Cell Surface in Focus

Selective emitters increase efficiency

The light-facing surface of solar cells still offers much potential for optimisation. For instance, this is the location of the emitter layer, which collects electrons and guides them to the cell contacts. Until now, this area of the silicon crystal has been useless for energy production. However, now the industry is finding ways in which to enhance it in terms of photovoltaics..

The innovation comes from Canada: Photovoltaics producer Canadian Solar has improved the efficiency of its silicon solar cells by almost one percent with the help of a so-called selective emitter. The emitter is the n-type layer on the front of the cell. It has the job of collecting the charge carriers generated in the silicon and guiding them to the front contacts with as little loss as possible. Now, Canadian Solar has manipulated the emitter layer in such a way that it also produces energy. In this way, the company is increasing the efficiency of multi-crystalline cells to 17 percent and mono-crystalline cells to 18.5 percent. “As a result, solar technology on the market will be more affordable,” says manager Shawn Qu.
Consequently, Canadian Solar is among the small group of companies which already use selective emitters as standard. For example, this group includes the Chinese manufacturers China Sunergy and Suntech. Since very recently, German photovoltaic suppliers Centrotherm and Schmid have also been offering industry-standard manufacturing equipment for selective emitters. Depending on the quality of the wafer and manufacturing process, this allows cells to be produced with up to 0.8 percent more efficiency.
Initially, this seems unspectacular, but even small gains in efficiency can provide companies with decisive competitive advantages. This is because the efficiency degree influences the profitability more than any other individual factor during manufacturing, including the scaling effect of a larger production quantity. As a rule of thumb, every percent more efficiency reduces the cost by five to seven percent as less cell area or module area is needed per watt of capacity.