Resolving the nanostructure of plasma-enhanced chemical vapor deposited nanocrystalline SiOx layers for application in solar cells

Abstract

Nanocrystalline silicon suboxides (nc-SiO x ) have attracted attention during the past years for the use in thin-film silicon solar cells. We investigated the relationships between the nanostructure as well as the chemical, electrical, and optical properties of phosphorous, doped, nc-SiO 0.8 :H fabricated by plasma-enhanced chemical vapor deposition. The nanostructure was varied through the sample series by changing the deposition pressure from 533 to 1067 Pa. The samples were then characterized by X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Raman spectroscopy, aberration-corrected high-resolution transmission electron microscopy, selected-area electron diffraction, and a specialized plasmon imaging method. We found that the material changed with increasing pressure from predominantly amorphous silicon monoxide to silicon dioxide containing nanocrystalline silicon. The nanostructure changed from amorphous silicon filaments to nanocrystalline silicon filaments, which were found to cause anisotropic electron transport. Published by AIP Publishing. [http://dx

Versatility of doped nanocrystalline silicon oxide for applications in silicon thin-film and heterojunction solar cells

“…Here, the nc-Si phase was approximated by defining a threshold density of 49.9 nm -3 of Si for a given voxel size of 0.5x0.5x0.5 nm 3 , while considering the detector efficiency of the APT measurement. A similar distribution of the nc-Si phase has been previously observed by high resolution transmission electron microscopy (HRTEM) at a comparable scale [1,2,14], supporting the Si density approximation for the nc-Si phase used here. Accordingly, Si iso density surfaces were constructed by connecting voxels attributed to the nc-Si phase.…”

“…These effects might distort the origin of a given ion and affect the reliability of the calculated atom densities and therefore the phase identification. However, a similar anisotropic microstructure has been observed by HRTEM [1,2,14] which qualitatively confirms the determined distribution of the nc -Si phase. Now, a detailed three-dimensional distribution of the nc-Si network could be reconstructed via APT, thereby revealing a large amount of lateral connections within the nc-Si network that explain the high lateral D of both films.…”

“…Hydrogenated nanocrystalline silicon oxide (nc-SiO x :H), often also called microcrystalline silicon oxide (µc-SiO x :H), attracts significant attention as a material for photovoltaics [1][2][3][4][5][6]. The unabated interest in doped, both n-and p-type, nc-SiO x :H prevails mainly due to its remarkable variability.…”

“…Particularly, the optical and electrical properties of this material can be varied in a broad range, providing a tunable refractive index, a low absorption coefficient in the relevant energy range, and a sufficient electrical conductivity. This is made possible by its characteristic microstructure, which is usually described as comprising of well conducting filaments or pearl-chain like arrangements of nanocrystalline silicon (nc-Si) embedded in a highly transparent, oxygen rich amorphous silicon oxide (a-SiO x :H) matrix as indicated by TEM investigations [1,2,7,8]. As a result, nc-SiO x :H is widely applicable as a window, back contact (BC) or intermediate reflector (IR) layer in various solar cell concepts.…”

Investigation of the Copper Gettering Mechanism of Oxide Precipitates in Silicon

“…Before doing this, the zero loss peak of each spectrum was extracted and used to calculate the single scattering distribution by Fourier logarithm deconvolution. 24,25 Examples of the deconvoluted spectra at characteristic positions can be found in Fig. 4.…”