Spherical silicon photovoltaic devices are bonded to flexible substrates to produce light-weight flexible solar modules. In
order to maximize the conversion efficiency, the optical loss must be minimized. The concept of conventional anti
reflection coating (ARC) does not directly apply to the spherical device due to different geometry.
The optimum design of the ARC must maximize the optical power transmission from air to the Si crystal bulk. In
addition to the refractive index and the thickness of the ARC, the power distribution on the exposed spherical surface,
incidence angle dependent reflection, and multiple reflections at the spherical air-ARC and ARC-silicon interfaces also
influence the ARC design.
The effects of the spherical shape on the variations of the reflection are analyzed. It is shown that the optimum design is
essentially different from the conventional ARC with uniform quarter-wavelength thickness. It is required that the design
compensates the effect of variation of the incidence angle across the spherical surface. To achieve this, the thickness
should have a zenith-angle dependence. Chemical vapor deposition techniques can potentially be employed for the
deposition of the designed films.
Silicon based thin film alloys are deposited using plasma enhanced chemical vapor deposition (PECVD) with silane,
ammonia, and nitrous oxide as precursors with different partial pressure ratios. Numerous deposition conditions have
been considered to produce films with a wide range of refractive indices. The optical properties of the films are mostly
affected by hydrogen content and stoichiometry, which are characterized by means of Fourier Transform Infrared
Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) respectively.
The results of spectroscopic ellipsometry measurement of the refractive index are correlated with stoichiometry extracted
using XPS to enable the prediction of optical properties from process conditions. Based on the film characterization
results, a graded index film is deposited to minimize the reflection loss. The optical properties of the film to be used as
anti-reflection coating (ARC), i.e. the transmittance and reflectance, are measured using an optical spectrophotometer. In
spite of the optical absorption in the high refractive index part of the film, it is shown that by employing a very thin layer
of amorphous silicon, it is possible to reduce reflection below conventional graded index films consisting of silicon
oxynitride, and still maintain the transmittance required for solar cell applications.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.