Three-stage formation of thin-films for photovoltaic devices
A method for producing a film of compound semiconductor includes providing a substrate and a compound bulk material having a first chemical composition that includes at least one first chemical element and a second chemical element. A film is deposited on the substrate using the compound bulk material as a single source of material. The deposited film has a composition substantially the same as the first chemical composition. A residual chemical reaction is induced in the deposited film using a source containing the second chemical element to thereby increase the content of the second chemical element in the deposited film so that the deposited film has a second chemical composition. The film may be employed in a photovoltaic device.
1. A method for producing a film of compound semiconductor comprising the steps of
providing a substrate;
providing a compound bulk material having a first chemical composition that includes at least one first chemical element and a second chemical element;
depositing a film on the substrate using the compound bulk material as a single source of material, wherein the deposited film has a composition substantially the same as the first chemical composition;
inducing a residual chemical reaction in the deposited film using a source containing the second chemical element to thereby increase the content of the second chemical element in the deposited film so that the deposited film has a second chemical composition.
2. A method of claim 1 wherein said at least one first chemical element comprises a plurality of chemical elements.
3. A method of claim 1 wherein said at least one first chemical element comprises at least one element from group I and group III chemical elements.
4. A method of claim 1 wherein said second chemical element comprises an element from group VI.
5. A method of claim 1 wherein said substrate comprises a first contact layer.
6. A method of claim 1 wherein the second element content in the deposited film is increased by at least 15%.
7. A method of claim 1 wherein said step of depositing the film comprises the steps of preparing the compound bulk material and sputtering the bulk material onto the substrate.
8. A method of claim 1 wherein said step of depositing the film comprises the steps of producing particles from the compound bulk material and coating the particles onto the substrate.
9. A method of claim 1 wherein said residual chemical reaction is produced at a temperature of at least 400° C.
10. A method of claim 1 wherein said second chemical composition is stoichiometric.
11. A method of claim 1 wherein said residual chemical reactions produce a film having a single crystalline phase.
12. A method of claim 1 wherein said first chemical composition comprises Cu, In, Ga and Se.
13. A method of claim 1 wherein said first chemical composition comprises Cd and Te.
14. A method for producing a thin-film solar cell comprising the steps of
depositing a first contact layer on a substrate;
producing an absorber layer over the first contact layer;
depositing a window layer and a second contact layer over the absorber layer, wherein the absorber layer is produced by a process that includes:
providing a compound bulk material having a first chemical composition that includes at least one first chemical element and a second chemical element;
depositing a film over the first contact layer using the compound bulk material as a single source of material, wherein the deposited film has a composition substantially the same as the first chemical composition;
inducing a residual chemical reaction in the deposited film using a source containing the second chemical element to thereby increase the content of the second chemical element in the deposited film so that the deposited film has a second chemical composition.
15. A thin-film solar cell formed in accordance with the method of claim 14 .