Surface nanocrystalline Si structure and its surface passivation for highly efficient black Si solar cells

19.5% conversion efficiency crystalline silicon (Si) solar cells having simple structure without antireflection coating have been fabricated using the surface structure chemical transfer method which produces a nanocrystalline Si layer simply by contacting catalytic platinum with Si wafers in hydrogen peroxide plus hydrofluoric acid solutions. The reflectivity becomes less than 3% after the surface structure chemical transfer method due to formation of black Si. Deposition of phosphosilicate glass and heat treatment at 925 degrees C performed for formation of pn-junction effectively passivate the nanocrystalline Si surface. With this phosphosilicate glass passivation plus the hydrogen treatment at 400 degrees C, the internal quantum efficiency is greatly improved and reaches 81% at a wavelength of 400nm. Analysis of ellipsometry data shows that incident light with wavelength shorter than 400nm is almost completely absorbed by the nanocrystalline Si layer. The high internal quantum efficiency for short wavelength light is attributed to effective surface passivation and the nanocrystalline Si layer band-gap energy which decreases with the distance from the top of the network structure of the nanocrystalline Si layer. Copyright (C) 2017 John Wiley & Sons, Ltd.