JP2011049460A - Photoelectric converter and substrate with transparent electrode layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric converter of high power generation efficiency by improving light transmittance to a photoelectric conversion layer by inserting a single layer of transparent thin film, having both of a reflection prevention function and an alkali-barrier function, between a translucent substrate and a transparent electrode layer. <P>SOLUTION: The photoelectric converter 90 is equipped with: the translucent substrate 1; and the transparent electrode layer 2 and the photoelectric conversion layer 3 provided on the translucent substrate 1. The transparent thin film 201 containing Y<SB>2</SB>O<SB>3</SB>as a main component is provided between the translucent substrate 1 and the transparent electrode layer 2, in the photoelectric converter 90. Thereby the photoelectric converter 90 is provided with the transparent thin film 201 which is single layer and has the reflection prevention function and the alkali-barrier function, and has high power generation efficiency. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device and a substrate with a transparent electrode layer, and more particularly to a thin film silicon solar cell using silicon as a power generation layer.

  As a photoelectric conversion device that receives light and converts it into electric power, for example, a thin film solar cell in which a thin film silicon layer is stacked on a power generation layer (photoelectric conversion layer) is known. A thin-film solar cell is generally configured by sequentially laminating a transparent electrode layer, a silicon-based semiconductor layer (photoelectric conversion layer), and a back electrode layer including a metal electrode film on a light-transmitting substrate.

  In order to improve the power generation efficiency of the solar cell, it is important to reduce the reflection at the interface between the translucent substrate and the transparent electrode layer and increase the amount of light reaching the photoelectric conversion layer. Patent Document 1 discloses a photovoltaic device in which a two-layer transparent thin film having different refractive indexes is inserted between a light-transmitting substrate and a transparent electrode layer to improve light transmittance.

No. 00/13237 (Claim 1)

  The first thin film of the photovoltaic device described in Patent Document 1 has a refractive index higher than that of the translucent substrate. Therefore, if the film is not accurately formed with an appropriate film thickness, there arises a problem that the light transmittance at the translucent substrate / transparent electrode layer interface is decreased.

Glass generally used for a light-transmitting substrate has an alkali component (Na). The glass is inexpensive, but it is known that when Na ⁺ contained in the glass diffuses into the transparent electrode layer, the transparent electrode layer is deteriorated and the polarity level of the silicon-based semiconductor film is disturbed. A base film such as a silicon oxide film (SiO ₂ film) is provided between the translucent substrate and the transparent electrode layer so that the alkali component does not diffuse into the transparent electrode layer. Since only the SiO ₂ film causes light reflection at the interface between the translucent substrate, the SiO ₂ film, and the transparent electrode layer, an antireflection layer such as a TiO ₂ film must be further provided. As described above, when a translucent substrate having an alkali component is used, it is necessary to provide a base film as an alkali barrier layer, so as to achieve both light transmissivity at the translucent substrate / transparent electrode layer interface. It was a complicated layer structure.

  The present invention has been made in view of such circumstances, and provides a photoelectric conversion device with high power generation efficiency that has a relatively simple layer configuration by increasing the amount of light transmitted to the photoelectric conversion layer. Objective.

In order to solve the above-described problems, the present invention includes a translucent substrate, a transparent electrode layer and a photoelectric conversion layer provided on the translucent substrate, and the translucent substrate, the transparent electrode layer, A photoelectric conversion device provided with a transparent thin film mainly composed of Y ₂ O ₃ is provided.

According to the present invention, the light reflection between the translucent substrate and the transparent electrode layer is reduced by the transparent thin film mainly composed of Y ₂ O ₃ , and the transmission characteristics at the translucent substrate / transparent electrode layer interface are reduced. Can be improved. Y ₂ O ₃ has a refractive index higher than that of the translucent substrate and lower than that of the transparent electrode layer. Therefore, when the film is inserted with a predetermined film thickness, an effect of improving the light transmission characteristics can be obtained, and the reflectance does not increase even if the film cannot be accurately formed to a desired film thickness.

