Giant and tunable excitonic optical anisotropy in single-crystal CsPbX3_3 halide perovskites

During the last years, giant optical anisotropy demonstrated its paramount importance for light manipulation which resulted in numerous applications ranging from subdiffraction light guiding to switchable nanolasers. In spite of recent advances in the field, achieving continuous tunability of optical anisotropy remains an outstanding challenge. Here, we present a solution to the problem through chemical alteration of the ratio of halogen atoms (X = Br or Cl) in single-crystal CsPbX$_3$ halide perovskites. It turns out that the anisotropy originates from an excitonic resonance in the perovskite, which spectral position and strength are determined by the halogens composition. As a result, we manage to continually modify the optical anisotropy by 0.14. We also discover that the halide perovskite can demonstrate optical anisotropy up to 0.6 in the visible range -- the largest value among non-van der Waals materials. Moreover, our results reveal that this anisotropy could be in-plane and out-of-plane, depending on perovskite shape -- rectangular and square. Hence, it can serve as an additional degree of freedom for anisotropy manipulation. As a practical demonstration, we created perovskite anisotropic nanowaveguides and show a significant impact of anisotropy on high-order guiding modes. These findings pave the way for halide perovskites as a next-generation platform for tunable anisotropic photonics.Comment: 18 pages, 3 figure

Silver nanowires on carbon nanotube aerogel sheets for flexible, transparent electrodes

Flexible, free-standing transparent conducting electrodes (TCEs) with simultaneously tunable transmittances up to 98% and sheet resistances down to 11 Ω/sq were prepared by a facile spray-coating method of silver nanowires (AgNWs) onto dry-spun multiwall carbon nanotube (MWNT) aerogels. Counterintuitively, the transmittance of the hybrid electrodes can be increased as the mass density of AgNWs within the MWNT aerogels increases, however, the final achievable transmittance depends on the initial transparency of the MWNT aerogels. Simultaneously, a strong decrease in sheet resistance is obtained when AgNWs form a percolated network along the MWNT aerogel. Additionally, anisotropic reduction in sheet resistance and polarized transmittance of AgNW/MWNT aerogels is achieved with this method. The final AgNW/MWNT hybrid TCEs transmittance and sheet resistance can be fine-tuned by spray-coating mechanisms or by choosing initial MWNT aerogel density. Thus, a wide range of AgNW/MWNT hybrid TCEs with optimized optoelectronic properties can be achieved depending of the requirements needed. Finally, the free-standing AgNW/MWNT hybrid TCEs can be laminated onto a wide range of substrates without the need of a bonding aid

Improvement of the perovskite photodiodes performance via advanced interface engineering with polymer dielectric

Halide perovskite-based photodiodes are promising for efficient detection across a broad spectral range. Perovskite absorber thin-films have a microcrystalline morphology, characterized by a high density of surface states and defects at inter-grain interfaces. In this work, we used dielectric-ferroelectric poly(vinylidene-fluoride-trifluoroethylene-P(VDF-TrFE) to modify the bulk interfaces and electron transport junction in p-i-n perovskite photodiodes. Our complex work demonstrates that interface engineering with P(VDF-TrFE) induces significant Fermi level pinning, reducing from 4.85 eV for intrinsic perovskite to 4.28 eV for the configuration with dielectric interlayers. The integration of P(VDF-TrFE) into the perovskite film did not affect the morphology and crystal structure, but significantly changed the charge transport and device performance. IV curve analysis and 2-diode model calculations showed enhanced shunt properties, a decreased non-ideality factor, and reduced saturation dark current. We have shown that the complex introduction of P(VDF-TrFE) into the absorbers bulk and on its surface is essential to reduce the impact of the trapping processes. For P(VDF-TrFE) containing devices, we increased the specific detectivity from 10^11 to 10^12 Jones, expanded the linear dynamic range up to 100 dB, and reduced the equivalent noise power to 10^-13 W*Hz^-0.5. Reducing non-radiative recombination contributions significantly enhanced device performance, improving rise/fall times from 6.3/10.9 us to 4.6/6.5 us. The cut-off frequency (3dB) increased from 64.8 kHz to 74.8 kHz following the introduction of the dielectric. These results provide new insights into the use of organic dielectrics and an improved understanding of trap-states and ion defect compensation for detectors based on perovskite heterostructures

