JP2010212614A - Compound thin film solar cell and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell formed by lamination of a back surface electrode layer effective for improving FF characteristics of the solar cell and avoiding decrease in yield, and a method of producing the solar cell. <P>SOLUTION: A compound thin film solar cell is formed by laminating a metal back surface electrode layer of molybdenum on a glass substrate. The metal back surface electrode layer is formed on the glass substrate by a sputtering method to have a surface reflection coefficient in a range of 10% or more and 35% or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a compound-based thin film solar cell obtained by laminating a metal back electrode layer on a glass substrate, and a method for producing the same.

In recent years, research and production of various types of solar cells have been actively conducted due to environmental concerns and policies.
Among various types of solar cells, particularly compound solar cells are remarkable for mass production due to their high conversion efficiency potential and high reliability against aging.

  In this regard, in Patent Document 1, an integrated thin-film solar cell including two or more unit cells connected in series on an insulating substrate, the first electrode film sequentially stacked on the insulating substrate, a semiconductor film including a pn junction; and a second electrode film, wherein the first electrode film, the semiconductor film, and the second electrode film are first, second, and third substantially parallel to each other, respectively. Two or more unit cells divided by the dividing groove, and the two adjacent unit cells are arranged such that the second electrode film of one unit cell is connected to the other unit via the second dividing groove. The semiconductor film is connected in series by being connected to the first electrode film of the cell, and the semiconductor film includes a group Ib element, a group IIIb element, and a group VIb element and is adjacent to the first electrode film A first electrode film having a semiconductor film; Include molybdenum, it is 0.3μm or less the thickness of the flat portion integrated thin-film solar cell of the first electrode film has been proposed.

JP 2008-21713 A

According to the technique described in Patent Document 1, when the Mo film as the first electrode is patterned by a laser, it is constant to prevent a bulge from occurring at the edge of the division groove of the Mo film and causing a short circuit. The effect of can be produced.
On the other hand, regarding the metal back electrode layer, which is a Mo film in the technique described in Patent Document 1, it is not sufficient to consider only burrs and debris that cause a short circuit in order to obtain a solar cell having high reliability and FF characteristics. .
That is, it is possible to improve the FF characteristics of the solar cell and reduce the yield by further considering the adhesion with the light absorption layer laminated on the metal back electrode layer and the resistivity of the entire solar cell. I can do it.

  Then, an object of this invention is to provide the compound type thin film solar cell which laminates | stacks the metal back electrode layer effective in the improvement of the FF characteristic of a solar cell, and the reduction of a yield, and its manufacturing method.

  In order to achieve the above object, a compound thin film solar cell according to one aspect of the present invention is a compound thin film solar cell in which a metal back electrode layer made of molybdenum is laminated on a glass substrate, and the metal back electrode The layer is formed on the glass substrate by sputtering so that the reflectance of the surface thereof is in the range of 10% to 35%.

  Moreover, the film thickness of molybdenum formed on the glass substrate may be 800 nm or less.

  In addition, in the method for manufacturing a metal back electrode layer constituting a compound solar cell according to another aspect of the present invention, the glass substrate is disposed as a sample in a predetermined vacuum chamber, and the molybdenum is disposed as a sputter target. In addition, the vacuum chamber is evacuated, and an inert gas is injected into the evacuated chamber at a gas flow rate of 60 to 70 sccm to maintain a film forming pressure of 20 mTorr or less. A step of driving a pair of sputter electrodes arranged to apply a voltage between the glass substrate and the molybdenum to form the molybdenum on the glass substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the solar cell which has low resistivity as an adhesiveness with a light absorption layer, the ease of patterning by a laser, and a solar cell can be obtained.

It is a figure which shows the laminated structure of the compound type thin film solar cell which concerns on embodiment of this invention. It is a figure which shows the patterning apparatus used in the experiment regarding a metal back surface electrode layer regarding the compound type thin film solar cell which concerns on this embodiment. It is a graph which shows the correlation of the reflectance of a metal back surface electrode layer, and film forming pressure in the experiment regarding the compound type thin film solar cell concerning this embodiment. It is a graph which shows the correlation of a reflectance and a resistivity in the experiment regarding the compound type thin film solar cell which concerns on this embodiment.

