Dirt Repellent Texture
lithography is a cost efficient technology to create an optimal
surface texture on solar cells, cover glasses and polymeric films. For
silicon solar cells anti-reflection surface texture not only decreases
reflection, but also increases the forward scattering of the incident
light. For thin film cells a large scattering angle increases the
optical path length of the photon within the cell. A reflection layer
at the backside of the cells enables light trapping within ultra-thin
film PV cells. Micro-optical elements enable the integration of beam
shaping elements with a very small form factor.
lithography allows to create optimal surface texture on large areas
directly on the cover glass as well as on the wafer level. The
imprinted film can be either used directly or as an etch mask. For
crystalline silicon cells the texture is optimized in such a way to
minimize reflection and optimize forward scattering. For thin film
cells the texture is optimized for light trapping within the cell.
Light trapping is an important concept which allows to minimize
material consumption and absorber layer thickness. The combination of
frontside texture, which deflects the incident photons into the cell,
and backside texture, which reflects the photons back into the cell
enable effective total reflection within ultra-thin film solar cells.
Even complex structures like photonic crystals and quasi-periodic
photonic crystals can be created by NIL on a large scale. Nanopillars
enable new thin film cell architectures for "electrically thin,
optically thick" cells.
Figure 1. SEM close up of
350 nm photonic crystal. Master provided by NILT.
Figure 2. Nanopillars
created by Nanoimprint Lithography (NIL).
Courtesy of CIHR-NRC Convergent Research Framework 2004
Dirt Repellent Texture
Debris and dirt on the PV module causes rapid deterioration of the
real performance. Dirt repellent films on the cover glass enable a self
cleaning effect thereby enhancing the real module performance
significantly over the whole module lifetime.
Figure 3. Dirt repellent
functional layers reduce accumulation of debris and enable a self
cleaning effect on the PV glass.
UV Imprinting provides an easy and cost efficient manufacturing
process for micro-optical elements. UV imprinting enables the
replication of any kind of optical features: spherical and a-spherical
lenses, diffractive optical elements and functional optical films.
Microlenses focus and concentrate the incident light directly on the
photovoltaic cell. With microlenses it is possible to use multiple
micro-PV cells instead of large CPV cells. The form factor of CPV
modules using micro-optics is significantly smaller enabling ultra-thin
and ultra-light CPV modules.
Figure 4. Microlenses
couple the light into a
waveguide, which allows superior form factor and reduced costs.
Photo courtesy of Jason Karp, UC San Diego
Figure 5. Aspherical
Figure 6. Diffractive
Figure 7. Process flow for
Figure 8. Process flow for
Figure 9. Process flow for
For more information on this source, please visit EV Group.