In the said invention, it is preferable to provide at least 2 or more of the said photoelectric converting layers.
In a solar cell having a plurality of photoelectric conversion layers, the photoelectric conversion layer provided on the side close to the substrate absorbs short wavelengths. The transparent thin film mainly composed of Y ₂ O ₃ has a particularly high function of increasing the amount of incident light with respect to the above-described photoelectric conversion layer.

In the said invention, it is preferable that the said translucent board | substrate is glass which has an alkali component.
The transparent thin film containing Y ₂ O ₃ as a main component has not only a light transmission property improving function but also an alkali barrier function. Therefore, even when an alkali component is contained in the light-transmitting substrate, dispersion of the alkali component from the light-transmitting substrate to the transparent electrode layer can be prevented. A conventionally used alkali barrier film such as a SiO ₂ film does not have a function of suppressing reflection loss at the interface between the light-transmitting substrate and the transparent electrode layer, and therefore light reflection occurs when inserted as a single layer. Therefore, it is necessary to combine with the antireflection layer to form a two-layer structure. On the other hand, the transparent thin film containing Y ₂ O ₃ as a main component can reduce light reflection even with a single layer.
Therefore, the transparent thin film containing Y ₂ O ₃ as a main component is a single layer and exhibits both an antireflection effect and an alkali barrier effect.

In the above invention, the surface opposite to the surface on which the transparent thin film is provided in the transparent substrate, it is preferable that the antireflection layer mainly composed of MgF ₂ or the porous silica are provided.
MgF ₂ or porous silica has a lower refractive index than the translucent substrate. Therefore, by inserting an antireflection layer, light reflection at the air / translucent substrate interface can be suppressed, and the amount of light transmitted to the photoelectric conversion layer can be further increased.

In the above invention, a translucent substrate and a transparent electrode layer provided on the translucent substrate are provided, and Y ₂ O ₃ is a main component between the translucent substrate and the transparent electrode layer. A substrate with a transparent electrode layer provided with a transparent thin film is provided. When such a substrate with a transparent electrode layer is used for a photoelectric conversion device, a photoelectric conversion device with high power generation efficiency can be obtained.

  The present invention improves the light transmittance to the photoelectric conversion layer by inserting a single-layer transparent thin film having a light transmission property improving function and an alkali barrier function between the light-transmitting substrate and the transparent electrode layer. A photoelectric conversion device with high power generation efficiency.

It is sectional drawing which showed typically the structure of the photoelectric conversion apparatus which concerns on this invention. It is the schematic explaining one Embodiment which manufactures a solar cell panel as a photoelectric conversion apparatus which concerns on this invention. It is the schematic explaining one Embodiment which manufactures a solar cell panel as a photoelectric conversion apparatus which concerns on this invention. It is the schematic explaining one Embodiment which manufactures a solar cell panel as a photoelectric conversion apparatus which concerns on this invention. It is the schematic explaining one Embodiment which manufactures a solar cell panel as a photoelectric conversion apparatus which concerns on this invention. The light transmittance when a transparent thin film is inserted is shown. 6 (a) shows the ideal medium A, FIG. 6 (b) _Al 2 _{O 3,} FIG. 6 (c) MgO, FIG. 6 (d) is a case of inserting the _Y 2 _{O 3.} The measurement result of the transmittance | permeability and reflectance of a double-sided antireflection board | substrate is shown. The measurement and calculation result of the transmittance | permeability of a double-sided antireflection board | substrate are shown.

  FIG. 1 is a schematic diagram illustrating a configuration of a photoelectric conversion device of the present invention. The photoelectric conversion device 90 is a tandem type silicon solar cell, and the first cell layer 91 (amorphous silicon type) as the translucent substrate 1, the transparent thin film 201, the transparent electrode layer 2, and the solar cell photoelectric conversion layer 3. And a second cell layer 92 (crystalline silicon), an intermediate contact layer 93, and the back electrode layer 4. Here, the silicon-based is a generic name including silicon (Si), silicon carbide (SiC), and silicon germanium (SiGe). Further, the crystalline silicon system means a silicon system other than the amorphous silicon system, and includes microcrystalline silicon and polycrystalline silicon.

