Fusion formable sodium free glass
A compositional range of fusion-formable, high strain point sodium free, silicate, aluminosilicate and boroaluminosilicate glasses are described herein. The glasses can be used as substrates for photovoltaic devices, for example, thin film photovoltaic devices such as CIGS photovoltaic devices. These glasses can be characterized as having strain points≧540° C., thermal expansion coefficient of from 6.5 to 10.5 ppm/° C., as well as liquidus viscosities in excess of 50,000 poise. As such they are ideally suited for being formed into sheet by the fusion process.
1. A glass comprising, in weight percent:
45 to 75 percent SiO 2 ;
3 to 15 percent Al 2 O 3 ;
3 to 20 percent B 2 O 3
21 to 25 percent K 2 O;
0 to less than 6 percent MgO;
0 to 10 percent CaO;
0 to less than 5 percent SrO;
0 to 3.32 percent BaO; and
greater than 0 to 1 percent SnO 2 ,
wherein the glass is substantially free of Na 2 O and wherein the glass is fusion formable and has a strain point of 540° C. or greater, a coefficient of thermal expansion of 50×10 −7 /° C. or greater, T 200 less than 1630° C., and having a liquidus viscosity of 150,000 poise or greater.
2. The glass according to claim 1 , comprising greater than 0 percent MgO, CaO, SrO, or combinations thereof.
3. The glass according to claim 1 , wherein the glass is in the form of a sheet.
4. The glass according to claim 3 , wherein the sheet has a thickness in the range of from 0.5 mm to 3.0 mm.
5. A photovoltaic device comprising the glass according to claim 1 .
6. The photovoltaic device according to claim 5 , comprising a functional layer comprising copper indium gallium diselenide or cadmium telluride adjacent to the glass.
7. The photovoltaic device according to claim 6 , further comprising a barrier layer disposed between the glass and the functional layer.
8. A glass comprising, in weight percent:
45 to 75 percent SiO 2 ;
3 to 15 percent Al 2 O 3 ;
1.6 to 20 percent B 2 O 3
greater than 20 to 25 percent 21 to 30 percent K 2 O;
0 to less than 6 percent MgO;
0 to 10 percent CaO
0 to less than 5 percent SrO;
0 to 3.32 percent BaO; and
greater than 0 to 1 percent SnO 2 ,
wherein the glass is substantially free of Na 2 O and wherein the glass is fusion formable and has a strain point of 540° C. or greater, a coefficient of thermal expansion of 50×10 −7 /° C. or greater, T 200 less than 1630° C., and having a liquidus viscosity of 150,000 poise or greater.
9. The glass according to claim 8 , comprising greater than 0 percent MgO, CaO, SrO, or combinations thereof.
10. The glass according to claim 8 , where the glass is in the form of a sheet.
11. The glass according to claim 10 , wherein the sheet has a thickness in the range of from 0.5 mm to 3.0 mm.
12. A photovoltaic device comprising the glass according to claim 8 .
13. The photovoltaic device according to claim 12 , comprising a functional layer comprising copper indium gallium diselenide or cadmium telluride adjacent to the glass.
14. The photovoltaic device according to claim 13 , further comprising a barrier layer disposed between the glass and the functional layer.