REACTION METHODS TO FORM GROUP IBIIIAVIA THIN FILM SOLAR CELL ABSORBERS
The present invention provides a method to form Group IBIIIAVIA solar cell absorber layers on continuous flexible substrates. In a preferred aspect, the method forms a Group IBIIIAVIA absorber layer for manufacturing photovoltaic cells by providing a workpiece having a precursor layer formed over a substrate, the precursor layer including copper, indium, gallium, selenium and a dopant of a Group IA material; heating the precursor layer to a first temperature; reacting the precursor layer at the first temperature for a first predetermined time to transform the precursor layer to a partially formed absorber structure; cooling down the partially formed absorber structure to a second temperature, wherein both the first temperature and the second temperature are above 400° C.; and reacting the partially formed absorber structure at the second temperature for a second predetermined time, which is longer than the first predetermined time, to form a Group IBIIIAVIA absorber layer.
1 . A method of forming a Group IBIIIAVIA absorber layer for manufacturing photovoltaic cells, comprising:
providing a workpiece having a precursor layer formed over a substrate, the precursor layer including copper, indium, gallium, selenium and a dopant including a Group IA material;
heating the precursor layer to a first temperature;
reacting the precursor layer in selenium vapor at the first temperature for a first predetermined time to transform the precursor layer to a partially formed absorber structure;
removing the selenium vapor after the step of reacting the precursor layer at the first temperature;
cooling down the partially formed absorber structure to a second temperature,
wherein the first temperature and the second temperature are each above 400° C., and the first temperature is greater than the second temperature; and
reacting the partially formed absorber structure in an inert gas atmosphere at the second temperature for a second predetermined time, which is longer than the first predetermined time, to form a Group IBIIIAVIA absorber layer.
2 . The method of claim 1 wherein the Group IA dopant material is provided in an amount that ranges from 0.03 to 3 atomic percent of the copper in the precursor layer.
3 . The method of claim 1 , wherein the Group IA material comprises one of Li and K.
4 . The method of claim 3 further comprising a Group VA material.
5 . The method of claim 4 , wherein the Group VA material comprises one of Bi, As and Sb.
6 . The method of claim 1 further comprising a Group VA material.
7 . The method of claim 6 , wherein the Group VA material comprises one of Bi, As and Sb.
8 . The method of claim 1 , wherein the first temperature is above 620° C.
9 . The method of claim 8 , wherein the second temperature is in the range of 450-525° C.
10 . The method of claim 9 , wherein the first predetermined time is in the range of 2-7 minutes and the second predetermined time is in the range of 15-25 minutes.
11 . The method of claim 10 , wherein the step of heating includes a ramp rate of at least 5° C./second.
12 . The method of claim 1 , wherein the method of forming the Group IBIIIAVIA absorber layer is performed in a roll to roll reactor.
13 . The method of claim 12 , wherein the step of providing comprises advancing the workpiece into the roll to roll reactor through an entrance opening.
14 . The method of claim 13 , wherein the workpiece is released from a supply spool adjacent the entrance opening by unwrapping the workpiece from the supply spool before the step of providing.
15 . The method of claim 14 , wherein the workpiece is received from an exit opening of the roll to roll reactor and wrapped around a receiving spool adjacent the entrance opening after the step of reacting the partially formed absorber structure.
16 . The method of claim 1 , wherein the step of reacting the precursor layer at the second temperature is carried out in an inert gas atmosphere.
17 . The method of claim 1 , wherein the first temperature is in the range of 525-650° C. and the second temperature is in the range of 450-525° C.
18 . The method of claim 17 , wherein the first predetermined time is in the range of 2-7 minutes and the second predetermined time is in the range of 15-25 minutes.
19 . The method of claim 1 , wherein the step of heating includes a ramp rate of at least 5° C./second.
20 . A method of forming a Group IBIIIAVIA absorber layer for manufacturing photovoltaic cells, comprising:
providing a workpiece having a precursor formed over a substrate, the precursor including copper, indium, gallium, selenium and a dopant including a Group IA material, wherein the dopant material is formed on a first stack layer of the precursor that is disposed directly on the substrate;
heating the precursor to a first temperature;
reacting the precursor in a selenium vapor to form a Group IBIIIAVIA absorber layer.
21 . The method of claim 20 wherein the Group IA dopant material is provided in an amount that ranges from 0.03 to 3 atomic percent of the copper in the precursor layer.
22 . The method of claim 20 , wherein the Group IA material comprises one of Na, Li and K.
23 . The method of claim 22 further comprising a Group VA material.
24 . The method of claim 23 , wherein the Group VA material comprises one of Bi, As and Sb.
25 . The method of claim 29 further comprising a Group VA material.
26 . The method of claim 25 , wherein the Group VA material comprises one of Bi, As and Sb.