  A method for manufacturing a photoelectric conversion device according to this embodiment will be described by taking a process for manufacturing a solar cell panel as an example. 2 to 5 are schematic views showing a method for manufacturing the solar cell panel of the present embodiment.

(1) FIG. 2 (a)
A soda float glass substrate (for example, 1.4 m × 1.1 m × plate thickness: 3.5 mm to 4.5 mm) is used as the translucent substrate 1. The end face of the substrate is preferably subjected to corner chamfering or R chamfering to prevent damage due to thermal stress or impact.

The transparent thin film 201 is formed by vapor deposition at a substrate temperature of 300 ° C. using a bulk of Y ₂ O ₃ as a vapor deposition source. The substrate temperature can be selected from room temperature to 300 ° C. The vapor deposition atmosphere may be a vacuum or a reactive vapor deposition method in an oxidizing gas atmosphere. The gas type and partial pressure may be selected as appropriate so as to enhance the optical characteristics of the transparent thin film 201, particularly the transparency. The (average) film thickness of the transparent thin film 201 is calculated from the equation (1) and is set to 70 nm to 90 nm. The center wavelength is a wavelength near the highest point of the wavelength characteristic function obtained by multiplying the quantum efficiency of the photoelectric conversion device and the sunlight spectrum. The center wavelength in this embodiment is about 500 to 600 nm. That is, the transmittance can be enhanced most at a wavelength with high quantum efficiency and high sunlight intensity.
d = λ / 4 × 1 / n (1)
(D: film thickness (nm), λ: center wavelength (nm), n: refractive index of the thin film)

An antireflection layer may be provided on the surface opposite to the surface on which the transparent thin film 201 of the translucent substrate 1 is formed. The antireflection layer 202 is formed by vapor deposition at a substrate temperature of 300 ° C. using a bulk of MgF ₂ as a vapor deposition source. The substrate temperature can be selected from room temperature to 300 ° C. The deposition atmosphere is a vacuum. The (average) film thickness of the antireflection layer 202 is calculated from the equation (1) in the same manner as the transparent thin film 201 and is set to 90 nm to 110 nm.
Although using a MgF ₂ for antireflection layer 202 may be a porous silica. As the porous silica, those having pores and having a refractive index close to 1.23 are used. In the case of porous silica, the (average) film thickness is calculated from the formula (1) in the same manner as the transparent thin film 201, and is 100 nm to 120 nm.
Moreover, although vapor deposition was employ | adopted as the film-forming method of the transparent thin film 201 and the antireflection layer 202, a sputtering method may be used.

(2) FIG. 2 (b)
As the transparent electrode layer 2, a transparent conductive film having a thickness of about 500 nm to 3000 nm mainly composed of GZO (Ga-doped ZnO) is formed at about 150 ° C. by a sputtering apparatus. The film forming temperature can be selected from room temperature to 200 ° C. At this time, a texture with appropriate irregularities is formed on the surface of the transparent conductive film. When the texture shape is insufficient, it may be adjusted to a desired texture shape by wet etching after film formation. As the etching solution, dilute hydrochloric acid is used. The concentration, liquid temperature, and treatment time may be adjusted as appropriate.
In addition, although the sputtering method was employ | adopted as the manufacturing method of the transparent electrode layer 2, MOCVD method and thermal CVD method may be sufficient. Although GZO is used as the transparent electrode layer 2, AZO (Al-doped ZnO) or SnO ₂ : F may be used.

