The key to improve the conversion efficiency of perovskite solar cells lies in the identification and control of different limiting factors. Both intrinsic and extrinsic losses are shown here to be detrimental on conversion efficiency well below the thermodynamic limit. The effect of varying radiative and Auger recombination processes as inevitable intrinsic losses on device performance is shown in this work. The extrinsic losses are shown to impose severe bounds on efficiency limits. Such extrinsic losses include realistic material optical properties, finite diffusion length, ideality factor, parasitic resistance, and parasite absorption. Thus, this work presents the roadmap and the possible approaches in achieving performance beyond what is currently demonstrated in the highest efficiency perovskite solar cells. Additionally, the impact of light concentration, important in Auger limited devices is investigated. Finally, the impact of Auger recombination for perovskite with finite diffusion length in a two-terminal perovskite/silicon tandem device is investigated.

AlGaN/GaN heterostructures were grown by metal–organic chemical vapor deposition (MOCVD) on sp2-bonded BN using AlN as a nucleation layer. The best x-ray diffraction rocking curve full-width-at-half-maximums (FWHMs) are 0.13° and 0.17° for the GaN (0002) and ( $10\bar 12$ ) diffraction peaks. Hall-effect measurements show room temperature mobility near 2000 cm/V·s with sheet carrier density of ∼1 × 1013 cm−2, comparable to the best values obtained on sapphire using Fe-doped GaN buffers. The best low temperature mobility of the 2-dimensional electron gas (2DEG) is ∼33,000 cm2/V·s; indicating that the dominant scattering mechanism limiting the transport of 2DEG is interface roughness. Good quality BN grown directly onto sapphire is shown to be effective for reducing parallel conduction that exists due to residual donor impurities in the buffer. Luminescence measurements indicate good optical quality of the GaN/BN/sapphire. The residual strain in the GaN layer is found to be almost completely eliminated when it is released from the substrate.

Laves phase NbCr2-based composites toughened with different volume fractions of Cr phase were fabricated by spark plasma sintering (SPS). The microstructural evolution and mechanical properties of these spark plasma sintered NbCr2/Cr composites were investigated. The mechanical properties evaluations indicate that the introducing of Cr phase consolidated by SPS has a beneficial effect on the mechanical properties of the NbCr2 Laves phase. When the content of Cr phase in the NbCr2 Laves phase increases to 30 wt%, the hardness measured by a Berkovich nanoindenter operated with the continuous stiffness measurements mode attains the maximum value of 13.44 GPa, which is increased by about 56% over the as-cast NbCr2 Laves phase. More importantly, the room-temperature fracture toughness of the NbCr2-30wt%Cr alloy is increased to 18.9 MPa·m1/2, which is 16 times higher than that of the as-cast NbCr2 Laves phase (1.2 MPa·m1/2). The microstructural analysis indicates that the residual of Cr phase and formation of Nb solid solution can provide remarkable toughening of the NbCr2 Laves phase by fine grain toughening, dual ductile phase toughening, and interface toughening mechanisms. A possible formation mechanism of Nb solid solution during SPS has been proposed by considering the composition distribution.

Bulk nanocrystalline (NC) silvers were fabricated by spark plasma sintering process. The effects of sintering temperature on physical and mechanical properties of the NC silvers were investigated. The results indicate that no impurities were introduced into the bulk compacts during the preparation procedure. Both the density and the electrical conductivity of the NC Ag increase with an increase in sintering temperature. However, the micro-hardness and ultimate tensile strength (UTS) of the bulk compacts increase initially and then decrease with increasing sintering temperature. The NC Ag sintered at 500 °C exhibits the highest micro-hardness of 85.3 HV along with the best compression yield strength of 379 MPa and the highest UTS of 534 MPa. The deterioration of the mechanical properties of the NC Ag sintered at 550 °C should be attributed to the rapid grain growth.

This paper presents an atomistic scale model on sintering of nickel particles in direct metal laser sintering process. Both sintering phenomena and mechanical strength of sintered particles are simulated using molecular dynamics method. A two-particle atomistic model is developed to investigate the diffusion of atoms during nickel sintering. The diffusion of particle surface is higher than the particle core, with calculated activation energy of nickel particle diffusion 6.10 kJ/mol in the particle core, and 6.24 kJ/mol on the particle surface, which are reasonably in agreement with the experimental data of 7.89 kJ/mol. The sintered model shows a 5-fold twinning structure at 1200 K, and two parallel twin boundaries at 1300 K. The mechanical properties of nickel nanoparticles sintered at various heating rates are investigated using uniaxial tensile test simulations. The results show that higher heating rate during sintering increases the mechanical strength of the sintered material. Deformation mechanism of sintered structures is illustrated from the correlation between stress and dislocation evolution.

