A Thienothiophene-Based Cation Treatment Allows Semitransparent Perovskite Solar Cells with Improved Efficiency and Stability

Perovskite surface treatment with additives has been reported to improve charge extraction, stability, and/or surface passivation. In this study, treatment of a 3D perovskite ((FAPbI₃)_1−x(MAPbBr₃)_x) layer with a thienothiophene-based organic cation (TTMAI), synthesized in this work, is investigated. Detailed analyses reveal that a 2D (n = 1) or quasi-2D layer does not form on the PbI₂-rich surface 3D perovskite. TTMAI-treated 3D perovskite solar cells (PSCs) fabricated in this study show improved fill factors, providing an increase in their power conversion efficiencies (PCEs) from 17% to over 20%. It is demonstrated that the enhancement is due to better hole extraction by drift-diffusion simulations. Furthermore, thanks to the hydrophobic nature of the TTMAI, PSC maintains 82% of its initial PCE under 15% humidity for over 380 h (the reference retains 38%). Additionally, semitransparent cells are demonstrated reaching 17.9% PCE with treated 3D perovskite, which is one of the highest reported efficiencies for double cationic 3D perovskites. Moreover, the semitransparent 3D PSC (TTMAI-treated) maintains 87% of its initial efficiency for six weeks (>1000 h) when kept in the dark at room temperature. These results clearly show that this study fills a critical void in perovskite research where highly efficient and stable semitransparent perovskite solar cells are scarce.     

Desiccant films made of low-density polyethylene with dispersed calcium oxide: Water vapor absorption,permeation and mechanical properties

Polymers with dispersed desiccants are relevant for various packaging applications to protect packaged goods from water vapor. The intention of this study was to analyze and to describe a relevant system. Therefore, films with calcium oxide (CaO) were investigated, because such materials are hardly described in scientific literature. Monolayer films with 0.14 to 0.51 g dispersed CaO per 1 g film (PE-LD) were prepared and they absorbed up to 0.2 g water vapor per 1 g of film. The water vapor absorption was described by effective diffusion coefficients. By the use of effective diffusion coefficients and the absorption capacity, the absorption behavior of layers with various thicknesses can be estimated. The steady state (effective) water vapor permeation coefficients of the films with dispersed CaO were a factor of 2 to 24 (8.4 to 101.5 mg cm [cm² s Pa]^–1 × 10¹², at 23 °C) higher than for pure PE-LD films (4.26 mg cm [cm² s Pa]⁻¹ × 10¹², 23 °C). The tensile stress changed only slightly (pure PE-LD: 9.5 N mm⁻²; PE-LD with 0.14 g dispersed CaO per 1 g film: 8.1 N mm⁻²; PE-LD with 0.51 g dispersed CaO per 1 g film: 10.5 N mm⁻²), while the tensile strain at break was reduced with higher CaO concentration from 318% (pure PE-LD) to 10% (PE-LD with 0.51 g dispersed CaO per 1 g film). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47460.     

An evaluation of the electrochemical frequency modulation (EFM) technique

The EFM technique has been used to calculate anodic and cathodic Tafel slopes as well as corrosion current densities for the systems Cu/NaCl, Al 5083/NaCl, stainless steel/NaCl and mild steel in H₂SO₄ and NaCl. These values have been compared with those obtained from the analysis of polarization curves determined in the vicinity of the corrosion potential. In addition, polarization resistance values calculated based on the analysis of EFM data have been compared with values obtained from analysis of impedance data collected for the same systems. In most cases the corrosion rates determined with the EFM technique were much higher than the values determined with the other two techniques. This result is mainly due to the fact that for systems with low corrosion rates the modulation frequencies that are used in the EFM technique are in the capacitive region of the impedance spectra. Good agreement of corrosion rates obtained with the EFM and the polarization techniques was only observed for the mild steel/H₂SO₄ system that has very high corrosion rates. Analysis of EFM data assuming charge transfer or diffusion control produced different Tafel slopes and corrosion rates, but the same polarization resistance (R_p) values. When the EFM technique was applied to a resistor, the calculated R_p value equaled the value of the resistance which is further proof that the EFM technique measures the impedance of a corroding system in a narrow frequency band. The difference to the traditional EIS technique is that the amplitude of the ac signal can be different at different frequencies.     

