Fluorinated Greenhouse Gases in Photovoltaic Module Manufacturing: Potential Emissions and Abatement Strategies

Abstract

Some fluorinated gases (F-gases) which are used, or considered to be used, in crystalline silicon photovoltaic solar cell and film silicon module manufacturing have a very high global warming effect. CF4, C2F6, SF6 and NF3 have global warming potentials 7390, 12200, 22800 and 17200 times higher than CO2. These gases can be used in texturing, phosphorus silicate glass removal (PSG), edge isolation and reactor cleaning operations from which unreacted species and reaction byproducts will be emitted. An inventory of the current use of fluorinated greenhouse gases by the European and U.S.A. photovoltaic industry shows that CF4 may be used in edge isolation and C2F6 or SF6 or NF3 for reactor cleaning after deposition of silicon nitride or film silicon. Currently only a few companies use these gases; however, dry texturing and PSG removal with F-gases is widely considered as replacement of wet processing. The environmental profile of these new processes can be improved by lowering the use and emissions of F-gases and energy consumption. Exhaust abatement is needed to decompose the unreacted fluorinated greenhouse gases if we want PV electricity to minimize the environmental impact of solar electricity. Although abatement equipment will also have a cost impact, we recommend installing such equipment to preserve the sustainable character of PV energy.