DE102010035569A1 - Continuous furnace - Google Patents

Abstract

Continuous furnace for the thermal conversion of a metallic precursor layer arranged on a substrate (3) in a gas flow, in particular for the conversion of a metallic precursor layer into a CIGSe layer, with a continuous tunnel that has a plurality of successive segments (5, 6, 7, 8 , 9), the cross section of the tunnel in a middle one of the segments (6, 7) being smaller than in a segment (5, 8, 9) adjoining the middle segment.

Description

The invention relates to a continuous furnace for the thermal conversion of a substrate arranged on a metallic precursor layer according to the preamble of claim 1 and the use of a continuous furnace according to the independent claim 14th

In the production of thin-film solar cells with a copper-indium-gallium-sulfide-selenide layer (CIGSSe), metallic precursor layers are converted into this CIGSSe layer in known production processes. Prior to conversion, precursor layers are placed on a substrate. The precursor layers contain the metallic precursor layer and may have selenium and / or sulfur-containing precursor layers.

From the WO 2009/033674 Methods and apparatus are known for converting such metallic precursor layers into CIGSSe layers. The reaction takes place at temperatures above 350 ° C. The thermal and atmospheric conditions necessary for the implementation can be generated in continuous furnaces. The above-mentioned WO application shows, in addition to known methods, also such a continuous furnace.

One possible environment for the reaction is under vacuum. However, the vacuum processes have the disadvantage that they require a very long process time for the implementation.

Processes in which process gases are passed through the continuous furnace, for example through an inlet into the furnace and out of the furnace by suction in a suction device, are generally more suitable. As the process gas, a carrier gas such as nitrogen, possibly mixed with other ingredients such as selenium and / or sulfur, used and passed over the substrate. The main task of the process gas is to create an oxygen-free environment.

However, it has been shown that inhomogeneities may occur in the CIGSSe layer formed. Such effects lead to a reduction in the efficiency of solar modules produced with these substrates.

It is an object of the invention to improve devices and methods of the prior art, in particular the object of the invention to provide a device or a method with which an improved implementation of a metallic precursor layer is possible in a homogeneous CIGSSe layer. The implementation should be possible within a short period of time.

The object is achieved with a device according to claim 1 and the use of such a device according to the independent claim 14.

Advantageous developments are the subject of dependent claims.

The invention makes use of the knowledge that inhomogeneities in the formed CIGSSe layer can arise due to flow inhomogeneities of the process gas flow. By reducing the cross-section of the tunnel of the continuous furnace in a segment in which the implementation of the metallic precursor layer takes place, the flow in this area is homogenized, since the remaining cross section between tunnel ceiling and substrate surface in the region of implementation is continuously uniform. In front of the reduced cross-section of the tunnel, a backflow of the process gas is formed so that process gas flows in uniformly at the beginning of the reduced cross-section. Here, the term "an average of the segments" means that the continuous furnace is divided into a plurality of successive segments, wherein a middle segment is a segment having at least one preceding segment and at least one subsequent segment. The middle segment according to the definition of this application does not necessarily lie exactly in the middle of the continuous furnace, but is merely not arranged on an edge of the continuous furnace. Preferably, the gas flow of the process gas is in the transport direction of the continuous furnace. As the process gas, it is expedient to use a gas which comprises the carrier gas or consists essentially of the carrier gas. The carrier gas used is preferably nitrogen. Other components of the process gas may be selenium and / or sulfur.

In one embodiment of the invention, at least one heating device and at least one cooling device are provided in the continuous furnace, so that the individual segments can be held independently of one another at a respectively predeterminable temperature.

The walls of the tunnel are preferably made of graphite and the at least one heating device and the at least one cooling device are embedded in the graphite. The term "walls" is understood to mean preferably the entire tunnel housing including the ceiling of the tunnel.

Preferably, in the middle segment, a ceiling element is arranged on a ceiling of the tunnel. The ceiling element can be integral be connected to the ceiling of the tunnel or attached as a separate element to the ceiling of the tunnel. The ceiling element causes the cross-section reduction in the middle segment. The ceiling element may for example be a block or a suspended ceiling, wherein it is preferably important that the effective flow cross-section is reduced. In this way, the reduced cross-section is created in a simple manner.

