Metal Cations in Efficient Perovskite Solar Cells: Progress and Perspective

Metal halide perovskite solar cells (PVSCs) have revolutionized photovoltaics since the first prototype in 2009, and up to now the highest efficiency has soared to 24.2%, which is on par with commercial thin film cells and not far from monocrystalline silicon solar cells. Optimizing device performance and improving stability have always been the research highlight of PVSCs. Metal cations are introduced into perovskites to further optimize the quality, and this strategy is showing a vigorous development trend. Here, the progress of research into metal cations for PVSCs is discussed by focusing on the position of the cations in perovskites, the modulation of the film quality, and the influence on the photovoltaic performance. Metal cations are considered in the order of alkali cations, alkaline earth cations, then metal cations in the ds and d regions, and ultimately trivalent cations (p‐ and f‐block metal cations) according to the periodic table of elements. Finally, this work is summarized and some relevant issues are discussed.     

Flexural and Split Cylinder Strengths of HSC at Elevated Temperatures

This paper investigates the effect of elevated temperature on the flexural strength (FS) and split cylinder strength (SCS) of high strength concrete (HSC). Four concrete mixes of 50, 90, 110, and 130 MPa grade were prepared and subjected to elevated temperature exposure of 200°C and 400°C, and cooled under slow and quick cooling conditions. In addition, 130 MPa grade concrete specimens were also subjected to 100°C and 600°C exposure temperatures to compare FS and SCS under elevated temperatures. It was observed that with the increase in the elevated temperature, the FS and SCS experienced significant losses. The loss was found to be higher for richer concretes. FS was observed to experience a sharp loss at low temperatures that became gradual later at high temperatures. SCS, however, experienced a gradual loss, though sharper than FS, with the increase in temperature. The results indicated that cooling had a significant effect on the residual values and quick cooling caused greater loss in FS and SCS, than slow cooling at elevated temperatures. The quick cooling was noted to produce maximum loss over slow cooling at temperatures around 400°C.     

Performance evaluation/analysis of Pakistan Research Reactor-1 (PARR-1) current core configuration

Neutronic and thermal hydraulic analyses have been carried out for current core of Pakistan Research Reactor-1 (PARR-1). Comparison was made between calculated and measured key neutronic parameters. Reactor core parameters important for reactor operation and safety have been calculated. Calculated neutronic parameters include: excess reactivity, shut down margin, control rod worth, peak power density location, criticality position, peaking factors, neutron flux in fuel elements and neutron flux at irradiation sites in the core. Calculated thermal hydraulic parameters include: steady-state temperatures and peak temperatures at fuel centerline, clad surface and in water coolant. In order to determine safety margins, heat fluxes at Onset of Nucleate Boiling (ONB), Onset of Flow Instability (OFI) and Departure from Nucleate Boiling (DNB) were determined using standard correlations. After assembling the core, performance of the core was also evaluated by experimentation. The core was assembled and some of the core parameters namely: excess reactivity, shut down margin, control rod worth and flux profile at in-core irradiation sites have been measured. On comparison with experimental data, reasonable agreement has been found between the calculated and the measured parameters.     

Radiation and cryogenic test results with a monolithic GaAs preamplifier in C-HFET technology

We report test results with a monolithic GaAs preamplifier fabricated in industrial C-HFET technology irradiated with a total dose of 10¹⁴ neutrons/cm² and 100 Mrad γ radiation and operated under cryogenic conditions. The measured gate current of the input transistor of a few nA increases by < 10% after irradiation. For a 330 μm input FET width, the equivalent noise charge (ENC) is typically 145 electrons per pF total input capacitance at a shaping time of 25 ns (bipolar) before irradiation and changes approximately by 10% after irradiation. Under cryogenic operation the corresponding input referred noise decreases by roughly a factor of two.     

