Patent Publication Number: US-2010116331-A1

Title: Photovoltaic device and process for producing same

Description:
RELATED APPLICATIONS 
     The present application is based on International Application Number PCT/JP2008/052125 filed Feb. 8, 2008, and claims priority from Japanese Application Number 2007-088753 filed Mar. 29, 2007, the disclosures of which are hereby incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a photovoltaic device and a process for producing the same. 
     BACKGROUND ART 
     Thin-film solar cells have undergone a variety of innovations, from both the voltage and electrical current perspectives, aimed at improving the electric power output. In particular, laminated (tandem) structures have been proposed in order to enable a more efficient absorption of the incident light and subsequent conversion to an electrical current, thereby increasing the open-circuit voltage. Moreover, in order to increase the electrical current from the photovoltaic layer at the light-incident side (the upper surface) of the cell, publications such as the non-patent citation 1 have proposed the use of a transparent conductive film structure (or intermediate reflective layer, abbreviated as “intermediate layer”) of optimized film thickness, which is disposed between an upper amorphous silicon photovoltaic layer and a lower polycrystalline thin-film photovoltaic layer. 
     Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2001-308354 
     Patent Citation 2: Japanese Unexamined Patent Application, Publication No. 2002-118273 
     Non Patent Citation 1: Report from Neuchatel University, Switzerland (pp. 728 to 731) at the 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, 1998, Vienna, Austria 
     Non Patent Citation 2: Tadatsugu Minami, Ceramics Japan, Vol. 42, No. 1 (2007), “Advantages and Problems of ZnO-based Substitute Materials”, FIG. 4. 
     DISCLOSURE OF INVENTION 
     However, the intermediate layer must optimize the light wavelength band reflected onto the upper photovoltaic layer, and must also increase the electrical current of the upper photovoltaic layer, and for example, although the patent citation 1 discloses a technique for improving the reflected light selectivity by providing a plurality of intermediate layers, the resulting increases in cost do not justify the level of increase in the electrical current. 
     Furthermore, another problem arises in that if, as described in the patent citation 2, an intermediate layer is introduced and a modularization is then performed to form series-connected circuits, then it is known that the intermediate layer acts as a current leakage pathway, causing a deterioration in the module properties. In the patent citation 2, although this phenomenon is suppressed by optimizing the electrical conductivity of the intermediate layer, there is a limit to how effectively the degradation can be suppressed. 
     The present invention has been developed in light of the above circumstances, and has an object of providing a photovoltaic device and a process for producing the device that enable a higher level of performance to be achieved at low cost. 
     As a result of conducting intensive investigations aimed at achieving the above object, the inventors of the present invention discovered that following formation of an intermediate layer after formation of the upper photovoltaic layer, the effect of the process for forming a lower photovoltaic layer using a plasma enhanced CVD film deposition apparatus (for example, hydrogen plasma exposure) causes a surface layer that increases light absorption to be formed on the surface of the intermediate layer that contacts the lower photovoltaic layer. Furthermore, they also discovered that this surface layer that increases light absorption is a degenerated layer formed by hydrogen reduction of the ZnO-based material such as Ga-doped ZnO (GZO) that is used as the material for the intermediate layer. This phenomenon causes light absorption loss at the intermediate layer, resulting in a reduction in the electric power generated by the entire solar cell. 
     The inventors discovered that by forming a thin coating of SiO 2 , which exhibits a high degree of plasma resistance, as a protective layer on the surface of the intermediate layer, the degeneration of the intermediate layer surface could be prevented. SiO 2  usually exhibits a high degree of electrical insulation, but, as a result of research, the inventors discovered that by performing sputtering with an Ar/O 2  gas composition against a SiC target, a layer of SiO 2-x C y  (wherein x and y are small values, hereafter this material is abbreviated as simply SiO 2 ) could be obtained that exhibited conductivity and was also optically transparent. 
     Furthermore, ZnO exhibits a property wherein a reduction in the film thickness causes an increase in the resistivity, and the inventors discovered that by using the technique described above, the film thickness of the intermediate layer could be reduced to increase the resistance of the intermediate layer, and that as a result of the reduced electrical conductivity within the in-plane direction, the current leakage pathway could be restricted. 
     The above technique possesses a more powerful current leakage preventative action than that of the patent citation 2, and also prevents plasma-induced degeneration of the intermediate layer, for which the patent citation 2 offers no countermeasures. 
     Furthermore, the inventors found that increasing the resistance of the intermediate layer was also effective in preventing the current leakage that occurs via the intermediate layer in a thin-film tandem solar cell having an intermediate layer. However in the patent citation 2, although attempts were made to increase the resistance of the Ga-doped ZnO (GZO) of the intermediate layer material by adjusting the quantity of Ga doping or increasing the oxygen concentration, there was a limit to the size of the increase in resistance. FIG. 4 in the non-patent citation 2 shows that as the ZnO film thickness is reduced, the ZnO resistivity also decreases. This is because as the film thickness is reduced, the particle size of the ZnO crystal grains that constitute the thin film decreases. Accordingly, in order to prevent current leakage through the intermediate layer, the film thickness of the ZnO film should be reduced as far as possible. However, in order to increase the selective reflectance of light of a specific wavelength, thereby increasing the electrical current from the light-incident side (the upper) photovoltaic layer, which represents the role of the intermediate layer, a ZnO film of a predetermined thickness is required. 
     Accordingly, in order to achieve a film thickness that exhibits the desired optical properties while maintaining a thin ZnO film, a laminated ZnO thin-film structure represented by ZnO/SiO 2 /ZnO may be adopted. By adopting such a structure, the film thickness of the conductive ZnO films can be kept thin, enabling a high resistivity to be obtained, whereas the presence of the SiO 2  means that an increase in the selective reflectance of light of the specified wavelength can also be achieved. 
     Moreover, if a laminated structure with a total of 5 layers represented by ZnO/SiO 2 /ZnO/SiO 2 /ZnO is adopted in order to achieve a film thickness that exhibits the desired optical properties while maintaining a thin ZnO film, then the film thickness of the conductive ZnO films can be kept thin, enabling a high resistivity to be obtained, and an even superior increase in the selective reflectance of light of the specified wavelength can be achieved. 
     Furthermore, by adopting a laminated structure with a total of 4 layers including a protective layer, as represented by ZnO/SiO 2 /ZnO/SiO 2 , the film thickness of the conductive ZnO films can be kept thin, enabling a high resistivity to be obtained, and formation of a light absorption layer due to plasma exposure can be prevented. 
