METHODS AND SYSTEMS FOR FORMING FUNCTIONALLY GRADED FILMS BY SPRAY PYROLYSIS

1 . A method for forming a plurality of cadmium-sulfide layers, the method comprising:

preparing at least a first solution for forming a first cadmium-sulfide layer and a second solution for forming a second cadmium-sulfide layer;

loading at least the first solution and the second solution into a pyrolysis-deposition system, the pyrolysis-deposition system including one or more first nozzles and one or more second nozzles, the one or more first nozzles and the one or more second nozzles being different;

placing a target structure into the pyrolysis-deposition system;

spraying the first solution through the one or more first nozzles towards the target structure;

forming, from the sprayed first solution, the first cadmium-sulfide layer, directly or indirectly, on the target structure, the first cadmium-sulfide layer including a first cadmium-sulfide material;

spraying the second solution through the one or more second nozzles towards the target structure with at least the first cadmium-sulfide layer; and

forming, from the sprayed second solution, the second cadmium-sulfide layer directly or indirectly, on the target structure, the second cadmium-sulfide layer including a second cadmium-sulfide material;

wherein:

the first solution includes a solute corresponding to a first solute concentration;

the second solution includes the solute corresponding to a second solute concentration; and

the first solute concentration and the second solute concentration are different;

wherein the first cadmium-sulfide material and the second cadmium-sulfide material are different in at least one material property.

2 . The method of claim 1 wherein the process for forming the second cadmium-sulfide layer includes forming the second cadmium-sulfide layer entirely on the first-cadmium-sulfide layer.

3 . The method of claim 1 wherein the process for forming the second cadmium-sulfide layer includes forming the second-cadmium sulfide layer between one or more regions of the first cadmium-sulfide layer.

4 . The method of claim 1 wherein the process for forming the first cadmium-sulfide layer includes forming the first cadmium-sulfide layer as a contiguous layer.

5 . The method of claim 1 wherein the process for forming the first cadmium-sulfide layer includes forming the first cadmium-sulfide layer as a plurality of discontiguous regions of the first cadmium-sulfide material.

6 . The method of claim 1 wherein the process for forming the second cadmium-sulfide layer includes forming the second cadmium-sulfide layer as a contiguous layer.

7 . The method of claim 1 wherein the process for forming the second cadmium-sulfide layer includes forming the second cadmium-sulfide layer as a plurality of discontiguous regions of the second cadmium-sulfide material.

8 . The method of claim 1 , and further comprising:

adjusting a first distance between the one or more first nozzles and the target structure; and

adjusting a second distance between the one or more second nozzles and the target structure;

wherein:

the process for forming the first cadmium-sulfide layer includes heating the target structure to a first temperature; and

the process for forming the second cadmium-sulfide layer includes heating the target structure to a second temperature.

9 . The method of claim 8 wherein the first distance and the second distance are the same.

10 . The method of claim 8 wherein the first temperature and the second temperature are the same.

11 . The method of claim 1 , and further comprising:

applying a first bias voltage between the one or more first nozzles and the target structure; and

applying a second bias voltage between the one or more second nozzles and the target structure.

12 . The method of claim 11 wherein the first bias voltage and the second bias voltage are the same.

13 . The method of claim 1 , and further comprising planarizing at least the second cadmium-sulfide layer.

14 . The method of claim 1 wherein:

the first solution includes water, a cadmium-containing solute, and a sulfur-containing solute; and

the second solution includes water, the cadmium-containing solute, and the sulfur-containing solute.

15 . The method of claim 14 wherein:

the cadmium-containing solute is present in the first solution with a first concentration of between 0.001 mol. and 0.1 mol.;

the sulfur-containing solute is present in the first solution with a second concentration of between 0.001 mol. and 0.1 mol;

the cadmium-containing solute is present in the second solution with a third concentration of between 0.2 mol. and 1.0 mol.; and

the sulfur-containing solute is present in the second solution with a fourth concentration of between 0.2 mol. and 1.0 mol.

16 . The method of claim 14 wherein:

the cadmium-containing solute is cadmium chloride; and

the sulfur-containing solute is thiourea.

