Papers by Keyword: Porous Si

Abstract: This work is focused on the study of photosensitive structures based on porous Si and film TiO₂, which are promising for solar energy. For numerical simulation of the transportation and accumulation of charge carriers in the considered heterostructure, the drift-diffusion approximation of the semiclassical approach was proposed. A device scheme of a solar cell model based on TiO₂/porous-Si/Si heterostructures is proposed. Production of photoconverters of solar cells based on the TiO₂/porous-Si/Si heterostructure can be carried out according to the standard method supplemented by additional technological operations. Ohmic contacts are formed in the upper and lower parts of the structure above the TiO₂ and Si layers. The strip system of contacts is a contact grid, with hatching, the surface coefficient should not exceed 5%. The thickness of the applied layer of photoresist should be 1 μm. Using the PC1D program, the light characteristics of the fabricated structure were calculated (open circuit voltage V_OC, short circuit current I_SC, fill factor FF and efficiency η), and current-voltage characteristics were plotted. The influence of the thickness and doping level N_d and N_a of porous Si and TiO₂ layers on the productivity of a heterojunction solar cell TiO₂/porous-Si/Si was studied in order to obtain a device with a good conversion efficiency. It was found that the energy conversion efficiency of a TiO₂/porous-Si/Si solar cell can reach 22.5 %. Based on the optimized simulation conditions, it was found that the maximum solar cell efficiency is achieved at thicknesses of 100 and 200 nm and donor concentration of N_d=1∙10¹⁷ cm^-3 and acceptor concentration of N_a=1∙10¹⁸ cm^-3 for TiO₂ and porous Si buffer layer, accordingly.

Abstract: In order to evaluate the degradation rate of porous Si in artificial cerebrospinal fluid and obtain more accurate results, the effect of solution aging time on the stability of the ammonium molybdate colorimetric assay was investigated. Following the protocol of the colorimetric assay, the blue colored solutions with various silicic acid concentrations were prepared and then aged for different time periods up to 7 h. On the basis of linear regression analyses, the absorbance value of the blue colored solution was directly proportional to the silicic acid concentration. Moreover, the optimal aging time span of the solution maintained until 7 h, depending on the stability of the solution.

Abstract: Silicon and related materials have recently received considerable attention as potential anodes in Li-ion batteries for their high theoretical specific capacities. To overcome the problem of volume change , composites comprising porous silicon, disordered carbon (DC) have been prepared by pyrolyzing the critic acid. This composite anode material showed a discharge capacity of 1390 mAh/g in the first cycle, and the initial columbic efficiency is 70%. After 20 cycles, the discharge capacity of the material is 511 mAh/g. The improved stability of this material is hypothesized to depend on the unique structure of porous Si and the coated DC. The morphologies of the composites were systematically investigated by the X-ray diffraction and scanning electron microscopy. It can be observed that porous Si particles were embedded into the matrix of the DC. The capacity and cycling stability of the composites were systematically evaluated by electrochemical charge/discharge tests.

Abstract: The influence of strongly absorbing N¬2 laser radiation on pores formation on a surface of Si single crystal has been investigated using optical microscope, atomic force microscope and photoluminescence. After irradiation by the laser and subsequent electrochemical etching in HF acid solution morphological changes of the irradiated parts of a surface of Si were not observed. At the same time, pores formation on the non-irradiated parts of Si surface took place. The porous part of the Si surface is characterized by strong photoluminescence in red part of spectra with maximum at 1.88 eV and intensity of photoluminescence increases with current density. Suppression of the pores formation by the laser radiation is explained with inversion of Si type conductivity from p-type to n-type. This fact is explained by Thermogradient effect – generation and redistribution of the intrinsic defects in gradient of temperature. It was shown that the depth of n-Si layer on p-Si substrate depends on intensity of laser radiation and it increases with intensity of laser radiation. The results of the investigation can be used for optical recording and storage of information on surface of semiconductors.