JP2005228953A - Photovoltaic element, formation method thereof, and manufacturing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems wherein photoelectromotive force cannot be effectively taken out when there are many short-circuiting portions in a photovoltaic element, which occurs stochastically following an increase in area, and hence yields are decreased in mass production. <P>SOLUTION: In the photovoltaic element, a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially laminated on a substrate in this order. In this case, the first electrode layer has an abnormal growth removal region, and the semiconductor layer is formed in the abnormal growth removal region. In the method for forming the photovoltaic element and the manufacturing device, a process and a method for breaking the abnormal growth grown on the substrate when forming the first electrode layer after the first electrode layer is formed, and a process and a means for removing the broken abnormal growth section, are provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a photovoltaic element in which a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially stacked on a substrate. More specifically, the present invention relates to prevention of characteristic failure due to short-circuit between electrodes of a photovoltaic element.

  Conventionally, photovoltaic devices using non-single-crystal silicon-based semiconductors are known. As a typical example of a photovoltaic element, a back surface reflection layer typified by ZnO or Ag is deposited on a stainless steel substrate by sputtering or the like, and amorphous silicon having a pin or nip junction parallel to the film surface is used. After depositing a non-single crystal semiconductor film by plasma CVD or the like, a light incident side electrode made of a light-transmitting conductive oxide such as ITO or SnO2 is laminated, or light incidence such as SnO2 on a glass substrate. After the side electrode is deposited, a non-single crystal semiconductor layer is deposited, and a back reflective layer made of ZnO, Ag, or the like is deposited. In particular, these non-single-crystal silicon photovoltaic devices can be made very thin, so that the material cost is low and they are used for power solar cells.

  The non-single-crystal silicon semiconductor layer is an extremely thin film having a thickness of 100 nm to several μm. When cracks or cracks occur due to thermal stress in the semiconductor formation process or external stress in the processing process, the first electrode layer and the second electrode The layer may be shorted. In addition, when fine dust adheres to the substrate deposition surface in the semiconductor layer forming process, the fine dust adhering portion becomes a pinhole or the like where the semiconductor layer is not formed, and the first electrode layer and the second electrode layer may be short-circuited. . If there are many short-circuited portions, there arises a problem that the photovoltaic power cannot be extracted effectively. Various countermeasures (optimization and cleaning of the semiconductor formation process, etc.) have conventionally been taken to deal with these problems. However, if the photovoltaic device is enlarged, it will occur probabilistically. In the case of mass production of the element, it becomes a factor for reducing the yield.

  In order to solve the problem, after forming the second electrode of the photovoltaic element, the element is immersed in an electrolytic solution, and the short-circuited portion is energized to selectively etch the second electrode in the short-circuit state. Patent Document 1 discloses a method for removing the above. However, even if the selective etching is performed, the short-circuit state of the photovoltaic element cannot be completely repaired, and there is a photovoltaic element in which the short-circuited portion remains, and the yield in manufacturing the element is not always sufficient. I could n’t go up to the level.

Further, Patent Document 2 discloses that pinholes are eliminated by removing fine dust adhering to the substrate deposition surface during the formation of the semiconductor layer, and the short-circuit portion is eliminated without performing the selective etching. Specific methods for removing fine dust are: electrify dust by electrically collecting fine dust, vibrate the substrate, blow gas on the deposition surface of the substrate, and the substrate temperature is different from the temperature of the semiconductor layer forming process The temperature is changed, and the fine dust interface is oxidized. However, with this method, it is possible to remove only in the case of fine dust adhering to the substrate deposition surface, but the first electrode grows abnormally due to foreign matter or irregularities on the substrate surface and becomes a short-circuit portion. If this happens, a sufficient effect cannot be obtained.
JP-A-1-286371 JP-A-9-107117

  FIG. 1 shows a schematic diagram of a short-circuit portion of the photovoltaic element. If the short-circuited portion due to cracks or cracks, or the short-circuited portion due to pinholes where the semiconductor layer is not formed due to the fine dust adhering to the substrate deposition surface, the second electrode can be selectively etched by immersing it in the electrolyte Removed and no longer shorted (FIG. 2). However, when there is an abnormally grown portion as shown in FIG. 1 and a short circuit occurs at the grain boundary of the abnormally grown portion, the complex surface structure of the abnormally grown portion causes a gap or There was a problem that the short-circuit state was not recovered because the shadowed second electrode could not be removed. On the other hand, if the selective etching time is increased so that the portion that is difficult to be etched is sufficiently etched, the normal portion is etched, and as a result, the device characteristics are deteriorated.

