Highly Luminescent Transparent Cs2AgxNa1−xBiyIn1−yCl6 Perovskite Films Produced by Single-Source Vacuum Deposition

Thermal deposition of halide perovskites as a universal and scalable route to transparent thin films becomes highly challenging in the case of lead-free double perovskites, requiring the evaporation dynamics of multiple metal halide sources to be balanced or a single-phase precursor preliminary synthesized to achieve a reliable control over the composition and the phase of the final films. In the present Letter, the feasibility of the single-source vacuum deposition of microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 double perovskites into corresponding transparent nanocrystalline films while preserving the bulk spectral and structural properties is shown. The perovskite films produced from the most emissive powders with x = 0.40 and y = 0.01 revealed a photoluminescence quantum yield of 85%, highlighting thermal evaporation as a promising approach to functional perovskite-based optical materials

Photocatalytic Formation and Photoinduced Charging of ZnO–Au Nanostructures

Photocatalytic NaAuCl4 reduction by ethanol with the participation of ZnO nanocrystals results in the formation of gold nanocrystals with the mean size of 25–30 nm. The strongly pronounced autocatalytic character of the process reflects the fact that the ZnO–Au nanostructure produced at the initial stage of the photoreaction is a much more efficient photocatalyst than the original ZnO nanocrystals. The charging of gold nanocrystals by photogenerated ZnO conduction band electrons is accompanied by the equilibration of Fermi energies of the metal and semiconductor resulting in the charge redistribution between the components of ZnO–Au nanostructure and photoinduced polarization of ZnO nanocrystals. A long lifetime of the charged state of ZnO–Au nanostructure reflects an exceptional capability of gold nanocrystals to accumulate and retain negative charge.Фотокаталітичне відновлення NaAuCl4 етанолом за участю нанокристалів ZnO приводить до утворення наночастинок золота з середнім розміром 25–30 нм. Яскраво виражений аутокаталітичний характер фотопроцесу свідчить про те, що наногетероструктури ZnO–Au, які формуються на початковому етапі реакції, є набагато ефективнішим фотокаталізатором, аніж вихідні нанокристали оксиду цинку. Зарядження нанокристалів золота електронами, фотогенерованими у зоні провідності ZnO, супроводжується вирівнюванням рівнів Фермі металу та напівпровідника, перерозподілом зарядів між компонентами наногетероструктури ZnO–Au та фотоіндукованою поляризацією нанокристалів ZnO. Тривале збереження зарядженного стану наноструктури ZnO–Au свідчить про виняткову здатність нанокристалів золота до накопичення та утримування негативного заряду.Фотокаталитическое восстановление NaAuCl4 этанолом при участии нанокристаллов ZnO приводит к формированию наночастиц золота со средним размером 25–30 нм. Ярко выраженный автокаталитический характер фотопроцесса свидетельствует о том, что формирующиеся на начальном этапе реакции наногетероструктуры ZnO–Au являются гораздо более активным фотокатализатором, чем исходные нанокристаллы оксида цинка. Зарядка нанокристаллов золота электронами, фотогенерированными в зоне проводимости ZnO, сопровождается выравниванием уровней Ферми металла и полупроводника, перераспределением заряда между компонентами наногетероструктуры ZnO–Au и фотоиндуцированной поляризацией нанокристаллов ZnO. Длительное пребывание наноструктур ZnO–Au в заряженном состоянии свидетельствует об исключительной способности нанокристаллов золота к аккумулированию и удерживанию отрицательного заряда

Quantum-sized effects in oxidized silicon structures with surface II-VI nanocrystals

The Si-SiO₂ interface in oxidized macroporous silicon structures with surface CdS and ZnO nanocrystals was investigated using the methods of electroreflectance and photoconductivity. The Franz-Keldysh effect, built-in electric field and surface quantization of charge carriers in the Si-SiO₂ region were revealed. The splitting of photoconductivity peaks was detected in the area of indirect band-to-band transition due to quantization of charge carriers in the surface silicon region, too. The latter data correlate with the results of the electroreflectance spectra measurements in the area of direct interband transition of oxidized macroporous silicon structures with surface CdS and ZnO nanocrystals

Possibility of obtaining TiO2 material by plasma dynamic method into an air atmosphere

This paper shows the possibility to synthesize directly the titanium dioxide in a supersonic jet of an electric discharge erosive plasma. Using the X-ray diffractometry it is shown that the obtained product contains two main crystalline phases: anatase and rutile with tetragonal syngony. The size of the coherent scattering region is less 100 nm

Band-gap and sub-band-gap photoelectrochemical processes at nanocrystalline CdS grown on ZnO by successive ionic layer adsorption and reaction method

Cadmium sulfide nanoparticle (NP) deposition by the successive ionic layer adsorption and reaction (SILAR) method on the surface of mesoporous ZnO micro-platelets with a large specific surface area (110 ± 10 m2g− 1) results in the formation of ZnO/CdS heterostructures exhibiting a high incident photon-to-current conversion efficiency (Y) not only within the region of CdS fundamental absorption (Ymax = 90%; 0.1 M Na2S + 0.1 M Na2SO3), but also in the sub-band-gap (SBG) range (Ymax = 25%). The onset potentials of SBG photoelectrochemical processes are more positive than the band-gap (BG) onset potential by up to 100 mV. A maximum incident photon-to-current conversion efficiency value for SBG processes is observed at larger amount of deposited CdS in comparison with the case of BG ones. The Urbach energy (EU) of CdS NPs determined from the photocurrent spectra reaches a maximal value on an early deposition stage (EU = 93 mV at SILAR cycle number N = 5), then lowers somewhat (EU = 73 mV at N = 10) and remains steady in the range of N from 20 to 300 (EU = 67 ± 1 mV). High efficiency of the photoelectrochemical SBG processes are interpreted in terms of light scattering in the ZnO/CdS heterostructures

Effect of [OH-] linkages on luminescent properties of ZnO nanoparticles

Optical properties of ZnO nanoparticles prepared from a simple chemical method using sodium zincate bath show strong white light emission. X-ray absorption fine structure studies reveal a completely different local environment around Zn in these ZnO nanoparticles. The observed luminescence properties and local structural changes have been explained on the basis of a linkage between Zn and OH- ions in the surface layers of ZnO nanoparticles.Comment: J. Phys. Chem. C. (2011) (in print

Lead-free hybrid perovskites for photovoltaics

This review covers the state-of-the-art in organo–inorganic lead-free hybrid perovskites (HPs) and applications of these exciting materials as light harvesters in photovoltaic systems. Special emphasis is placed on the influence of the spatial organization of HP materials both on the micro- and nanometer scale on the performance and stability of perovskite-based solar light converters. This review also discusses HP materials produced by isovalent lead(II) substitution with Sn2+ and other metal(II) ions, perovskite materials formed on the basis of M3+ cations (Sb3+, Bi3+) as well as on combinations of M+/M3+ ions aliovalent to 2Pb2+ (Ag+/Bi3+, Ag+/Sb3+, etc.). The survey is concluded with an outlook highlighting the most promising strategies for future progress of photovoltaic systems based on lead-free perovskite compounds