A coverglass for GaAs solar cells

A new borosilicate-type coverglass material, CMG, with a thermal expansion coefficient matched to GaAs over a temperature range in excess of -180°C to +520°C is described. The glass also has the standard coverglass properties of excellent optical transmission, radiation stability, low solar absorptance, and high emissivity. By using CMG coverglasses on GaAs cells, a more advanced and lighter solar cell assembly can be produced. Because the glass is expansion-matched, it significantly reduces any stresses within the cell assembly caused by thermal cycling. It also allows advanced bonding techniques such as electrostatic bonding to be implemented or, alternatively, the use of Teflon or a rigid adhesive layer. For GaAs cells the elimination of the coverglass adhesive would be very significant since it would be the first step towards the realization of ultrathin GaAs cells relying on the coverglass for strength