The cross-section of the tunnel in the middle segment preferably comprises at least one side channel oriented in the transport direction. Particularly preferred two side channels are provided in the continuous furnace, advantageously one right and one left of the ceiling element. Thus, a side channel can be created on both sides of the ceiling element with a centrally arranged on the ceiling of the tunnel ceiling element. This offers the advantage that a calm flow can be created over the substrate so that selenium deficiency and / or sulfur deficiency in the reaction can be avoided.

The side channel is preferably arranged in the transport direction of the continuous furnace in the region of the reduced cross section of the middle segment. Particularly preferably, it is arranged in one of the corners of the tunnel, with two side channels each having one arranged in one of the two upper corners of the tunnel. The top of the tunnel or the ceiling of the tunnel is the opposite side of the tunnel to a transport device of the tunnel. The transport device serves to transport substrates through the continuous furnace. In general, the transport device is arranged at the bottom of the tunnel, so that the substrates can be arranged horizontally in the transport device. However, the invention is not limited to such an arrangement, wherein in a `different arrangement, the terms 'ceiling' and 'top' are to be reinterpreted accordingly.

Preferably, a guide element is arranged in the tunnel upstream of the ceiling element. In this case, upstream against the flow direction of the process gas, ie. H. preferably counter to the transport direction of the substrate. The guide element is suitable for at least partially introducing the gas or process gas flowing through the tunnel into the side channel (s). Particularly preferably, the guide element is designed as a guide wedge, in particular as a triangular guide wedge, which serves to introduce at least a portion of a gas flowing through the tunnel into two side channels. Preferably, the continuous furnace is designed such that at least 30%, preferably at least 50% of the process gas are passed through the side channels. The formation of the side channels of the guide element and possibly other internals is advantageously carried out to achieve the specified proportions. This offers the advantage that a particularly calm flow, independent of a flow in the side channels, can be created above the substrate.

Preferably, the continuous furnace comprises at least one arranged in the transport direction or flow direction in the tunnel guide bar. The guide bar is preferably arranged to at least partially define the side channel. The guide rail makes it possible to at least partially increase a flow in the side channel from a flow over the substrate. decouple. This offers the advantage that a particularly homogeneous flow can be created above the substrate.

Preferably, the at least one guide strip is arranged on a side edge of the ceiling element. Particularly preferred are arrangements with a centrally arranged on the ceiling of the tunnel ceiling element, which creates two side channels. On the two side edges of the ceiling element guide strips are preferably mounted. The guide rails preferably have a rectangular cross section, which has a greater height than width, so that the guide bar protrude down into the interior of the tunnel cross section. In this way, side channels are created reliably. The guide strips preferably extend at least over half, more preferably at least 90%, of the entire length of the ceiling element. The guide rails may also be interrupted in typical embodiments. When interruptions only over a short distance, it does not come to a significant mixing of the currents in the side channels with the. Flow over the substrates.

Preferably, at least one shielding lip is arranged on the ceiling element or on the guide element. The arm-shield lip is preferably arranged at least substantially transversely to the tunnel direction. The shielding lip is expediently arranged so that the cross-section of the tunnel is further reduced in relation to the reduced cross-section present in the middle segment. In this way, upstream of the area in which the reaction is to take place, a flow accumulation is generated. Behind the shielding lip created in this way a calm flow. In connection with the side channels, which are preferably arranged so that they absorb a predominant portion of the volume flow of the gas flow of the process gas, results in a particularly favorable flow situation over the substrate.

Advantageously, a front shield lip and a rear shield lip are provided, wherein the front shield lip is arranged at or in front of an upstream end of the ceiling member transversely to the flow direction. The rear shield lip is disposed at a downstream end of the ceiling member transversely of the tunnel direction. In this case, the front end and the rear end respectively mean that the shielding lip is arranged in a respective region, ie preferably within the first 20%, more preferably the first 10%, or within the last 20%, more preferably 10% of the ceiling element. Between the shield lips a particularly calm flow is achieved.

