Scalable Lead Acetate-Based Perovskite Thin Films Prepared via Controlled Nucleation and Growth under Near Ambient Conditions.

Lead acetate (PbAc2) is a promising precursor salt for large-scale production of perovskite solar cells, as its high solubility in polar solvents enables the use of scalable deposition methods such as inkjet printing and dip coating. In this study, uniform (40-230 nm) PbAc2 thin films were prepared via dip coating under near ambient lab conditions by tuning the PbAc2 precursor concentration. In a second step, these PbAc2 films were converted to methylammonium lead iodide (MAPI) perovskite by immersing them into methylammonium iodide (MAI) solutions. The nucleation and growth processes at play were controlled by altering key parameters, such as air humidity during the lead acetate deposition and MAI concentration when converting the PbAc2 film to MAPI. The research revealed that lead acetate is sensitive toward humidity and can undergo hydroxylation reactions affecting the reproducibility and quality of the produced solar cells. However, drying the PbAc2 films under low relative humidity (<1%) prior to conversion enables the production of high-quality MAPI films without the need of glovebox processing. Furthermore, SEM characterization revealed that the surface coverage of the MAPI film increased significantly with an increase of the MAI concentration at the conversion stage. The resulting morphology of the MAPI films can be explained by a standard nucleation and growth mechanism. Preliminary solar cells were produced using these MAPI films as the active layer. The best performing devices were obtained with a 140 nm thick lead acetate film converted to MAPI using a 12 mg/mL MAI solution, as these parameters resulted in a good surface coverage of the MAPI film. The results show that the methodology holds potential toward large-scale production of perovskite solar cells under near ambient conditions, which substantially simplifies the fabrication and lowers the production costs.

In Situ Synthesis of Crystalline MoS2@ZIF-67 Nanocomposite for the Efficient Removal of Methyl Orange Dye from Aqueous Media.

The zeolitic imidazolate framework-67 (ZIF-67) adsorbent and its composites are known to effectively remove organic dyes from aqueous environments. Here, we report a unique crystalline MoS2@ZIF-67 nanocomposite adsorbent for the efficient removal of methyl orange (MO) dye from an aqueous medium. In situ synthetic techniques were used to fabricate a well-crystalline MoS2@ZIF-67 nanocomposite, which was then discovered to be a superior adsorbent to its constituents. The successful synthesis of the nanocomposite was confirmed using XRD, EDX, FTIR, and SEM. The MoS2@ZIF-67 nanocomposite exhibited faster adsorption kinetics and higher dye removal efficiency compared with its constituents. The adsorption kinetic data matched well with the pseudo-second-order model, which signifies that the MO adsorption on the nanocomposite is a chemically driven process. The Langmuir model successfully illustrated the MO dye adsorption on the nanocomposite through comparing the real data with adsorption isotherm models. However, it appears that the Freundlich adsorption isotherm model was also in competition with the Langmuir model. According to the acquired thermodynamics parameters, the adsorption of MO on the MoS2@ZIF-67 nanocomposite surface was determined to be spontaneous and exothermic. The findings of this research open an avenue for using the MoS2@ZIF-67 nanocomposite to efficiently remove organic dyes from wastewater efflux.

Improving Convergence Speed of Bat Algorithm Using Multiple Pulse Emissions along Multiple Directions.

Metaheuristic algorithms are effectively used in searching some optical solution space. for optical solution. It is basically the type of local search generalization that can provide useful solutions for issues related to optimization. Several benefits are associated with this type of algorithms due to that such algorithms can be better to solve many issues in an effective way. To provide fast and accurate solutions to huge range of complex issues is one main benefit metaheuristic algorithms. Some metaheuristic algorithms are effectively used to classify the problems and BAT Algorithm (BA) is one of them is more popular in use to sort out issues related to optimization of theoretical and realistic. Sometimes BA fails to find global optima and gets stuck in local optima because of the absence of investigation and manipulation. We have improved the BA to boost its local searching ability and diminish the premature problem. An improved equation of search with more necessary information through the search is set for the generation of the solution. Test set of benchmark functions are utilized to verify the proposed method's performance. The results of simulation showed that proposed methods are best optimal solution as compare to others.

Investigation of Well-Defined Pinholes in TiO2 Electron Selective Layers Used in Planar Heterojunction Perovskite Solar Cells.

The recently introduced perovskite solar cell (PSC) technology is a promising candidate for providing low-cost energy for future demands. However, one major concern with the technology can be traced back to morphological defects in the electron selective layer (ESL), which deteriorates the solar cell performance. Pinholes in the ESL may lead to an increased surface recombination rate for holes, if the perovskite absorber layer is in contact with the fluorine-doped tin oxide (FTO) substrate via the pinholes. In this work, we used sol-gel-derived mesoporous TiO2 thin films prepared by block co-polymer templating in combination with dip coating as a model system for investigating the effect of ESL pinholes on the photovoltaic performance of planar heterojunction PSCs. We studied TiO2 films with different porosities and film thicknesses, and observed that the induced pinholes only had a minor impact on the device performance. This suggests that having narrow pinholes with a diameter of about 10 nm in the ESL is in fact not detrimental for the device performance and can even, to some extent improve their performance. A probable reason for this is that the narrow pores in the ordered structure do not allow the perovskite crystals to form interconnected pathways to the underlying FTO substrate. However, for ultrathin (~20 nm) porous layers, an incomplete ESL surface coverage of the FTO layer will further deteriorate the device performance.

Impact of Film Thickness of Ultrathin Dip-Coated Compact TiO2 Layers on the Performance of Mesoscopic Perovskite Solar Cells.

Uniform and pinhole-free electron-selective TiO2 layers are of utmost importance for efficient perovskite solar cells. Here we used a scalable and low-cost dip-coating method to prepare uniform and ultrathin (5-50 nm) compact TiO2 films on fluorine-doped tin oxide (FTO) glass substrates. The thickness of the film was tuned by changing the TiCl4 precursor concentration. The formed TiO2 follows the texture of the underlying FTO substrates, but at higher TiCl4 concentrations, the surface roughness is substantially decreased. This change occurs at a film thickness close to 20-30 nm. A similar TiCl4 concentration is needed to produce crystalline TiO2 films. Furthermore, below this film thickness, the underlying FTO might be exposed resulting in pinholes in the compact TiO2 layer. When integrated into mesoscopic perovskite solar cells there appears to be a similar critical compact TiO2 layer thickness above which the devices perform more optimally. The power conversion efficiency was improved by more than 50% (from 5.5% to ∼8.6%) when inserting a compact TiO2 layer. Devices without or with very thin compact TiO2 layers display J-V curves with an "s-shaped" feature in the negative voltage range, which could be attributed to immobilized negative ions at the electron-extracting interface. A strong correlation between the magnitude of the s-shaped feature and the exposed FTO seen in the X-ray photoelectron spectroscopy measurements indicates that the s-shape is related to pinholes in the compact TiO2 layer when it is too thin.