Annealing materials and methods for annealing photovoltaic devices with annealing materials

1. A method for treatment of an absorber layer on a layer stack for a photovoltaic device, comprising:

preparing an annealing material comprising cadmium chloride and a thickening agent,

wherein:

a ratio of the cadmium chloride to the thickening agent in the annealing material is in a range from 1:1 to 160:1, by weight;

the thickening agent comprises at least one of Methyl Cellulose, HydroxyPropyl Methyl Cellulose, or Propylene Glycol; and

the annealing material has a viscosity in a range of 5 to 250 millipascal seconds;

applying a substantially uniform coating of the annealing material to a surface of the absorber layer, wherein the absorber layer comprises cadmium and tellurium, and the absorber layer is doped with a group V dopant;

forming a film having area density in a range of 0.15 mg/cm 2 to 1.20 mg/cm 2 by drying the annealing material applied to the absorber layer; and

processing the absorber layer with the film in contact with the surface of the absorber layer, at an annealing temperature in a range of 350° C. to 650° C. for between 5 minutes and 60 minutes.

2. The method of claim 1 wherein forming the film further comprises:

exposing the annealing material on the absorber layer to a temperature in a range of 25′ C to 200° C.

3. The method of claim 1 , comprising: measuring the gel of the annealing material with a material sensor; communicating a signal to one or more processors communicatively coupled to the material sensor, wherein the signal is indicative of the viscosity of the gel of the annealing material; and determining, automatically with the one or more processors, the density of the gel of the annealing material, wherein the surface of the absorber layer is contacted when the viscosity of the gel of the annealing material is greater than or equal to 5 millipascal seconds.

4. The method of claim 1 , comprising roll coating the surface of the absorber layer with the annealing material, wherein the surface of the absorber layer is directly contacted with an application roller.

5. The method of claim 4 , comprising: capturing overflow of the gel of the annealing material from the absorber layer and recirculating the gel of the annealing material that is captured to the application roller.

6. The method of claim 1 , wherein the step of forming a film comprises transforming the gel of the annealing material into a film of the annealing material by heating the gel of the annealing material, prior to annealing the absorber layer.

7. The method of claim 6 , wherein the gel is heated to a temperature greater than or equal to 30° C. and less than or equal to 60° C.

8. The method of claim 1 , comprising: mixing a solution of the annealing material at a mixing temperature; and transforming the solution of the annealing material into the gel of the annealing material, before the surface of the absorber layer is contacted with the gel of the annealing material, wherein: the gel of the annealing material is at an application temperature, and the application temperature is less than the mixing temperature.

9. The method of claim 1 , comprising exposing the absorber layer to a reducing environment, while the absorber layer is annealed.

10. The method of claim 1 , wherein the thickening agent is Methyl Cellulose.

11. The method of claim 1 , wherein the thickening agent is HydroxylPropyl Methyl Cellulose.

12. The method of claim 1 , wherein the thickening agent comprises Propylene Glycol, and wherein a ratio of the cadmium chloride to the Propylene Glycol in the gel of the annealing material, by weight, is greater than or equal to 1 to 1, and equal to or less than 30 to 1.