     In other words, in order to achieve the object described above, the present invention adopts the aspects described below. 
     A first aspect of the present invention provides a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers and connects the two photovoltaic layers electrically and optically, wherein the surface of the intermediate layer has a plasma-resistant protective layer. 
     In the photovoltaic device according to the first aspect, the plasma-resistant protective layer may comprise mainly SiO 2 . 
     Furthermore, in the photovoltaic device according to the first aspect, the plasma-resistant protective layer may be a layer comprising Si, O and C, in which the proportion of O is not less than 20% and not more than 60%, and the proportion of C is not less than 5% and not more than 30%. 
     In the photovoltaic device according to the first aspect, the plasma-resistant protective layer may have a film thickness of not less than 2 nm and not more than 30 nm. 
     A second aspect of the present invention provides a process for producing a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers, and connects the two photovoltaic layers electrically and optically, the process comprising forming a plasma-resistant protective layer on the surface of the intermediate layer by performing sputtering with an Ar/O 2  gas composition. 
     A third aspect of the present invention provides a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers and connects the two photovoltaic layers electrically and optically, wherein the intermediate layer has a laminated structure with a total of 3 layers represented by transparent conductive film/transparent film/transparent conductive film. 
     In the photovoltaic device according to the third aspect, the transparent conductive films may be formed using a material that comprises ZnO. 
     In the photovoltaic device according to the third aspect, the transparent film may be a layer comprising mainly SiO 2 . 
     Furthermore, in the photovoltaic device according to the third aspect, the transparent film may be a layer comprising Si, O and C, in which the proportion of O is not less than 20% and not more than 60%, and the proportion of C is not less than 5% and not more than 30%. 
     In the photovoltaic device according to the third aspect, the transparent conductive films may have a film thickness of not less than 5 nm and not more than 100 nm. 
     In the photovoltaic device according to the third aspect, the transparent film may have a film thickness of not less than 2 nm and not more than 30 nm. 
     A fourth aspect of the present invention provides a process for producing a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers and connects the two photovoltaic layers electrically and optically, wherein the intermediate layer has a laminated structure with a total of 3 layers represented by transparent conductive film/transparent film/transparent conductive film, and the transparent film is formed by performing sputtering with an Ar/O 2  gas composition. 
     A fifth aspect of the present invention provides a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers and connects the two photovoltaic layers electrically and optically, wherein the intermediate layer has a laminated structure with a total of 5 layers represented by transparent conductive film/transparent film/transparent conductive film/transparent film/transparent conductive film. 
     In the photovoltaic device according to the fifth aspect, the transparent conductive films may be formed using a material that comprises ZnO. 
     In the photovoltaic device according to the fifth aspect, the transparent films may be layers comprising mainly SiO 2 . 
     Furthermore, in the photovoltaic device according to the fifth aspect, the transparent films may be layers comprising Si, O and C, in which the proportion of O is not less than 20% and not more than 60%, and the proportion of C is not less than 5% and not more than 30%. 
     In the photovoltaic device according to the fifth aspect, the transparent conductive films may have a film thickness of not less than 5 nm and not more than 100 nm. 
     In the photovoltaic device according to the fifth aspect, the transparent films may have a film thickness of not less than 2 nm and not more than 30 nm. 
     A sixth aspect of the present invention provides a process for producing a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers and connects the two photovoltaic layers electrically and optically, wherein the intermediate layer has a laminated structure with a total of 5 layers represented by transparent conductive film/transparent film/transparent conductive film/transparent film/transparent conductive film, and the transparent films are formed by performing sputtering with an Ar/O 2  gas composition. 
     A seventh aspect of the present invention provides a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers and connects the two photovoltaic layers electrically and optically, wherein the intermediate layer has a laminated structure with a total of 4 layers represented by transparent conductive film/transparent film/transparent conductive film/transparent film. 
     In the photovoltaic device according to the seventh aspect, the transparent conductive films may be formed using a material that comprises ZnO. 
     In the photovoltaic device according to the seventh aspect, the transparent films may be plasma-resistant protective layers comprising mainly SiO 2 . 
     Furthermore, in the photovoltaic device according to the seventh aspect, the transparent films may be plasma-resistant protective layers comprising Si, O and C, in which the proportion of O is not less than 20% and not more than 60%, and the proportion of C is not less than 5% and not more than 30%. 
     In the photovoltaic device according to the seventh aspect, the transparent conductive films may have a film thickness of not less than 5 nm and not more than 100 nm. 
     In the photovoltaic device according to the seventh aspect, the transparent films may have a film thickness of not less than 2 nm and not more than 30 nm. 
     An eighth aspect of the present invention provides a process for producing a photovoltaic device comprising at least two laminated photovoltaic layers, and an intermediate layer that is disposed between the two photovoltaic layers and connects the two photovoltaic layers electrically and optically, wherein the intermediate layer has a laminated structure with a total of 4 layers represented by transparent conductive film/transparent film/transparent conductive film/transparent film, and the transparent films are formed by performing sputtering with an Ar/O 2  gas composition. 
     According to the photovoltaic device and production process of the present invention, the selective reflectance of light of a specific wavelength provided by the intermediate layer is increased, while current leakage through the intermediate layer caused by modularization can be prevented. As a result, a high level of performance can be achieved at low cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A schematic view showing the structure of a photovoltaic device according to a first embodiment of the present invention. 
         FIG. 2  A schematic view showing a portion of a process for producing the photovoltaic device. 
         FIG. 3  A schematic view showing a portion of a process for producing the photovoltaic device. 
         FIG. 4  A schematic view showing a portion of a process for producing the photovoltaic device. 
         FIG. 5  A schematic view showing a portion of a process for producing the photovoltaic device. 
         FIG. 6  A schematic view showing the structure of a photovoltaic device according to a second embodiment of the present invention. 
         FIG. 7  A schematic view showing the structure of a photovoltaic device according to a third embodiment of the present invention. 
         FIG. 8  A schematic view showing the structure of a photovoltaic device according to a fourth embodiment of the present invention. 
     
