Method for Producing a Nitrogen-Free Layer Comprising Silicon Carbide

Abstract

The present invention relates to a method for producing a thin nitrogen-free layer of silicon carbide by means of a carbon- and silicon-containing solution or dispersion.

Claims

1-20. (canceled)

21. A method for producing a silicon carbide-containing layer, the layer being nitrogen-free, wherein (a) in a first method step, a liquid carbon- and silicon-containing solution or dispersion, in particular a SiC precursorsol, is applied to a carrier, (b) in a second method step following the first method step (a), the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is converted to silicon carbide, wherein the carbon- and silicon-containing solution or dispersion is subjected to a multi-stage thermal treatment, wherein (i) in a first thermal process stage (i) the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is heated to temperatures of 300 C. or higher, in particular 300 to 1800 C., preferably 800 to 1000 C., and (ii) in a second thermal process stage following the first thermal process stage (i), the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is heated to temperatures of 1800 C. or higher, in particular 1800 to 2200 C.

22. Method according to claim 21, characterized in that the thermal process stage (i) is carried out for at least about 5 to 150 minutes, and/or that the thermal process stage (ii) is carried out for at least about 10 to 90 minutes.

23. Method according to claim 21, characterized in that in a process stage preceding the first thermal process stage (i) the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is heated to temperatures in the range of from 50 to 800 C., for at least substantially 5 to 30 minutes.

24. Method according to claim 21, characterized in that in process stage (i) nitrogen-containing compounds contained in the carbon- and silicon-containing solution or dispersion . . . the SiC precursorsol . . . are decomposed and/or transferred into the gas phase, wherein all nitrogen-containing compounds are decomposed by the temperature treatment, and transferred into the gas phase.

25. Method according to claim 21, characterized in that in process stage (i) the carbon- and silicon-containing solution or dispersion . . . the SiC precursorsol . . . is converted into a glass.

26. Method according to claim 25, characterized in that in process stage (ii) the glass obtained in process stage (i), is converted into crystalline silicon carbide.

27. Method according to claim 21, characterized in that a dopant is added to the SiC precursorsol.

28. Method according to claim 21, characterized in that for the first method step (a), the carbon- and silicon-containing solution or dispersion . . . the SiC precursorsol . . . is applied as a layer, in particular as an homogeneous layer, to a carrier selected from the group consisting of a silicon carbide-comprising carrier, a 3C-SiC-comprising carrier, and an n-doped, carrier.

29. Method according to claim 21, characterized in that in method step (a) the carbon- and silicon-containing solution or dispersion . . . the SiC precursorsol . . . is applied to the carrier by a coating process selected from the group consisting of dip coating, spin coating, spraying, rolling, pressing, and printing.

30. Method according to claim 21, characterized in that in method step (a) the carbon- and silicon-containing solution or dispersion . . . the SiC precursorsol . . . is applied to the carrier as a layer having thickness in the range from 1 m to 1,000 m.

31. Method according to claim 21, characterized in that the material of the carrier is selected from the group consisting of carbon, ceramic materials, mineral materials and metals.

32. Method according to claim 31, characterized in that the material of the carrier is selected from the group consisting of graphite, silicon carbide, silicon dioxide, corundum, sapphire, aluminium oxide, steel, and mixtures thereof.

33. Method according to claim 31, characterized in that after the thermal treatment, the carrier is removed.

34. A silicon carbide layer, produced by a method according to claim 21, wherein the silicon carbide layer consists of a silicon carbide layer selected from the group consisting of a SiC layer and a 3C-SiC layer, wherein, the silicon carbide layer or wafer is completely nitrogen-free.

35. Method for producing a solar cell, in particular an intermediate band solar cell having a layered structure with at least one, thin, nitrogen-free layer comprising silicon carbide, produced according to a method according to claim 21 wherein, in order to produce the nitrogen-free layer, (a) in a first method step, a liquid carbon- and silicon-containing solution or dispersion, in particular a SiC precursorsol, is applied to a carrier or a layer of the layered carrier, (b) in a second method step following the first method step (a), the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is converted to silicon carbide, wherein the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is subjected to a multi-stage thermal treatment, wherein (i) in a first thermal process stage (i) the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is heated to temperatures of 300 to 1800 C., and (ii) in a second thermal process stage (ii) following the first thermal process stage (i), the carbon- and silicon-containing solution or dispersion, in particular the SiC precursorsol, is heated to temperatures of 1800 to 2200 C.