This paper describes the direct-foaming of plaster of Paris (CaSO4·½H2O) with up to 1.7 wt% of a nonionic surface-active agent to obtain highly porous, lightweight gypsum (CaSO4·2H2O) with 65–70% total porosity and a homogeneous, bimodal pore size distribution. Based on viscosity and temperature changes in the setting plaster of Paris slurry, the nonionic surfactant is seen to retard gypsum crystallization and thus extend the working time at higher water to solid ratios. The increase in viscosity during gypsum crystallization stabilizes the macropores formed during foaming. Gypsum foams of 32% density with a submicron matrix pore size, and relatively uniform macropore size of ∼100 µm were obtained. Seeding the process with 0.5 wt% 100 µm diameter gypsum particles accelerates gypsum crystallization in the presence of the nonionic surfactant and results in a more uniform, finer (92 µm) macropore structure due to less time for bubble coalescence.

Visible-light responsive plasmonic Ag2O/Ag/g-C3N4 nanosheets (NS) were successfully prepared by a simple and green photodeposition method. The obtained composites were characterized by XRD, Fourier transform infrared, transmission electron microscopy, UV-vis, and the photoluminescence (PL) results indicated that the Ag2O/Ag/g-C3N4 NS composites showed better photoabsorption performance than g-C3N4 due to the surface plasmon resonance effect of Ag nanoparticles. Meanwhile, the composite exhibited excellent photocatalytic activities, which was ∼3.8 and ∼3.0 times higher than those of bulk g-C3N4 and pure g-C3N4 NS, respectively. Moreover, the as-prepared composites showed a high structural stability in the photodegradation of Rhodamine B. A possible photocatalytic and charge separation mechanism was suggested based on the PL spectra and the active species trapping experiment.

To improve the lower contrast ratio of yellow-white dual color electrophoretic display cell, dispersion polymerization, and miniemulsion polymerization method were used to obtain good performance of Pigment Yellow 110 (PY110) composite particles. Crude PY110 particles and Span80 were suspended into the ethanol by dispersion method to obtain PY110-S, which were subsequently coated with styrene (St) through a mini-emulsion polymerization procedure to acquire PS/PY110-S as an electronic ink material. The modified pigments were characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), UV–vis spectroscopy. Furthermore, the Pigment Red 146 which coated with styrene (St) through a miniemulsion polymerization procedure was doped into the PS/PY110-S. Then, the obtained mixed particles were successfully incorporated in an electrophoretic display cell. And the contrast ratio of yellow-white electrophoretic display cell was significantly improved. The contrast ratio reached 1.58.

Red-emitting (La,Eu)2O2SO4 phosphors have been successfully prepared using the layered hydroxide of (La,Eu)2(OH)4SO4·2H2O as the precursor. The precursor compound was firstly crystallized via hydrothermal reaction (100 °C and pH = 9.0) as well-dispersed nanoplates, followed by dehydration and dehydroxylation in the 400–1200 °C temperature range in ambient air to yield (La,Eu)2O2SO4. The phosphors show intense red emissions originated from the f–f transitions of Eu3+, dominantly peaking at 617 nm, under O–Eu charge transfer excitation at 284 nm. The optimal Eu3+ content was experimentally determined to be 5 at.%, agreeing well with theoretical analysis, and the concentration quenching of luminescence was suggested to be due to exchange interactions. Fluorescence decay analysis indicates that a higher calcination temperature or Eu3+ content would decrease the lifetime of the 617 nm emission.

Carbon nanotube (CNT) reinforced A356 aluminum alloys cast nanocomposites containing lower CNT contents were successfully fabricated where the way of introducing diluted Al–8 wt% CNT master nanocomposite in A356 melts was used. The differential thermal analysis and x-ray diffraction results showed that aluminum carbide phases (Al4C3) were formed before Al melting. The formation of Al4C3 was then proved to improve the wettability of CNTs during Al melting. Effect of CNT addition on microstructure and mechanical properties of CNTs/A356 nanocomposites were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, and universal tensile testing machine. The results showed that CNTs (<0.4 wt%) were well distributed in the CNTs/A356 nanocomposites. CNTs could greatly refine the microstructure of A356 alloy. The mechanical properties of CNTs/A356 nanocomposites were also enhanced by CNT addition. Fractography analysis revealed that CNTs were distributed uniformly throughout the fracture surface.

Herein is described the preparation and characterization of conductive materials for application in energy storage devices, such as fuel cells. The synthetic approach uses commercially available materials and simple experimental procedures to decorate multi-walled carbon nanotubes (MWCNTs) with plain and thiolated gold nanoparticles (Au NPs). The compositional characterization data (x-ray photoelectron spectroscopy) and the electrical conductivity data (cyclic voltammetry (CV) and oxygen reduction reaction (ORR)) for the MWCNT-Au NP composites, both pre- and post-anneal, is reported.