    
    
     EXPLANATION OF REFERENCE 
     
         
           50 : Solar cell panel 
           90 : Photovoltaic device 
           91 : First cell layer 
           92 : Second cell layer 
           93 : Intermediate layer 
           93 A: Plasma-resistant protective layer 
           101 : Substrate 
           102 : Transparent electrode layer 
           103 : Photovoltaic layer 
           104 : Back electrode layer 
           190 : Photovoltaic device 
           191 : First cell layer 
           192 : Second cell layer 
           193 : Intermediate layer 
           193 A: Transparent conductive film 
           193 B: Transparent film 
           193 C: Transparent conductive film 
           201 : Substrate 
           202 : Transparent electrode layer 
           203 : Photovoltaic layer 
           204 : Back electrode layer 
           290 : Photovoltaic device 
           291 : First cell layer 
           292 : Second cell layer 
           293 : Intermediate layer 
           293 A: Transparent conductive film 
           293 B: Transparent film 
           293 C: Transparent conductive film 
           293 D: Transparent film 
           293 E: Transparent conductive film 
           301 : Substrate 
           302 : Transparent electrode layer 
           303 : Photovoltaic layer 
           304 : Back electrode layer 
           390 : Photovoltaic device 
           391 : First cell layer 
           392 : Second cell layer 
           393 : Intermediate layer 
           393 A: Transparent film 
           393 B: Transparent conductive film 
           393 C: Transparent film 
           393 D: Transparent conductive film 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A first embodiment of the present invention is described below with reference to the drawings. 
       FIG. 1  is a schematic view showing the structure of a photovoltaic device according to this embodiment. The photovoltaic device  90  is a silicon-based solar cell, and comprises a substrate  1 , a transparent electrode layer  2 , a solar cell photovoltaic layer  3  comprising a first cell layer (a second photovoltaic layer)  91  and a second cell layer (a first photovoltaic layer)  92 , and a back electrode layer  4 . In this embodiment, the first cell layer  91  is an amorphous silicon-based photovoltaic layer, and the second cell layer  92  is a crystalline silicon-based photovoltaic layer. 
     In this description, the term “silicon-based” is a generic term that includes silicon (Si), silicon carbide (SiC) and silicon-germanium (SiGe). Furthermore, the term “crystalline silicon-based” describes a silicon system other than an amorphous silicon system, namely other than a non-crystalline silicon system, and includes both microcrystalline silicon and polycrystalline silicon systems. 
     An intermediate layer  93  formed from a transparent conductive film is provided between the first cell layer  91  and the second cell layer  92 . A plasma-resistant protective layer  93 A comprising SiO 2-x C y  is provided on the bottom surface of the intermediate layer  93 . 
     Next is a description of a process for producing a solar cell panel according to this embodiment. The description presents an example in which an amorphous silicon-based photovoltaic layer and a crystalline silicon-based photovoltaic layer are deposited sequentially, as solar cell photovoltaic layers  3 , on top of a glass substrate that functions as a substrate  1 .  FIG. 2  through  FIG. 5  are schematic views showing the process for producing a solar cell panel according to this embodiment. 
     (1)  FIG. 2(   a ) 
     A soda float glass substrate (1.4 m×1.1 m×thickness: 4 mm) is used as the substrate  1 . The edges of the substrate are preferably subjected to corner chamfering or R-face chamfering to prevent damage. 
     (2)  FIG. 2(   b ) 
     Based on the embodiment described above, a transparent electrode layer  2  is deposited on top of the substrate  1 , thereby forming a transparent electrode-bearing substrate. In addition to the transparent electrode film, the transparent electrode layer  2  may also include an alkali barrier film (not shown in the figure) that is formed between the substrate  1  and the transparent electrode film. The alkali barrier film is formed by using a heated CVD apparatus to deposit a silicon oxide film (SiO 2 ) of not less than 50 nm and not more than 150 nm at a temperature of approximately 500° C. 
     (3)  FIG. 2(   c ) 
     Subsequently, the substrate  1  is mounted on an X-Y table, and the first harmonic of a YAG laser (1064 nm) is irradiated onto the film surface of the transparent electrode film, as shown by the arrow in the figure. The laser power is adjusted to ensure an appropriate process speed, and the transparent electrode film is then moved in a direction perpendicular to the direction of the series connection of the electric power generation cells, thereby causing a relative movement between the substrate  1  and the laser light, and performing laser etching across a strip with a width of not less than approximately 6 mm and not more than 10 mm, thereby forming a slot  10 . 
     (4)  FIG. 2(   d ) 
     Using a plasma enhanced CVD apparatus under conditions including a reduced pressure atmosphere of not less than 30 Pa and not more than 150 Pa and a substrate temperature of approximately 200° C., a p-layer, i-layer and n-layer, each formed from a thin film of amorphous silicon, are deposited sequentially as the first cell layer (the top layer)  91  of a photovoltaic layer  3 . The first cell layer  91  is deposited on top of the transparent electrode layer  2  using SiH 4  gas and H 2  gas as the main raw materials. The p-layer, i-layer and n-layer are deposited in this order, with the p-layer closest to the surface from which incident sunlight enters. 
     In this embodiment, the p-layer of the first cell layer  91  is preferably an amorphous B-doped SiC film generated by reaction of SiH 4 , H 2 , CH 4  and B 2 H 6  gas using an RF plasma, and the film thickness is preferably not less than 4 nm and not more than 16 nm. The i-layer of the first cell layer  91  is preferably an amorphous Si film generated by reaction of SiH 4  and H 2  using an RF plasma, and the film thickness is preferably not less than 100 nm and not more than 400 nm. The n-layer of the first cell layer  91  is preferably a Si film containing a crystalline component, generated by reaction of SiH 4 , H 2 , and PH 3  gas using an RF plasma, wherein the Raman ratio of the lone n-layer film is not less than 2, and the film thickness is preferably not less than 10 nm and not more than 80 nm. The “Raman ratio” refers to the ratio, determined by Raman spectroscopic evaluation, between the crystalline Si intensity at 520 cm −1  and the a-Si intensity at 480 cm −1  (crystalline Si intensity/a-Si intensity) (this definition also applies below). Furthermore, in order to improve the interface properties, a buffer layer (not shown in the figure) may also be provided between the p-layer film and the i-layer film. 
     Next, using a plasma enhanced CVD apparatus under conditions including a reduced pressure atmosphere of not more than 300 Pa, a substrate temperature of approximately 200° C., and a plasma generation frequency of not less than 40 MHz and not more than 100 MHz, a microcrystalline p-layer, microcrystalline i-layer and microcrystalline n-layer, each formed from a thin film of microcrystalline silicon, are formed sequentially, as the second cell layer (the bottom layer)  92 , on top of the first cell layer  91 . 
