Femtosecond Pulse Laser Preparation For Silicon-based Nanostructures Photovoltaic Material Research

When the monocrystalline silicon surface irradiated in a certain gas atmosphere by femtosecond pulse laser, the surface area observed by the naked eye appears black, while the microscopic surface displays directed cone shaped peak structure. This material is commonly known as "black silicon". The special material has more than 90% of the spectrum absorption from nearly ultraviolet to mid-infrared. The higher of the height of micro-cones formed on the surface of―black silicon‖, the better the absorption efficiency.We mainly introduced the research on femtosecond pulse laser preparation for silicon-based micro-nano structure photovoltaic material. In the project, we successfully built the experiment system to fabricate the "black silicon" photovoltaic material, used the system successfully to produce "black silicon" photovoltaic material with higher micro-cones, and summarized the experiment procedure and the experimental parameters of manufacturing "black silicon" photovoltaic material.In this paper, we created―black silicon‖photovoltaic material successfully and studied the surface morphology law under various experimental parameters. 1, Studied the relation between the height of micro-cones formed at "black silicon" surface and the number of femtosecond laser pulses under a certain femtosecond pulse laser power, certain SF6 gas pressure; 2, studied the influence of femtosecond pulse laser power volume on the "black silicon" surface morphology, and summarized the curve of the height of micro-cones formed on the "black silicon" surface via laser power volume ; 3, studied the height of micro-cones formed on the "black silicon" surface under different SF6 gas pressure;4, studied under constant femtosecond pulse laser fluence, change the number of femtosecond laser pulses and volume of femtosecond laser power respectively, the variation on the surface of "black silicon". Through the above research, we found that the height of micro-cones is determined by both of femtosecond laser pulse induced plasmas enhanced etching effect and laser melt effect. Both of effects can be enhanced by adding number of the laser pulses. However, laser melt effect can exceed plasmas enhanced etching effect when the number of laser pulses exceeding a threshold. The variation trend of height of micro-cones as a function of the number of laser pulses is almost the same under various pressure of SF6.We set up the micro-cones model by using software simulation approach for―black silicon‖microstructure, and calculated that the surface of―black silicon‖was 20 times larger than that of normal silicon, which greatly increased the incident light absorption area and optical path. According to the "black silicon" surface structure model, we simulated the reflectivity in full spectrum ranges which was close to actual one. Finally, we set solar cells manufacturing solutions based on the―black silicon‖photovoltaic material.