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Fundamental studies are needed to advance our understanding of selective adsorption in aqueous environments and develop more effective sorbents and filters for water treatment. Vapor-phase grafting of functional silanes is an effective method to prepare well-defined surfaces to study selective adsorption. In this investigation, we perform vapor phase grafting of five different silane compounds on aluminum oxide (Al2O3) surfaces prepared by atomic layer deposition. These silane compounds have the general formula L3Si–C3H6–X where the ligand, L, controls the reactivity with the hydroxylated Al2O3 surface and the functional moiety, X, dictates the surface properties of the grafted layer. We study the grafting process using in situ Fourier transform infrared spectroscopy and ex situ x-ray photoelectron spectroscopy measurements, and we characterize the surfaces using scanning electron microscopy, atomic force microscopy, and water contact angle measurements. We found that the structure and density of grafted aminosilanes are influenced by their chemical reactivity and steric constraints around the silicon atom as well as by the nature of the anchoring functional groups. Methyl substituted aminosilanes yielded more hydrophobic surfaces with a higher surface density at higher grafting temperatures. Thiol and nitrile terminated silanes were also studied and compared to the aminosilane terminated surfaces. Uniform monolayer coatings were observed for ethoxy-based silanes, but chlorosilanes exhibited nonuniform coatings as verified by atomic force microscopy measurements.
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A novel electrochemical dopamine sensor was fabricated based on a composite film solely consisting of kappa-carrageenan and hierarchical porous carbon drop-casted onto a glassy carbon electrode in a conventional three electrode system. Graphene oxide was synthesized in a one-step thermal conversion from base-catalyzed alkali lignin. Five ratios by mass of a novel hierarchical porous activated carbon and kappa-carrageenan were studied for dopamine quantification without synthetic binders such as polytetrafluoroethylene. Various tests were performed to explicate structure and electrochemical properties of the films. Utilizing differential pulse voltammetry for detection, the optimized 10:1 ratio system elicited a linear range of 1–250
μ mol l−1and a limit of detection of 0.14μ mol l−1(S/N = 3). Results suggested an effective new combination of materials for non-enzymatic dopamine sensing. -
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Perovskite solar cells (PSCs) have received considerable attention in recent years due to their low processing cost and high‐power conversion efficiency. However, the mechanisms of PSCs are not fully understood. A model based on a probabilistic and statistical approach needs to be developed to simulate, optimize, and predict the photovoltaic (PV) performance of PSC. Herein, the 3D model based on the kinetic Monte Carlo (KMC) approach is developed to simulate 3D morphology of perovskite‐based solar cells and predict their PV performances and charge dynamics. The developed 3D model incorporates the temporal and physical behavior of perovskites, such as charge generation, transport, and recombination. The KMC simulation results show that pin holes‐free perovskite films with a homogenous 400 nm thick perovskite capping layer achieve the highest power conversion efficiency of 20.85%. However, the shortest apparent charge transport time (
τ t) and the longest apparent charge carrier recombination lifetime (τ r) are found for the champion device. PV performance from the fabricated device is used to validate this simulation model. This model can provide a significant conceptual advance in identifying bottlenecks and guiding novel device designs to further improve the performance of perovskite PVs. -
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Development of high‐performance wide‐bandgap perovskites is a key component to enable tandem solar cells with either a silicon or low‐bandgap perovskites. However, the presence of defects in the Br‐rich wide‐bandgap perovskites, especially in the grain boundaries (GBs) has been particularly challenging and limits its performance. Herein, to accomplish the passivation of these defects, a combination of cation management with rubidium (Rb) introduction into the triple cation combination of cesium/formamidinium/methylammonium (CsFAMA) is exercised. Passivation is further enhanced by secondary growth (SG) using guanidinium iodide. In‐depth assessments of GB defect passivation are performed using Kelvin probe force microscopy (KPFM) and nanoscale charge‐carrier dynamics mappings provide insightful details on the presence of GBs defects and their suppression by the cation management and SG techniques. Reduction of unreacted PbX2to realize a highly crystalline perovskite surface is achieved after incorporating Rb and SG treatment. As a result, a champion cell for 1.78 eV (FA0.79MA0.16Cs0.05)0.95Rb0.05Pb(I0.6Br0.4)3wide‐bandgap perovskite with an efficiency of 17.71% along with enhancement in all photovoltaic parameters is achieved. This study introduces a new way to analyze GB defects and reveals the consequence of defect passivation on charge‐carrier dynamics for realizing efficient perovskites.
