| Wafer Stack Splitting, Loading/Inspection
Silicon solar cells are produced from raw wafers. After unloading from transport boxes, these wafers are tested to ensure that they have the right dimensions and weight and to check for any damage to the edges and surfaces. Good wafers are loaded into the system. Saw Damage Etch (SDE) and Texturing
Batch-type wet benches (SILEX-series) are one choice for cleaning and either alkaline texturing of mono crystalline or acidic texturing of multi crystalline wafers. Another option is inline wet chemical processing of the cells with the LINEA machine from STANGL. In this process step any residue and saw damage is removed from the raw wafers and a light trapping structure (texture) is applied by wet chemical process. The etching and rinsing is done automatically in separate baths in an automized sequence. Junction Formation
Today’s standard raw material is positively doped silicon (p-type). To generate the p-n junction, the wafers are doped with phosphorous. For this process, the substrates are loaded into Silicon Carbide process boats and are inserted into a tube furnace. Inside the furnace the wafers are exposed to a phosphorus containing gas (POCl3). At high temperatures of about 900 °C phosphorus atoms diffuse into the wafers. As a result a negatively doped surface layer is created. Selective Emitter
Laser-based procedure using an additional laser-processing step, the level of doping under the contact structure which is applied in a later stage of the process is increased significantly. Phosphor Silicate Glass Removal/Edge Isolation
For this process step STANGL offers the SILEX batch and LINEA inline wet processing systems. The phosphorus silicate glass produced as a by-product of the diffusion process is removed in an acid bath. Additionally edge isolation can be realized with the LINEA inline system (PSG-EE).
| | SINGULAR – Static Inline Tool for High Uptime ICP-PECVD Anti Reflection Coatings
SINGULAR is a PECVD coating tool for passivation and anti reflection coating (ARC) for crystalline silicon solar cells. The tool offers an innovative static inline concept, which combines the advantages of static processing and inline substrate transport. During static processing, the substrates are not moved, therefore layer stacks and gradient layers are easily possible. Superior passivation and optical properties can be applied. The fully automated inline cleaning process guarantees a high uptime of the tool for production. SINGULUS developed a proprietary, fully-automated wafer handling system for the integration and connection of the SINGULAR with the wet-chemical cleaning and etching equipment. Printing/Firing
To extract the electrical power from the solar cell a silver paste contact grid is applied to the the front surface of cell by a screen printing process. This creates the characteristic grid pattern on the front of the cell. The back of the cell also receives two silver paste contact strips plus an aluminum layer known as the back surface field. This acts on the electrons as a kind of a mirror. The contacts are burnt into the cell in a hot furnace with around 900 °C. The high temperature causes the silver paste to penetrate into the silicon, thus forming a reliable electrical contact. Testing/Sorting
Tested and classified PV cells need to be sorted and placed safely into storage or transportation boxes. For this purpose the sorter takes over the cells together with their identifier from the upstream testing machine. The cells are picked up by a vacuum suction cup and moved to the respective bins which are predefined by the testing and classification unit. Standard styrofoam boxes are used for taking up the cells. The basic machine allows for sorting into 16 classes. Optionally this may be extended to 32 or 48 classes. |
