The adoption of solar cell power generation has increased dramatically over the past decade.
The application of solar energy technology will play a crucial role in areas such as smart grids, diversified power generation methods, and maximizing individual participation in energy consumption. Large-scale solar power generation will become increasingly common, and the price per kilowatt-hour is now comparable to that of traditional energy sources such as nuclear power and natural gas.
Photovoltaic equipment manufacturing
Due to the significant economies of scale in the photovoltaic manufacturing industry, fully automated continuous production is very common. Standard monocrystalline photovoltaic cells use phosphorus-doped silicon (Si) as the substrate (absorber), with a nitrogen-doped thin layer and an anti-reflective coating on the surface. The potential barrier between the n-type and p-type semiconductors is called a pn junction, which allows electrons and holes (positive charges) to accumulate on opposite sides without recombination.
When sunlight shines on a photovoltaic cell, the charge absorbs photon energy, escapes, and flows to the cell electrodes, generating an open-circuit voltage. Multiple cells are integrated into a solar module, which is then connected to other modules, thereby generating a large amount of electrical energy.
Components of a solar cell module
The basic manufacturing process of solar panels can be summarized as follows:
●Silicon wafer fabrication
● Surface texture (reduces reflectivity)
● PN junction formation (wet chemical process)
●Oxide etching (removal of unwanted surface layers)
●Anti-reflective coating
● Metal contact printing (screen printing)
●Metal-to-metal heat treatment (sintering)
●Edge isolation (laser ablation)
●Testing and Classification
Motion control technology is required at every stage of manufacturing and in all processing steps. The most challenging process is the precise deposition of the metal contact layer. Silver and aluminum pastes are screen-printed onto the front and back of each silicon wafer. The sun-facing side of the photovoltaic cell has a series of fine contact fingers, approximately 100 micrometers wide and 2 mm apart, covered by two or three vertical busbars. The back side of the cell has a corresponding set of busbars in the metallized area. The main function of the front and back busbars is to collect current and make mechanical contact with the conductive electrodes.
Chip Screen Printing System
Motion control technology requirements
Currently, the energy conversion efficiency of monocrystalline photovoltaic cells is close to 20%, while the maximum theoretical limit efficiency of silicon single-junction cells is about 29%. Improving conversion efficiency can reduce the cost of generating electricity per kilowatt-hour and reduce the physical size of solar power generation devices, so manufacturers have been continuously working to improve manufacturing processes to increase efficiency.
A typical silicon solar cell manufacturing process requires multiple screen printing operations. To improve conversion efficiency, the contact lines on the front of the cell must be printed as finely as possible without reducing conductivity, which necessitates multi-layer printing with extremely high precision and repeatability.
By making the contact lines thinner and thicker, more cell area can participate in solar energy conversion. For example, reducing the contact finger linewidth from 120µm to 70µm while doubling the thickness could potentially increase conversion efficiency by 0.5%. Another technique to improve cell performance is the use of selective emitters—that is, differentiated doping of the silicon wafer of the solar cell. By heavily doping the area directly beneath the metal contact fingers and lightly doping only in other areas, the short-wavelength response of light is improved, thereby increasing cell conversion efficiency.
Reducing the linewidth of metal contact fingers can improve the conversion efficiency of solar cells.
(1-Metal contact finger, 2-Doped edge, 3-Substrate)
Each metal contact finger has a larger nitrogen-doped area below it.
(1-Selective emitter nitrogen-doped region)
Currently, various technologies are available for manufacturing selective emitters, most of which involve high-precision alignment and deposition of each printed layer. Since subsequent printed layers must be precisely placed on top of the previous one, screen alignment accuracy is the most critical indicator for ensuring the excellent quality of multilayer printed contacts. Advanced alignment systems equipped with high-resolution cameras can now achieve alignment accuracy of ±10µm. High-precision position encoders, such as the Renishaw RESOLUTE™ absolute grating system, are key to improving the accuracy and control performance of printed screen overlap. The RESOLUTE grating operates at speeds up to 100m/s, with a resolution of up to 1nm and a period error as low as ±40nm.
Solar energy is likely to become the primary source of electricity for humankind in the coming decades.
Motion control technology can be applied to all stages of the photovoltaic cell manufacturing process, and is particularly important for high-precision screen printing. Renishaw's expertise in motion control and its extensive portfolio of grating products provide OEMs and end-users with cutting-edge measurement solutions to meet their motion control needs.