Determination of the minimum sampling frequency in bandpass sampling by geometric approach and geometric programming

This paper presents a simple and fast approach to find a minimum sampling frequency for multi-band signals. Instead of neighbor and boundary conditions, constraints on the sampling frequency were derived by using the geometric approach to the bandpass sampling theorem. Reformulation of the constraints on the minimum sampling frequency enabled to represent the problem as an optimization problem which was structured by the geometric programming and mixed-integer nonlinear programming methods. The convex optimization problem was then solved by the proposed algorithm applying interior point approach in the line search framework. It was demonstrated that this unified structure directly linked the geometric approach of the bandpass sampling theorem to the optimization problem. The proposed method was verified through numerical simulations in terms of the minimum sampling frequency and the computational efficiency. Results illustrated the feasibility of the geometric approach and the proposed algorithm in the determination of the minimum sampling frequency by providing the savings in the number of iterations and the decrease in the valid minimum sampling frequency.     

Fabrication,characterization, and performance of YbDSB ternary compounds for IT‐SOFC applications

(Yb₂O₃)_x(Dy₂O₃)_y(Bi₂O₃)_1?x?y (0.04≤x+y≤0.20) powders (xYbyDSB) were synthesized by modified sol‐gel Pecchini method. The powders were characterized for structural, surface morphological, thermal, and electrical properties and power density measurements by means of X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis/thermal gravimetry (DTA/TG), and impedance spectroscopy, respectively. Lattice parameters and crystalline size of δ‐phase of Yb₂O₃‐ and Dy₂O₃‐doped Bi₂O₃ samples were calculated from the X‐ray diffraction data. Surface and grain properties of the related phases were determined by SEM analysis. In the investigated system, the maximum electrical conductivity was observed as σ=0.954 S cm^?1 for 6% mol Yb₂O₃ and 6% mol Dy₂O₃ at 800°C among all δ‐YbDSB systems. Cathode supported electrochemical cell was fabricated and 6Yb6DSB was used as the electrolyte. Maximum power density of single cell with an active area of 1.5 cm² is 72.50 mW/cm² at 700°C.     

A Huffman compression based text steganography method

In this study, capacity and security issues of text steganography have been considered by proposing a compression based approach. Because of using textual data in steganography, firstly, the employed data compression algorithm has to be lossless. Accordingly, Huffmann coding has been chosen due to its frequent use in the literature and significant compression ratio. Besides, the proposed method constructs and uses stego-keys in order to increase security. Secret information has been hidden in the chosen text from the previously constructed text base that consists of naturally generated texts. Email has been chosen as communication channel between the two parties, so the stego cover has been arranged as a forward mail platform. As the result of performed experiments, average capacity has been computed as 7.962 % for the secret message with 300 characters (or 300?8 bits). Finally, comparison of the proposed method with the other contemporary methods in the literature has been carried out in Section 5.     

Isoamylacetate production by entrapped and covalently bound Candida rugosa and porcine pancreatic lipases

Candida rugosa lipase (CRL) and porcine pancreatic lipase (PPL) were immobilised by entrapping and also by covalent binding for use in synthesis of isoamyl acetate (IAAc), which has a typical banana flavour. Lipase entrapment was carried out by dripping sodium alginate (Na-Alg)-chitosan (Chi)-lipase mixture into CaCl₂-glutaraldehyde (GAL) solution to obtain Ca-Alg/Chi_CRL/PPL. Immobilisation conditions were optimised as 1.5% Na-Alg, 1.5% chitosan and 0.15% GAL. Ca-Alg/Chi_CRL/PPL samples showed the highest activity when they were dried upon reaching 27% of their initial weights. Covalent binding was achived with Chi modified with spacerarm via glutaraldehyde to get Chi_CRL/PPL. The highest IAAc production was observed when 1,3-diaminopropane was used as a spacer arm. The best ester yield was achieved in heptane, at 40 and 45 °C reaction temperatures, 50 mM IAA and 50 or 75 mM AA concentrations. The amount of IAAc was nearly 10 times higher for the batch type than for the continuous packed bed column reactor.