  An object of the present invention is to propose a method for forming a photovoltaic element that can improve the above-described problems and can effectively extract photovoltaic power.

  In the present invention, there is provided a photovoltaic element in which at least a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially laminated on a substrate in this order, and the first electrode layer has an abnormal growth portion removal region. In addition, a photovoltaic device in which the semiconductor layer is formed in the abnormal growth portion removal region is obtained. The first electrode layer is a photovoltaic element that is a back surface reflection layer composed of a light-transmitting conductive film and a reflective conductive film.

In the present invention, in the method for forming a photovoltaic device including the step of sequentially laminating at least the first electrode layer, the semiconductor layer, and the second electrode layer in this order on the substrate, before the step of forming the semiconductor layer. A method for forming a photovoltaic device comprising: crushing an abnormally grown portion grown on the substrate at the time of forming the first electrode layer; and removing the crushed abnormally grown portion. Furthermore, the step of crushing the abnormally grown portion is either a mechanical friction or a physical impact, or a method for forming a photovoltaic element that combines these. A method of forming a photovoltaic device in which the number of remaining abnormally grown portions is 50 pieces / mm ² or less after the abnormally grown portions are crushed and removed.

  Further, in the present invention, in the photovoltaic device manufacturing apparatus having means for forming a semiconductor layer on a substrate having at least the first electrode layer, the abnormally grown portion existing on the first electrode layer is crushed. A photovoltaic device manufacturing apparatus having means and means for removing a crushed abnormally grown portion. In addition, even if the position of the substrate changes, the means for crushing the abnormally grown portion is pressed against the surface of the first electrode layer with a pressure that does not damage the surface of the first electrode layer other than the abnormally grown portion. It is preferable to use a photovoltaic device manufacturing apparatus. The photovoltaic device manufacturing apparatus is a roll-to-roll apparatus, and has a slip sheet between the back surface of the substrate and the surface of the first electrode layer, and has means for vibrating the slip sheet. It is set as the manufacturing apparatus of an electromotive force element. Furthermore, it is preferable to provide a photovoltaic device manufacturing apparatus that crushes the abnormally grown portion by transmitting vibrations of sound waves and ultrasonic waves to the slip sheet.

  According to the method for forming a photovoltaic element of the present invention, the abnormally grown portion grown at the time of forming the first electrode is removed and the short-circuit state is eliminated, so that a photovoltaic element that can effectively extract the photovoltaic element can be formed. It is possible to improve the yield when producing photovoltaic elements.

  FIG. 2 shows a schematic diagram of the growth process of the abnormally grown portion. Even after a cleaning process or a polishing process on a stainless steel substrate or a glass substrate, foreign matter or residue may remain on the substrate. In particular, in the case of a long metal substrate, there are cases where minute scratches, protrusions, and irregularities exist on the surface of the substrate.

  When the first electrode is formed, a conductive oxide such as ZnO that forms the first electrode layer may cause abnormal growth with foreign matter and residue on the substrate or minute irregularities on the surface of the substrate as a nucleus. is there.

  Furthermore, when the semiconductor layer is formed on the first electrode layer having the abnormally grown portion, the semiconductor layer is deposited on the abnormally grown portion while maintaining the shape thereof. As a result, the grain boundary around the abnormally grown portion tends to increase the number of structural defects and surface states, and is often short-circuited.

  FIG. 3A is an SEM photograph of an abnormally grown portion formed on the surface of the deposited film after forming the first electrode layer on the substrate. There were many abnormally grown portions having a major axis of 2 to 4 μm. FIG. 3B is an SEM photograph of a portion where the abnormally grown portion of the first electrode layer has been removed by the step of crushing and removing the abnormally grown portion according to the present invention. The abnormally grown portion was successfully removed, resulting in a depression with a major axis of about 3 μm.

FIG. 4 shows the relationship between the number of abnormally grown portions remaining after removal and the short-circuit resistance RshDark of the photovoltaic element. When the number of abnormally grown portions is 50 / mm ² or less, RshDark increases. However, abnormal since the number of growing portion is no longer RshDark difference between If 1-10 / mm ^2, the present invention is effective against a photovoltaic element in which at least the abnormal growth portions exist 10 pieces / mm ² or more Works. The number of abnormally grown portions left after removal in the present invention is effective at 50 / mm ² or less, and more effective at 10 / mm ² or less. Therefore, the present invention is carried out so that the abnormally grown portions are preferably 50 pieces / mm ² or less, more preferably 10 pieces / mm ² or less.