     In this embodiment, the p-layer of the second cell layer  92  is preferably a Si film containing a crystalline component, generated by reaction of SiH 4 , H 2 , and B 2 H 6  gas using an RF plasma, wherein the Raman ratio of the lone p-layer film is not less than 2, and the film thickness is preferably not less than 10 nm and not more than 60 nm. The i-layer of the second cell layer  92  is preferably a Si film containing a crystalline component, generated by reaction of SiH 4  and H 2  using an RF plasma, wherein the Raman ratio when the i-layer is deposited with a film thickness of 1.5 μm is not less than 5 (8 in the case of this embodiment), and the film thickness is preferably not less than 1,000 nm and not more than 2,000 nm. The n-layer of the second cell layer  92  is preferably a Si film containing a crystalline component, generated by reaction of SiH 4 , H 2 , and PH 3  gas using an RF plasma, wherein the Raman ratio of the lone n-layer film is not less than 2, and the film thickness is preferably not less than 10 nm and not more than 80 nm. 
     During formation of the microcrystalline silicon thin films and particularly the microcrystalline i-layer by plasma enhanced CVD, the distance d between the plasma discharge electrode and the surface of the substrate  1  is preferably not less than 3 mm and not more than 10 mm. If this distance is less than 3 mm, then the precision of the various structural components within the film deposition chamber required for processing large substrates means that maintaining the distance d at a constant level becomes difficult, which increases the possibility of the electrode getting too close and making the discharge unstable. If the distance exceeds 10 mm, then achieving a satisfactory film deposition rate (of not less than 1 nm/s) becomes difficult, and the uniformity of the plasma also deteriorates, causing a deterioration in the quality of the film due to ion impact. The i-layer of the second cell layer  92  is preferably deposited under conditions including an RF frequency of not less than 40 MHz and not more than 200 MHz, a gas pressure of not less than 500 Pa and not more than 3,000 Pa, and a film deposition rate of not less than 1 nm/s and not more than 3 nm/s, and in this embodiment, film deposition is performed using an RF frequency of 60 MHz, a gas pressure of 1.6 kPa, and a film deposition rate of 2 nm/s. 
     With the objective of forming a semi-reflective film to achieve electrical current consistency between the first cell layer  91  and the second cell layer  92 , a ZnO-based film with a film thickness of not less than 10 nm and not more than 200 nm is deposited, using a sputtering apparatus, as an intermediate layer  93 . In this intermediate layer  93 , the light absorption for the lone ZnO film within a wavelength range from λ=450 nm to 1,000 nm is preferably less than 1%. 
     By performing sputtering with an Ar/O 2  gas composition against a SiC target, a plasma-resistant protective layer  93 A is formed on the surface of the intermediate layer  93 . This enables the formation of a SiO 2-x C y  layer that is both conductive and optically transparent. 
     The above x and y are small values, and a favorable protective layer is obtained in those cases where the proportion of C is within a range from 5 to 30% (Si: 1, O: 2, C: 0.15 to 0.9 (x=0, y=0.15 to 0.9)). 
     The sputtering film deposition conditions for the plasma-resistant protective layer  93 A are as shown below. 
     Gas pressure: 5×10 −3  Torr 
     Gas composition: Ar+O 2    
     Power: 1 W/cm 2    
     Apparatus name: DC sputter device, SiC+Si target 
     The film composition can be altered by altering the Ar/O 2  gas ratio. A SiO 2-x C y  layer with a suitable C ratio can be obtained by setting the ratio of argon:oxygen to a value within a range from 50 to 1,000, and particularly from 100 to 400. 
     The film thickness of the plasma-resistant protective layer  93 A is typically not less than 2 nm and not more than 30 nm, and particularly favorable effects are obtained when the film thickness is not less than 5 nm and not more than 20 nm. The minimum value of 2 nm is set to ensure a reliable coating and to improve the coverage, whereas from the viewpoint of conductivity, a SiO 2  layer that is overly thick can impair the electrical conduction, and consequently the maximum value is set to 30 nm. 
     Compared with the light absorption for a structure in which the plasma-resistant protective layer is not formed, namely a structure represented by glass/GZO/p-Si (average light absorption 0.3% for the wavelength region from 600 to 1,100 nm), the light absorption for the structure of this embodiment in the wavelength region from 600 to 1,100 nm is, on average, not more than 0.1%, meaning light absorption can be essentially eliminated. 
     Formation of the intermediate layer  93  may be achieved either by continuous sputter deposition, with the targets arranged in sequence for the transparent conductive film and the plasma-resistant protective layer (the transparent film)  93 A, or by batch sputter deposition in which individual sputtering chambers are prepared for the transparent conductive film and the plasma-resistant protective layer (the transparent film)  93 A. 
     (5)  FIG. 2(   e ) 
     The substrate  1  is mounted on an X-Y table, and the second harmonic of a laser diode excited YAG laser (532 nm) is irradiated onto the film surface of the photovoltaic layer  3 , as shown by the arrow in the figure. With the pulse oscillation set to not less than 10 kHz and not more than 20 kHz, the laser power is adjusted so as to achieve a suitable process speed, and laser etching is performed at a target not less than approximately 100 μm and not more than 150 μm to the side of the laser etching line within the transparent electrode layer  2 , thereby forming a slot  11 . Provided the positions of the laser etching lines are not inverted, no particular problems arise, but in consideration of positioning tolerances, the target is preferably set to a numerical value listed above. 
     (6)  FIG. 3(   a ) 
     Using a sputtering apparatus, an Ag film is then deposited as the back electrode layer  4  under a reduced pressure atmosphere and at a temperature of approximately 150° C. In this embodiment, the Ag film of the back electrode layer  4  is deposited with a film thickness of not less than 150 nm, and in order to reduce the contact resistance between the n-layer and the back electrode layer  4  and improve the light reflectance, a ZnO-based film (such as a GZO (Ga-doped ZnO) film) with a film thickness of not less than 10 nm is deposited between the photovoltaic layer  3  and the back electrode layer  4  using a sputtering apparatus. 
     (7)  FIG. 3(   b ) 
     The substrate  1  is mounted on an X-Y table, and the second harmonic of a laser diode excited YAG laser (532 nm) is irradiated onto the substrate  1 , as shown by the arrow in the figure. The laser light is absorbed by the photovoltaic layer  3 , and by using the high gas vapor pressure generated at this point, the back electrode layer  4  is removed by explosive fracture. With the pulse oscillation set to not less than 1 kHz and not more than 10 kHz, the laser power is adjusted so as to achieve a suitable process speed, and laser etching is performed at a target not less than approximately 250 μm and not more than 400 μm to the side of the laser etching line within the transparent electrode layer  2 , thereby forming a slot  12 . Provided the positions of the laser etching lines are not inverted, no particular problems arise, but in consideration of positioning tolerances, the target is preferably set to a numerical value listed above. 
     (8)  FIG. 3(   c ) 
