KEYWORDS: Reflection, Diffraction gratings, Absorption, Light scattering, Air contamination, Thin film solar cells, Silver, Thin films, Solar cells, Sol-gels
For thin-film silicon solar cells, light trapping schemes are of uppermost importance to harvest as much as possible of the
available sunlight. Typically, one uses randomly textured front TCOs to scatter the light diffusively in pin-cells on glass.
Here, we investigate methods to texture the back contact with both random and periodic textures for use in nip-cells on
opaque foil. We applied an electrically insulating SiOx-polymer coating on a stainless steel substrate, and textured this
barrier layer by embossing. On this barrier layer the back contact is deposited for further use in the solar cell stack.
Replication of stamps with various random and periodic patterns was investigated, and, using scanning electron
microscopy, replicas were found to compare well with the originals. Masters with U-grooves of various submicrometer
widths have been used to investigate the optimum dimensions of regular patterns for light trapping in the silicon layers.
Angular reflection distributions were measured to evaluate the light scattering properties of both periodic and random
patterns. Diffraction gratings show promising results in scattering the light to specific angles, enhancing the total internal
reflection in the solar cell.
KEYWORDS: Diffraction gratings, Light scattering, Reflection, Solar cells, Air contamination, Thin film solar cells, Thin films, Diffraction, Silicon solar cells, Nanoimprint lithography
For thin-film silicon solar cells, light trapping schemes are of uppermost importance to harvest all available sunlight.
Typically, randomly textured TCO front layers are used to scatter the light diffusively in p-i-n cells on glass. Here, we
investigate methods to texture the back contact with both random and periodic textures, for use in n-i-p cells on opaque
foil. We applied an electrically insulating SiOx-polymer coating on a stainless steel substrate, and textured this barrier
layer by nanoimprint. On this barrier layer the back contact is deposited for further use in the solar cell stack. Replication
of masters with various random and periodic patterns was tested, and, using scanning electron microscopy, replicas were
found to compare well with the originals. Masters with U-grooves of various sub micrometer widths have been used to
investigate the optimal dimensions of regular patterns for light trapping in the silicon layers. Angular reflection
distributions were measured to evaluate the light scattering properties of both periodic and random patterns. Diffraction
gratings show promising results in scattering the light to specific angles, enhancing the total internal reflection in the
solar cell.
ECN is aiming at the development of fabrication technology for roll-to-roll production lines for high efficiency thin film
amorphous and microcrystalline silicon solar cells. The intrinsic layer will be deposited with high deposition rate
microwave plasma enhanced chemical vapour deposition. This plasma source, however, is not suitable for the deposition
of doped layers. Therefore, we use a novel, linear RF source for the deposition of doped layers. In this RF source, the
substrate is electrically disconnected from the RF network. As a result, the ion bombardment onto the substrate is very
mild, with ion energies typically < 10 eV. The low ion energies make this source very attractive for surface treatments
like passivation of crystalline silicon wafers by thin SiNx or a-Si layers. In this contribution, we will introduce the novel
RF source and discuss the deposition of device quality amorphous and microcrystalline intrinsic Si layers with the novel
linear RF source.
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