If the number of remaining abnormally grown portions exceeds 50 / mm ² , RshDark becomes as low as 2000 Ωcm ² or less, a short circuit current flows, and the photoelectric conversion characteristics of the photovoltaic device are degraded by this short circuit current component. However, when the semiconductor layer and the second electrode layer are stacked on the first electrode layer from which the abnormally grown portion has been removed by carrying out the present invention, the short circuit state is recovered and a photovoltaic device having a high RshDark can be obtained. .

  The process of crushing the abnormally grown portion may be mechanical friction or physical impact. Specific examples of mechanical friction include brushing with a resin or metal brush or brush, friction with a slip sheet sandwiched between substrates when the substrates are stacked. Examples of the physical impact include a method of removing abnormally grown portions by blowing a gas such as air or an inert gas onto the substrate surface.

  The device for crushing the abnormally grown part is intended to crush only the abnormally grown part, but may damage the surface of the first electrode layer other than the abnormally grown part. In order to obtain a photovoltaic device with higher photoelectric conversion efficiency, it is necessary to sufficiently scatter incident light on the surface of the first electrode layer and to multiplex-reflect it in the semiconductor. The first electrode layer is also desired to have high conductivity as an electrode. The apparatus for crushing the abnormally grown portion must have a structure that crushes the abnormally grown portion while satisfying those conditions, and the first pressure layer is not damaged so as not to damage the surface of the first electrode layer other than the abnormally grown portion. The abnormally grown portion is crushed by pressing against the electrode layer surface. When the position of the substrate changes, a sufficient effect cannot be obtained unless the structure can be automatically moved to a location that matches the position.

  When the photovoltaic device manufacturing apparatus is a roll-to-roll apparatus and the substrate is long and flexible, when winding up the substrate on which the first electrode layer is formed, When inserting a slip sheet between the back surface of the substrate and the front surface of the first electrode layer, the abnormally grown portion can be crushed by friction generated by vibrating the slip sheet. The vibration may be a sound wave ranging from a low frequency to a high frequency, or an ultrasonic wave. If the displacement of the slip sheet due to the vibration is at least ± 1 mm or more, the abnormally grown portion can be crushed, more preferably the displacement is It is ± 2 mm or more. The vibration may be directly transmitted to the slip sheet by a vibration generator, or a loud sound may be generated by a speaker or a noise generator and transmitted to the slip sheet through a medium such as gas.

  Hereinafter, although the formation method of the photovoltaic device based on this invention is demonstrated in detail based on an Example, this invention is not limited at all by these Examples.

As an example of the present invention, a pin junction type microcrystalline silicon single cell as shown in FIG. 5 was fabricated.
(1) First, a substrate 501 (width 356 mm × length 100 m) made of stainless steel 430 on a roll was washed with a surfactant and washed with water, and dried to remove dirt and foreign matters on the surface.
(2) On the substrate 501, a back reflective layer 502 of 800 nm thick Ag 502 a and 2 μm thick ZnO 502 b was deposited by a known roll-to-roll type sputtering apparatus as shown in FIG.
(3) Further, an n-type layer 503a made of an n-type amorphous silicon film, an i-type layer 503b made of an i-type microcrystalline silicon film, on the back reflective layer 502 by a roll-to-roll type plasma CVD apparatus, A p-type layer 503c made of a p-type microcrystalline silicon film was stacked to form a semiconductor layer 503.
(4) A transparent conductive layer 504 made of ITO (In 2 O 3 + SnO 2) having a thickness of 80 nm was formed on the semiconductor layer 503 by a roll-to-roll type sputtering apparatus.
(5) A stainless steel substrate on which elements are formed up to the transparent conductive layer 504 is cut to a length of 248 mm, patterned by a known chemical etching method, and 1% sulfuric acid is prepared as an electrolytic solution in a known electrolytic processing apparatus. The back surface of the electromotive element is brought into contact with the stainless steel plate, the negative electrode is connected to the negative electrode, the counter electrode is connected to the positive electrode, and an application voltage of 2 V, an application time of 1 sec, and an application interval of 0.5 sec are applied. After removing the short-circuit portion, washing and drying were performed.
(6) Furthermore, the electrode which coat | covered the copper wire with the carbon paste was adhere | attached with the thermocompression bonding apparatus, and the grid electrode 505 was formed.
(7) Thereafter, the positive electrode using copper foil and the grid electrode 505 are connected, the negative electrode is connected to the substrate 501, voltage-current characteristics in the dark state are measured, and the short-circuit resistance RshDark is measured from the inclination near the origin. Asked.