36. Method according to claim 35, characterized in that in method step (a) the carbon- and silicon-containing solution or dispersion, (the SiC precursorsol), is applied with a layer thickness in the range from 1 nm to 1,000 m.

37. Method according to claim 35, characterized in that an at least two-layer structure is applied, wherein the at least two-layer structure has a further layer, comprising silicon carbide, produced according to at least one method feature according to claim 21.

38. Method according to claim 27, characterized in that first the further layer is applied to the carrier and then the nitrogen-free layer is applied to the further layer.

39. Method according to claim 37, characterized in that the further layer is doped, preferably n-doped, in particular by nitrogen and/or phosphorus.

40. An intermediate band solar cell, produced according to claim 35, including a SiC layer or wafer with at least one layer comprising silicon carbide, preferably 3C-SiC, wherein, the at least one layer is completely free of nitrogen.

Description

[0192] It is shown according to:

[0193] FIG. 1 a schematic representation of the layer structure of a solar cell according to the invention,

[0194] FIG. 2 a schematic representation of the layer structure of a further embodiment of a solar cell according to the invention,

[0195] FIG. 3 a schematic representation of the layer structure of a further embodiment of a solar cell according to the invention,

[0196] FIG. 4 a schematic representation of the layer structure of a further embodiment of a solar cell according to the invention,

[0197] FIG. 5 a schematic perspective representation of a further embodiment of a solar cell according to the invention and

[0198] FIG. 6 a schematic representation of the process for producing a nitrogen-free layer as invented.

[0199] FIG. 1 shows a schematic layer structure of a solar cell 1, whereby the solar cell 1 has a carrier 4. Preferably, carrier 4 is a strongly nitrogen-doped silicon carbide or a transparent substrate, for example of quartz glass. A further layer 3 has been applied to carrier 4. On the further layer 3 a nitrogen-free layer 2 has been applied.

[0200] In the design example shown, carrier 4 has a layer density of at least essentially 100 m. Furthermore, the carrier 4 is made of silicon carbide, which is also n-doped.

[0201] The other layer 3 and the nitrogen-free layer 2 have a layer thickness of at least essentially 100 nm. It is not shown that the further layer 3 has been applied to the carrier 4 by dip coating and the nitrogen-free layer 2 has been sprayed on. Furthermore, the nitrogen-free layer 2 is p-doped. Boron is used as the dopant for the nitrogen-free layer in the example shown. The other layer 3 is n-doped. The other layer 3 is doped with nitrogen. Accordingly, the further layer 3 has nitrogen, whereas the nitrogen-free layer 2 is completely nitrogen-free. In the example shown, both the further layer 3 and the nitrogen-free layer 2 have silicon carbide as material.

[0202] Furthermore, FIG. 2 shows another possible layer structure of the solar cell 1, where the nitrogen-free layer 2 has been applied to the carrier 4, while the nitrogen-free layer 2 serves as a carrier for the further layer 3. The further layer 3 and the nitrogen-free layer 2 have the material composition that has already been explained in the design example in FIG. 1.

[0203] FIG. 3 shows that after the layered structure of the solar cell 1 has been produced, the carrier 4, which previously served as a carrier for the further layer 3, can be removed.

[0204] Furthermore, FIG. 4 shows that an electrode, in particular a metal grid 6, can be arranged on top of the solar cell 1, i.e. in the present case on top of the nitrogen-free layer 2 and thus on the side of the solar cell 1 opposite the carrier 4. In the example shown, the metal grid 6 is configured as an aluminum drainage grid. The aluminium grid is used for contacting the solar cell 1.

[0205] FIG. 5 also shows that a further electrically conductive layer 5, in particular a metal layer or a TCO anode, can be arranged on the side of the solar cell 1 facing away from the metal grid 6. In other embodiments a mirror coating can be provided instead of and/or in addition to the electrically conductive layer. In the example shown, a TCO anode is provided as electrically conductive.

[0206] What is not shown is that in addition to the nitrogen-free layer 2 and the further layer 3, a protective layer, preferably undoped, can be provided, which can be arranged below and/or above layers 2, 3, for example.

[0207] The solar cell 1 shown in FIG. 5 is designed as a so-called intermediate band solar cell, whereby it uses an intermediate band energy level (intermediate band) between the conduction and valence band to increase the efficiency of solar cell 1. In this context, it is essential that the nitrogen-free layer 2 does not contain nitrogen. In the nitrogen-free layer 2, the material used is 3C-SiC, which is suitable for use within an intermedia band solar cell due to its large band gap.

