Technology

Since the first delivery of the first photovoltaic products 30 years ago, we have been working on the development of processes for solar cell production and of the equipment required. We have now established ourselves as a top international provider of photovoltaic equipment to the best-known solar cell manufacturers and as the leading supplier of of turnkey production lines for the manufacture of mono and multi-crystalline solar cells. To date we have planned, set up and commissioned the largest number of turnkey production lines worldwide for our customers.

Our solar cell technology offers a leading-edge level of efficiency in mass production. Thanks to our highly efficient processes, our new turnkey production lines achieve a degree of efficiency of 18.4% for mono-crystalline cells and 17% for multi-crystalline cells. Drawing on our extensive know-how of process and production technology for turnkey production lines, we can guarantee our customers key performance parameters. These include level of cell efficiency, yield and output – i.e. also production capacity. This enables our customers to manufacture crystalline solar cells extremely cost-efficiently (in terms of euro/Wp).

With diffusion furnaces, PECVD systems and drying and annealing furnaces, we provide the key equipment for solar cell production.

A solar cell is an electrical component that converts part of the radiant energy contained in light into electrical energy. Wafers are the initial product in the manufacturing process of silicon wafer-based solar cells involving several stages. The product is a simple solar cell structure based on two differently doped layers. In analogy to transistors in the electronics industry they are called emitter (n-type doping) and base (p-type doping). Using this so-called p-n junction, the charge carriers produced by the photoeffect are separated and extracted for external use as electricity via metallic contacts.

Wafers are cut from high purity crystalline silicon blocks with wire saws in wafer plants. The surface damage caused by the sawing process is removed by wet chemical etching treatment in the first cell manufacturing process step. It is also possible to texture the wafer’s surface in this etching treatment step, which increases the absorption of sunlight. After the etching, the wafers are cleaned using a wet chemical process and then dried.

The next step in the process is phosphor diffusion. The wafers are exposed to a phosphorous gas in a diffusion furnace at around 900 °C and oxygen is introduced causing a phosphorous oxide to form on the surface. Phosphor atoms then diffuse into the silicon and the n-type emitter is created. The penetration depth is determined by various factors, in particular temperature and the duration of diffusion. The diffusion furnaces required for this stage of the process are part of centrotherm photovoltaics’ product portfolio.

In the next stage of the process, the phosphorus glass produced on the surface is removed using a wet chemical treatment.

An anti-reflection coating is applied to the front side of the wafer to increase the solar cells’ absorption of sunlight and to improve the electrical properties of the surface and base material. The most effective method for applying the anti-reflection coating made from silicon nitride is plasma enhanced chemical vapor deposition in a “PECVD” (plasma enhanced chemical vapor deposition) system, also supplied by centrotherm photovoltaics.

Using a silk screen-printing process, narrow contact fingers containing silver are printed on the front side, as well as two to three wider strips perpendicular to the contact fingers – the so-called “bus bars”. On the back side bus bars are applied using a silver/aluminum paste. The remaining back surface is imprinted with aluminum in a further printing stage.  A drying process in a special furnace takes place after each printing step. When all printed contact materials are dried, they are thermally fired (i.e. "sintered") to ensure good electrical contact with the silicon. centrotherm photovoltaics supplies its customers with drying and fast firing furnaces for these processes.

A solar module is a photovoltaic component designed for direct use by end customers and which has the electrical contacts required for connection to an entire solar system. In solar modules based on crystalline solar cells, the individual solar cells are electrically connected in series using contact ribbons. The matrix of solar cells is laminated between a glass panel and several foils of plastic materials at sub-atmospheric pressure and at an elevated temperature to make it weather-resistant. The solar modules are then fitted with a frame and a junction box, and are then ready for installation on rooftops or in solar power stations. With its new "Module Technology" business area, GP Solar , is supplementing centrotherm photovoltaics Group's range of products to include crystalline module production.