ABSTRACT
It is critical to prepare smooth and dense perovskite films for the fabrication of high efficiency perovskite solar cells. However, solution casting process often results in films with pinhole formation and incomplete surface coverage. Herein, we demonstrate a fast and efficient vacuum deposition method to optimize the surface morphology of solution-based perovskite films. The obtained planar devices exhibit an average power conversion efficiency (PCE) of 13.42% with a standard deviation of ±2.15% and best efficiency of 15.57%. Furthermore, the devices also show excellent stability of over 30 days with a slight degradation <9% when stored under ambient conditions. We also investigated the effect of vacuum deposition thickness on the electron transportation and overall performance of the devices. This work provides a versatile approach to prepare high-quality perovskite films and paves a way for high-performance and stable perovskite photovoltaic devices.
ABSTRACT
The objectives of this study are to investigate the possible occurrence status of formamide in the intercalation system, the founction of water and the molecular configurations and orientations of formamide inserted into the interlayer of kaolinite, by washing the products with acetone to eliminate the interferences due to the outersurface absorbed formamide molecules in FTIR spectrometry. The results show that the intercalated, absorbed and free formamide probably exist in the intercalation system. Free formamide is easily to be eliminated selectively by drying, whereas the absorbed formamide is removed only by washing with the proper eluting reagent. H2O also is inserted into the interlayer during the formamide molecules' intercalation, which is deintercalated after the compounds being dried. Intercalation caused blue shifts of the inner surface OH stretching bands from 3 687 to 3 692 cm(-1), and deforming bands from 911 to 906 cm(-1), the bands at 3 651 cm(-1) disappeared with a new band appearing at 3 539 cm(-1). The frequency of the Si-O bands of kaolinite was slightly shifted. These IR bands changes implied the breaking of the H-bonds between layers of kaolinite, and the formation of new H-bonds between the kaolinite and the inserting formamide molecules in the intercalation compounds. The formamide molecules intercalated were oriented with the C-N bond perpendicular or nearly perpendicular to the (001) surface of the kaolininte and formed 2 types of H-bonding with inner-surface hydroxyls and siloxane layer of the kaolinite respectively through NH2. A novel model was provided to analyse the microstructure of kaolinite-formamide intercalation compounds. The results show that computation data is in good agreement with experimental data.
ABSTRACT
The processes of extraction and insertion of lithium ions in LiCoO(2) cathode are investigated by galvanostatic cycling and electrochemical impedance spectroscopy (EIS) at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The spectra exhibit three semicircles and a slightly inclined line that appear successively as the frequency decreases. An appropriate equivalent circuit is proposed to fit the experimental EIS data. Based on detailed analysis of the change in kinetic parameters obtained from simulating the experimental EIS data as functions of potential and temperature, the high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step, respectively. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiCoO(2) changes dramatically at early delithiation as a result of a polaron-to-metal transition. In an electrolyte solution of 1 mol L(-1) LiPF(6)-EC (ethylene carbonate) :DMC (dimethyl carbonate), the activation energy of the ion jump (which is related to the migration of the lithium ions through the SEI film), the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are 37.7, 39.1 and 69.0 kJ mol(-1), respectively.
ABSTRACT
Benzamide was intercalated into kaolinite by replacing DMSO pre-intercalated. Pure kaolinite-benzamide intercalation compounds were obtained by washing resulting products with acetone. The analysis of XRD shows that the basal spacing of kaolinite-benzamide intercalation compounds increased to 1.437 nm from 0.717 nm of kaolinite. The analysis of FTIR shows that intercalation caused the shifts of the inner surface OH stretching bands from 3 696 and 3 657 cm(-1) of the raw kaolinite to 3 701 and 3 651 cm(-1) of the kaolinite-benzamide intercalation compounds, respectively, and the blue shift of C=O stretching bands from 1 659 cm(-1) of benzamdie to 1 640 cm(-1) of the kaolinite-benzamide intercalation compounds, and the NH vibrations at 3 368 and 3 172 cm(-1) of benzamdie shifted to 3 474 and 3 184 cm(-1), respectively. These changes in IR bands implied the breaking of the H-bonds between layers of kaolinite and the formation of new H-bonds between the inner-surface hydroxyls of the kaolinite and the benzamide in the intercalation compounds. The experimental results show that the intercalation reaction comes to equilibrium rapidly during 30 min, and the highest intercalation ratio occurs when the reaction temperature is 180 degrees C. Washed by acetone, the residual benzamide and that adsorbed on the surface of the resulting products could be eliminated without significant influence on the structure of the intercalation compounds.
