Deposition of photovoltaic thin films by plasma spray deposition
In particular embodiments, a method is described for depositing thin films, such as those used in forming a photovoltaic cell or device. In a particular embodiment, the method includes providing a substrate suitable for use in a photovoltaic device and plasma spraying one or more layers over the substrate, the grain size of the grains in each of the one or more layers being at least approximately two times greater than the thickness of the respective layer.
1. A method, comprising:
providing a substrate suitable for use in a photovoltaic device;
plasma spraying one or more layers over the substrate, the average grain size of the grains in each of the one or more layers being at least approximately two times greater than the thickness of the respective layer, wherein a grain size of a grain is a measure of a dimension of the respective grain along a plane parallel to the one or more layers and wherein the thickness of a respective layer is a measure of a dimension of the respective layer along a plane perpendicular to the one or more layers; and
after one or more of the one or more layers are plasma-sprayed, subjecting the one or more of the one or more plasma-sprayed layers to one or more thermo-processes.
2. The method of claim 1 , wherein the grain size of the grains in each of the one or more layers is at least approximately ten times greater than the thickness of the respective layer.
3. The method of claim 1 , wherein plasma spraying one or more layers comprises, for each layer to be deposited over the substrate, injecting a feedstock material into a Plasma Spray Deposition system, and wherein the feedstock material includes the constituent elements, compounds, or alloys that form the respective layer upon plasma spraying the respective layer.
4. The method of claim 3 , further comprising altering the feedstock material blend during the Plasma Spray Deposition process to obtain composition grading in the respective plasma-sprayed layer.
5. The method of claim 3 , further comprising altering the feedstock material blend during the Plasma Spray Deposition process to compensate for stoichiometric variability between the feedstock material and the respective plasma-sprayed layer including compensating for losses of relatively more volatile or lower melting point constituents in the feedstock material.
6. The method of claim 5 , further comprising adding one or more additives to the feedstock material blend including one or more varieties of oxide particles.
7. The method of claim 1 , wherein the one or more layers comprise an absorber layer of the photovoltaic device.
8. The method of claim 7 , wherein the absorber layer is comprised of a chalcogenide material at least a substantial portion of which is in the form of a chalcopyrite phase.
9. The method of claim 1 , wherein the one or more layers comprise a buffer layer of the photovoltaic device.
10. The method of claim 1 , wherein the one or more layers comprise a top contact layer or a bottom contact layer of the photovoltaic device.
11. The method of claim 1 , wherein the one or more layers comprise a transparent conductive layer of the photovoltaic device.
12. The method of claim 1 , wherein the one or more layers comprise a protective transparent layer of the photovoltaic device.
13. The method of claim 1 , wherein one or more of the thermo-processes comprise one or more annealing or hot-isostatic-pressing.
14. The method of claim 13 , wherein one or more of the one or more annealing processes are carried out in a high temperature environment in the presence of one or more of sulfur (S), selenium (Se), or hydrogen sulfide (H 2 S).