Photovoltaic Electricity
When sunlight hits a solar cell, the sun's energy activates electrons. This effect, now known as Photovoltaic (PV), was originally discovered over 160 years ago by Edmund Becquerel and initially turned into a working solar cell by Charles Fritts about 120 years ago in 1884.
The basic mechanism of a solar cell is very simple. Light energy from the sun hits a solar module. The light energy excites electrons to move away from the atom to which they are attached. The movement of electrons is an electrical current. The structure built on the silicon wafer then collects the current created by the free electrons to produce electricity. The individual wafers are wired together inside of a module and the module has electrical connections that allow the electricity to power our homes, offices or any electrical device.
Crystalline Silicon Solar Technology
Crystalline solar modules are made from an array of silicon wafers that have been connected together. By appropriately doping the silicon and coating with thin films, a structure is created on the silicon surface that is sensitive to incoming solar energy. This structure is called a photovoltaic (PV) cell.
The key to successful crystalline solar cells are to get the most possible electricity (known as conversion efficiency) from the least amount of silicon (measured in grams per watt). Higher efficiencies coupled with lower amounts of silicon are the continuous goal of the PV industry. By creating more complex structures involving multiple levels of silicon and other high-tech materials, the efficiency of the cell can be increased. Industry announcements of 20% or better are no longer uncommon. And, the most effective way to reduce the amount of silicon per watt is to use thinner wafers.
Applied's technology addresses both of these key issues. Our experience in integrated circuit wafer fabrication is characterized by continuous improvements in the electronic function of the devices at ever reduced cost of manufacture. That same creativity, technology and innovation is being brought to crystalline solar cell manufacturing.
Sputtered Technology
Sputtering technology is used in solar cell manufacturing to provide silicon nitride depositions, used for anti-reflective coatings and bulk passivation layers. Applied Materials' ATON Series provides:
- High throughput technology
- Excellent deposition uniformity
- Directional coatings allow for longer service cycles with high tool availability
- Bulk silicon delivered using a silicon source, silane-free solution
- Production proven mature technology for large area applications
Thin Film Solar Technology
Thin Film (TF) solar technology is an emerging solution for solar electricity production. Rather than using silicon wafers to build the PV device, TF is manufactured on glass. Glass substrates require less sophistication to manufacture, making them more abundant than silicon wafers and less costly. The active silicon layer is deposited using almost identical processes as those used to make LCD TFT flat panel displays. By piggybacking on the scale of manufacturing used in the display industry, Applied is able to bring volume manufacturing of large sized substrates to the solar industry.
The goal for TF modules is the same as crystalline: higher electrical conversion efficiency from the least amount of silicon. Thin film has an inherent advantage in silicon consumption rates because only micrometer-thick layers of silicon are deposited on the glass substrate, compared to crystalline wafers that require hundreds of micrometers of silicon. Since silicon is a major cost factor in the manufacturing of a solar cell, the inherent cost of the TF module is less.
Manufacturing of TF modules is also less complicated. Glass is the raw material, and in a handful of steps, a solar module is created. Sequentially depositing and patterning three layers of material (transparent conductive oxide, silicon and metal) creates a fully functional TF module. This process draws on know-how from the display industry for high volume, low-cost manufacturing methods.
TF modules currently convert sunlight to electricity at about half the rate of crystalline wafers. Several different paths are being explored to improve TF conversion efficiency ranging from improved materials in the film stacks to multiple sandwiches of solar cells. Given today’s state of the technology, TF solar modules are most likely to be used in large area installations such as solar farms or industrial roof top settings, where installation costs savings can be substantial. Fewer electrical connections, less complicated framing and faster installation times are required because fewer individual panels are needed to create attractive cost per watt energy production.
Large glass substrates can be configured to produce smaller modules using the same glass cutting and separation techniques now employed by the display industry. This allows customers to produce virtually any size module at very favorable manufacturing costs.
The measure of the effectiveness of a solar module is determined by the ‘cost per watt’. For a given amount of incoming sunlight, the TF module currently produces more electricity per dollar spent, thus delivering outstanding cost per watt value.
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