The present invention relates to a device for applying an even, thin fluid layer, in particular a phosphoric acid layer, to substrates, in particular silicon cells for photovoltaic application, in accordance with the preambles of Claim 1 and of Claim 14, as well as a method for applying an even, thin fluid layer, in particular a phosphoric acid layer, to substrates, in particular silicon cells for photovoltaic application, in accordance with the preamble of Claim 18.
To be able to manufacture photovoltaic cells made of silicon, a phosphorus doping of the unfinished cells is first necessary. In the first step, the cell is wetted using phosphoric acid, and the wetted cells are placed in a high-temperature oven at ca. 800° to 900° C., where the phosphorus diffuses from the dried acid into the silicon substrate. The coating is designed to be very even to achieve equal distribution in the diffusion process, and it is also designed to be very economical since the excess phosphoric acid melts onto the cell as “phosphorus glass,” and it can only be removed using hydrofluoric acid, which is accomplished with difficulty.
Phosphoric acid is usually applied to the silicon substrates in such a way that the phosphoric acid is atomized by a high-frequency ultrasound device, and the phosphoric acid mist is deposited onto the silicon substrates. The phosphoric acid mist is conveyed from the process chamber into a dropping shaft, which is relatively wide and is arranged at a relatively large distance above the silicon substrates, i.e., cells, that are conveyed past it. One disadvantage in this known device lies in the fact that it offers no guarantee that the mist will be homogenized, because even light air currents are sufficient to “blow” the mist. In addition, the configuration of the process chamber leads to damaging condensate drops falling onto the silicon cells, which works against achieving a homogeneous wetting or coating result. The attempt has been made to catch condensate drops of this type using a drip pan beneath the dropping shaft, which however has the effect of preventing the mist even more from being evenly spread.
The objective of the present invention is therefore to create a device for applying an even, thin fluid layer, in particular a phosphoric acid layer, onto substrates, in particular silicon cells for photovoltaic application of the aforementioned type, which permits an application of fluid, in particular phosphoric acid, onto the substrates in question, in particular the silicon cells, that is substantially more homogeneous with respect to both surface area and volume.
The features indicated in Claim 1 are provided to achieve this objective in a device for applying an even, thin fluid layer, in particular a phosphoric acid layer, onto substrates, in particular silicon cells for photovoltaic application of the aforementioned type.
The measures proposed according to the invention achieve, within an essentially closed circulation system, both homogeneous mist creation as well as a homogeneous conveying of the fluid mist from the production location (process chamber) to the application location, as well as during the application to the substrates, in particular silicon cells. This homogeneity relates to deposition on the silicon substrates in terms of both surface area and quantity. In addition, the fluid mist is compressed and additionally homogenized due to the tapering of the fluid-mist dropping shaft and the resulting backing up of the mist.
The features according to Claim 2 indicate a design of the dropping shaft that is simple from the point of view of manufacturing technique.
The features according to Claim 3 indicate that the cover of the passage shaft arrangement disposed above the silicon substrates, which are passing by, is maintained at a certain temperature, so that the fluid mist cannot condense and thus drop formation is not possible, which also promotes the homogeneity of the fluid mist and of its application.
On the basis of the features according to Claim 4 and/or 5, a regulatable, homogeneous, and active conveyance of the fluid mist is achieved from the point of origin to the point of application, as well as during the application phase. In this context, when the exhaust air duct is used, it is expedient to provide the features according to Claim 6 so as to not impair the homogeneity of the fluid mist at the passage end of the shaft arrangement and to impart to the fluid mist a defined flow velocity.
The features according to Claim 7, in a preferred and advantageous manner, provide that the fluid mist is deposited evenly and in sufficient quantity on the silicon substrates due to the gravity that acts upon the fluid mist and the duration of the reaction time extending beyond the time needed for transport.
According to the features of Claim 8, in the area where the fluid mist is produced, an impact element is provided, which has the advantage that its plastic web catches the fluid without spatter and causes it to flow back into the fluid pan. An advantageous configuration for this purpose can be derived from the features according to Claim 9.
According to the features of Claim 10, a configuration of the cover of the process chamber has the advantage, regarding the homogeneity of the fluid mist, that the condensate that collects there can be conveyed back to the fluid pan due to the tilted arrangement.