(3) FIG. 2 (c)
Thereafter, the substrate 1 is placed on an XY table, and the first harmonic (1064 nm) of the YAG laser is irradiated from the film surface side of the transparent conductive film as indicated by the arrow in the figure. The laser power is adjusted to be suitable for the processing speed, and the transparent conductive film is moved relative to the direction perpendicular to the series connection direction of the power generation cells so that the substrate 1 and the laser beam are moved relative to each other to form the groove 10. And laser etching into a strip shape having a predetermined width of about 6 mm to 15 mm.

(4) FIG. 2 (d)
As the first cell layer 91, a p layer, an i layer, and an n layer made of an amorphous silicon thin film are formed by a plasma CVD apparatus. Using SiH ₄ gas and H ₂ gas as main raw materials, a reduced pressure atmosphere: 30 Pa to 1000 Pa, a substrate temperature: about 200 ° C., an amorphous silicon p layer on the transparent electrode layer 2 from the side on which sunlight is incident, An amorphous silicon i layer and an amorphous silicon n layer are formed in this order. The amorphous silicon p layer is mainly composed of amorphous B-doped silicon and has a thickness of 10 nm to 30 nm. The amorphous silicon i layer has a thickness of 200 nm to 350 nm. The amorphous silicon n layer is mainly P-doped silicon containing microcrystalline silicon in amorphous silicon and has a thickness of 30 nm to 50 nm. A buffer layer may be provided between the amorphous silicon p layer and the amorphous silicon i layer in order to improve interface characteristics.

  Next, a crystalline material as the second cell layer 92 is formed on the first cell layer 91 by a plasma CVD apparatus at a reduced pressure atmosphere: 3000 Pa or less, a substrate temperature: about 200 ° C., and a plasma generation frequency: 40 MHz or more and 100 MHz or less. A silicon p layer, a crystalline silicon i layer, and a crystalline silicon n layer are sequentially formed. The crystalline silicon p layer is mainly composed of B-doped microcrystalline silicon and has a thickness of 10 nm to 50 nm. The crystalline silicon i layer is mainly microcrystalline silicon and has a film thickness of 1.2 μm or more and 3.0 μm or less. The crystalline silicon n layer is mainly P-doped microcrystalline silicon and has a film thickness of 20 nm to 50 nm.

  In forming the i-layer film mainly composed of microcrystalline silicon by the plasma CVD method, the distance between the plasma discharge electrode and the surface of the substrate 1 is preferably 3 mm or more and 10 mm or less. When it is smaller than 3 mm, it is difficult to keep the distance constant from the accuracy of each component device in the film forming chamber corresponding to the large substrate, and there is a possibility that the discharge becomes unstable because it is too close. When it is larger than 10 mm, it is difficult to obtain a sufficient film forming speed (1 nm / s or more), and the uniformity of the plasma is lowered and the film quality is lowered by ion bombardment.

  An intermediate contact layer 93 serving as a semi-reflective film is provided between the first cell layer 91 and the second cell layer 92 in order to improve the contact property and achieve current matching. As the intermediate contact layer 93, a GZO (Ga-doped ZnO) film having a thickness of 20 nm to 100 nm is formed by sputtering using a target: Ga-doped ZnO sintered body. Further, the intermediate contact layer 93 may not be provided.

(5) FIG. 2 (e)
The substrate 1 is placed on an XY table, and the second harmonic (532 nm) of the laser diode-pumped YAG laser is irradiated from the film surface side of the photoelectric conversion layer 3 as indicated by an arrow in the figure. Pulse oscillation: 10 kHz to 20 kHz, laser power is adjusted so as to be suitable for the processing speed, and laser etching is performed so that grooves 11 are formed on the lateral side of the laser etching line of the transparent electrode layer 2 from about 100 μm to 150 μm. To do. Further, this laser may be irradiated from the substrate 1 side. In this case, the photoelectric conversion layer is formed by utilizing a high vapor pressure generated by the energy absorbed in the amorphous silicon-based first cell layer of the photoelectric conversion layer 3. Since 3 can be etched, a more stable laser etching process can be performed. The position of the laser etching line is selected in consideration of positioning tolerances so as not to intersect with the etching line in the previous process.