Preferably, the ceiling element is at least as wide as a transportable by the transport substrate. Particularly preferred are arrangements in which the guide rails are arranged laterally next to, possibly also above, of transported substrates, so that over the entire width of the substrate, a uniform flow is achieved.

Preferably, the cross-sectional area of the tunnel in the area of the middle segment is reduced by at least 20% with respect to an adjacent area of the tunnel. Particularly preferred is a reduction of the cross-sectional area by at least 30% or more preferably by at least 40%. In the area of the shielding lips, the height of the tunnel is preferably reduced by a further at least 5%, more preferably at least 10%, of the total height of the tunnel in the unreduced cross section. It should be noted that the reduced height is usually not in the range of side channels, but in between. The width of the Abschirmlippe is preferably at most three times, more preferably at most twice their height. In this way, the flow resistance is increased at the Abschirmlippe. In the cross-sectional area of the shielding lip, the height of the tunnel is preferably reduced by at least 30% from the unreduced cross-section, more preferably by at least 40% or 50%. In the area of the side channels, the height of the tunnel is preferably not reduced in relation to an adjacent segment. The side channels preferably have a width which corresponds to at least half the tunnel height.

Preferably, an inlet lock is provided at a first end of the tunnel for introducing substrates into the tunnel. In a preferred embodiment of the invention, the inlet lock is provided at the first end of the tunnel and an outlet lock at the second end of the tunnel. The locks make it possible to feed in and out of substrates in the oven while ensuring oxygen freedom in the continuous furnace. The locks may have mechanical flaps or slides, preferably the inlet lock and / or the outlet lock each comprise a gas lock. Contamination of components can be prevented by using gas locks.

Preferably, the inlet lock comprises a gas inlet for introducing process gas into the tunnel. The gas inlet may be formed integrally with the gas lock. This can be achieved, for example, by the use of gas locks, in which the gas flows on both sides of the gas lock can be set independently of one another. Preferably, the inlet lock comprises a plurality of inlet openings or slots, wherein some of the openings for the gas lock and at least one of the openings are used as a gas inlet. In typical embodiments, a separation of gas lock and gas inlet into two components is possible. This offers the advantage of greater flexibility in the configuration of the plant.

Preferably, the process gas is introduced at the gas inlet directed into the tunnel of the continuous furnace. Downstream of the middle segment, a suction device for sucking off the process gas is preferably arranged. The introduction and suction at certain points of the tunnel has the advantage that the flow direction is set and defined conditions are created in the continuous furnace. In particular, condensation of, for example, selenium and / or sulfur upstream of the middle segment is reduced.

Preferably, a heater is arranged in the middle segment. This offers the advantage that in the reaction zone, which preferably comprises the middle segment or several middle segments, a predeterminable temperature profile can be set or regulated.

Preferably, the tunnel comprises a warm-up zone, a reaction zone and a cooling zone. The middle segment is preferably arranged in the reaction zone. One of the zones may explicitly comprise several segments. For example, the reaction zone preferably includes at least two segments to provide a sufficiently long distance for the shift. Expressly encompassed by the invention are arrangements in which interruptions, for example of the ceiling element or the guide rails, are present between the segments. Such short breaks, which are preferably shorter than a width of the tunnel, are of secondary importance to the flows. The gas inlet is preferably at the upstream end of the segment lying in the warm-up zone.

The abovementioned guide element is preferably located in the warm-up zone, preferably at the transition to the reaction zone, and thus sets certain flow conditions upstream of the reaction zone, so that there are only defined flow conditions downstream of the guide element in the reaction zone. The front shielding lip is preferably located at the end of the baffle or at the beginning of the ceiling member, as noted above. The cooling zone in turn comprises at least one segment, depending on the required length for the cooling zone may also have multiple segments. The suction device is preferably located in the cooling zone, more preferably at the downstream end of a first segment of the cooling zone. In this way, in a further, downstream segment of the cooling zone, a selenium and / or sulfur-free or substantially selenium and / or sulfur-free atmosphere is reached, so that the further cooling can be carried out without selenium and / or without sulfur and none Condensation of selenium and / or sulfur takes place. At the end of a last segment, which is part of the cooling zone, there is preferably a further lock, which can prevent the penetration of oxygen from the outside into the continuous furnace.

