Reaction methods to form group IBIIIAVIA thin film solar cell absorbers
View Patent ↗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 and selenium; 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 sodium dopant;
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 first temperature is above 620° C.
3. The method of claim 2 , wherein the second temperature is in the range of 450-525° C.
4. The method of claim 3 , 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.
5. The method of claim 4 , wherein the step of heating includes a ramp rate of at least 5° C./second.
6. The method of claim 1 , wherein the method of forming the Group IBIIIAVIA absorber layer is performed in a roll to roll reactor.
7. The method of claim 6 , wherein the step of providing comprises advancing the workpiece into the roll to roll reactor through an entrance opening.
8. The method of claim 7 , 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.
9. The method of claim 8 , 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.
10. 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.
11. 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.
12. The method of claim 11 , 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.
13. The method of claim 1 , wherein the step of heating includes a ramp rate of at least 5° C./second.