The surface microstructure of shot peened (TiB + TiC)/Ti–6Al–4V is investigated using Rietveld whole pattern fitting method. The domain size and microstrain of them are obtained. By comparing the calculated results between them, it can be found that the microstructure variations of Ti–6Al–4V are more severe than those of (TiB + TiC)/Ti–6Al–4V, which is due to the effect of reinforcements' resistance to the deformation of the surface layer. The distribution of average domain size and microstrain of (TiB + TiC)/Ti–6Al–4V at varying depths are calculated, and the results are discussed in detail. Moreover, the probability distribution of the domain size at different depths is obtained using the lognormal distribution model. Based on the discussion, the results obtained from Rietveld whole pattern fitting method agree with the results calculated using the Voigt method, which reveals that the Rietveld method is an effective method of characterizing the surface microstructure of titanium matrix composites after shot peening treatments.

Zeolite–zeolite composite composed of alumina-rich hierarchically porous ZSM-5 cores and high-silicon MFI shells was prepared by a hydrothermal synthesis procedure, in which a commercial ZSM-5 zeolite with a SiO2/Al2O3 of 36 was treated by an alkaline solution and then used as a supporter for epitaxial growth of a polycrystalline Silicalite-1 zeolite shell (denoted as MMZsa). Acid sites associated with framework Al on exterior surfaces of ZSM-5 zeolite cores are therefore passivated in different degrees by the epitaxial MFI zeolite shell. The structural, crystalline, and textural properties of the as-synthesized samples were characterized by x-ray powder diffraction (XRD), energy-dispersive x-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), N2 adsorption-desorption, in situ IR spectra of pyridine and NH3-TPD. Aluminum species were observed to transfer from the alumina-rich cores to the high-silica shells. The adjustable thickness and SiO2/Al2O3 ratio of the shell offer the as-synthesized composite a potential and high-efficiency catalyst for methanol conversion into gasoline and diesel. As compared with the commercial ZSM-5 zeolite, the composite catalyst exhibits excellent catalytic performances with a longer catalytic life as well as a higher conversion and a slightly higher yield of diesel oil.

Ni-doped ZnO hollow microspheres were fabricated by calcining the mixture of zinc and nickel citrate precursors at 500 °C for 2 h. The structure, composition, Barrett–Emmett–Teller specific surface area, and optical properties of Ni-doped ZnO samples were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, wave length dispersive x-ray fluorescence spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, N2 adsorption–desorption isotherms, and ultraviolet (UV)-visible diffuse reflectance spectroscopy. The photocatalytic results demonstrated that the as-synthesized Ni-doped ZnO microcrystals possessed much higher photocatalytic activity than pure ZnO in the decomposition of methylene blue under UV-light irradiation. The present work suggests that Ni-doped ZnO hollow microspheres can be applied as an efficient photocatalyst for water polluted by some chemically stable azo dyes.

Potassium titanyl phosphate crystals in both x-cut and z-cut were irradiated with 185 MeV Au ions. The morphology of the resulting ion tracks was investigated using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). SAXS measurements indicate the presence of cylindrical ion tracks with abrupt boundaries and a density contrast of 1 ± 0.5% compared to the surrounding matrix, consistent with amorphous tracks. The track radius depends on the crystalline orientation, with 6.0 ± 0.1 nm measured for ion tracks along the x-axis and 6.3 ± 0.1 nm for those along the z-axis. TEM images in both cross-section and plan-view show amorphous ion tracks with radii comparable to those determined from SAXS analysis. The protruding hillocks covering the sample surface detected by AFM are consistent with a lower density of the amorphous material within the ion tracks compared to the surrounding matrix. Simulations using an inelastic thermal-spike model indicate that differences in the thermal conductivity along the z- and x-axis can partially explain the different track radii along these directions.

Zn–Ni alloy coatings were deposited on rolled copper foil via electro-brush plating with different micro-force. Surface morphologies, microhardness, roughness, and bending performance were characterized. Mechanisms and influences of electro–brush plating micro-force on coatings performances were investigated and revealed. With the increase of electro-brush plating micro-force, surface morphologies of coatings become smooth and dense, and the grain size was refined. Microhardness of coatings had a gradually increasing tendency when the increasing amplification was reduced. However, surface roughness of coatings as well as bending performance increased firstly and then decreased. The mechanisms of micro-force generation and action were explained by mechanics theory and principle model. Plastic deformation and work hardening are generated and performances are improved. Consequently, the performance of electro-brush plating coatings has a tight relevance with micro-force.

An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multiwall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes.