Investigation On Plasma Immersion Ion Implantation Applying To Solar Cells

Reducing the surface recombination furthermore and improving the quality of PN junction are important ways to enhance the conversion efficiency of solar cells. So far, the surface reflectance of monocrystalline silicon and multicrystalline silicon after texturing still reaches about11%and25%, besides, the response of spectrum in short wavelength is weak, so a new process to solve these problems is needed. Plasma immersion ion implantation (PHI) provides a good future to previous problems. To improve the quality of PN junction, an ultra-shallow junction can be acquired through PⅢ compared to the traditional diffusion ways, and our research shows that this PN junction is fit for solar cells. To reduce the surface reflectance,"black silicon" with nanohills on the surface can be acquired by PⅢ, these nanohills can greatly reduce the loss of light by reflecting. After that we optimize other processes and the conversion efficiency is enhanced obviously. In this paper, the following work has been done:1. PN junctions have been made by PⅢ on P-type monocrystalline silicon with area of125cm X125cm, and a rapid thermal annealing (RTA) process was taken to activate the doping ions. The influence of the time and temperature of RTA process, the value and width of bias voltage to the sheet resistance has been studied. We found that when the value and width of bias voltage are2KV and50μs, the temperature and time of RTA are1100℃and20s, the best PN junction we got. The sheet resistance was10.12Ω/sq at minimal, and the non-uniformity is2.98%, and this PN junction is well to produce solar cells, In addition, PⅢ on multicrystalline silicon has been studied as well, we found that the result of multicrystalline silicon is much worse than that on monocrystalline silicon.2. black silicon have been made by PⅢ on P-type monocrystalline silicon with area of156cm X156cm, and a defect removal etching (DRE) process has been taken. NaNO2/HF solution was used compared to traditional HNO3/HF solution. It have been found that DRE process will increase the surface reflectance of silicon wafers, but it can reduce the damage of PⅢ and surface area to decrease the surface recombination. In our work we used HNO3/HF solution and NaNO2/HF solution in the DRE process of black silicon, then the black silicon wafers were made to solar cells. We found that the black silicon solar cells have a best performance when the condition of DRE process is NaNO2:HF:H2O=6.4g:10mL:240mL,20min. The highest conversion efficiency of black silicon solar cell is17.46%, with a Voc of623mV and an Isc of35.99mA/cm2, which is 0.72%higher than that of traditional...