Roll-to-roll reactor for processing flexible continuous workpiece

Abstract

The present invention provides a reactor for preparing thin films of compound semiconductors for photovoltaic devices. The reactor includes a chamber that has a bottom surface that, in some locations, has protrusions that contact the bottom surface of the substrate having the compound semiconductor to provide uniform heating and cooling of the substrate. Interior walls of the chamber can also be lined with high thermal conductivity portions and low thermal conductivity portions interposed between high thermal conductivity portions.

1 . A roll-to-roll thermal reactor to heat and react a precursor material disposed over a continuous workpiece to form a solar cell absorber, the reactor comprising:
 an elongated process enclosure defined by a peripheral wall including a top wall, side walls and a bottom wall, wherein the continuous workpiece enters the elongated process enclosure from an entrance opening, advances through the elongated process chamber while contacting the bottom wall, and exits from an exit opening; and   at least one reduced contact surface region formed in an inner surface of the bottom wall so that the physical contact between the workpiece and the bottom wall is reduced, wherein the reduced contact surface region includes a plurality of fixed protrusions projecting upwardly from the inner surface of the bottom wall and wherein the workpiece touches topmost ends of the plurality of fixed protrusions.   
     
     
         2 . The reactor of  claim 1 , wherein the elongated process enclosure includes at least one heating section to heat the workpiece to a reaction temperature, at least one reaction section to react the precursor material of the workpiece at the reaction temperature and at least one cooling section to cool the workpiece with the reacted precursor. 
     
     
         3 . The reactor of  claim 2 , wherein the reduced contact surface region is formed in at least one of the heating and cooling sections. 
     
     
         4 . The reactor of  claim 3 , wherein the shape of the fixed protrusions includes at least one of a hemispherical shape, a cylindrical shape, a conical shape, pyramidal shape and rectangular shape. 
     
     
         5 . The reactor of  claim 4 , wherein the height of the fixed protrusions is in the range of 0.5-15 mm and the distance between the topmost ends is in the range of 25-500 mm. 
     
     
         6 . The reactor of  claim 5 , wherein the fixed protrusions are cylindrical rods extending along the width of the bottom wall. 
     
     
         7 . The reactor of  claim 6 , wherein the height of the cylindrical rods is in the range of 0.5-15 mm and wherein the distance between top most end of the cylindrical rods is in the range of 25-500 mm. 
     
     
         8 . The reactor of  claim 3  wherein the heating, reaction and cooling sections of the elongated process enclosure are formed of a layer of a first material, and wherein each section is separated from one another by a layer of a second material, and wherein the thermal conductivity of the second material is less than the thermal conductivity of the first material. 
     
     
         9 . The reactor of  claim 8  wherein thermal conductivity of the first material is greater than 5 W/m-K, and the thermal conductivity of the second material is less than 2 W/m-K. 
     
     
         10 . The reactor of  claim 8 , wherein the first material includes one of silicon carbide, aluminum nitride and graphite, and the second material includes one of fused silica, amorphous ceramics, ceramoplastics, glass-ceramic, microporous ceramics. 
     
     
         11 . The reactor of  claim 10 , wherein the plurality of fixed protrusions are made of the first material. 
     
     
         12 . The reactor of  claim 11 , wherein the plurality of fixed protrusions are made of the second material. 
     
     
         13 . The reactor of  claim 1 , wherein the bottom wall is made of a first material and the plurality of fixed protrusions are made of a second material, and wherein the thermal conductivity of the first material is greater than the second material. 
     
     
         14 . The reactor of  claim 13 , wherein the bottom wall and the plurality of fixed protrusions are made of a first material. 
     
     
         15 . The reactor of  claim 14 , wherein the first material includes one of silicon carbide, aluminum nitride, alumina, zirconia, magnesia-stabilized zirconia, yttria-stabilized zirconia and graphite, and the second material includes one of fused silica, and other amorphous ceramics, ceramoplastics, glass-ceramic, microporous ceramics. 
     
     
         16 . The reactor of  claim 1 , wherein the elongated process enclosure is an insert placed in a space defined by a peripheral reactor wall, and wherein the peripheral reactor wall include heating elements. 
     
