Vapour deposition process to halve cost of photovoltaic silicon wafers

A new process for purifying silicon and making it into crystalline wafers could reduce the cost of solar cells by up to a fifth, according to the process’s developers at the Fraunhofer Institute for Solar Energy Research in Freiburg, southwest Germany. The method is far less wasteful of material than conventional wafer manufacture, and also uses less energy.

Solar cell production starts with impure silicon, which is melted down and reacted with chlorine, to produce a material called chlorosilane. When hydrogen comes into contact with chlorosilane, it’s converted into pure silicon. But conventionaly, this process creates chunks of amorphous silicon rather than the precisely-ordered crystals needed for photovoltaic cells. To make this, the amorphous lumps have to be crushed, melted at 1450°C and crystallised into ingots weighing upwards of 200kg, which have to be sawn into wafers. The repeated heating uses a large amount of energy, and the sawing means that up to half of the silicon produced is lost as dust.