Searches for rare B-s(0) and B-0 decays into four muons

Searches for rare B-s(0) and B-0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). Direct decays and decays via light scalar and J/psi resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 x 10(-10) and 2.6 x 10(-9) are set

Searches for rare Bs0 and B 0 decays into four muons

Searches for rare Bs0 and B0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. Direct decays and decays via light scalar and J/ψ resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 × 10−10 and 2.6 × 10−9 are set. [Figure not available: see fulltext.

Study of charmonium and charmonium-like contributions in B+ -> J/psi eta K+ decays

A study of B+ -> J/psi eta K+ decays, followed by J/psi -> mu(+)mu(-) and eta -> gamma gamma, is performed using a dataset collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The J/psi eta mass spectrum is investigated for contributions from charmonia and charmonium-like states. Evidence is found for the B+ -> (psi(2)(3823) -> J/psi eta)K+ and B+ -> (psi(4040) -> J/psi eta)K+ decays with significance of 3.4 and 4.7 standard deviations, respectively. This constitutes the first evidence for the psi(2)(3823) -> J/psi eta decay

Современное состояние и перспективы развития технологии органогалогенидных перовскитных солнечных ячеек: кристаллическая структура и формирование тонких пленок, морфология, обработка, деградация и повышение стабильности с использованием углеродных нанотрубок

The fundamental problems of the modern state of the studies of organic-inorganic organo-halide perovskites (OHP) as basis for high efficiency thin film solar cells are discussed. Perovskite varieties and background properties are introduced. The chronology of development of the studies in this direction has been presented — structural aspects of these OHP perovskites, from early 2D to recent 3D MAPbI3 perovskites and important technological aspects of smooth thin film structure creation by various techniques, such as solvent engineering, spin- and dip-coating, vacuum deposition, cation exchange approach, nanoimprinting (particularly, a many-sided role of polymers). The most important theoretical problems such as electronic structure of lattice, impurity and defect states in pure and mixed perovskites, suppressed electron-hole recombination, extra-long lifetimes, and diffusion lengths are analyzed. Degradation effects associated with moisture and photo irradiation, as well as degradation of metallic electrodes to OHP solar cells have been considered. The application of carbon nanostructures: carbon nanotubes (CNT) and graphene as stable semitransparent charge collectors to OHP perovskites is demonstrated on the example of original results of authors.Рассмотрены фундаментальные проблемы современного состояния исследований в области органо-неорганических органогалогенидных перовскитов (ОГП) в качестве основы для создания солнечных ячеек с повышенной эффективностью. Приведены данные о разнообразии перовскитов и их основных свойствах. Дана хронология развития исследований в данном направлении — структурные аспекты ОГП-перовскитов, от самых первых двумерных до современных трехмерных перовскитов с формулой MAPbI3, а также важных технологических аспектов создания структуры гладких тонких пленок с использованием разнообразных методов, в частности, подбора растворителей, нанесения покрытий методами центрифугирования и погружения, вауумного осаждения,технологии катионного обмена, наноимпринта (в особенности, разносторонней роли полимеров). Проанализированы наиболее важные теоретические проблемы, в частности, электронная структура решетки, дефектно-примесные состояния в чистых и смешанных перовскитах, подавление электронно-дырочной рекомбинации, сверхбольшие времена жизни и диффузионные длины. Рассмотрены эффекты деградации, связанные с влажностью и фотооблучением, а также деградация металлических электродов на солнечных ячейках на основе ОГП. Продемонстрировано применение углеродных наноструктур — углеродных нанотрубок (УНТ) и графена — в качестве стабильных полупрозначных коллекторов заряда на поверхности ОГП-перовскитов на примере оригинальных результатов, полученных авторами