A further aspect of the invention relates to the use of a continuous furnace with the inventive or preferred features described above for the thermal conversion of a metallic precursor layer arranged on a substrate, in particular for converting a metallic precursor layer into a CIGSSe layer.

In addition to the above-mentioned advantages, the invention has the particular advantages that a quasi-steady flow is generated for converting the precursor layers, so that a homogenized CIGSSe layer can be created. The lowered ceiling with the guide element, the guide rails and the Abschirmlippen enhance their respective individual effects, but each of these measures is independent of the other measures suitable to improve the flow conditions for a conversion metallic precursor layers.

Hereinafter, a preferred embodiment of the invention will be explained with reference to figures. Show it:

1 A schematic longitudinal section with a vertical sectional plane through a continuous furnace according to the invention

2 In a simplified schematic view, a top view from below of the ceiling of the continuous furnace 1

3 The location of various sections of the 4 to 7 of the continuous furnace of the invention 1 in a schematic representation

4 A first vertical cross section through the continuous furnace of 1 in a schematic view

5 Another cross section through the continuous furnace of the invention 1 in a schematic view.

6 Another cross section through the continuous furnace of 1 in a schematic view

7 Another cross section through the continuous furnace of the invention 1 ,

In the 1 an inventive continuous furnace is shown schematically in a vertical sectional view of a longitudinal section. Particular attention has been paid to an exact representation of an inlet lock 1 and an outlet lock 2 waived.

The Indian 1 schematically illustrated continuous furnace can be used to advantage, one on substrates 3 thermally arranged arranged precursor layer in a CIGSSe layer. For details of the relevant procedure, reference is made in particular to the above-mentioned WO application.

The substrates 3 be through the inlet lock 1 introduced into the continuous furnace. The inlet lock 1 includes a plurality of openings. During operation, some of the openings form a gas lock to ensure oxygen-free interior of the continuous furnace. The outlet lock 2 also includes a gas lock. At least one of the openings of the inlet lock 1 and the opening which is furthest downstream in the direction of transport in the inlet lock 1 is arranged, is used as a gas inlet. The openings are formed as slots. In the illustrated embodiment is in the tunnel of the continuous furnace via the gas inlet of the inlet lock 1 Nitrogen introduced as a process gas introduced. In the presentation of the 1 So runs a gas flow, ie the flow direction, as well as a transport direction of the substrates 3 from left to right up to a suction device 13 ,

On their way through the continuous furnace go through the substrates 3 different segments 5 . 6 . 7 . 8th and 9 , The boundaries between the segments are each marked by dotted lines. In the segment 5 there is a warm-up zone of the continuous furnace. The segments 6 to 7 form a reaction zone and a cooling zone is in the segments 8th and 9 arranged the continuous furnace. To warm up, the continuous furnace in the segment includes 5 , ie in the warm-up zone, a warm-up heating 10 , In addition, in the segments 6 and 7 , ie in the reaction zone, a heater 11 arranged to maintain a certain temperature within the reaction zone.

In the segments 8th and 9 , ie in the cooling zone, is in each case a cooling 12 arranged. At the downstream end of the segment 8th that is, in a central region of the cooling zone, is a suction device 13 provided to suck the process gas from the channel of the continuous furnace. Through the suction device 13 at the end of the segment 8th will be in the second segment 9 the cooling zone reaches a selenium-free atmosphere. In this way is a quiet cooling in the segment 9 possible.

In the context of the invention is in a central region of the continuous furnace, more precisely in at least one middle segment, more precisely the middle segments 6 and 7 , Provided a cross-sectional constriction of the tunnel of the continuous furnace. The cross-sectional constriction is by a ceiling element 15 reached. The ceiling element 15 extends over the entire reaction zone, namely the segments 6 and 7 , The ceiling element 15 and its configuration will be described in connection with the description of 2 to 7 explained in more detail.