17 . The method of claim 1 wherein:

the process for spraying the first solution includes spraying the first solution at a first flow rate;

the process for spraying the second solution includes spraying the second solution at a second flow rate; and

the first flow rate and the second flow rate are different.

18 . The method of claim 1 wherein the material property is selected from a group consisting of electrical properties, crystal structures, and optical reactive properties.

19 . A method for forming a photovoltaic module, the method comprising:

providing a substrate;

depositing one or more first electrodes directly or indirectly on the substrate;

spraying a first solution through one or more first nozzles towards at least the substrate;

forming, from the sprayed first solution, a first cadmium-sulfide layer, directly or indirectly, on the substrate, the first cadmium-sulfide layer including a first cadmium-sulfide material;

spraying a second solution through one or more second nozzles towards at least the substrate;

forming, from the sprayed second solution, a second cadmium-sulfide layer, directly or indirectly, on the substrate, the second cadmium-sulfide layer including a second cadmium-sulfide material;

depositing a cadmium-telluride layer, directly or indirectly, on the second cadmium-sulfide layer; and

depositing one or more second electrodes at least partially on the cadmium-telluride layer;

wherein:

the first solution includes a solute corresponding to a first solute concentration;

the second solution includes the solute corresponding to a second solute concentration; and

the first solute concentration and the second solute concentration are different;

wherein the first cadmium-sulfide material and the second cadmium-sulfide material are different in at least one material property.

20 . The method of claim 19 wherein the process for forming the first cadmium-sulfide layer includes forming the first cadmium-sulfide layer on the one or more first electrodes.

21 . The method of claim 19 wherein the process for forming the second cadmium-sulfide layer includes forming the second cadmium-sulfide layer on the first cadmium-sulfide layer.

22 . The method of claim 19 wherein the process for forming the cadmium-telluride layer includes forming the cadmium-telluride layer on a third cadmium-sulfide layer.

23 . The method of claim 19 wherein the substrate includes glass.

24 . The method of claim 19 wherein the material property is selected from a group consisting of electrical properties, crystal structures, and optical reactive properties.

25 . A photovoltaic module with at least two cadmium-sulfide layers, the module comprising:

a substrate;

one or more first electrodes directly or indirectly on the substrate;

a first cadmium-sulfide layer, directly or indirectly, on the substrate, the first cadmium-sulfide layer including a first cadmium-sulfide material;

a second cadmium-sulfide layer, directly or indirectly, on the substrate, the second cadmium-sulfide layer including a second cadmium-sulfide material;

a cadmium-telluride layer, directly or indirectly, on the second cadmium-sulfide layer; and

one or more second electrodes at least partially on the cadmium-telluride layer;

wherein the first cadmium-sulfide material and the second cadmium-sulfide material are different in at least one material property.

26 . The module of claim 25 wherein the material property is selected from a group consisting of electrical properties, crystal structures, and optical reactive properties.

27 . A system for forming cadmium-sulfide layers, the system comprising:

a first liquid supply for providing a first solution including a cadmium-containing solute corresponding to a first concentration, a sulfur-containing solute corresponding to a second concentration, and water;

a second liquid supply for providing a second solution including the cadmium-containing solute corresponding to a third concentration, the sulfur-containing solute corresponding to a fourth concentration, and water;

a holder configured to support a target structure;

one or more heating devices configured to heat the target structure;

one or more first nozzles configured to spray the first solution towards the target structure; and

one or more second nozzles configured to spray the second solution towards the target structure;

wherein:

a first distance between the one or more first nozzles and the target structure is configured to be adjustable; and

a second distance between the one or more second nozzles and the target structure is configured to be adjustable;

wherein the first concentration and the third concentration are different or the second concentration and the fourth concentration are different;

wherein:

the system is further configured to form a first cadmium-sulfide layer, directly or indirectly, on the target structure using the sprayed first solution; and

the system is further configured to form a second cadmium-sulfide layer, directly or indirectly, on the target structure using the sprayed second solution, the second cadmium-sulfide material being different from the first cadmium-sulfide material in at least one material property.

28 . The system of claim 27 wherein the material property is selected from a group consisting of electrical properties, crystal structures, and optical reactive properties.

29 . The system of claim 27 wherein the first concentration and the third concentration are different, and the second concentration and the fourth concentration are different.