(6) FIG. 3 (a)
An Ag film / Ti film is formed as the back electrode layer 4 by a sputtering apparatus at a reduced pressure atmosphere and at a film forming temperature of 150 ° C. to 200 ° C. In this embodiment, an Ag film: 150 nm to 500 nm and a Ti film having a high anticorrosion effect: 10 nm to 20 nm are stacked in this order as a protective film. Alternatively, the back electrode layer 4 may have a laminated structure of an Ag film having a thickness of 25 nm to 100 nm and an Al film having a thickness of 15 nm to 500 nm. For the purpose of reducing contact resistance between the crystalline silicon n layer and the back electrode layer 4 and improving light reflection, a GZO film having a thickness of 50 nm to 100 nm is formed between the photoelectric conversion layer 3 and the back electrode layer 4 by a sputtering apparatus. A (Ga-doped ZnO) film may be formed.

(7) FIG. 3 (b)
The substrate 1 is placed on an XY table, and the second harmonic (532 nm) of the laser diode-pumped YAG laser is irradiated from the substrate 1 side as indicated by the arrow in the figure. The laser light is absorbed by the photoelectric conversion layer 3, and the back electrode layer 4 is exploded and removed using the high gas vapor pressure generated at this time. Pulse oscillation: laser power is adjusted so as to be suitable for the processing speed from 1 kHz to 10 kHz, and laser etching is performed so that grooves 12 are formed on the lateral side of the laser etching line of the transparent electrode layer 2 from 250 μm to 400 μm. .

(8) FIG. 3 (c) and FIG. 4 (a)
The power generation region is divided, and the film edge around the substrate edge is laser-etched to eliminate the effect of short circuit at the serial connection portion. The substrate 1 is placed on an XY table, and the second harmonic (532 nm) of the laser diode pumped YAG laser is irradiated from the substrate 1 side. The laser light is absorbed by the transparent electrode layer 2 and the photoelectric conversion layer 3, and the back electrode layer 4 explodes using the high gas vapor pressure generated at this time, and the back electrode layer 4 / photoelectric conversion layer 3 / transparent electrode layer 2 is removed. Pulse oscillation: 1 kHz or more and 10 kHz or less, the laser power is adjusted so as to be suitable for the processing speed, and the position of 5 mm to 20 mm from the end of the substrate 1 is placed in the X-direction insulating groove as shown in FIG. Laser etching is performed to form 15. In addition, in FIG.3 (c), since it becomes X direction sectional drawing cut | disconnected in the direction in which the photoelectric converting layer 3 was connected in series, the back surface electrode layer 4 / photoelectric conversion is originally in the position of the insulating groove 15 A state (see FIG. 4A) where there is a peripheral film removal region 14 where the layer 3 / transparent electrode layer 2 is polished and removed should appear, but for convenience of explanation of processing to the end of the substrate 1, The insulating groove formed to represent the Y-direction cross section at the position will be described as the X-direction insulating groove 15. At this time, the Y-direction insulating groove does not need to be provided because the film surface polishing removal processing of the peripheral film removal region of the substrate 1 is performed in a later process.

  The insulating groove 15 exhibits an effective effect in suppressing external moisture intrusion into the solar cell module 6 from the end portion of the solar cell panel by terminating the etching at a position of 5 mm to 15 mm from the end of the substrate 1. Therefore, it is preferable.

  In addition, although the laser beam in the above process is made into a YAG laser, there exists what can use a YVO4 laser, a fiber laser, etc. similarly.