Upstream of the ceiling element 15 is a guiding element 16 arranged, which serves the process gas flowing through the tunnel of the continuous furnace in side channels (in 1 not shown). At the downstream end of the baffle 16 is a front shield lip 17 arranged, which projects down into the channel or the free cross section of the continuous furnace. A rear shield lip 18 is in an analogous manner at the downstream end of the ceiling element 15 arranged. The front shielding lip 17 and the rear shield lip 18 cause a calming of the flow between the shielding lips 17 and 18 so that a homogeneous flow area is achieved in the reaction zone. Still to mention is a transport device 20 which serves the substrates 3 through the continuous furnace to transport.

The operation of the tunnel kiln according to the invention 1 is subsequently explained in conjunction with the following figures, wherein the following 2 to 7 for like parts, like reference numerals are used as in 1 , Therefore, not all references in connection with the 2 to 7 again explained individually, it is rather on the explanation of 1 directed.

The 2 shows a view of the ceiling of the continuous furnace from below in a highly schematic plan view. With an arrow 21 the direction of the gas flow and the transport direction are marked. Part of the gas flow is shared by the guide element 16 , The function of the guide element 16 is through the front shield lip 17 reinforced, which additionally the cross section below the guide element 16 reduced. The guiding element 16 directs a portion of the flow into two side channels 22 , which by arranging the ceiling element 15 in the continuous furnace on both sides of the ceiling element 15 be formed. For better training of the side channels 22 are at the bottom of the ceiling element 15 also guide rails 23 arranged, which are explained in more detail in connection with the following figures.

In the preferred embodiment shown in the figures, the ceiling element decreases 15 the free cross section of the continuous furnace in the region of the middle segments 6 and 7 at a height which is between 50% and 60% of the total height of the canal in the non-height restricted segments 5 . 8th and 9 equivalent. The shielding lips 17 and 18 cause a further lowering of the height in the area under the shield lips 17 and 18 to only 40% to 50% of the total height of the cross section of the continuous furnace. In this way, in interaction with the side channels 22 a calm flow over the substrates 3 created in the reaction zone to achieve a homogeneous conversion of the material into homogeneous CIGSSe layers.

For a better understanding of the preferred embodiment are in the 3 to 7 Section views of cross sections of the continuous furnace shown. The sectional views were partially details such as the heating 11 omitted for clarity.

In the 3 is a sketch showing the location of the individual sections. Otherwise the representation is in the 3 a repetition of the presentation of the 2 , so a top view of the ceiling of the continuous furnace from below.

The 4 shows schematically in a cross section the situation of the continuous furnace in the segment 5 ie in the warm-up zone. The airspace 25 above the substrate 3 which is on the transport device 20 is not reduced.

The 5 shows the situation downstream at the end of the segment 5 ie at the transition from the warm-up zone to the reaction zone. At this point already engages the guide element 16 in the airspace 25 above the substrate 3 one. Thereby, the process gas is laterally in the direction of the side channels (not shown in the 4 and 5 ).

Farther downstream to the front shield lip 17 is the cut CC the 6 arranged. The ceiling element 15 now takes a width, which is substantially the width of the transport device 20 equivalent. In this way it is achieved that over the substrates 3 , which are usually slightly narrower than the transport device 20 , completely a calm flow in the airspace 25 over the substrates 3 is reached.

Side of the ceiling element 15 are the side channels 22 , in which a large part of the process gas is bypassed. In combination with the front shield lip cause the side channels 22 a constant back pressure in an approximately constant pressure area above the front shielding lip 17 , so that downstream of the front shielding lip 17 in the airspace 25 over the substrates 3 in the area of the ceiling element 15 a calmer and more homogeneous flow is achieved.

Further downstream is in the section DD of 7 also to recognize how the guide rails 23 the side channels 22 additionally limit. In this way the flows in the side channels become 22 better from the flow in the area between the ceiling element 15 and the substrates 3 separated. The guide rails 23 do not have to over the entire length of the ceiling element 15 run, it is preferred that the guide rails 23 at least half the length of the ceiling element 15 shield. It should be noted that in the 4 to 7 the ceiling element 15 and the guide element 16 are shown as in addition to the ceiling of the tunnel of the continuous furnace mounted parts. Likewise, the guide element 16 and the ceiling element 15 however, be integral with the tunnel. This also applies to the shielding lips and the guide rails.

