Fusion formable sodium free glass

Abstract

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.

What is claimed is: 
     
         1 . A glass comprising, in weight percent:
 35 to 75 percent SiO 2 ;   0 to 15 percent Al 2 O 3 ;   0 to 20 percent B 2 O 3 ;   3 to 30 percent K 2 O;   0 to 15 percent MgO;   0 to 10 percent CaO;   0 to 12 percent SrO;   0 to 40 percent BaO; and   0 to 1 percent SnO 2 ,   wherein the glass is substantially free of Na 2 O.   
     
     
         2 . The glass according to  claim 1 , comprising: greater than 0 percent B 2 O 3 . 
     
     
         3 . The glass according to  claim 1 , wherein the glass is substantially free of B 2 O 3 . 
     
     
         4 . The glass according to  claim 1 , comprising: at least 45 percent SiO 2 . 
     
     
         5 . The glass according to  claim 1 , comprising: greater than 0 percent MgO, CaO, SrO, or combinations thereof. 
     
     
         6 . The glass according to  claim 1  comprising, in weight percent:
 35 to 75 percent SiO 2 ; 
 greater than 0 to 15 percent Al 2 O 3 ; 
 greater than 0 to 20 percent B 2 O 3 ; 
 3 to 30 percent K 2 O; 
 greater than 0 to 15 percent MgO; 
 greater than 0 to 10 percent CaO; 
 greater than 0 to 12 percent SrO; 
 greater than 0 to 40 percent BaO; and 
 greater than 0 to 1 percent SnO 2 , 
 wherein the glass is substantially free of Na 2 O. 
 
     
     
         7 . The glass according to  claim 1 , comprising:
 39 to 75 percent SiO 2 ;   2 to 13 percent Al 2 O 3 ;   1 to 11 percent B 2 O 3 ;   3 to 30 percent K 2 O;   0 to 7 percent MgO;   0 to 10 percent CaO;   0 to 12 percent SrO;   0 to 40 percent BaO; and   0 to 1 percent SnO 2 ,   wherein the glass is substantially free of Na 2 O.   
     
     
         8 . The glass according to  claim 1 , comprising:
 50 to 70 percent SiO 2 ;   2 to 13 percent Al 2 O 3 ;   1 to 11 percent B 2 O 3 ;   3 to 30 percent K 2 O;   0 to 7 percent MgO;   0 to 7 percent CaO;   0 to 5 percent SrO;   1 to 40 percent BaO; and   0 to 0.3 percent SnO 2 ,   wherein the glass is substantially free of Na 2 O.   
     
     
         9 . The glass according to  claim 1 , wherein the glass is in the form of a sheet. 
     
     
         10 . The glass according to  claim 9 , wherein the sheet has a thickness in the range of from 0.5 mm to 3.0 mm. 
     
     
         11 . A photovoltaic device comprising the glass according to  claim 1 . 
     
     
         12 . The photovoltaic device according to  claim 11 , comprising a functional layer comprising copper indium gallium diselenide or cadmium telluride adjacent to the substrate or superstrate. 
     
     
         13 . The photovoltaic device according to  claim 12 , further comprising a barrier layer disposed between the superstrate or substrate and the functional layer. 
     
     
         14 . The glass according to  claim 1 , having a strain point of 540° C. or greater. 
     
     
         15 . The glass according to  claim 1 , having a coefficient of thermal expansion of 50×10 −7  or greater. 
     
     
         16 . The glass according to  claim 1 , having a coefficient of thermal expansion in the range of from 50×10 −7  to 90×10 −7 . 
     
     
         17 . The glass according to  claim 1 , having a strain point of 560° C. or greater and a coefficient of thermal expansion of 50×10 −7  or greater. 
     
     
         18 . The glass according to  claim 1 , having a liquidus viscosity of 50,000 poise or greater. 
     
     
         19 . The glass according to  claim 1 , having a T 200  less than 1580° C. and a liquidus viscosity of 400,000 poise or greater. 
     
     
         20 . The glass according to  claim 1 , 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  or greater, T 200  less than 1630° C., and having a liquidus viscosity of 150,000 poise or greater. 
     
     
         21 . A glass consisting essentially of, in weight percent:
 35 to 75 percent SiO 2 ;   0 to 15 percent Al 2 O 3 ;   0 to 20 percent B 2 O 3 ;   3 to 30 percent K 2 O;   0 to 15 percent MgO;   0 to 10 percent CaO;   0 to 12 percent SrO;   0 to 40 percent BaO; and   0 to 1 percent SnO 2 ,   wherein the glass is substantially free of Na 2 O.   
     
     
         22 . A glass comprising, in weight percent:
 45 to 75 percent SiO 2 ;   3 to 15 percent Al 2 O 3 ;   0 to 20 percent B 2 O 3 ;   14 to 25 percent K 2 O;   0 to 15 percent MgO;   0 to 10 percent CaO;   0 to 12 percent SrO;   0 to 40 percent BaO; and   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  or greater, T 200  less than 1630° C., and having a liquidus viscosity of 150,000 poise or greater.   
     
     
         23 . A glass comprising, in weight percent:
 45 to 75 percent SiO 2 ;   3 to 15 percent Al 2 O 3 ;   0 to 20 percent B 2 O 3 ;   3 to 30 percent K 2 O;   0 to 15 percent MgO;   0 to 10 percent CaO;   0 to 12 percent SrO;   0 to 40 percent BaO; and   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  or greater, T 200  less than 1630° C., and having a liquidus viscosity of 150,000 poise or greater.