     The electric power generation regions are compartmentalized, by using laser etching to remove the effect wherein the serially connected portions at the film edges near the edges of the substrate are prone to short circuits. The substrate  1  is mounted on an X-Y table, and the second harmonic of a laser diode excited YAG laser (532 nm) is irradiated onto the substrate  1 . The laser light is absorbed by the transparent electrode layer  2  and the photovoltaic layer  3 , and by using the high gas vapor pressure generated at this point, the back electrode layer  4  is removed by explosive fracture, meaning the back electrode layer  4 , the photovoltaic layer  3  and the transparent electrode layer  2  are removed. With the pulse oscillation set to not less than 1 kHz and not more than 10 kHz, the laser power is adjusted so as to achieve a suitable process speed, and laser etching is conducted at a point not less than approximately 5 mm and not more than 15 mm from the edge of the substrate  1 , thereby forming an X-direction insulation slot  15 . A Y-direction insulation slot need not be provided at this point, because a film surface polishing and removal treatment is performed on the peripheral regions of the substrate  1  in a later step. 
     Performing the etching at a position not less than approximately 5 mm and not more than 10 mm from the edge of the substrate  1  is preferred, as it ensures that the insulation slot  15  is effective in inhibiting external moisture from entering the interior of the solar cell module  6  via the edges of the solar cell panel. 
     (9)  FIG. 4(   a ) 
     In order to ensure favorable adhesion and sealing of a backing sheet via EVA or the like in a subsequent step, the deposited films around the periphery of the substrate  1  (in a peripheral region  14 ) are removed, as they tend to be uneven and prone to peeling. First, grinding or blast polishing or the like is used to remove the back electrode layer  4 , the photovoltaic layer  3 , and the transparent electrode layer  2  from a region that is not less than 5 mm and not more than 15 mm from the edge of the substrate, and is closer to the substrate edge than the insulation slot  15  provided in the step of  FIG. 3(   c ) described above. Grinding debris or abrasive grains are removed by washing the substrate  1 . 
     (10)  FIG. 4(   b ) 
     A terminal box attachment portion is prepared by providing an open through-window in the backing sheet and exposing a collecting plate. A plurality of layers of an insulating material are provided in the open through-window portion in order to prevent external moisture and the like entering the solar cell. 
     Processing is conducted so as to enable current collection, using a copper foil, from the series-connected solar cell electric power generation cell at one end and the solar cell electric power generation cell at the other end, and to enable electric power to be extracted from a terminal box portion on the rear surface of the solar cell panel. In order to prevent short circuits between the copper foil and the various portions, an insulating sheet that is wider than the width of the copper foil is provided. 
     Following arrangement of the collecting copper foil and the like at predetermined positions, a sheet of a filling material such as EVA (ethylene-vinyl acetate copolymer) is arranged so as to cover the entire solar cell module  6 , but not protrude beyond the substrate  1 . 
     A backing sheet  21  with a superior waterproofing effect is positioned on top of the EVA. In this embodiment, in order to achieve a superior waterproofing and moisture-proofing effect, the backing sheet  21  is formed with a three-layer structure comprising a PTE sheet, Al foil, and a PET sheet. 
     The structure comprising the components up to and including the backing sheet  21  arranged in predetermined positions is subjected to internal degassing under a reduced pressure atmosphere and pressing at not less than approximately 150° C. and not more than 160° C. using a laminator, thereby causing cross-linking of the EVA that tightly seals the structure. 
     (11)  FIG. 5(   a ) 
     A terminal box is attached to the rear surface  24  of the solar cell module  6  using an adhesive. 
     (12)  FIG. 5(   b ) 
     The copper foil and an output cable  23  from the terminal box are connected using solder or the like, and the interior of the terminal box is filled and sealed with a sealant (a potting material). This completes the production of the solar cell panel  50 . 
     (13)  FIG. 5(   c ) 
     The solar cell panel  50  formed via the steps up to and including  FIG. 5(   b ) is then subjected to an electric power generation test, as well as other tests for evaluating specific performance factors. The electric power generation test is conducted using a solar simulator that emits a standard sunlight of AM 1.5 (1,000 W/m 2 ). 
     (14)  FIG. 5(   d ) 
     In tandem with the electric power generation test (FIG.  5 ( c )), a variety of specific performance factors including the external appearance are evaluated. 
     As described above, in the photovoltaic device  90  of this embodiment, by depositing a thin coating of highly plasma-resistant SiO 2  as a plasma-resistant protective layer  93 A on the surface of the intermediate layer  93 , degradation of the intermediate layer surface can be prevented, meaning light absorption loss at the intermediate layer  93  can be inhibited. Accordingly, a photovoltaic device  90  with a high level of performance can be obtained at low cost. 
     A second embodiment of the present invention is described below with reference to the drawings. 
       FIG. 6  is a schematic view showing the structure of a photovoltaic device according to this embodiment. The photovoltaic device  190  is a silicon-based solar cell, and comprises a substrate  101 , a transparent electrode layer  102 , a solar cell photovoltaic layer  103  comprising a first cell layer (a second photovoltaic layer)  191  and a second cell layer (a first photovoltaic layer)  192 , and a back electrode layer  104 . In this embodiment, the first cell layer  191  is an amorphous silicon-based photovoltaic layer, and the second cell layer  192  is a crystalline silicon-based photovoltaic layer. 
     In this description, the term “silicon-based” is a generic term that includes silicon (Si), silicon carbide (SiC) and silicon-germanium (SiGe). Furthermore, the term “crystalline silicon-based” describes a silicon system other than an amorphous silicon system, namely other than a non-crystalline silicon system, and includes both microcrystalline silicon and polycrystalline silicon systems. 
     An intermediate layer  193  is provided between the first cell layer  191  and the second cell layer  192 . The intermediate layer  193  is formed from a total of three layers, namely a transparent conductive film  193 A, a transparent film  193 B, and a transparent conductive film  193 C. The transparent film  193 B is a layer composed of SiO 2-x C y . 
     In the description of a process for producing a solar cell panel of this embodiment, detailed descriptions are omitted for those steps that are common to the first embodiment. 
     In this embodiment, in order to form a semi-reflective film to achieve electrical current consistency between the first cell layer  191  and the second cell layer  192 , ZnO-based films (such as GZO (Ga-doped ZnO)) with a film thickness of not less than 5 nm and not more than 100 nm are deposited, using a sputtering apparatus, as the transparent conductive films  193 A and  193 C of the intermediate layer  193 . In this intermediate layer  193 , the light absorption for a single ZnO film within a wavelength range from λ=450 nm to 1,000 nm is preferably less than 1%. The transparent film  193 B is formed by performing sputtering with an Ar/O 2  gas composition against a SiC target. This enables the formation of a SiO 2-x C y  layer that is both conductive and optically transparent. 
     The above x and y are small values, and favorable results are obtained in those cases where the proportion of C is within a range from 5 to 30% (Si: 1, O: 2, C: 0.15 to 0.9 (x=0, y=0.15 to 0.9)). 
     The sputtering film deposition conditions for the transparent film  193 B are as shown below. 