(Example 1)
When the roll-shaped substrate 501 on which the back surface reflection layer 502 is deposited is wound on the take-up bobbin 606 in FIG. 6, a polyimide interleaf 608 is attached to the back surface of the substrate 501 and the back surface reflection layer 502. In this example, the conventional one-time winding process is performed a plurality of times to increase the friction between the interleaf paper 608 and the substrate surface, thereby attempting to crush the abnormally grown portion. It was. Since ZnO used as the back surface reflection layer has high conductivity, the crushed abnormally grown portion has high conductivity and is difficult to electrostatically adsorb, so it can be removed sufficiently even in free fall. Gas gate 604 (width 400 mm, height 10 mm, length 200 mm slit) of the roll-to-roll device (FIG. 6) during the multiple winding process to remove the abnormally crushed abnormally grown portion Then, H2 gas (flow rate 1000 sccm) was blown from 150 gas holes having a diameter of 2 mm onto the substrate surface 609 to try to remove the crushed abnormally grown portion. 120 photovoltaic elements were produced for each, and the short-circuit resistance RshDark was measured. FIG. 9 shows a distribution diagram of the short-circuit resistance RshDark of the photovoltaic element obtained in this example. By implementing the present invention, the number of elements having a low short circuit resistance RshDark is reduced and the number of elements having a high RshDark is increased.

7A and 7B are SEM photographs of the surface of the deposited film over a relatively wide range after the first electrode is formed on the substrate. FIG. 7A shows a state where the abnormally grown portion of the first electrode is removed by the step of crushing and removing the abnormally grown portion according to this embodiment. From the SEM photograph, the number of abnormally grown portions removed on the surface of the deposited film was 100 to 200 / mm ² , and the number of remaining abnormally grown portions was 20 / mm ² or less. When this example was implemented after forming the first electrode, the short-circuit resistance RshDark of the obtained photovoltaic element was high enough not to affect the characteristics of the photovoltaic element. FIG. 7B shows a state in which this example was not carried out, and there are 100 to 300 abnormal growth portions / mm ² . For this reason, sufficient short-circuit removal cannot be performed, and the photovoltaic device has low short-circuit resistance RshDark and low photoelectric conversion efficiency.

(Example 2)
In this embodiment, when the roll-shaped substrate 501 having the back-surface reflective layer 502 deposited thereon is wound around the take-up bobbin 606 in FIG. 6, as shown in FIG. 8, a vibration generator 808 that vibrates the interleaf 807 as shown in FIG. Thus, friction was applied to the substrate surface side 804. The amount of displacement of the vibration part of the vibration generator 808 was set to about ± 2 mm, and the vibration frequency was changed in the range of 10 Hz to 100 kHz to try to crush the abnormally grown part. In order to more effectively remove the crushed abnormally grown portion, when the substrate 804 is wound around the winding bobbin 805 and then the substrate 804 is unwound in the next semiconductor formation step, as in the first embodiment. An attempt was made to remove the crushed abnormally grown portion by blowing H2 gas (flow rate 1000 sccm) onto the substrate surface 809 with the gas gate 604 of the roll-to-roll apparatus (FIG. 6). FIG. 11 shows the relationship between the vibration frequency applied to the slip sheet and the obtained short-circuit resistance RshDark of the photovoltaic element. Here, the solid line means the peak value of the frequency distribution, and the upper and lower ends of the gray portion mean the upper and lower limits of RshDark where the number of elements is 5 or less. The resistance of RshDark can be increased over a wide range, and the number of low RshDark elements is reduced. However, the result that the crushing effect of the abnormal growth part is higher is obtained when the vibration frequency is higher. When an experiment similar to that in Example 2 was performed with the displacement amount of the vibration part of the vibration generator 808 set to ± 0.5 mm, no change in RshDark was observed. Therefore, when the amplitude of vibration was small, the abnormal growth part was sufficiently removed. It is considered impossible.

(Example 3)
In this embodiment, when the roll-shaped substrate 501 having the back-surface reflective layer 502 deposited thereon is wound around a roll, the abnormal growth portion is obtained by brushing the substrate surface side 904 with a resin brush 908 as shown in FIG. Tried crushing. When the substrate 904 is wound around the winding bobbin 905, the diameter changes and the position of the substrate 804 also moves. However, the brush 908 is adjusted to the position of the substrate 904 by the brush height automatic adjusting device 910. The force for pressing the brush 908 against the substrate surface 904 was the weight of the brush (weight: about 900 g). An attempt was made to remove the abnormally grown portion crushed by blowing H2 gas from a gas introduction pipe 909 that moves along with the brush after brushing. In the present embodiment, the present invention can be realized at low cost because it is constituted by an inexpensive brush and a gas pipe. H2 gas was blown in the form of pulses in the range of 50 to 200 Hz, and changes in the short-circuit resistance distribution of the photovoltaic elements were examined. FIG. 12 shows the relationship between the H2 gas pulse frequency and the obtained photovoltaic element short-circuit resistance RshDark. Here, the solid line means the peak value of the frequency distribution, and the upper and lower ends of the gray portion mean the upper and lower limits of RshDark where the number of elements is 5 or less. The resistance of the RshDark can be increased over a wide range, and the number of low RshDark elements is reduced. However, if the H2 gas pulse frequency is large, the effect of removing the crushed abnormally grown portion is slightly low, probably because it approaches a constant state from the pulse shape, but a sufficiently high RshDark element was obtained at 100 Hz or less.

