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

Abstract

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 °C performed for formation of pn‐junction effectively passivate the nanocrystalline Si surface. With this phosphosilicate glass passivation plus the hydrogen treatment at 400 °C, the internal quantum efficiency is greatly improved and reaches 81% at a wavelength of 400 nm. Analysis of ellipsometry data shows that incident light with wavelength shorter than 400 nm 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 © 2017 John Wiley & Sons, Ltd.

High conversion efficiency of crystalline Si solar cells using black − Si fabricated by SSCT method

“…Since SiO 2 is the main composition of PSG, it is likely that the characteristics of the nanocrystalline Si/PSG interface are similar to those of Si/SiO 2 interface with an ultralow interface state density [31]. Analysis of ellipsometry data clarifies that incident light with wavelength shorter than 400 nm is almost completely absorbed by the nanocrystalline Si layer [16]. Therefore, to obtain a high conversion efficiency from the < nanocrystalline Si layer/crystalline Si> solar cells, electron-hole pairs generated in the nanocrystalline Si layer should contribute to a photocurrent.…”

“…(The presence of 4.9 nm nanocrystalline Si is evident from the measurement of photoluminescence spectra of the < nanocrystalline Si layer/mono − Si> structure with a peak at 705 nm [16]). Figure 6 shows ε m of the nanocrystalline Si layer vs. the depth estimated from analysis of the ellipsometry data for the nanocrystalline Si/mono − Si structure.…”

“…Black− Si wafers have been produced using reactive ion etching [1][2][3][4], metal-assisted chemical etching [5][6][7][8][9][10], stain etching [11], electrochemical etching [11,12], vapor chemical etching [13], surface structure chemical transfer (SSCT) [14][15][16], etc. Reactive ion etching [1][2][3][4] requires an expensive apparatus, and throughput is considerably low, leading to high fabrication costs.…”

Black silicon – correlation between microstructure and Raman scattering

“…In the present study the nanocrystalline Si layers were formed by using the surface structure chemical transfer method (SSCT) [8][9][10][11]. In this procedure silicon surface is etched in solution of H 2 O 2 and HF.…”

“…Self-similarity property of formed particles causes importance of fractal properties of resulting structure. This kind of structure show very low spectral reflectance in wide range of wavelengths [8][9][10][11].…”