     
         17 . A solar cell processing system comprising:
 a continuous workpiece containing a precursor material used to form a solar cell absorber;   a reactor having a inlet and an outlet and a central chamber disposed between the inlet and the outlet, wherein the continuous workpiece is provided into the inlet of the reactor and extends through the central chamber and exits via the outlet wherein a portion of the reactor includes a reduced contact surface where the bottom surface of the continuous workpiece is intermittently supported by the reduced contact surface;   a heating system that heats the reactor; and   a gas supply system that provides a reactive gas into the reactor so that the combination of the reactive gas and the heat from the heating system transforms the precursor material on the continuous workpiece into the solar cell absorber.   
     
     
         18 . The system of  claim 17 , wherein gas is introduced into the reactor via the gas supply system adjacent the inlet and the exhaust gas is removed through an exhaust located between the inlet and outlet. 
     
     
         19 . The system of  claim 18 , wherein the reactor has an expansion region interposed between the inlet and the central chamber where the gas expands as a result of the heating system heating the central chamber and a contraction region interposed between the central chamber and the outlet where the gas contacts as a result of the gas cooling after leaving the central chamber. 
     
     
         20 . The system of  claim 19 , wherein the reduced contact surface is located in the gas expansion region. 
     
     
         21 . The system of  claim 20 , wherein the reduced contact surface is also located in the gas contraction region. 
     
     
         22 . The system of  claim 20 , wherein the reduced contact surface comprises a plurality of fixed protrusions that contact the bottom side of the continuous workpiece at intermittent locations. 
     
     
         23 . The system of  claim 22 , wherein the plurality of fixed protrusions comprise ridges that extend substantially across the width of the continuous workpiece. 
     
     
         24 . The system of  claim 23 , wherein the ridges are approximately 25-500 mm apart. 
     
     
         25 . The system of  claim 22 , wherein the plurality of fixed protrusions comprise discrete protrusions that are spaced apart from each other having an average density of 100 10,000 protrusion per m 2 . 
     
     
         26 . The system of  claim 22 , wherein the fixed protrusions are formed of a low thermal conductivity material. 
     
     
         27 . The system of  claim 26 , wherein the fixed protrusions are formed of fused silica. 
     
     
         28 . The system of  claim 21 , wherein the reduced contact area is formed on an insert that is positioned in the reactor. 
     
     
         29 . The system of  claim 28 , wherein the insert layer is a continuous layer including high thermal conductivity portions defining at least one heating section, at least one reaction section and at least one cooling section and low thermal conductivity portions placed between the sections. 
     
     
         30 . A solar cell processing system comprising:
 a continuous workpiece containing a precursor material used to form a solar cell absorber;   a reactor having a inlet and an outlet and a central chamber disposed between the inlet and the outlet, wherein the continuous workpiece is provided into the inlet of the reactor and extends through the central chamber and exits via the outlet wherein the reactor includes heating, reaction and cooling sections and wherein the heating, reaction and cooling sections of the reactor are formed of a layer of a first material, and wherein each section is separated from one another by a layer of a second material, and wherein the thermal conductivity of the second material is less than the thermal conductivity of the first material;   a heating system that heats the reactor; and   a gas supply system that provides a reactive gas into the reactor so that the combination of the reactive gas and the heat from the heating system transforms the precursor material on the continuous workpiece into the solar cell absorber.   
     
     
         31 . The system of  claim 30 , wherein a portion of the reactor includes a reduced contact surface where the bottom surface of the continuous workpiece is intermittently supported by the reduced contact surface. 
     
     
         32 . The system of  claim 31 , wherein the reduced contact surface is located in the heating section. 
     
     
         33 . The system of  claim 32 , wherein the reduced contact surface is also located in the cooling section. 
     
     
         34 . The system of  claim 32 , wherein the reduced contact surface comprises a plurality of fixed protrusions that contact the bottom side of the continuous workpiece at intermittent locations. 
     
     
         35 . The system of  claim 34 , wherein the plurality of fixed protrusions comprise ridges that extend substantially across the width of the continuous workpiece. 
     
     
         36 . The reactor of  claim 30  wherein thermal conductivity of the first material is greater than 5 W/m-K, and the thermal conductivity of the second material is less than 2 W/m-K. 
     
     
         37 . The reactor of  claim 30 , wherein the first material includes one of silicon carbide, aluminum nitride and graphite, and the second material includes one of fused silica, amorphous ceramics, ceramoplastics, glass-ceramic, microporous ceramics.