Hereinafter, a compound-based thin film solar cell according to an embodiment of the present invention and a manufacturing method thereof will be described with reference to the drawings.
In FIG. 1, the laminated structure of the compound type thin film solar cell which concerns on this embodiment is shown.
As shown in FIG. 1, the compound thin film solar cell 1 is formed by sequentially laminating a metal back electrode layer 12, a light absorption layer 13, a high resistance buffer layer 14, and a window layer 15 on a glass substrate 11.

The glass substrate 11 is made of, for example, blue plate glass.
The glass substrate 11 is made of, for example, silica having a thickness of about 50 nm in order to prevent alkali metal components such as sodium (Na) and potassium (K) contained in the soda glass from diffusing into the light absorption layer. SiO ₂₎ an alkali-barrier layer may be composed of a coated soda lime glass made of, or the like.

The metal back electrode layer 12 is a thin film made of molybdenum (Mo), and is formed on the glass substrate 11 by a DC sputtering method.
Here, the molybdenum (Mo) film is used as the metal back electrode layer 12 because it has high corrosion resistance with respect to selenium (Se) used in the process of forming the light absorption layer 13, and is a sputtering technique that is a general-purpose technique. Can be easily formed into a large area, and the molybdenum selenide (MoSe ₂ ) layer formed on the molybdenum (Mo) film by reaction with selenium (Se) absorbs light by a mechanical scriber using a metal needle. This is because it acts as a solid lubricant when patterning the layer 13 and the high-resistance buffer layer 14 and does not penetrate the metal back electrode layer 12 and damage the glass substrate 11.
The metal back electrode layer 12 according to the present embodiment is formed into a three-layer structure by DC sputtering using three molybdenum (Mo) targets. The reason why the three-layer structure is used in this way is that in the case of an in-line type sputtering apparatus, cracks are likely to occur in a long glass substrate due to heat input to the molybdenum (Mo) film and the compressive stress generated. is there.
Details of the metal back electrode layer 12 according to this embodiment will be described later.

The light absorption layer 13 is, for example, a thin film having a thickness of 1 to 3 μm and having a p-type conductivity I-III-VI ₂ group chalcopyrite structure, CuInSe ₂ , Cu (InGa) Se ₂ , Cu (InGa) ( SSe) composed of a multi-component compound semiconductor thin film such as ₂ . Other examples of the p-type CIS light absorption layer include a selenium compound-based CIS light absorption layer, a sulfide-based CIS light absorption layer, and a selenide / sulfide-based CIS light absorption layer. The CIS light absorption layer is made of CuInSe ₂ , Cu (InGa) Se ₂ or CuGaSe ₂ , and the sulfide-based CIS light absorption layer is made of CuInS ₂ , Cu (InGa) S ₂ , CuGaS ₂ , and the selenium. reduction and sulfide-based CIS light absorption _{layer, CuIn (SSe) 2, Cu} (InGa) (SSe) 2, consists CuGa _{(SSe) 2,} also, as having a surface layer, CuIn _{(SSe) 2} with a _{Cu (InGa) Se 2, CuIn} (SSe) 2 having a CuInSe _2, CuIn _{(SSe) 2} as a surface layer having a surface layer as a surface layer _{u (InGa) (SSe) 2} , with a CuIn _{(SSe) 2} as a surface layer _{CuGaSe 2, Cu (InGa) (} SSe) Cu with ₂ as a surface layer (InGa) Se 2, Cu ( InGa) (SSe) 2 There are CuGaSe ₂ having Cu as a surface layer, CuGaIn ₂ having Cu (InGa) Se ₂ as a surface layer and CuGaSe ₂ having CuGa (SSe) ₂ as a surface layer.
The light absorption layer 13 is formed on the metal back electrode layer 12 by a selenization / sulfurization method or a multi-source co-evaporation method.

  The high resistance buffer layer 14 is a layer for forming an electrical junction with the light absorption layer. The buffer layer can be formed of a thin film of a zinc mixed crystal compound such as zinc sulfide (ZnS) by a metal organic chemical vapor deposition (MOCVD) method, a vacuum deposition method, or the like.

