Solar cell manufacturing and packaging process
Currently, solar cells essentially are manufactured from mono
crystalline, polycrystalline amorphous and thin-film-based
materials. A more recent undisclosed solar technology, known as
organic photovoltaics, is also currently under commercial
development. Each of the technologies have unique physical,
chemical, manufacturing, and performance characteristics and are
best suited for specialized applications.
In this section we will discuss the basic manufacturing principles,
and in subsequent chapters we will review the production and
manufacturing process of several solar power cell technologies.
Introduction to monocrystalline and polycrystalline silicon cells
The heart of the most monocrystalline and polycrystalline
photovoltaic solar cells is a crystalline silicon semiconductor.
This semiconductor is manufactured by a silicon purification
process, ingot fabrication, wafer slicing, etching, and doping which
finally forms a PNP junction that traps photons, resulting in the
release of electrons within the junction barrier, thereby creating a
current flow.
The manufacturing of a solar photovoltaic cell in itself is only a
part of the process of manufacturing a solar panel product. To
manufacture a functionally viable product that will last over 25
years requires that the materials be specially assembled, sealed,
and packaged to protect the cells from natural climatic conditions
and to provide proper conductivity, electrical insulation, and
mechanical strength.
One of the most important materials used in sealing solar cells is
the fluoropolymer manufactured by DuPont called Elvax. This chemical
compound is manufactured from ethylene vinyl acetate resin. It is
then extruded into a film and used to encapsulate the silicon wafers
that are sandwiched between tempered sheets of glass to form the
solar panel. One special physical characteristic of the Elvax
sealant is that it provides optical clarity while matching the
refractive index of the glass and silicon, thereby reducing photon
reflections. Figure 1.5 depicts various stages of monocrystalline
solar power manufacturing process.
Another chemical material manufactured by DuPont, called Tedlar, is
a polyvinyl fluoride film that is coextruded with polyester film and
applied to the bottom of silicon-based photovoltaic cells as a
backplane that provides electrical insulation and protection against
climatic and weathering conditions. Other manufacturing companies
such as Mitsui Chemical and Bridgestone also manufacture comparable
products to Tedlar which are widely used in the manufacture and
assembly of photovoltaic panels.
Another important product manufactured by DuPont chemical is Solamet,
which is a silver metallization paste used to conduct electric
currents generated by individual solar silicon cells within each
module. Solamet appears as micronwide conductors that are so thin
that they do not block the solar rays.
A dielectric silicon-nitride product used in photovoltaic
manufacturing creates a sputtering effect that enhances silicon to
trap sunlight more efficiently. Major fabricators of polycrystalline
silicon are Dow Corning and General Electric in the United States
and Shin-Etsu Handotai and Mitsubishi Material in Japan.