     Gas pressure: 5×10 −3  Torr 
     Gas composition: Ar+O 2    
     Power: 1 W/cm 2    
     Apparatus name: DC sputter device, SiC+Si target 
     The film composition can be altered by altering the Ar/O 2  gas ratio. A SiO 2-x C y  layer with a suitable C ratio can be obtained by setting the ratio of argon:oxygen to a value within a range from 50 to 1,000, and particularly from 100 to 400. 
     The film thickness of the transparent film  193 B is typically not less than 2 nm and not more than 30 nm, and particularly favorable effects are obtained when the film thickness is not less than 5 nm and not more than 20 nm. The minimum value of 2 nm is set to ensure a reliable coating and to improve the coverage, whereas from the viewpoint of conductivity, an SiO 2  layer that is overly thick can impair the electrical conduction, and consequently the maximum value is set to 30 nm. The film thickness dimension for the transparent conductive films  193 A and  193 C is not less than 5 nm and not more than 100 nm. 
     Compared with the light absorption for a structure in which the transparent film  193 B is not formed, namely a structure represented by glass/GZO/p-Si (average light absorption 0.3% for the wavelength region from 600 to 1,100 nm), the light absorption for the structure of this embodiment in the wavelength region from 600 to 1,100 nm is, on average, not more than 0.1%, meaning light absorption can be essentially eliminated. 
     Formation of the intermediate layer  193  may be achieved either by continuous sputter deposition, with the targets arranged in sequence for the transparent conductive film  193 C, the transparent film  193 B and the transparent conductive film  193 A, or by batch sputter deposition in which individual sputtering chambers are prepared for the transparent conductive films  193 A and  193 C and the transparent film  193 B. 
     As described above, in the photovoltaic device  190  of this embodiment, by using an intermediate layer  193  with a laminated structure containing three layers, namely the transparent conductive film  193 A, the transparent film  193 B and the transparent conductive film  193 C, the desired optical properties can be achieved while the transparent conductive films are kept thin, meaning a high resistivity can be obtained for the intermediate layer, current leakage via the intermediate layer can be prevented, and an increase or decrease can also be achieved in the selective reflectance of light of the specified wavelength caused by the intermediate layer. In other words, the electrical properties (a high resistance) can be improved without causing degradation of the optical properties of the intermediate layer. As a result, an intermediate layer with a resistivity equal to or exceeding the 1×10 −3  Ω·cm of the aforementioned patent citation 2 can be achieved. 
     A third embodiment of the present invention is described below with reference to the drawings. 
       FIG. 7  is a schematic view showing the structure of a photovoltaic device according to this embodiment. The photovoltaic device  290  is a silicon-based solar cell, and comprises a substrate  201 , a transparent electrode layer  202 , a solar cell photovoltaic layer  203  comprising a first cell layer (a second photovoltaic layer)  291  and a second cell layer (a first photovoltaic layer)  292 , and a back electrode layer  204 . In this embodiment, the first cell layer  291  is an amorphous silicon-based photovoltaic layer, and the second cell layer  292  is a crystalline silicon-based photovoltaic layer. 
     In this description, the term “silicon-based” is a generic term that includes silicon (Si), silicon carbide (SiC) and silicon-germanium (SiGe). Furthermore, the term “crystalline silicon-based” describes a silicon system other than an amorphous silicon system, namely other than a non-crystalline silicon system, and includes both microcrystalline silicon and polycrystalline silicon systems. 
     An intermediate layer  293  is provided between the first cell layer  291  and the second cell layer  292 . The intermediate layer  293  is formed from a total of five layers, namely a transparent conductive film  293 A, a transparent film  293 B, a transparent conductive film  293 C, a transparent film  293 D, and a transparent conductive film  293 E. The transparent films  293 B and  293 D are layers composed of SiO 2-x C y . 
     In the description of a process for producing a solar cell panel of this embodiment, detailed descriptions are omitted for those steps that are common to the first embodiment. 
     In this embodiment, in order to form a semi-reflective film to achieve electrical current consistency between the first cell layer  291  and the second cell layer  292 , ZnO-based films (such as GZO (Ga-doped ZnO)), each with a film thickness of not less than 5 nm and not more than 100 nm, are deposited, using a sputtering apparatus, as the transparent conductive films  293 A,  293 C and  293 E of the intermediate layer  293 . In this intermediate layer  293 , the light absorption for a single ZnO film within a wavelength range from λ=450 nm to 1,000 nm is preferably less than 1%. The transparent films  293 B and  293 D are formed by performing sputtering with an Ar/O 2  gas composition against a SiC target. This enables the formation of SiO 2-x C y  layers that are both conductive and optically transparent. 
     The above x and y are small values, and favorable results are obtained in those cases where the proportion of C is within a range from 5 to 30% (Si: 1, O: 2, C: 0.15 to 0.9 (x=0, y=0.15 to 0.9)). 
     The sputtering film deposition conditions for the transparent films  293 B and  293 D are as shown below. 
     Gas pressure: 5×10 −3  Torr 
     Gas composition: Ar+O 2    
     Power: 1 W/cm 2    
     Apparatus name: DC sputter device, SiC+Si target 
     The film composition can be altered by altering the Ar/O 2  gas ratio. A SiO 2-x C y  layer with a suitable C ratio can be obtained by setting the ratio of argon:oxygen to a value within a range from 50 to 1,000, and particularly from 100 to 400. 
     The film thickness of each of the transparent films  293 B and  293 D is typically not less than 2 nm and not more than 30 nm, and particularly favorable effects are obtained when the film thickness is not less than 5 nm and not more than 20 nm. The minimum value of 2 nm is set to ensure a reliable coating and to improve the coverage, whereas from the viewpoint of conductivity, an SiO 2  layer that is overly thick can impair the electrical conduction, and consequently the maximum value is set to 30 nm. The film thickness dimension for the transparent conductive films  293 A,  293 C and  293 E is not less than 5 nm and not more than 100 nm. 
     Compared with the light absorption for a structure in which the transparent films  293 B and  293 D are not formed, namely a structure represented by glass/GZO/p-Si (average light absorption 0.3% for the wavelength region from 600 to 1,100 nm), the light absorption for the structure of this embodiment in the wavelength region from 600 to 1,100 nm is, on average, not more than 0.1%, meaning light absorption can be essentially eliminated. 
     Formation of the intermediate layer  293  may be achieved either by continuous sputter deposition, with the targets arranged in sequence for the transparent conductive film  293 E, the transparent film  293 D, the transparent conductive film  293 C, the transparent film  293 B and the transparent conductive film  293 A, or by batch sputter deposition in which individual sputtering chambers are prepared for the transparent conductive films and the transparent films. 