  The window layer 15 is composed of an n-type transparent conductive film. The window layer 15 is formed on the high resistance buffer layer 14 by MOCVD.

  As described above, the metal back electrode layer 12, the light absorption layer 13, the high resistance buffer layer 14, and the window layer 15 laminated on the glass substrate 11 are subjected to patterning P1, P2, and P3 in the manufacturing process.

  The patterning P1 is a patterning performed after the high-melting-point, high-corrosion-resistant metal molybdenum (Mo) is formed as a metal back electrode layer 12 by the DC sputtering method, and has high linearity, reproducibility, and high speed. Pattern formation is required.

In the formation of the pattern groove in the patterning P1, it is necessary to prevent the glass substrate 11 or the alkali barrier layer coated on the glass substrate 11 from being scratched which causes the substrate to crack. Therefore, an excimer laser, particularly a Kr-F excimer laser is used in the present embodiment, regardless of a mechanical scriber using a metal needle.
Unlike the first harmonic Nd-YAG laser (wavelength: 1064nm), which melts and cuts metal with infrared light, the Kr-F excimer laser sublimates the metal with ultraviolet light and cuts the pattern. Form. As a result, damage to the glass substrate can be prevented.
In the present embodiment, the metal back electrode layer 12 is patterned using an excimer laser. However, the present invention is not limited to this, and an Nd-YAG laser of the second harmonic or higher is used instead of the excimer laser. In other words, it may be an Nd-YAG laser having a wavelength of 532 nm or less, and more preferably a fourth harmonic Nd-YAG laser (wavelength: 266 nm).

  The patterning P2 is a patterning performed after the high resistance buffer layer 14 is formed. In the formation of the pattern groove in the patterning P2, it is necessary to avoid the laser method and the mechanical scribing method using a metal needle because the light absorption layer 13 needs to absorb light and to prevent the film from being affected by heat. Is done.

  Patterning P3 is patterning performed after the window layer 15 is formed. In the formation of the pattern groove in the patterning P3, the laser method is difficult to apply because the transparent conductive film configured as the window layer 15 is hard and transparent. Therefore, a mechanical scribing method using a metal needle is applied.

  In the solar cell module 1 manufactured as described above, the metal back electrode layer 12 is required to have adhesiveness with the light absorption layer 13, ease of patterning P1 by laser, and low resistivity.

  Here, the adhesiveness with the light absorption layer 13 indicates that the light absorption layer 13 is required not to peel from the metal back electrode layer 12.

  In addition, the ease of patterning P1 by laser indicates that it is required to form a single continuous linear pattern groove without disconnection when the patterning P1 is formed. In this regard, it is further required that protrusions such as debris and burrs are generated in the vicinity of the pattern grooves and that the formation of the heat affected zone is minimized.

The low resistivity indicates that a resistance component that causes a decrease in power generation efficiency of the compound thin film solar cell 1 is required to be as small as possible. In this respect, the point that the metal back electrode layer 12 is related to the low resistivity is that molybdenum (at the time of vapor phase selenization in the process of peeling the metal back electrode layer 12 and the light absorption layer 13 and forming the light absorption layer 13). Molybdenum selenide (MoSe ₂ ) layer formed by the reaction of Mo) and selenium (Se) causes an increase in series resistance component.

  Here, the inventor of the present application described the metal back electrode layer as factors determining the adhesion to the light absorption layer 13 required for the metal back electrode layer 12, the ease of patterning P1 by laser, and the low resistivity as described above. Focusing on the surface shape of 12 and its film thickness, the correlation was verified.

First, an experiment performed on the surface shape of the metal back electrode layer 12 will be described.
In the present embodiment, the metal back electrode layer 12 is produced by a DC sputtering method, and the inventors of the present application have found that the surface shape of the metal back electrode layer 12 changes depending on the film forming pressure of sputtering.
That is, when the film forming pressure is low, the film density or the density of molybdenum (Mo) particles becomes high, so that the surface smoothness increases. On the other hand, when the film forming pressure is high, the film density on the surface of the film or the density of molybdenum (Mo) particles becomes small, so that the shape has many gaps.
Then, in order to quantitatively evaluate the film density on the surface of the metal back electrode layer 12 or the density of molybdenum (Mo) particles, the metal back electrode layer 12 is produced by changing only the film forming pressure. An experiment for measuring the reflectance on the surface of the layer 12 was performed.