Correspondingly, in accordance with Claim 11, measures are provided in the fluid-mist dropping shaft that are capable of removing the condensate that forms on the walls of the dropping shaft without permitting drops to form. For this purpose, it is expedient to provide the features according to Claim 12, so that the condensate can be drained off to the side via the channels.
A further preferred design configuration can be derived from the features of Claim 13, having the advantage that the width of a device of this type can be extended to a virtually unrestricted degree.
In the known device cited above, a high-frequency ultrasound device is used whose high-frequency ultrasound transmitter, or generator, is not resistant to phosphoric acid. Therefore, it is necessary to use an intermediate receptacle that is filled with water, evacuated, and connected to a tempering circuit. The high-frequency ultrasound generator is attached on the lower side of the intermediate receptacle, and a diaphragm is attached on the upper side of the intermediate receptacle, whereby the water and the diaphragm function to transfer the sound from the high-frequency ultrasound transmitter to the phosphoric acid basin or pan, situated above it. Disadvantageous in this respect are the cumbersome and expensive technology, the frequent ruptures of the diaphragm due to fatigue, the resulting laborious and time-consuming process of replacing the diaphragm, and the damping characteristics of a sound transfer means of this type.
To avoid these disadvantages, the features indicated in Claim 14 are provided in a device of the aforementioned type.
As a result of the measures according to the present invention, both the phosphoric acid and the sound are focused in the quartz glass nozzle. It is expedient to provide the features in accordance with Claim 15 so that the fluid that is compressed in the quartz glass nozzle can flow back through the supply lines.
One preferred design configuration in this regard is indicated by the features according to Claim 16.
The features according to Claim 17 enable the high-frequency ultrasound device to be in essence directly connected to the phosphoric acid without resulting in disadvantages regarding the intensity of the high-frequency ultrasound generation.
Furthermore, the present invention relates to a method for applying an even, thin fluid layer, in particular a phosphoric acid layer, onto substrates, in particular silicon cells for photovoltaic application, in accordance with the preamble of Claim 18.
As previously mentioned, the heretofore comparable methods demonstrate a lack of homogeneity in the conveying of the fluid mist and therefore in the depositing of the phosphoric acid.
To improve this aspect of a method of the aforementioned type, the features indicated in Claim 18 are provided.
On the basis of the measures according to the invention, the fluid mist can be actively and homogeneously conveyed from the point of generation of the fluid mist to the point of application, or deposition, of the fluid-mist layer onto the substrates.
Advantageous embodiments in this regard are indicated by the features according to Claim 19 and/or 20.
Further details of the present invention can be derived from the following description, in which the invention is described and discussed in greater detail on the basis of the exemplary embodiment depicted in the drawing.
In the drawing:
Device 10 as depicted in
According to
In accordance with
In the upper area of right sidewall 22 of process chamber 14, an impact element 27 is attached, which, sloping diagonally downwards, i.e., towards fluid pan 16, protrudes into process chamber 14 and terminates at a distance before dam 27, creating a passage 29.
Impact element 28 has a frame that is covered with plastic web 30, whereby plastic web 30 in a spatter-free manner catches the phosphoric acid droplets within phosphoric acid mist 15 that are hurled by high-frequency ultrasound device 11, and it causes the droplets to flow back into fluid pan 16. Thus only the phosphoric acid mist goes through passage 29 and plastic web 30 of impact element 28 into the space of process chamber 14 situated behind them. Plastic web 30 of impact element 28 also permits the condensate that collects on cover 24 of process chamber 14 and that flows back towards right sidewall 22 to pass through and flow off into fluid pan 16.
In the area between fluid surface 20 of pan 16 and impact element 28, an air supply connector 31 is provided, whose supply line is furnished with a regulating device 32. In this way, the phosphoric mist that is produced is pushed, i.e., actively moved through regulatable air supply line 31, 32, and over dam 27 towards the intake of dropping shaft 25.
Both the parts of left sidewall 23, 23′, which pass into each other, as well as sidewall 26 of dropping shaft 25 are provided with a web covering 34, so that the condensate of phosphoric acid mist 15 that is deposited on the walls of dropping shaft 25 can be conducted away from this web covering 34 towards the bottom without the formation of drops. For this purpose, the lower edges of sidewalls 23, 23′, and 26 terminate above channels 36 and 37, which drain the condensate off to the side in a manner that is not depicted in detail, i.e., in a direction that is perpendicular to the plane of the drawing.
