Hole‐Transport Materials for Perovskite Solar Cells

The pressure to move towards renewable energy has inspired researchers to look for ideas in photovoltaics that may lead to a major breakthrough. Recently the use of perovskites as a light harvester has lead to stunning progress. The power conversion efficiency of perovskite solar cells is now approaching parity (>22 %) with that of the established technology which took decades to reach this level of performance. The use of a hole transport material (HTM) remains indispensable in perovskite solar cells. Perovskites can conduct holes, but they are present at low levels, and for efficient charge extraction a HTM layer is a prerequisite. Herein we provide an overview of the diverse types of HTM available, from organic to inorganic, in the hope of encouraging further research and the optimization of these materials.     

Two-step laser excitation of the highly excited even-parity states of atomic mercury

We report term energies and quantum defects of highly excited even-parity states of mercury in the 83 876–84 140 cm^-1 energy range, employing a two-step laser excitation scheme via the S₀↦6s6p³P₁ inter-combination transition. Two dye lasers, pumped by a common Nd:YAG laser, were frequency doubled by BBO crystals and used to record the spectra in conjunction with a thermionic diode ion detector. Our new observations include the much extended D₂ (22 ≤n ≤52) series and a few members of the S₁ (24 ≤n ≤30) Rydberg series. Members of the D₂ Rydberg series with such a high n value are reported for the first time. The relative intensities of the D₂ and S₁ transitions (m = 4, 5 and 6) of group II-B elements excited from the P₁ inter-combination states are also discussed.     

Step-wise laser excitation of the 4snf 3F Rydberg states of neutral zinc

The new experimental results on the effective quantum numbers and term energies of the highly excited odd-parity 4s4d ³D_1,2,3 →4snf ³F_2,3,4 Rydberg transitions of zinc have been presented. The experiment was performed using the three dye lasers simultaneously pumped by the second harmonic (532?nm) of the Q-switched Nd:YAG laser. The new observation includes the 4snf ³F₃ (12?≤n?≤?50) series excited from the 4s4d ³D₂ intermediate level. In addition, the 4snf ³F₂ (12?≤n?≤?28) and 4snf³F₄ (12?≤n?≤?33) series are observed from the thermally populated 4s4d ³D_1,3 fine structure components. The ionization potential of zinc has been determined from the unperturbed 4snf ³F₃ series as 75769.31?±?0.15?cm^?1, which is in excellent agreement with the previously reported value.     

Short Total Synthesis of Ajoene, (E,Z)-4,5,9-Trithiadodeca-1,6,11-triene 9-oxide,in Batch and (E,Z)-4,5,9-Trithiadodeca-1,7,11-triene in Continuous Flow

A short total synthesis of ajoene, (E,Z)-4,5,9-trithiadodeca-1,6,11-triene 9-oxide, has been achieved over six steps. In addition, a continuous flow synthesis under mild reaction conditions to (E,Z)-4,5,9-trithiadodeca-1,7,11-triene is described starting from simple and easily accessible starting materials. Over four steps including propargylation, radical addition of thioacetate, deprotection, and disulfide formation/ allylation, the target product can be obtained at a rate of 0.26 g h⁻¹ in an overall yield of 12 %.     

X-ray peak profiling,optical parameters and catalytic properties of pure and CdS doped ZnO–NiO nanocomposites

Russian Journal of Applied Chemistry - In the current study, XRD peak profile analysis, optical and catalytic properties of pure ZnO–NiO and CdS doped ZnO-NiO nanocomposites were...     

UV-absorption and fluorimetric methods for the determination of alprazolam in pharmaceutical formulation

The development of UV and fluorescence spectrophotometric methods for the quantitative determination of alprazolam in dosage forms using As(III)?SDS system. The two simple and sensitive, spectrophotometric and spectrofluorimetric methods were developed for the determination of alprazolam (ALP) in tablets. These methods are based on formation of ALP?As(III) complex in the presence of SDS. The UV-spectrum of 30% methanolic solution of ALP (5 × 10^?5 M) at pH 6.5 (Mclivaine buffer) was run between 200 and 380 nm. The absorption spectrum of ALP exhibits two peaks with a λ_max. at 255 nm and a weak band at 325 nm. When the spectra of the drug were run at varying pH in the region 200–380 nm, one isosbestic point at 290 nm was observed, which indicated the presence of two ionic conditions in solution. The complex exhibited an absorption maximum at 265 nm and emission peak at 520 nm with respect to the excitation wavelength of 325 nm. The spectrophotometric method was found to be linear in 8.0–17.0 μg ml^?1 range with detection limit of 13.520 μg ml^?1, while 0.05–9.5 μg ml^?1 range was with detection limit of 1.048 × 10^?2 μg ml^?1 by spectrofluorimetric method. The mean percentage recovery of the added quantity was found to be 99.54 (spectrophotometric method) and 100.22 (spectrofluorimetric method) and the %RSD are lower than 0.478 and 0.296 determined spectrophotomerically and spectrofluorimtrically, respectively. This indicates that the proposed method is accurate. The apparent ionization constant of ALP was found to be 9.29. The spectra, experimental conditions were set followed by determination stoichiometry, stability constant and thermodynamic parameters of the As(III), Co(II), Ni(II), and Zn(II) complexes with ALP at pH 6.5. The proposed methods have been successfully applied to the assay of ALP in tablets and the results were statistically evaluated.     

Unraveling the Role of Monovalent Halides in Mixed‐Halide Organic–Inorganic Perovskites

The performance of perovskite solar cells is strongly influenced by the composition and microstructure of the perovskite. A recent approach to improve the power conversion efficiencies utilized mixed‐halide perovskites, but the halide ions and their roles were not directly studied. Unraveling their precise location in the perovskite layer is of paramount importance. Here, we investigated four different perovskites by using X‐ray photoelectron spectroscopy, and found that among the three studied mixed‐halide perovskites, CH₃NH₃Pb(I_0.74Br_0.26)₃ and CH₃NH₃PbBr_3?xCl_x show peaks that unambiguously demonstrate the presence of iodide and bromide in the former, and bromide and chloride in the latter. The CH₃NH₃PbI_3?xCl_x perovskite shows anomalous behavior, the iodide content far outweighs that of the chloride; a small proportion of chloride, in all likelihood, resides deep within the TiO₂/absorber layer. Our study reveals that there are many distinguishable structural differences between these perovskites, and that these directly impact the photovoltaic performances.