FIG. 2 shows a patterning apparatus used for patterning P1.
In the measurement of the reflectance, the patterning apparatus shown in FIG. 2 was used.
The irradiation conditions of the patterning apparatus are as shown in Table 1, and the total reflection of the metal back electrode layer 12 at a position of a wavelength of 250 nm, which substantially coincides with the wavelength of 248 nm, is measured with a Kr-F excimer laser having a wavelength of 248 nm. did.

  In addition, Table 2 shows the film forming conditions of the metal back electrode layer 12 for which the reflectance was measured in this experiment.

  Regarding the power in Table 2, the metal back electrode layer 12 in the present embodiment is formed in a three-layer structure, and is formed in order of 0.66 kW, 2.88 kW, 2.88 kW on the glass substrate 11. Is formed into a film. The thickness of each of the three layers of the metal back electrode layer 12 is about 90 nm, 360 nm, and 360 nm in order from the glass substrate 11 side, and the total thickness is 800 to 820 nm.

FIG. 3 shows the measurement results of the reflectance of the metal back electrode layer 12 produced by changing only the film forming pressure under the above film forming conditions.
As shown in FIG. 3, the reflectance increases as the film forming pressure decreases. This indicates that when the film forming pressure is low, the film density or the density of molybdenum (Mo) particles is increased, and the smoothness of the surface is increased.
In this regard, if the reflectance is too high, it is assumed that the energy density on the irradiated surface is reduced and patterning becomes difficult.
Further, since the surface is smooth, the adhesion between the light absorption layer 13 and the metal back electrode layer 12 is lowered, and the light absorption layer 13 may be peeled off from the metal back electrode layer 12.
Further, when the adhesion between the metal back electrode layer 12 and the light absorption layer 13 is poor, peeling occurs, a gap is formed between the joint surfaces of both layers, and the series resistance component increases.

Conversely, the reflectivity decreases as the film forming pressure increases. This means that when the film forming pressure is high, the film density or the density of molybdenum (Mo) particles is reduced, and the surface has a shape with many gaps.
In this respect, the shape having many gaps is effective for adhesion to the light absorption layer 13. However, when there are too many gaps, in other words, when the reflectance is too low, the reactivity with selenium (Se) increases during vapor phase selenization in the film forming process of the light absorption layer 13, and molybdenum selenide (MoSe ₂ ) The layer is formed excessively. Then, due to the volume expansion due to the formation of the molybdenum selenide (MoSe ₂ ) layer, the adhesion between the light absorption layer 13 and the metal back electrode layer 12 is lowered, and the light absorption layer 13 may be peeled off from the metal back electrode layer 12. is there.
Further, the molybdenum selenide (MoSe2) layer causes an increase in the series resistance component and deteriorates the solar cell characteristics. As is apparent from FIG. 4 showing the correlation between the resistivity of the metal back electrode layer 12 and the reflectance, when the reflectance is less than 10%, the resistivity is very high and the solar cell characteristics are poor.

Based on the above experimental results, by forming the metal back electrode layer 12 having a reflectance in the range of 10% to 35%, the resistivity is low, and the adhesion between the metal back electrode layer 12 and the light absorption layer 13 is low. It was revealed that a compound-based thin film solar cell 1 that is high and easy to pattern P1 can be obtained.
From the above experimental results, it is clear that the metal back electrode layer 12 having a reflectance in the range of 10% to 35% can be formed at a film forming pressure of 20 mTorr or less.

Next, an experiment focusing on the film thickness of the metal back electrode layer 12 was performed.
The film thickness is determined by the combination of the power applied to the sputtering target and the transport speed of the substrate. In this experiment, the experiment was performed by changing the transport speed.

  Table 3 shows the film forming conditions of the metal back electrode layer 12 in the film thickness evaluation experiment.

  Also in this experiment, the metal back electrode layer 12 is formed in a three-layer structure, and is formed at 0.66 kW, 2.88 kW, and 2.88 kW in the order of film formation on the glass substrate 11.

