Fusion Formable Sodium Containing Glass

Abstract

Sodium-containing 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 9.5 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.

What is claimed is: 
     
         1 . A glass comprising, in weight percent:
 65 to 75 percent SiO 2 ;   1 to 20 percent Al 2 O 3 ;   0 to 3 percent TiO 2 ;   0 to 8 percent B 2 O 3 ;   12 to 25 percent total M 2 O;   2 to 5 percent Na 2 O;   8 to 15 percent K 2 O;   1 to 6 percent CaO; and   1 to 29 percent total RO; and   0 to 6 percent SrO,   wherein, M is an alkali metal selected from Na, K, Li, Rb, and Cs,   wherein R is an alkaline earth metal selected from Mg, Ba, Ca, and Sr,   wherein the glass has a strain point of 540° C. or greater,   wherein the glass has a liquidus viscosity greater than or equal to 50,000 poise,   wherein the glass has a specific gravity greater than 2.42 and less than 2.60, and   wherein said glass comprises less than or equal to 0.05% by weight of ZrO 2 .   
     
     
         2 . The glass according to  claim 1 , wherein the glass is free of ZrO 2 . 
     
     
         3 . The glass composition according to  claim 1 , comprising:
 66.1 to 69.6 percent SiO 2 ;   2.7 to 8.8 percent Al 2 O 3 ;   2.8 to 4 percent Na 2 O; and   8 to 15 percent K 2 O,   and wherein the glass composition exhibits a liquidus viscosity of 630,000 Poise or higher.   
     
     
         4 . The glass according to  claim 3 , comprising:
 67.8 percent SiO 2 ;   7.6 percent Al 2 O 3 ;   0.9 percent B 2 O 3 ;   3.8 percent Na 2 O;   11.7 percent K 2 O;   3.6 percent MgO;   1.9 percent CaO;   2.5 percent SrO; and   0 percent BaO.   
     
     
         5 . The glass according to  claim 3 , comprising:
 67.8 percent SiO 2 ;   7.6 percent Al 2 O 3 ;   0.9 percent B 2 O 3 ;   3.8 percent Na 2 O;   11.7 percent K 2 O;   3.6 percent MgO;   1.9 percent CaO;   2.5 percent SrO; and   0 percent BaO.   
     
     
         6 . The glass according to  claim 1 , comprising:
 67.8 percent SiO 2 ;   7.9 percent Al 2 O 3 ;   2.5 percent B 2 O 3 ;   3.0 percent Na 2 O;   14.1 percent K 2 O;   0.3 percent MgO;   4.4 percent CaO;   0 percent SrO; and   0 percent BaO.   
     
     
         7 . The glass according to  claim 1 , comprising
 69.6 percent SiO 2 ;   7.8 percent Al 2 O 3 ;   2.3 percent B 2 O 3 ;   2.8 percent Na 2 O;   13 percent K 2 O;   0.3 percent MgO;   4.0 percent CaO;   0 percent SrO; and   0 percent BaO.   
     
     
         8 . The glass according to  claim 1 , comprising:
 66.1 percent SiO 2 ;   5.2 percent Al 2 O 3 ;   1.9 percent B 2 O 3 ;   3.0 percent Na 2 O;   14.6 percent K 2 O;   4.4 percent MgO;   2.8 percent CaO;   1.7 percent SrO; and   0 percent BaO.   
     
     
         9 . The glass according to  claim 1 , comprising:
 67 percent SiO 2 ;   5.3 percent Al 2 O 3 ;   1.9 percent B 2 O 3 ;   3.1 percent Na 2 O;   14.8 percent K 2 O;   3.1 percent MgO;   2.9 percent CaO;   1.7 percent SrO; and   0 percent BaO.   
     
     
         10 . The glass according to  claim 1 , comprising:
 66.5 percent SiO 2 ;   7.45 percent Al 2 O 3 ;   0.85 percent B 2 O 3 ;   3.76 percent Na 2 O;   8.6 percent K 2 O;   3.52 percent MgO;   1.9 percent CaO;   2.45 percent SrO; and   4.67 percent BaO.   
     
     
         11 . The glass according to  claim 1 , comprising:
 66.4 percent SiO 2 ;   7.43 percent Al 2 O 3 ;   0.43 percent B 2 O 3 ;   3.75 percent Na 2 O;   11.4 percent K 2 O;   3.52 percent MgO;   2.98 percent CaO;   3.78 percent SrO; and   0 percent BaO.   
     
     
         12 . The glass according to  claim 1 , comprising:
 66.7 percent SiO 2 ;   7.47 percent Al 2 O 3 ;   0 percent B 2 O 3 ;   3.77 percent Na 2 O;   11.5 percent K 2 O;   3.53 percent MgO;   3 percent CaO;   3.8 percent SrO; and   0 percent BaO.   
     
     
         13 . A glass, comprising
 56.9 percent SiO 2 ;   8.8 percent Al 2 O 3 ;   7.1 percent B 2 O 3 ;   4.0 percent Na 2 O;   8.1 percent K 2 O;   0.9 percent MgO;   2.7 percent CaO;   0.15 percent SrO; and   11.4 percent BaO.   
     
     
         14 . A glass, comprising:
 59.6 percent SiO 2 ;   7.4 percent Al 2 O 3 ;   5.6 percent B 2 O 3 ;   3.1 percent Na 2 O;   10.2 percent K 2 O;   0 percent MgO;   3.2 percent CaO;   0.1 percent SrO; and   8.5 percent BaO.   
     
     
         15 . The glass according to  claim 1 , having a T 200  less than 1580° C. and a liquidus viscosity of 1,500,000 poise or greater. 
     
     
         16 . The glass according to  claim 1 , wherein the glass is in the form of a sheet. 
     
     
         17 . The glass according to  claim 15 , wherein the sheet has a thickness in the range of from 0.5 mm to 3.0 mm. 
     
     
         18 . A photovoltaic device comprising the glass according to  claim 1 . 
     
     
         19 . The photovoltaic device according to  claim 17 , wherein the glass is in the form of a sheet and is a substrate or a superstrate. 
     
     
         20 . The photovoltaic device according to  claim 18 , comprising a functional layer comprising copper indium gallium diselenide or cadmium telluride adjacent to the substrate or superstrate.