Fabrication Of Porous Silicon And Its Application On Solar Cells

With the development of the society, the human demands for the more energy. Currently the conventional energy is not only limited, but also causes the environmental pollution and the destruction of ecological balance. But the solar energy is non-toxic harmless, inexhaustible green energy, so it’s very important to try our best to develop the photovoltaic (PV) technologies.There are two important factors that influence solar cell performance, the amount of reflection from a surface is one of the main obstacles in efficient solar cell performance, and another main difficulty in improving the efficiency of PV energy conversion lies in the spectral mismatch between the energy distribution of photons in the incident solar spectrum and the bandgap of Si semiconductor material. To increase the efficiency of solar cells, on the one hand, we can develop antireflection technology to reduce surface reflection, on the other hand, the spectral converters which are capable of converting a broad spectrum of light into photons of a particular wavelength can be used to reduce the losses in the photoelectric conversion process. In this work, we made porous silicon antireflection structure with silver catalytic method and improved the performance enhancement of crystalline silicon solar cells by coating with luminescent silicon nanostructures prepared by electrochemical corrosion method, then modified. In the following are the main innovative results of this thesis:The evolution of the surface reflection with the reaction time and temperature was studied. With the reaction temperature 30～40 ℃, the average reflectivity of the crystalline silicon surface was the minimum. With the prolongation of the reaction time, the reflectivity of the wafer became lower. In the reaction time range of 2-5 min, the reflectivity of the wafer could be under 5%.We present a systematic study to fabricate the luminescent porous silicon by electrochemical corrosion and to explore the law of the photoluminescence of porous silicon using fluorescence spectrometer. When we applied small current, with the prolongation of the reaction time and current density, the depth of the porous Si layer and the intensity of PL increased significantly. PL measurements show that the emissions mainly located at 600～700 nm, the change of current density doesn’t cause the position shift.The influences on the PL properties of porous silicon via the ratio of electrolyte and silicon substrates were studied. We found the photoluminescence intensity of porous silicon is better when the electrolytic liquid product concentration ratio V(HF): V(C2HsOH)= 1:1, and the PL intensity of porous silicon fabricated by lightly doped p-type silicon wafers is stronger.Fluorescence spectrometer was employed to characterize the photoluminescence of porous silicon when we applied big current density. The result was that the photoluminescence peak position and luminescent mechanism were different for different silicon substrates.The reflectivity of solar cells coated a certain concentration of porous silicon particles solvent became lower, and the external quantum efficiency (EQE) increased, the efficiency was also improved.