[0208] Furthermore, according to an embodiment of the solar cell 1 not shown in the figure, it is possible that the solar cell has a transparent substrate 4, in particular a quartz glass substrate, on which the electrically conductive layer 5 is applied, in particular in the form of a TCO anode. An n-doped further layer 3, in particular an n-doped silicon carbide layer, is applied to the electrically conductive layer 5. The further silicon carbide layer is preferably n-doped with nitrogen or phosphorus. The nitrogen-free layer 2, which is p-doped, is applied to the further layer, in particular by using boric acid. An electrode, in particular a cathode, in the form of an aluminium grid is then applied to the nitrogen-free layer 2. Furthermore, it is possible that one or more protective layers, in particular based on silicon carbide, are applied to the electrode.

[0209] FIG. 6 shows a schematic representation of the method for producing a nitrogen-free layer 2. In step (1), the nitrogen-free layer 2 is applied to a carrier. Possible methods of application include printing, dipping, spin coating, dip coating, spraying, rolling or pressing. Preferably, the nitrogen-free layer 2 is applied to the substrate by dipping in step (1). Here, the nitrogen-free layer 2 is initially provided as a carbon- and silicon-containing solution or dispersion, especially SiC precursorsol.

[0210] In step (2), the carbon- and silicon-containing solution or dispersion is heated for drying and/or preheating to a temperature of at least substantially 200 C. for 15 minutes.

[0211] In steps (3) to (5) the carbon- and silicon-containing solution or dispersion is converted to silicon carbide, a thermal treatment being provided for this conversion. If necessary, the carbon- and silicon-containing solution and dispersion may contain doping reagents.

[0212] In step (3), in a first thermal process stage (i) it is provided that the carbon- and silicon-containing solution or dispersion is heated to 900 C. for 60 minutes.

[0213] In addition, step (4) provides that the carbon- and silicon-containing solution, in particular the glass obtained from step (3), is cooled, preferably quenched.

[0214] In step (5), in a second thermal process stage (ii), the carbon- and silicon-containing solution or dispersion is heated to at least substantially 2000 C. for at least substantially 40 minutes.

[0215] In addition, the process for the production of a nitrogen-free layer 2 described above provides for a doping of the nitrogen-free layer 2. Doping of the nitrogen-free layer 2 is preferably effected by using a solution or dispersion containing boric acid and carbon and nitrogen. However, it is also possible to adjust the electrical properties of the nitrogen-doped layer 2 by the targeted generation of grid gaps, for example by irradiation with high-energy electromagnetic radiation in step (6).

[0216] In step (7) the carrier 4 or substrate can be removed from the nitrogen-free layer 2.

[0217] In further process steps it may be provided that a further layer 3 and/or a protective layer, preferably undoped, can be applied to the nitrogen-free layer 2. In addition, the nitrogen-free layer 2 can also be applied to the further layer 3 and/or to the protective layer, preferably undoped. In this case, the aforementioned layers and/or a substrate can serve as a carrier 4 for depositing the carbon- and silicon-containing solution or dispersion for producing the nitrogen-free layer 2.

[0218] It is also intended that in step (1) the carbon- and silicon-containing solution or dispersion is applied with a layer thickness of 10 m. The application is carried out in such a way that a homogeneous layer, in particular of the SiC precursor sol, is formed on the substrate.

[0219] Furthermore, it is also intended that crystalline silicon carbide is obtained from the carbon- and silicon-containing solution or dispersion by the thermal treatment in steps (3) and (5), whereby a glass is obtained in step (3). Accordingly, step (3) provides that the carbon- and silicon-containing solution or dispersion is converted into a glass.

[0220] The thermal treatment in step (3) is carried out at such a temperature or for such a long time that it can be ensured that all nitrogen-containing compounds have been decomposed by the temperature treatment, whereby the nitrogen-containing compounds can be transferred into the gas phase so that the nitrogen-free layer 2 obtained from the carbon- and silicon-containing solution or dispersion has the properties of a nitrogen-free layer 2.

REFERENCE SIGNS

[0221] 1 Solar cell [0222] 2 Nitrogen-free layer [0223] 3 Further layer [0224] 4 Carrier [0225] 5 Electrically conductive layer [0226] 6 Metal grid