight loss calculations. Proton conductivities of all samples increased with an increase in relative humidity (40–90 %), indicating that continuous paths suitable for proton conduction were developed when glasses heat treated at 300 °C due to the adsorption of water. The temperature dependence of the conductivity for all compositions increases with increasing temperature in the range 30–90 °C with relative humidity 70 %. The overall conductivity was in the range 10⁻⁴–10⁻³ S/cm for compositions.     

Relative humidity influence on proton conduction of hydrated pellicular zirconium phosphate in hydrogen form

Admittance measurements have been carried out as a function of temperature (20/-20°C) and relative humidity (5–90%) on pellets made up of pressed sheets of hydrated α-zirconium phosphate (pellicular zirconium phosphate). Their dc conductivities have been calculated on the basis of a suitable equivalent circuit using a nonlinear least squares procedure: at 20°C and 90% relative humidity they lie in the range 3-0.9×10^-4 S cm^-1 when the sheets are oriented parallel to the electric field and are about seven times lower in the case of perpendicular orientation. Changes in relative humidity from 90 to 5% cause the conductivity to decrease by two orders of magnitude and the activation energy to rise from 6.7 to 12.2 kcal/mol. A comparison of the Arrhenius equation parameters with those previously determined for polycrystalline α-Zr(HPO₄)₂·H₂O reveals that the same transport mechanism is present in both materials, the higher conductivity of pellicular zirconium phosphate arising from a larger effective number of carriers.     

Relative humidity influence on the water content and on the protonic conductivity of the phosphatoantimonic acids HnSbnP2O3n+5, xH2O (n = 1, 3, 5)

The phosphatoantimonic acids H_nSb_nP₂O_3n+5, xH₂O (n = 1, 3, 5) have been prepared from the corresponding potassium compounds by ion-exchange in acidic medium. For n = 1 and 3 they are layered materials. When n = 5 the covalent framework is three dimensional with large interconnected channels. The title acids are all hydrated and their water content, lattice parameters and protonic conductivity have been studied at 20°C as a function of the relative humidity. When n = 1 a great part of the water content is physisorbed and the electrical behavior is that of a particle hydrate. For n = 3, the compound is a true lattice hydrate and the protonic conductivity is closely related to the water content. This is also the case when n = 5; however the contribution of surface water to the proton diffusion is clearly evidenced.     

Investigation of quasi lateral-field-excitation on (yxl)-17° LiNbO3 single crystal

Quasi lateral-field-excitation (LFE) on LiNbO₃ crystal is investigated both theoretically and experimentally. It is found that when the driving electric field direction is parallel to the crystallographic X-axis of the piezoelectric substrate, (yxl)-17° LiNbO₃ LFE bulk acoustic wave devices work on quasi-LFE mode. The experimental results agreed with the theoretical prediction well. The results provide the cut of LiNbO₃ crystal for quasi-LFE bulk acoustic wave devices, which is important for designing high performance LFE sensors on LiNbO₃ substrates.     

Ignition and combustion behavior of zirconium-based pyrotechnic igniters and pyrotechnic delays under aging

Pyrotechnic materials often necessitate high reliability and stability to be utilized in energetic devices. However, prolonged storage of these materials degrades their performance in many ways and results in failure of these devices. Only a few studies have focussed on their burning characteristics, and reported limited understanding on the effect of aging on this behavior of such materials. In this study, ignition and combustion behavior of pyrotechnic materials based on zirconium (Zr) as fuel and potassium perchlorate (KClO₄) or iron(III) oxide (Fe₂O₃) as oxidant are investigated, for various aging conditions. Pristine samples are compared with samples subjected to aging under 91 °C (thermally aged) and seasonal changes (naturally aged). The ignition delay time as a function of maximum wire temperature is obtained through high-speed combustion photography for these samples. Surface features and oxide content are analyzed using scanning electron microscopy and x-ray photoelectron spectroscopy techniques. Results indicate that ignition delay time increases significantly with aging period for both pyrotechnic igniter and pyrotechnic delay samples. However, this time reduces as the maximum wire temperature is increased for all samples. Naturally aged samples exhibit longer ignition delay times and higher metal oxide content when compared to thermally aged ones. Both pre-oxidation of metallic fuel and prior thermal decomposition of oxidizer play an important role in causing this behavior with aged samples.     

Al2O3/SiO2 films prepared by electron-beam evaporation as UV antireflection coatings on 4H-SiC

Al₂O₃/SiO₂ films have been deposited as UV antireflection coatings on 4H-SiC by electron-beam evaporation and characterized by reflection spectrum, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The reflectance of the Al₂O₃/SiO₂ films is 0.33% and 10 times lower than that of a thermally grown SiO₂ single layer at 276 nm. The films are amorphous in microstructure and characterize good adhesion to 4H-SiC substrate. XPS results indicate an abrupt interface between evaporated SiO₂ and 4H-SiC substrate free of Si-suboxides. These results make the possibility for 4H-SiC based high performance UV optoelectronic devices with Al₂O₃/SiO₂ films as antireflection coatings.     

Thermal contact between Na3[Ce(C7H3NO4)3] · 15H2O and liquid 3He at millikelvin temperatures

Very short thermal equilibrium times have been observed at millikelvin temperatures between powdered Na₃[Ce(C₇H₃NO₄)₃] · 15 H₂O, and pure ³He. Both a large increase in these times and a change in their temperature dependence occurs when 1% ⁴He. Both a large increase in these times and a change in their temperature dependence occurs when 1% ⁴He is added.     

Third-order nonlinear optical properties of Bi2S3 and Sb2S3 nanorods studied by the Z-scan technique

Bismuth sulfide (Bi₂S₃) and antimony sulfide (Sb₂S₃) nanorods were synthesized by hydrothermal method. The products were characterized by UV-vis spectrophotometer, X-ray powder diffraction (XRD) and transmission electron microscope (TEM). Bi₂S₃ and Sb₂S₃ nanorods were measured by Z-scan technique to investigate the third-order nonlinear optical (NLO) properties. The result of NLO measurements shows that the Bi₂S₃ and Sb₂S₃ nanorods have the behaviors of the third-order NLO properties of both NLO absorption and NLO refraction with self-focusing effects. The third-order NLO coefficient χ⁽³⁾ of the Bi₂S₃ and Sb₂S₃ nanorods are 6.25×10⁻¹¹ esu and 4.55×10⁻¹¹ esu, respectively. The Sb₂S₃ and Bi₂S₃ nanorods with large third-order NLO coefficient are promising materials for applications in optical devices.     

Über den zeitlichen Verlauf des Stromes einer Gasentladung in Wasserstoff

The transient growth of currents in a Townsend gas discharge system under uniform dc field conditions in Hydrogen is examined. The discharge is started by 10³ to 10⁶ electrons released from the cathode by an UV light pulse within some 10^?7 seconds. Observed oscillations of the current are found to be due to the motion of the electrons through the gap creating new electrons by photoelectron emission at the cathode due to photons generated in the gap. At sparking threshold conditions (Μ ₀=1) the electron current becomes self-sustaining after a few electron transit times. The positive ion current soon exceeds the electron current and grows linearly with time (Μ ₀=1) until the positive ions of the first generation enter the cathode. For times greater than a positive-ion transit time the current becomes self-sustaining. Neglecting space-charge effects one would not expect a spark to occur. The space-charge of the positive ions, however, causes a distortion of the field changing the ionization efficiency of the electrons. It is shown that an observed rapid growth of current leading to breakdown after some positive-ion transit times is in agreement to this conception.