Above transport device 13, i.e., upper side 39 of transport device 13, on which silicon substrates 12 lie and are moved in the direction of arrow A, a passage shaft arrangement 40 is provided which has an intake area 41 upstream of dropping shaft 25 and an outlet area 42 downstream of dropping shaft 25. Between intake area 41 and outlet area 42, shaft arrangement 40 is open on the top, dropping shaft 25 discharging into this open area. At the rear end in the direction of passage A, outlet area 42 of shaft arrangement 40 is provided with an extraction box 43, within whose opening, which is facing side 39 of transport device 13, a roof-shaped plastic web 45 is arranged so as to create a laminar flow box. At this end of extractor box 43, facing away from this plastic web 45, an extractor line 46 is attached, in which a regulating device 47 is arranged that has a suction fan 48 for actively moving phosphoric acid mist 15, i.e., causing it to flow. Behind suction fan 48 a condensate return line 49 is provided which discharges into phosphoric acid tank 19.
Based on both regulating devices 32 and 47 for supplying and removing air, phosphoric acid mist 15, once produced, can be moved in regulatable fashion from its production location, namely process chamber 14, via dropping shaft 25, which extends below process chamber 14 and fluid pan 16, into shaft arrangement 42 and finally to the location at which silicon substrates 12 are to be coated. Due to the wedge-shaped configuration of dropping shaft 25, the phosphoric acid mist is compressed by the backup and is homogenized. Because of the direct transition from dropping shaft 25 to relatively low shaft arrangement 40, phosphorus mist 15 remains homogeneous and compressed and therefore completely fills outlet area 42 of shaft arrangement 40. Because extraction box 43 uniformly suctions off the portion of phosphoric acid mist 15 that was not deposited from the entire width of outlet area 42 of shaft arrangement 40, the homogeneity of the phosphoric acid mist is maintained within outlet area 42. Therefore, due to the gravity acting upon the phosphoric acid mist and the duration of the reaction time extending beyond the time needed for transport, the phosphoric acid is deposited on substrates 12 evenly and in sufficient volume. The phosphoric acid mist is dosed in a sensitive manner by regulating the supply and removal of air as well as by regulating the power supplied to high-frequency ultrasound device 11. A homogeneous and (in time and space) even action of the phosphoric acid mist on silicon substrates 12 is also achieved due to the fact that the transport velocity of transport device 13 for silicon substrates 12 is coordinated with the velocity of the phosphoric acid mist 15 as it moves through the substantially closed circulation system from process chamber 14 via dropping shaft 25 and shaft arrangement 42 to extraction box 43, and the former is advantageously synchronized with the latter, i.e., is equal to it.
For an evenly homogeneous conveyance of phosphoric acid mist 15 over the entire path, it is important that the dimensioning or, in other words, the discharge end, of vertical fluid-mist dropping shaft 25 and of passage shaft arrangement 40 bordering the deposition chamber for substrates 12 are coordinated with each other, and preferably are identical.
In order to prevent condensate of phosphoric acid mist 15 from forming on cover 51 of shaft arrangement 40 beneath outlet area 42 of shaft arrangement 40, a return shaft 52 whose base is formed by cover 51 is provided above outlet area 42. Return shaft 52 is connected by a line 53 to a filling level tube 54 of phosphoric acid pan 16 in an area of the entry end of outlet area 42 of shaft arrangement 40, so that tempered phosphoric acid that overflows from pan 16 can flow over shaft arrangement 40 in transport direction A. At the end of return shaft 52 behind a dam-like element 56, a tubular line 57 is connected which returns the excess phosphoric acid to phosphoric acid tank 19.
The phosphoric acid that is compressed in quartz glass nozzle 68 so as to form the phosphoric acid mist 15 can flow out of pan 16 via radial boreholes 69.
It should be noted that device 10 depicted in
Number | Date | Country | Kind |
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10 2005 019 686.1 | Apr 2005 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2006/002797 | 3/28/2006 | WO | 00 | 10/22/2007 |