The side channels 22 each preferably occupies at least 5% of the total width of the tunnel of the continuous furnace. In this way, a sufficient width and a sufficient cross section of the side channels 22 reached. In the area of the guide rails 23 is preferably the remaining free height below the guide rails 23 to less than 50% of the total height of the canal (see cross section in 4 ) decreased. In this way, a separation of the flow is achieved.

The rear shield lip 18 can form in typical execution at the beginning of the segment 8th , ie in the cooling zone. In this case, the rear shield lip 18 not on the underside of the ceiling element 15 attached, but preferably protrudes from the ceiling of the tunnel.

LIST OF REFERENCE NUMBERS

1

inlet sluice

2

outlet lock

3

substrates

5

segment

6

segment

7

segment

8th

segment

9

segment

10

warm Heating

11

heater

12

cooling

13

suction

15

ceiling element

16

vane

17

front shielding lip

18

rear shield lip

20

transport means

21

Arrow (flow direction)

22

side channel

23

guide rail

25

airspace

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2009/033674 [0003]

Claims (14)

Continuous furnace for the thermal conversion of a material on a substrate ( 3 ) arranged metallic precursor layer in a gas flow, in particular for the implementation of a metallic precursor layer in a CIGSSe layer, with a continuous tunnel having a plurality of successive segments ( 5 . 6 . 7 . 8th . 9 ), characterized in that the cross section of the tunnel in a middle of the segments ( 6 . 7 ) is smaller than in a segment adjacent to the middle segment ( 5 . 8th ). Continuous furnace according to claim 1, characterized in that in the middle segment ( 6 . 7 ) a ceiling element ( 15 ) is arranged on a ceiling of the tunnel. Continuous furnace according to claim 1 or 2, characterized in that in the middle segment ( 6 . 7 ) at least one aligned in the transport direction side channel ( 22 ) is arranged in the cross section. Continuous furnace according to claim 3, characterized by a in the tunnel upstream of the ceiling element ( 15 ) arranged guide element ( 16 ), by means of which at least part of a gas flowing through the tunnel into the side channel ( 22 ) is conductive. Continuous furnace according to claim 3 or 4, characterized by at least one guide bar arranged in the transport direction in the transport direction ( 23 ). Continuous furnace according to claim 5, characterized in that the at least one guide strip ( 23 ) the side channel ( 22 ) at least partially limited. Continuous furnace according to claim 5 or 6, characterized in that the at least one guide strip ( 23 ) on a side edge of the ceiling element ( 15 ) is arranged. Continuous furnace according to one of claims 3 to 7, characterized in that on the ceiling element ( 15 ) or on the guide element ( 16 ) at least one shielding lip ( 17 . 18 ) is arranged. Continuous furnace according to one of the preceding claims, characterized in that the height and / or the cross-sectional area of the tunnel in the region of the middle segment ( 6 . 7 ) is reduced by at least 20% with respect to an adjacent area of the tunnel. Continuous furnace according to one of the preceding claims, characterized by a gas inlet arranged at a first end of the tunnel for introducing process gas into the tunnel and / or a downstream of the middle segment ( 6 . 7 ) arranged suction device ( 13 ) for extracting process gas. Continuous furnace according to one of the preceding claims, characterized in that at the first end of the tunnel an inlet lock ( 1 ) and / or at a second end an outlet lock ( 2 ) is provided. Continuous furnace according to claim 11, characterized in that the inlet lock ( 1 ) and / or the outlet lock ( 2 ) each comprise a gas lock. Continuous furnace according to claim 11 or 12, characterized in that the inlet lock ( 1 ) includes the gas inlet. Use of a continuous furnace according to one of claims 1 to 13 for the thermal reaction of a material on a substrate ( 3 ) arranged metallic precursor layer in a gas flow, in particular for converting a precursor layer in a CIGSSe layer.

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