(9) FIG. 4 (a: view from the solar cell film side, b: view from the substrate side of the light receiving surface)
Since the laminated film around the substrate 1 (peripheral film removal region 14) has a step and is easy to peel off in order to ensure a sound adhesion / seal surface with the back sheet 24 via EVA or the like in a later process, The film is removed to form a peripheral film removal region 14. In removing the film over the entire circumference of the substrate 1 at 5 to 20 mm from the end of the substrate 1, the X direction is closer to the substrate end than the insulating groove 15 provided in the step of FIG. The back electrode layer 4 / photoelectric conversion layer 3 / transparent electrode layer 2 are removed by using grinding stone polishing, blast polishing, or the like on the substrate end side with respect to the groove 10 near the side portion.
Polishing debris and abrasive grains were removed by cleaning the substrate 1.

(10) FIGS. 5 (a) and 5 (b)
An attachment portion of the terminal box 23 is provided with an opening through window in the back sheet 24 to take out the current collector plate. Insulating materials are installed in a plurality of layers in the opening through window portion to suppress intrusion of moisture and the like from the outside.
Processing so that power can be taken out from the terminal box 23 on the back side of the solar battery panel by collecting copper foil from one end of the photovoltaic power generation cells arranged in series and the other end of the solar power generation cell. To do. In order to prevent a short circuit with each part, the copper foil arranges an insulating sheet wider than the copper foil width.
After the current collecting copper foil or the like is disposed at a predetermined position, an adhesive filler sheet made of EVA (ethylene vinyl acetate copolymer) or the like is disposed so as to cover the entire solar cell module 6 and not protrude from the substrate 1. .
A back sheet 24 having a high waterproof effect is installed on the EVA. In this embodiment, the back sheet 24 has a three-layer structure of PET sheet / Al foil / PET sheet so that the waterproof and moisture-proof effect is high.
The EVA sheet is placed in a predetermined position until the back sheet 24 is deaerated with a laminator in a reduced pressure atmosphere and pressed at about 150 to 160 ° C., and EVA is crosslinked and brought into close contact.

(11) FIG. 5 (a)
The terminal box 23 is attached to the back side of the solar cell module 6 with an adhesive.
(12) FIG. 5 (b)
The copper foil and the output cable of the terminal box 23 are connected by solder or the like, and the inside of the terminal box 23 is filled with a sealing agent (potting agent) and sealed. Thus, the solar cell panel 50 is completed.
(13) FIG. 5 (c)
A power generation inspection and a predetermined performance test are performed on the solar cell panel 50 formed in the steps up to FIG. The power generation inspection is performed using a solar simulator of AM1.5 and solar radiation standard sunlight (1000 W / m ² ).
(14) FIG. 5 (d)
Before and after the power generation inspection (FIG. 5C), a predetermined performance inspection is performed including an appearance inspection.

The basis for determining the transparent thin film material will be described below.
(Conditions for ideal medium A)
The conditions (refractive index, film thickness) of the ideal medium A used for the transparent thin film 201 inserted between the translucent substrate 1 and the transparent electrode layer 2 were estimated.
The translucent substrate 1 was barium borosilicate glass (Corning Corp., # 7059), and the transparent electrode layer 2 was a GZO film. The refractive index of the ideal medium A was calculated from equation (2).
n _A = √n _g × √n _t (2)
(N _A : refractive index of ideal medium A, n _g : refractive index of translucent substrate, n _t : refractive index of transparent electrode layer)

The results are shown in Table 1. From Table 1, it was confirmed that a material having a refractive index of 1.85 to 1.63 between 320 nm and 900 nm can be the ideal medium A.

(Selection of actual materials)
Al ₂ O ₃ , MgO, and Y ₂ O ₃ were selected as materials having a high refractive index between 320 nm and 900 nm and a refractive index of 1.85 to 1.63 and a wide band (350 to 1000 nm). The refractive indexes of the materials at the wavelength of 550 nm were 1.77, 1.74, and 1.78, respectively.

When the ideal medium A, Al ₂ O ₃ , MgO, and Y ₂ O ₃ are used as the transparent thin film 201, the light transmittance at the # 7059 / GZO interface is calculated using optical thin film calculation software (Cybernet OPTAS-FILM). Calculated. The film thickness of the transparent thin film 201 was a value calculated from the formula (3) (ideal medium A: 70 nm, Al ₂ O ₃ : 80 nm, MgO: 80 nm, Y ₂ O ₃ : 77 nm).
d = λ / 4 × 1 / n (3)
(D: film thickness (nm), λ: center wavelength (nm), n: refractive index)
As Comparative Example 1, the light transmittance when the ideal medium A: 0 nm was used was also calculated.

