Plasma spray deposition of photovoltaic thin films with grain boundary minimization
View Patent ↗Methods are described for depositing thin films, such as those used in forming a photovoltaic cell or device. In particular embodiments, one or more layers are deposited on a substrate by plasma spraying over the substrate. A grain size of grains in each of the one or more layers is at least approximately two times greater than a thickness of the respective layer. Accordingly, large flat-grained structures are formed in each respective layer, and grain boundaries within each respective layer can be minimized.
1. A method, comprising:
providing a substrate suitable for use in a photovoltaic device;
plasma spraying one or more layers over the substrate, an average grain size of grains in each of the one or more layers being at least approximately two times greater than a thickness of the respective layer,
wherein a grain size of the grains is a measure of a dimension of the respective grains along a plane parallel to the one or more layers and the thickness of the respective layer is a measure of a dimension of the respective layer along a plane perpendicular to the one or more layers.
2. The method of claim 1 , wherein the average 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 the plasma spraying of the one or more layers comprises, for each of the one more layers to be deposited over the substrate, injecting a feedstock material into a Plasma Spray Deposition system, and wherein the feedstock material for each of the one more layers 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 a blend of the feedstock material during the Plasma Spray Deposition process to obtain composition grading in the respective layer.
5. The method of claim 3 , further comprising:
altering a blend of the feedstock material during the Plasma Spray Deposition process to compensate for stoichiometric variability between the feedstock material and the respective 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 blend of the feedstock material 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 in which at least a substantial portion is in 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 , further comprising:
subjecting at least one of the one or more layers to one or more thermo-processes after plasma spraying.
14. The method of claim 13 , wherein one or more of the thermo-processes comprise one or more annealing or hot-isostatic-pressing.
15. The method of claim 14 , wherein annealing is carried out in a high temperature environment in the presence of one or more of sulfur (S), selenium (Se), or hydrogen sulfide (H.sub.2S).