Technology
centrotherm photovoltaics has been advancing processes and technologies in the manufacture of mono-crystalline and multi-crystalline silicon solar cells for three decades and ranks as a pioneer in the field of turnkey solutions. We have extended our services from this field of expertise into crystalline module technology and are benefitting from the synergies achieved, enabling us to develop into the market-leading provider of integrated solutions.
Thanks to our extensive expertise in cell and module manufacturing processes, we are able to guarantee our customers key performance parameters, such as efficiency, production capacity and output. Our solar cell technologies achieve leading-edge levels of efficiency in mass production.
We enable our customers to manufacture solar cells and modules extremely efficiently (measured in Euro/Wp) thanks to the optimally matching technology and production equipment to ensure a highly efficient overall process.
Standard solar cell technology
The raw material product required for the manufacturing of solar cells is high-purity silicon wafers which undergo a comprehensive incoming inspection prior to processing.
The first process step is the wet-chemical removal of the saw damage caused in wafer production. The subsequent texturization creates a specific surface roughness which increases light coupling in the solar cells.
The p-n junction is produced through phosphorous diffusion. centrotherm photovoltaics uses a residue-free gas-phase diffusion with POCl3 whereby the p-doped wafer is heated in the diffusion furnace and exposed to the phosphorous gas. A phosphorous oxide (phosphosilicate glass), from which phosphorous atoms diffuse into the silicon and create an n-doped layer, forms on the surface.
The phosphosilicate glass (PSG) is subsequently removed wet-chemically in a short etching process.
An anti-reflective coating is applied to the front side of the wafer in order to further increase the absorption of sunlight and to improve the electrical cell properties. The coating is produced by direct plasma deposition of silicon nitride in our PECVD equipment.
The metal contacts are then fitted using a screen printing method. Thin “contact fingers” and generally 2 to 3 busbars, which connect these contact fingers, are printed on the front side. The same number of busbars is applied on the rear side in an additional printing procedure with an aluminum layer covering the entire back surface. The metal paste is dried in drying furnaces after each of the three printing procedures.
They are then thermally fired in the fast firing furnace. This brings the metal grid on the front side into contact with the n-doped silicon and generates the aluminum back-surface field (Al-BSF) on the rear side.
The front and rear sides of the cell are electrically insulated from one another on the edges to avoid short circuits and recombination losses. The cell is processed with a laser to create a groove along the cell edge.
The finished cells are then classified according to electrical and optical characteristics, sorted and prepared for module production.
Module technology
Fracture, pressure and heat-proof panels of solar glass are firstly cleaned and fitted with the first encapsulation foil which serves as a moisture barrier.
In the meantime, the solar cells are connected by metal ribbons to form strings and then positioned on the sheet with the encapsulation foil. The interconnection ribbons, which connect the individual strings to form a matrix, are positioned and soldered here.
The second encapsulation foil and the back sheet are then attached to the cell matrix in the form of a composite film.
In the next production stage, the modules are then pressed together at around 140° C in the laminator and laminated. The two encapsulation foils develop into a three-dimensional interconnected synthetic layer in which the cells are embedded and which is firmly connected to the cover glass and back sheet.
After lamination, the overlapping foil is removed, the edges are treated and the module is fitted with an aluminum frame.
After junction box assembly, the modules undergo a subsequent IV measurement, are characterized, sorted and packaged.