FIG. 6A shows the light transmittance to the GZO film when the ideal medium A is inserted as the transparent thin film 201. From the light incident side, a layer structure of translucent substrate / ideal medium A / transparent electrode layer is formed, and each layer is arranged infinitely in parallel. It is the result of calculating | requiring the transmittance | permeability of the light from a translucent board | substrate to a transparent electrode layer by calculation. In the figure, the horizontal axis represents the wavelength, and the vertical axis represents the light transmittance to the GZO film. Compared with Comparative Example 1, the transmittance was improved by about 2.0% at the center wavelength of 450 nm.
FIG. 6B shows the light transmittance to the GZO film when Al ₂ O ₃ is inserted as the transparent thin film 201. In the figure, the horizontal axis represents the wavelength, and the vertical axis represents the light transmittance to the GZO film. Compared to Comparative Example 1, the transmittance was improved by about 1.5% at the center wavelength of 550 nm.
FIG. 6C shows the light transmittance to the GZO film when MgO is inserted as the transparent thin film 201. In the figure, the horizontal axis represents the wavelength, and the vertical axis represents the light transmittance to the GZO film. Compared to Comparative Example 1, the transmittance was improved by about 1.5% at the center wavelength of 550 nm.
FIG. 6D shows the light transmittance to the GZO film when Y ₂ O ₃ is inserted as the transparent thin film 201. In the figure, the horizontal axis represents the wavelength, and the vertical axis represents the light transmittance to the GZO film. Compared to Comparative Example 1, the transmittance was improved by about 1.5% at the center wavelength of 550 nm.
From the above results, it was found that the transmittance was improved when any material of Al ₂ O ₃ , MgO, and Y ₂ O ₃ was used as the transparent thin film 201. Further, since the light transmittance is maximized on the short wavelength side, when the above material is used, the function of increasing the amount of incident light with respect to the first cell layer that absorbs the short wavelength is enhanced. Although data not shown, as a real material, the improved mixed film _{(50% TiO 2 -50% SiO} 2) But likewise transmittance of TiO ₂ and SiO ₂ with an adjusted refractive index 1.79 .

(Confirmation of absorption of double-sided antireflection substrate)
An antireflection layer 202 was provided on the light incident side of the translucent substrate 1, and a transparent thin film 201 was provided on the opposite surface to produce a double-sided antireflection substrate.
As the translucent substrate 1, aluminoborosilicate glass (manufactured by Corning, # 1737, 50 mm × 50 mm × plate thickness: 1.1 mm) was used. An antireflection layer 202 mainly composed of MgF ₂ was formed on the light incident side of the translucent substrate 1. A transparent thin film 201 containing Y ₂ O ₃ as a main component was formed on the surface opposite to the surface on which the antireflection layer 202 of the translucent substrate 1 was formed. The (average) film thicknesses of the antireflection layer 202 and the transparent thin film 201 were 100 nm and 77 nm, respectively. The film thickness was calculated from the above formula (4) with the refractive indexes of MgF ₂ and Y ₂ O ₃ at the center wavelength of 550 nm being 1.38 and 1.78, respectively.

The transmittance and reflectance of # 1737 and the double-sided antireflection substrate produced above were measured using a spectrophotometer (
It was measured using a HITACHI U-3500 integrating sphere (φ60). FIG. 7 shows the measurement results. In the figure, the horizontal axis represents wavelength, and the vertical axis represents the sum of light transmittance and light reflectance.
At a wavelength of 400 nm or more, the sum of the light transmittance and the light reflectance of the double-sided antireflection substrate was almost 100% as in # 1737. Accordingly, it was confirmed that the film made of MgF ₂ and Y ₂ O ₃ produced by the above method had no absorption.