     As described above, in the photovoltaic device  290  of this embodiment, by using an intermediate layer  293  with a laminated structure containing five layers, namely the transparent conductive film  293 A, the transparent film  293 B, the transparent conductive film  293 C, the transparent film  293 D, and the transparent conductive film  293 E, a high resistivity can be obtained for the intermediate layer, current leakage via the intermediate layer can be prevented, and an increase or decrease can also be achieved in the selective reflectance of light of the specified wavelength caused by the intermediate layer. In other words, the electrical properties (a high resistance) can be improved without causing degradation of the optical properties of the intermediate layer. As a result, an intermediate layer with a resistivity equal to or exceeding the 1×10 −3  Ω·cm of the aforementioned patent citation 2 can be achieved. 
     A fourth embodiment of the present invention is described below with reference to the drawings. 
       FIG. 8  is a schematic view showing the structure of a photovoltaic device according to this embodiment. The photovoltaic device  390  is a silicon-based solar cell, and comprises a substrate  301 , a transparent electrode layer  302 , a solar cell photovoltaic layer  303  comprising a first cell layer (a second photovoltaic layer)  391  and a second cell layer (a first photovoltaic layer)  392 , and a back electrode layer  304 . In this embodiment, the first cell layer  391  is an amorphous silicon-based photovoltaic layer, and the second cell layer  392  is a crystalline silicon-based photovoltaic layer. 
     In this description, the term “silicon-based” is a generic term that includes silicon (Si), silicon carbide (SiC) and silicon-germanium (SiGe). Furthermore, the term “crystalline silicon-based” describes a silicon system other than an amorphous silicon system, namely other than a non-crystalline silicon system, and includes both microcrystalline silicon and polycrystalline silicon systems. 
     An intermediate layer  393  is provided between the first cell layer  391  and the second cell layer  392 . The intermediate layer  393  is formed from a total of four layers which, listed from the bottom layer upwards, are a transparent film  393 A, a transparent conductive film  393 B, a transparent film  393 C, and a transparent conductive film  393 D. The transparent films  393 A and  393 C are plasma-resistant protective layers composed of SiO 2-x C y . 
     In the description of a process for producing a solar cell panel of this embodiment, detailed descriptions are omitted for those steps that are common to the first embodiment. 
     In this embodiment, in order to form a semi-reflective film to achieve electrical current consistency between the first cell layer  391  and the second cell layer  392 , ZnO-based films (such as GZO (Ga-doped ZnO)) with a film thickness of not less than 5 nm and not more than 100 nm are deposited, using a sputtering apparatus, as the transparent conductive films  393 B and  393 D of the intermediate layer  393 . In this intermediate layer  393 , the light absorption for a single ZnO film within a wavelength range from λ=450 nm to 1,000 nm is preferably less than 1%. The transparent films  393 A and  393 C are formed by performing sputtering with an Ar/O 2  gas composition against a SiC target. This enables the formation of SiO 2-x C y  layers that are both conductive and optically transparent. 
     The above x and y are small values, and favorable results are obtained in those cases where the proportion of C is within a range from 5 to 30% (Si: 1, O: 2, C: 0.15 to 0.9 (x=0, y=0.15 to 0.9)). 
     The sputtering film deposition conditions for the transparent films  393 A and  393 C are as shown below. 
     Gas pressure: 5×10 −3  Torr 
     Gas composition: Ar+O 2    
     Power: 1 W/cm 2    
     Apparatus name: DC sputter device, SiC+Si target 
     The film composition can be altered by altering the Ar/O 2  gas ratio. A SiO 2-x C y  layer with a suitable C ratio can be obtained by setting the ratio of argon:oxygen to a value within a range from 50 to 1,000, and particularly from 100 to 400. 
     The film thickness of each of the transparent films  393 A and  393 C is typically not less than 2 nm and not more than 30 nm, and particularly favorable effects are obtained when the film thickness is not less than 5 nm and not more than 20 nm. The minimum value of 2 nm is set to ensure a reliable coating and to improve the coverage, whereas from the viewpoint of conductivity, an SiO 2  layer that is overly thick can impair the electrical conduction, and consequently the maximum value is set to 30 nm. The film thickness dimension for the transparent conductive films  393 B and  393 D is not less than 5 nm and not more than 100 nm. 
     Compared with the light absorption for a structure in which the transparent films  393 A and  393 C are not formed, namely a structure represented by glass/GZO/p-Si (average light absorption 0.3% for the wavelength region from 600 to 1,100 nm), the light absorption for the structure of this embodiment in the wavelength region from 600 to 1,100 nm is, on average, not more than 0.1%, meaning light absorption can be essentially eliminated. 
     Formation of the intermediate layer  393  may be achieved either by continuous sputter deposition, with the targets arranged in sequence for the transparent conductive film  393 D, the transparent film  393 C, the transparent conductive film  393 B and the transparent film  393 A, or by batch sputter deposition in which individual sputtering chambers are prepared for the transparent conductive films and the transparent films. 
     As described above, in the photovoltaic device  390  of this embodiment, by using an intermediate layer  393  with a laminated structure containing four layers, namely the transparent film  393 A, the transparent conductive film  393 B, the transparent film  393 C, and the transparent conductive film  393 D, in which a thin film of highly plasma-resistant SiO 2  functions as a protective layer, the desired optical properties can be achieved while the transparent conductive films are kept thin, meaning a high resistivity can be obtained for the intermediate layer, current leakage via the intermediate layer can be prevented, and an increase or decrease can also be achieved in the selective reflectance of light of the specified wavelength caused by the intermediate layer. Furthermore, the transparent films act as protective layers, meaning the transparent conductive films do not conduct the photovoltaic layer directly, and enabling the formation of a surface layer of increased light absorption to be suppressed. In other words, the electrical properties (a high resistance) can be improved without causing degradation of the optical properties of the intermediate layer. As a result, an intermediate layer with a resistivity equal to or exceeding the 1×10 −3  Ω·cm of the aforementioned patent citation 2 can be achieved. 
     Test Example 1 
     The composition of the SiO 2-x C y  film that is a structural component in each of the above embodiments was investigated. 
     Samples (a) to (d) were prepared with a 3-layer laminated structure in which a SiO 2-x C y  film (film thickness: 10 nm) with a composition shown in Table 1 was sandwiched between two layers of a GZO film (film thickness of each film: 40 nm). For each sample, the resistance in a direction perpendicular to the film surface and the optical absorption were measured. The results are also shown in Table 1. For comparison, the resistance in a direction perpendicular to the film surface for a lone GZO film (film thickness: 40 nm), which represents a conventional intermediate layer, was 6Ω. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Sample 
                 (a) 
                 (b) 
                 (c) 
                 (d) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Si ratio within SiO 2-x C y  (%) 
                 50 
                 42 
                 35 
                 34 
               
