Abstract :
Absract
en cyanide (HCN) aqueous solutions are found to possess a great ability of removal of copper contaminants on Si as well as a Si defect passivation effect. Copper (Cu) contaminants of 1013 cm−2 order concentrations can be reduced below 3×109 cm−2 taking only 10 s even at room temperature when the pH of the HCN aqueous solution is set at 10. The cleaning ability of HCN solutions increases with pH, indicating that cyanide ions are the reaction species with Cu contaminants. Even when HCN solutions are contaminated with 64 ppm Cu2+ ions, the cleaning ability is unchanged, indicating avoidance of re-adsorption. Ultraviolet absorption spectra show that after the cleaning, Cu–cyanide complexes are formed in the HCN solutions. The main Cu species in the HCN solutions are Cu ( CN ) 3 2 − , and due to its stability, re-adsorption does not occur. When SiO2/Si structure is immersed in the HCN aqueous solutions for 24 h, the SiO2 thickness is unchanged at all, showing that etching does not occur during the cleaning process. The energy conversion efficiency of pn-junction Si solar cells with a spherical shape is increased to 1.07–1.48 times by immersion in the HCN aqueous solutions, and the improvement is attributed to passivation of defect states in Si by cyanide ions.