(Light transmittance of double-sided anti-reflection substrate)
FIG. 8 shows the light transmittance of the double-sided antireflection substrate measured above. In FIG. 8, the horizontal axis represents wavelength, and the vertical axis represents light transmittance. Comparative Example 2 is an expected light transmittance (calculated value) when MgF ₂ is used for the antireflection layer 202 and Y ₂ O ₃ is used for the transparent thin film 201. This calculation was performed using optical thin film calculation software (Cybernet, OPTAS-FILM) with a layer configuration of air / MgF ₂ / glass substrate / Y ₂ O ₃ / air from the light incident side. The light transmittance (actually measured value) of the double-sided antireflection substrate was changed in substantially the same manner as the expected light transmittance. The actual measurement value was measured by measuring the light emitted from Y ₂ O ₃ by making light incident on the MgF ₂ surface in the same manner as in the calculation layer configuration. The medium around the double-sided antireflection substrate is air, which is the same as the calculated layer structure. Thus, according to the present embodiment, it was shown that the light transmission characteristic improvement effect can be obtained almost equal to the calculation result.

When only the antireflection layer 202 made of MgF ₂ was provided on the light incident side of the translucent substrate 1, the light reflection loss reduction effect at the air / translucent substrate interface was 2.5%. Since the light transmittance improvement effect of the transparent thin film 201 was 1.5%, the light reflection loss reduction effect of about 4% can be obtained by inserting the antireflection layer 202 on both surfaces of the translucent substrate 1. Can do.

The Y ₂ O ₃ was confirmed alkali barrier properties of the transparent thin film mainly. The film thickness of the transparent thin film used for the study was 30 nm to 100 nm. Data is not shown, transparent thin film composed mainly of Y ₂ O ₃ is at 100nm following thickness above 30 nm, was confirmed to exert an alkali barrier effect.

According to the above embodiment, if the material has a refractive index close to that of the ideal medium A (Al ₂ O ₃ , MgO, TiO ₂ —SiO ₂ mixed film, etc.), the translucent substrate / transparent electrode layer interface is used. It is possible to reduce light reflection. However, among such materials, by inserting Y ₂ O ₃ with a predetermined thickness, the transparent thin film 201 having not only an antireflection function but also an alkali barrier function can be obtained.

  Although the tandem solar cell has been described as the solar cell in the above embodiment, the present invention is not limited to this example. For example, the present invention can be similarly applied to other types of thin film solar cells such as amorphous silicon solar cells, crystalline silicon solar cells including microcrystalline silicon, silicon germanium solar cells, and triple solar cells.

DESCRIPTION OF SYMBOLS 1 Translucent board | substrate 2 Transparent electrode layer 3 Photoelectric conversion layer 4 Back surface electrode layer 6 Solar cell module 90 Photoelectric conversion apparatus 91 1st cell layer 92 2nd cell layer 93 Intermediate contact layer 201 Transparent thin film 202 Antireflection layer

Claims (5)

A translucent substrate;
A transparent electrode layer and a photoelectric conversion layer provided on the translucent substrate;
A photoelectric conversion device in which a transparent thin film mainly composed of Y ₂ O ₃ is provided between the translucent substrate and the transparent electrode layer.   The photoelectric conversion device according to claim 1, comprising at least two photoelectric conversion layers.   The photoelectric conversion device according to claim 1, wherein the translucent substrate is glass having an alkali component. The photoelectric conversion device according to claim 1, wherein an antireflection layer containing MgF ₂ or porous silica as a main component is provided on a surface opposite to the surface on which the transparent thin film is provided on the translucent substrate. A translucent substrate;
A transparent electrode layer provided on the translucent substrate,
Wherein between the transparent substrate and the transparent electrode layer, a transparent thin film is a transparent electrode layer-substrate provided mainly composed of Y ₂ O _3.

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