Impact of Distribution Type in Bayes Probability Flood Forecasting

Bayesian forecasting system (BFS) is widely applied to the hydrological forecast. Hydrological forecast processor (HUP), a key part of the Bayesian probability prediction, is conducted at the assumption that the rainfall is certain, which can simultaneously quantify the uncertainty of hydrological model and parameter. In the HUP, the runoff is usually assumed to obey Logweibull distribution or Normal distribution. However, Distribution type of the runoff is not certain at different areas, and there are few distribution types of HUP in existence. So common distribution types are needed to develop the HUP to provide an effective forecast result. In this paper, Nonparametric kernel density estimation, Pearson III and Empirical distribution were introduced as the prior distribution of HUP to eliminate the parameter uncertainty of probability density function. Also, the five distributions were compared in this study to get the diversity of distribution types and search the best appropriate distribution type. The 52 floods during 2004a-2014a of ZheXi basin are employed to calibrate and validate the different distribution types of BFS. The results show that the LogWeibull and Empirical Bayesian probabilistic model has the best performance on average results compared with the other four distribution models. Meanwhile the other distribution types proposed in this study have the similar ability on interval width and the containing rate of probability forecasting results. This demonstrates that more new distributions are required to make BFS more robust.     

Time-dependent reliability prediction using transfer learning

Structural and Multidisciplinary Optimization - One of the key challenges in reliability estimation is the acquisition of failure information especially under real-life scenarios or computationally...     

Grain Boundary Shortening in CuTl-1234 Superconductor by the Addition of ZnO Nanoparticles

The superconducting properties of Cu_0.5Tl_0.5 Ba₂Ca₃Cu₄O_12?x are studied after the inclusion of ZnO nanoparticles. The ZnO nanoparticles prepared by a sol-gel method were incorporated during the second stage of the synthesis of Cu_0.5Tl_0.5Ba₂Ca₃Cu₄O_12?x phase in y =?0, 3.0, 5.0, and 7.0 wt%. It is observed that the structure, the morphology, and the superconductivity properties are greatly influenced by the inclusion of ZnO nanoparticles. The lattice parameters of the orthorhombic phase of Cu_0.5Tl_0.5Ba₂Ca₃Cu₄O_12?x superconductor are decreased with the increase of x. Similarly, the grain morphology has been changed from needle-like to spherical grains. One of the major benefits of the inclusion of ZnO nanoparticles is the increase in critical temperature, critical magnetic fields, and critical current density as observed from the theoretical calculations of fluctuation-induced conductivity analysis.     

Nanoplastic removal function and the mechanical nature of colloidal silica slurry polishing

The nanomechanical deformations on a broad range of optical material surfaces (single crystals of Al₂O₃ [sapphire], SiC, Y₃Al₅O₁₂ [YAG], CaF₂, and LiB₃O₅ [LBO]; a SiO₂–Al₂O₃–P₂O₅–Li₂O glass-ceramics [Zerodur]; and glasses of SiO₂:TiO₂ [ULE], SiO₂ [fused silica], and P₂O₅–Al₂O₃–K₂O–BaO [Phosphate]) near the elastic-plastic load boundary have been measured by nanoindentation and nanoscratching to mimic the nanoplastic removal caused by a single slurry particle during polishing. Nanoindenation in air was performed to determine the workpiece hardness at various loads using a commercial nanoindenter with a Berkovich tip. Similarly, an atomic force microscope (AFM) with a stiff diamond coated tip (150 nm radius) was used to produce nanoplastic scratches in air and aqueous environments over a range of applied loads (~20-170 μN). The resulting nanoplastic deformation of the nanoscratches were used to calculate the removal function (i.e., depth per pass) which ranged from 0.18 to 3.6 nm per pass for these materials. A linear correlation between the nanoplastic removal function and the polishing rate (using a fixed polishing process with colloidal silica slurry on a polyurethane pad) of these materials was observed implying that: (a) the polishing mechanism using colloidal silica slurry can be dominated by mechanical rather than chemical interactions; and (b) the nanoplastic removal function, as opposed to interface particle interactions, is the controlling factor for the polishing material removal rate. Furthermore, this correlation is consistent with the Ensemble Hertzian Multi-Gap (EHMG) microscopic material removal rate model described previously. The nanoplastic removal depth was also found to correlate to the measured nanoindentation hardness (H₁) of the optical material, scaling as H₁^−3.5. Two-dimensional (2D) finite element analysis simulations of nanoindentation showed a similar nonlinear dependence of plastic deformation with the workpiece material hardness. The findings of this study are used to determine an effective Preston coefficient for the material removal rate expression and enhance the predictive nature of the nanoplastic polishing rate for various materials utilizing their material properties.