  Table 4 shows the contents of the metal back electrode layer 12 obtained under each film forming condition.

As shown in Table 4, the sheet resistance decreased as the film thickness increased.
If the film thickness is in the range of 340 to 820 nm, the reflectance of the metal back electrode layer 12 belongs to the above-described reflectance of 10% or more and 35% or less, and a compound-based thin film solar capable of obtaining effective solar cell characteristics. It is clear that the battery 1 can be produced.

  Table 5 shows the characteristics of the compound-based thin film solar cell 1 produced using the metal back electrode layer 12 formed under each film forming condition.

As a result, even if the film thickness was changed to 820 nm, 560 nm, and 340 nm, no change was observed in the characteristics of the solar cell.
From the above, it was found that the resistance value of the series resistance hardly changed regardless of the film thickness of the metal back electrode layer 12.
Further, in any case where the film thickness is 820 nm, 560 nm, or 340 nm, the metal back electrode layer 12 does not peel from the glass substrate 11 and the light absorption layer 13 does not peel from the metal back electrode layer 12, and the metal back electrode Little difference was observed in the adhesion due to the difference in the film thickness of the layer 12.
In addition, as a result of patterning by the patterning apparatus shown in FIG. 2 described above, in any case of film thicknesses of 820 nm, 560 nm, and 340 nm, a pattern groove consisting of one continuous straight line is formed, and The insulation was ensured, and almost no difference was observed in the patterning property due to the difference in film thickness.

  However, when the film thickness is thick, the patterning P1 tends to cause protrusions such as debris and burrs in the vicinity of the pattern groove, or a bridge that causes a short circuit inside the pattern groove. This problem can be solved by reducing the film thickness. Moreover, when making a film thickness thin, a conveyance speed will be raised and manufacturing efficiency will become high in a manufacturing process.

  Further, regarding the ease of patterning P1, as a result of patterning with the patterning apparatus shown in FIG. 2 described above, it was found that the metal back electrode layer 12 having a film thickness of 800 nm or less and a reflectance of 35% or less can be cut.

When the metal back electrode layer 12 having a film thickness of 800 nm or less and a reflectance of 35% or less is manufactured, first, the glass substrate 11 is placed as a sample in a predetermined vacuum chamber, and molybdenum (Mo) is sputtered. After being arranged as a target, the inside of the vacuum chamber is evacuated.
Then, argon (Ar) gas is injected into the vacuum chamber at a gas flow rate of 60 to 70 sccm to keep the inside of the vacuum chamber in an atmosphere having a film forming pressure of 20 mTorr or less, and a pair of sputter electrodes disposed in the vacuum chamber. Is driven to apply a voltage between the glass substrate 11 as a sample and molybdenum (Mo) as a sputtering target to form molybdenum (Mo) on the glass substrate 11.
As a result, the metal back electrode layer 12 having a reflectance by laser of 35% or less is produced.

DESCRIPTION OF SYMBOLS 1 Compound type thin film solar cell 11 Glass substrate 12 Back surface electrode layer 13 Light absorption layer 14 High resistance buffer layer 15 Window layer P1 Patterning 1
P2 patterning 2
P3 Patterning 3

Claims (3)

A compound-based thin film solar cell in which a metal back electrode layer made of molybdenum is laminated on a glass substrate,
The metal back electrode layer is formed on the glass substrate by a sputtering method so that the reflectance of the surface is in the range of 10% to 35%.
A compound-based thin film solar cell. The film thickness of molybdenum formed on the glass substrate is 800 nm or less;
The compound-based thin film solar cell according to claim 1. A method for producing a metal back electrode layer constituting the compound solar cell according to claim 1 or 2,
Placing the glass substrate as a sample in a predetermined vacuum chamber, placing the molybdenum as a sputter target, and evacuating the vacuum chamber;
An inert gas is injected into the evacuated chamber at a gas flow rate of 60 to 70 sccm to maintain a film forming pressure of 20 mTorr or less, and a pair of sputter electrodes disposed in the vacuum chamber is driven to drive the glass. Applying a voltage between the substrate and the molybdenum, and forming the molybdenum on the glass substrate.
A method for producing a compound-based thin-film solar cell.

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