               
                   
                 O ratio within SiO 2-x C y  (%) 
                 15 
                 33 
                 59 
                 66 
               
               
                   
                 C ratio within SiO 2-x C y  (%) 
                 35 
                 25 
                 6 
                 0 
               
               
                   
                 Resistance in perpendicular 
                 — 
                 4 
                 6 
                 14 
               
               
                   
                 direction (Ω) 
               
               
                   
                 Optical absorption 
                 Yes 
                 No 
                 No 
                 No 
               
               
                   
                   
               
            
           
         
       
     
     Upon investigation of the properties of the prepared samples (a) to (d) it was clear that, as shown in Table 1, the sample (a) exhibited optical absorption, and could therefore not be used as an intermediate layer. Furthermore, the sample (d) had a higher resistance than the lone GZO film of the conventional example, and could therefore not be used as an intermediate layer. 
     Accordingly, upon consideration of the resistance of the intermediate layer in the perpendicular direction and the optical absorption, it was clear that the composition of the SiO 2-x C y  that constitutes the intermediate layer in each of the above embodiments preferably has an oxygen composition within a range from 20 to 60%, and a carbon composition within a range from 30 to 5%. 
     The SiO 2-x C y  film in these test examples was positioned in the same manner as the transparent film  193 B that represents one of the structural elements in the 3-layer structure of the second embodiment, but a SiO 2-x C y  film with the preferred composition described above can also be applied to the transparent films in other structures (such as the plasma-resistant protective layer  93 A of the first embodiment, or the transparent films  293 B,  293 D,  393 A and  393 C in the multilayer structures of the third embodiment and fourth embodiment). 
     Test Example 2 
     The film thickness dependency of the resistance of the single film of GZO that represents one of the structural elements within each of the above embodiments was investigated. 
     Using a set of low-temperature film deposition conditions (A) and a set of high-temperature film deposition conditions (B), samples were formed by depositing a GZO film at one of the two film thickness values shown in Table 2, and the resistivity within the in-plane direction was then measured for each sample. The results are also shown in Table 2. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Temperature conditions 
               
            
           
           
               
               
               
            
               
                   
                 (A) 
                 (B) 
               
            
           
           
               
               
               
               
               
            
               
                 Film thickness 
                 50 nm 
                 80 nm 
                 40 nm 
                 80 nm 
               
               
                   
               
               
                 Resistivity in the 
                 1.3E5 
                 5.5E4 
                 6.7E2 
                 1.8E2 
               
               
                 in-plane direction (Ωcm) 
               
               
                   
               
            
           
         
       
     
     From the results shown in Table 2 it is evident that regardless of the film deposition temperature conditions, the resistivity increases as the GZO film thickness is reduced, indicating that reducing the film thickness of the GZO film is effective in preventing current leakage via the intermediate layer. 
     Modified Example 1 
     In the second embodiment described above, a configuration was adopted in which ZnO-based films (such as GZO films), each with a film thickness of not less than 5 nm and not more than 100 nm, were provided as the transparent conductive films  193 A and  193 C of the intermediate layer  193 , and a SiO 2-x C y  film with a film thickness of not less than 2 nm and not more than 30 nm, and preferably not less than 5 nm and not more than 20 nm, was provided as the transparent film  193 B, but instead of this configuration, a modified configuration may be adopted in which ZnO-based films (such as GZO films) with a film thickness of not more than 10 nm are provided as the transparent conductive films  193 A and  193 C, and a SiO 2-x C y  film with a film thickness of not less than 10 nm and not more than 30 nm is provided as the transparent film  193 B. 
     In this modified example, in order to increase the resistivity within the in-plane direction by altering the structure of the lone GZO film (of thickness 50 to 100 nm) that is used as a conventional intermediate layer, instead of simply reducing the film thickness of the lone GZO film, a SiO 2-x C y  film is inserted between two GZO layers, and the film thickness of the SiO 2-x C y  film is adjusted so as to achieve the desired optical properties upon optical analysis. As a result, the conductivity within the in-plane direction of the GZO layer is minimal. 
     Modified Example 2 
     In the second embodiment described above, a configuration was adopted in which ZnO-based films (such as GZO films), each with a film thickness of not less than 5 nm and not more than 100 nm, were provided as the transparent conductive films  193 A and  193 C of the intermediate layer  193 , and a SiO 2-x C y  film with a film thickness of not less than 2 nm and not more than 30 nm, and preferably not less than 5 nm and not more than 20 nm, was provided as the transparent film  193 B, but instead of this configuration, a modified configuration may be adopted in which ZnO-based films (such as GZO films) with a film thickness of not more than 5 nm are provided as the transparent conductive films  193 A and  193 C, and a SiO 2-x C y  film with a film thickness of not less than 10 nm and not more than 30 nm is provided as the transparent film  193 B. 
     In this modified example, in order to increase the resistivity within the in-plane direction by altering the structure of the lone GZO film (of thickness 50 to 100 nm) that is used as a conventional intermediate layer, instead of simply reducing the film thickness of the lone GZO film, a SiO 2-x C y  film is inserted between two GZO layers, and the film thickness of the SiO 2-x C y  film is adjusted so as to achieve the desired optical properties upon optical analysis. In this modified example, the GZO films function only as contact layers for electrical conduction in a perpendicular direction.