Ma Guofeng

EFFECT OF MOLE FRACTION OF HF AND H202 ONMORPHOLOGY OF POROUS SILICON FORMEDBY Ag ASSISTED CHEMICAL ETCHING

The research of silicon solar cells mainly focuses on reducing cost and improving con- version efficiency, and one of the effective methods of improving photoelectric conversion efficiency of solar cells is to decrease the reflection of incident sunlight onto the light-receiving surface. The porous Si layer can work for the antireflection of Si surfaces, which can be prepared by noble metal assisted chemical etching. In this work, the effects of HF, H2O2 and their volume ratio on morphology and growth of pores on single-crystalline Si surface by using Ag (with a small cluster) metal assisted etching were investigated in order to produce a highly efficient antireflecting structure. The metal particles were deposited onto Si wafer by electroless deposition from a metal salt solution including HF. The surface and cross-sectional morphologies of the porous Si surfaces were observed with field-emission scanning electron microscope. The reflectivity of the etched Si surface was measured with a UV-Vis spectrophotometer equipped with an integrating sphere accessory. The experimental results show that the growth rate and morphology of the pores formed on the Ag metallized Si surfaces are strongly de- pendent on the volume ratio of HF and H2O2. It is not beneficial for the pore growth when mole fraction �=(HF)/((HF)+(H2O2)) is too low or too high, and the etching goes well only whenis between 60%— 80%; in this case, the pore growth rate is up to 1050—1260 nm/min, and the pores grow straightly and