Enhancement of output performance of Cu2ZnSnS4 thin film solar cells—A numerical simulation approach and comparison to experiments

The formation of stable, low resistance and nonrectifying contacts to Cu₂ZnSnS₄ (CZTS) thin film photovoltaic material are the major and critical challenges associated with its effect over the output performance of fabricated solar cells. The solution of continuity equation in one dimension for a soda lime glass substrates (SLG) |Mo | CZTS | CdS | ZnO:Al cell structure is considered in the simulation of its current–voltage characteristics that is governed by the back contact material, acceptor concentration as well as thickness of the CZTS layer. Our primary simulation shows a 6.44% efficiency of the CZTS solar cell which is comparable to reported experimental data if these parameters are not optimized. However, by optimizing them a simulated conversion efficiency as high as 13.41% (V_oc=1.002 V, J_sc=19.31 mA/cm², fill factor (FF)=69.35%) could be achievable. The solar cell with a back contact metal work function of 5.5 eV, an absorber layer's thickness of 2.68 μm and an acceptor concentration of 5×10¹⁶ cm⁻³ were optimum. The presented optimization is ideal and subject to experimental verification with a precise control of the process parameters along with reduced surface as well as bulk recombination, secondary phases and thermalization losses.     

Enhanced magneto-optic activity of magnetite-based ferrofluids subjected to gamma irradiation

We report here the effect of γ-irradiation on the particle size and size distribution dependent spectroscopic and magneto-optic properties of ferrofluids, synthesized by a co-precipitation method. The X-ray diffraction (XRD) study exhibits magnetite (Fe₃O₄) phase of the particles while electron microscopic and dynamic light scattering (DLS) studies have predicted particle growth upon γ-irradiation. Further, Fourier transform infrared (FT-IR) spectroscopy studies ensured that no dissociation has occurred due to irradiation effect. As a consequence of magneto-optic behavior reflected in the Faraday rotation (FR) measurement, the Verdet constant increased from a value of 0.64×10⁻² for the pristine sample to 5.6×10⁻² deg/Gauss-cm for the sample irradiated with the highest dose (2.635 kGy). The substantial enhancement in the FR is assigned to the improvement in associated chaining effect owing to adequate particle growth where an increased stoichiometry variation of Fe²⁺/Fe³⁺ is assured.     

Structure and coordination in mono and dinuclear Zn(II)-pyrrolidine dithiocarbamate complexes

The structures of the chelate Zn(PDTC)₂ and its dimeric form Zn₂(PDTC)₄ are investigated theoretically at B3LYP/cc-pVDZ level. The natural bond orbital (NBO) analysis has been performed to explore the metal–ligand coordination of these chelates. In Zn(PDTC)₂, the sulfur atoms mainly use 3p sub-shells to coordinate with mixed (4s + 4p _x  + 4p _y  + 4p _z ) orbital of zinc having sp ³ hybridization. In Zn₂(PDTC)₄, each zinc atom coordinates with one terminal and two bridging PDTC ligands. The contribution of bridging sulfur atoms in chelation is much more than terminal sulfurs. The bridging sulfur atoms use 3s and 3p sub-shells to coordinate with 4s and 4p sub-shells of metal center zinc. The charge transfer interactions between sulfur and metal center involving 4d, 5s, and 5p sub-shells of zinc are much feeble compared to those involving 4s and 4p sub-shells of zinc.     

Offline estimation of decay time for an optical cavity with a low pass filter cavity model

This Letter presents offline estimation results for the decay-time constant for an experimental Fabry-Perot optical cavity for cavity ring-down spectroscopy (CRDS). The cavity dynamics are modeled in terms of a low pass filter (LPF) with unity DC gain. This model is used by an extended Kalman filter (EKF) along with the recorded light intensity at the output of the cavity in order to estimate the decay-time constant. The estimation results using the LPF cavity model are compared to those obtained using the quadrature model for the cavity presented in previous work by Kallapur et?al. The estimation process derived using the LPF model comprises two states as opposed to three states in the quadrature model. When considering the EKF, this means propagating two states and a (2×2) covariance matrix using the LPF model, as opposed to propagating three states and a (3×3) covariance matrix using the quadrature model. This gives the former model a computational advantage over the latter and leads to faster execution times for the corresponding EKF. It is shown in this Letter that the LPF model for the cavity with two filter states is computationally more efficient, converges faster, and is hence a more suitable method than the three-state quadrature model presented in previous work for real-time estimation of the decay-time constant for the cavity.     

Asymptotic expansions for the coupled wavenumbers in an infinite orthotropic flexible fluid-filled cylindrical shell

Analytical expressions are found for the coupled wavenumbers in flexible, fluid-filled, circular cylindrical orthotropic shells using the asymptotic methods. These expressions are valid for arbitrary circumferential orders. The Donnell-Mushtari shell theory is used to model the shell and the effect of the fluid is introduced through the fluid-loading parameter μ. The orthotropic problem is posed as a perturbation on the corresponding isotropic problem by defining a suitable orthotropy parameter ε, which is a measure of the degree of orthotropy. For the first study, an isotropic shell is considered (by setting ε=0) and expansions are found for the coupled wavenumbers using a regular perturbation approach. In the second study, asymptotic expansions are found for the coupled wavenumbers in the limit of small orthotropy (ε?1). For each study, isotropy and orthotropy, expansions are found for small and large values of the fluid-loading parameter μ. All the asymptotic solutions are compared with numerical solutions to the coupled dispersion relation and the match is seen to be good. The differences between the isotropic and orthotropic solutions are discussed. The main contribution of this work lies in extending the existing literature beyond in vacuo studies to the case of fluid-filled shells (isotropic and orthotropic).     

A two component thermoreversible hydrogel of riboflavin and melamine: Enhancement of photoluminescence in the gel form

A new thermoreversible hydrogel of riboflavin and melamine supramolecular complex (> or =0.02%, w/v) shows enhanced photoluminescence properties through H-bonding.     

Experimental investigation of fluid drop spreading on heterogeneous and anisotropic porous media

Study of spreading phenomena on porous substrates is important from theoretical as well as applications point of view. An example of such applications is composite processing, where operations involve displacement of air/volatiles by polymeric fluids through porous media composed of fibers. In this work, dynamics of drop spreading was investigated on fibrous porous substrates used in composite processing. These porous media are heterogeneous and anisotropic. Spreading front of silicon oil drops was tracked on borosilicate glass, quartz, and two different kinds of glass fiber mats: woven fabric and unidirectional. For the woven fabric, spreading front was observed to progress in steps of increasing and decreasing rate. For the unidirectional mat, the spreading front progressed with decreasing rate. The dynamics of spreading were fitted to power law in order to compare results with other porous substrates.     

Chemistry of andrographolide: formation of novel di-spiropyrrolidino and di-spiropyrrolizidino-oxindole adducts via one-pot three-component [3+2] azomethine ylide cycloaddition

A facile synthesis of novel di-spiro compounds has been achieved via 1,3-dipolar cycloaddition of azomethine ylides generated in situ from isatin derivatives and sarcosine to the conjugated double bond of andrographolide. When the amino acid was changed from sarcosine to l-proline, the product formation took a different course as determined by 2D NMR and X-ray crystallographic analysis.     

Microwave enhanced ligand- and base-free cross-coupling of potassium aryltrifluoroborates salts with aryl triflates

A microwave enhanced ligand- and base-free protocol for the cross-coupling of potassium aryltrifluoroborate salts with triflates is reported.