Schematic diagram of the short circuit part of a general photovoltaic device Schematic diagram of abnormal growth process SEM photograph of abnormally grown part and trace of removed abnormally grown part Relationship between number of abnormally grown portions remaining after removal and short-circuit resistance RshDark Schematic cross-sectional view of a photovoltaic device used in one embodiment of the present invention Schematic diagram of roll-to-roll equipment Wide range SEM photograph of deposited film surface after first electrode formation Schematic diagram of the roll-up roll roll Schematic diagram of the roll-up roll roll Frequency distribution of short-circuit resistance RshDark of photovoltaic element Relationship between short-circuit resistance RshDark of photovoltaic element and vibration frequency of slip sheet Relationship between short-circuit resistance Rshdark of photovoltaic element and H2 gas pulse frequency

Explanation of symbols

101 Substrate 102 Semiconductor 103 ITO
104 crack 105 hole 106 nucleus of abnormally grown portion 107 short-circuited portion such as grain boundary 108 abnormally grown portion 109 foreign matter such as dust 201 portion where ITO has been removed 202 portion where ITO cannot be removed 203 trace of foreign matter removed 501 stainless steel substrate 502 back surface Reflective layer 502a Ag
502b ZnO
503 Semiconductor layer 503a n-type layer 503b i-type layer 503c p-type layer 504 transparent conductive layer 505 grid electrode 601 unwind chamber 602 take-up chamber 603 film-forming chamber 604 gas gate 605 unwind bobbin 606 take-up bobbin 607 idling roller 608 Bobbin 609 stainless steel substrate (front side)
801, 901 Winding chamber 802, 902 Gas gate 803, 903 Idling roller 804, 904 Stainless steel substrate (front side)
805, 905 Winding bobbins 806, 906 Interleaving bobbins 807, 907 Interleaving paper 808 Vibration generating device 809 Portion where interleaving paper and substrate surface contact 908 Brush 909 Gas introduction pipe 910 Brush height automatic adjustment device

Claims (9)

  A photovoltaic device in which at least a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially laminated on a substrate in this order, wherein the first electrode layer has an abnormal growth portion removal region, and an abnormal growth portion A photovoltaic element, wherein the semiconductor layer is formed in a removal region.   2. The photovoltaic element according to claim 1, wherein the first electrode layer is a back surface reflective layer composed of a translucent conductive film and a reflective conductive film.   In the method of forming a photovoltaic device, which includes a step of sequentially stacking at least a first electrode layer, a semiconductor layer, and a second electrode layer in this order on a substrate, the first electrode is formed before the step of forming the semiconductor layer. A method for forming a photovoltaic device, comprising: a step of crushing an abnormally grown portion that has grown on the substrate during layer formation; and a step of removing the crushed abnormally grown portion.   The method for forming a photovoltaic device according to claim 3, wherein the step of crushing the abnormally grown portion is one of mechanical friction and physical impact, or a combination thereof. Abnormal growth portion by crushing, after removal, the remaining number of the abnormal growth portions which is 50 / mm ² or less forming method of the photovoltaic device according to claim 3.   In a photovoltaic device manufacturing apparatus having means for forming a semiconductor layer on a substrate having at least a first electrode layer, means for crushing abnormal growth portions existing on the first electrode layer, and crushed abnormal growth And a means for removing the portion of the photovoltaic device.   Even if the position of the substrate changes, the means for crushing the abnormal growth portion has means for pressing the first electrode layer surface with a pressure that does not damage the surface of the first electrode layer other than the abnormal growth portion. The photovoltaic device manufacturing apparatus according to claim 6.   The photovoltaic device manufacturing apparatus is a roll-to-roll apparatus, and has a slip sheet between the back surface of the substrate and the surface of the first electrode layer, and has means for vibrating the slip sheet. The photovoltaic device manufacturing apparatus according to claim 6.   The apparatus for manufacturing a photovoltaic element according to claim 8, wherein the abnormally grown portion is crushed by transmitting vibrations of sound waves and ultrasonic waves to the slip sheet.

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