Passivation of trap states in polycrystalline Si by cyanide treatments

The cyanide treatment in which polycrystalline Si is immersed in a KCN solu tion followed by rinsing in boiling water increases the energy conversion e fficiency of [ITO/silicon oxide/polycrystalline Si] junction solar cells to 12.5%. The XPS measurements under bias show that the trap density in polyc rystalline Si is markedly decreased by the cyanide treatment, especially th e decrease near the Fermi level being remarkable. The dark current density for the cells without the cyanide treatment depends only weakly on the temp erature, indicating that tunneling is a dominant mechanism for the current how through the Si depletion layer. The cyanide treatment increases the tem perature-dependence markedly, showing that thermal excitation of majority c arriers becomes necessary for the current flow due to the elimination of th e trap states in the Si depletion layer. (C) 1999 Elsevier Science Ltd. All rights reserved.