JP2001007361A - Thin optoelectronic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin optoelectronic transducer, which is equipped with surface texture structure, optimized to improve light absorption efficiency, in a glass face incident of thin optoelectronic transducer. SOLUTION: A thin optoelectronic transducer is equipped with a glass board 1, a transparent conductive oxide layer 2, a thin optoelectronic transducer unit 3, a buffer layer 4 and an electrode layer, and a metallic layer 5. The thin optoelectronic transducer unit 3 includes a p-type silicon layer 3p formed on the transparent conductive oxide layer 2, an i-type thin optoelectronic transducer layer 3i consisting substantially of the p-type silicon layer 3p, and an n-type silicon layer 3n made of the thin optoelectronic transducer layer 3i. The interface between the transparent conductive oxide layer 2 and the p-type silicon layer 3b includes an irregular face, which has a level difference within the range of not less than 0.1 μm and not more than 0.5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin-film photoelectric conversion device, and more particularly to a thin-film photoelectric conversion device having improved photoelectric conversion efficiency in a polycrystalline photoelectric conversion layer.

[0002]

2. Description of the Related Art In recent years, as is typically used in thin film polycrystalline silicon solar cells as a thin film photoelectric conversion device,
Thin-film photoelectric materials sensitive to light in a wide wavelength range have been developed. However, when the photoelectric material is a thin film, the absorption coefficient of the photoelectric material decreases as the wavelength of light increases, so that the light absorption of the entire thin film is limited by the film thickness, and effective photoelectric conversion in the entire sensitivity wavelength region is not achieved. It has become difficult.

[0003] In order to solve the above problems, the light absorption coefficient,
In particular, Japanese Patent Application Laid-Open No. HEI 10-117006 proposes a structure of a thin film photoelectric conversion device in which a light absorption coefficient in a long wavelength region is improved and high photoelectric conversion efficiency can be obtained. In this thin-film photoelectric conversion device, the surface of the substantially polycrystalline photoelectric conversion layer includes fine irregularities having a height difference substantially in the range of 0.05 to 3 μm. Since the surface of the polycrystalline photoelectric conversion layer has a surface texture structure including fine irregularities, a light scattering structure is formed in which light incident on the photoelectric conversion layer is difficult to escape to the outside. As a result, high photoelectric conversion efficiency is achieved.

[0004]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open
The thin-film photoelectric conversion device proposed in Japanese Patent Publication No. 117006 has a polycrystalline photoelectric conversion layer in which an n-type layer, an i-type layer, and a p-type layer are sequentially formed on a glass substrate. In the thin film photoelectric conversion device, the above publication discloses the absorption characteristics and photoelectric conversion efficiency of the photoelectric conversion device when light enters from a transparent conductive layer formed on a p-type layer.

[0005] However, a p-type layer on a glass substrate,
The above publication does not discuss in detail the thin film photoelectric conversion device in which an i-type layer and an n-type layer are formed in this order and light is incident from the surface of a glass substrate. In particular, in a thin film photoelectric conversion device of a type in which light enters from the surface of a glass substrate, it is necessary to form a thick transparent conductive oxide layer between the glass substrate and the photoelectric conversion unit. Therefore, there is a problem that the light absorption characteristics and the photoelectric conversion efficiency of the photoelectric conversion device are affected by the light transmittance (or absorptance) of the thick transparent conductive oxide layer. Therefore, when the surface texture structure including fine irregularities disclosed in the above publication is applied to a photoelectric conversion device of a type in which light is incident from the surface of a glass substrate to improve light absorption characteristics and photoelectric conversion efficiency, It is necessary to optimize the fine irregularities.

Accordingly, an object of the present invention is to provide a thin-film photoelectric conversion device of a glass surface incidence type, in which a light absorption coefficient, particularly a light absorption coefficient in a long wavelength region, is improved and a surface optimized to obtain high photoelectric conversion efficiency is obtained. An object of the present invention is to provide a thin-film photoelectric conversion device having a texture structure.

[0007]

A thin-film photoelectric conversion device according to the present invention comprises a glass substrate having first and second main surfaces, and a transparent substrate formed on the first main surface of the glass substrate. The device includes a conductive oxide layer, a photoelectric conversion unit formed on the transparent conductive oxide layer, and an electrode layer formed on the photoelectric conversion unit. The photoelectric conversion unit includes a p-type silicon layer formed on the transparent conductive oxide layer, an i-type photoelectric conversion layer substantially made of polycrystalline silicon formed on the p-type silicon layer, An n-type silicon layer formed on the photoelectric conversion layer. Light is
Light is incident from the second main surface of the glass substrate. In the thin film photoelectric conversion device configured as described above, the interface between the transparent conductive oxide layer and the p-type silicon layer is 0.1 μm or more,
It is characterized by including an uneven surface having a height difference within a range of 0.5 μm or less.

[0008] By optimizing the shape of the uneven surface at the interface between the transparent conductive oxide layer and the p-type silicon layer as described above, when light is incident from the glass surface,
Even if light is absorbed in the transparent conductive oxide layer, a light scattering structure in which light incident on the photoelectric conversion layer is hard to escape to the outside can be provided. Thereby, in the glass surface incident type photoelectric conversion device, the light absorption coefficient in a long wavelength region can be improved, and high photoelectric conversion efficiency can be obtained.

In the thin film photoelectric conversion device of the present invention, the interface between the transparent conductive oxide layer and the p-type silicon layer is 0.2
It is preferable to include an uneven surface having a height difference within the range of μm or less.

In particular, when light absorption in the transparent conductive oxide layer is remarkable as determined from a transmission spectrum, for example, when the light transmittance at a long wavelength (wavelength of 1000 nm) is 80% or less, the transparent conductive oxide By limiting the height difference of the uneven surface at the interface between the oxide layer and the p-type silicon layer to within 0.2 μm or less, absorption of light that does not contribute to photoelectric conversion, that is, absorption of parasitic light, is suppressed. can do. In this way, even when light absorption in the transparent conductive oxide layer is remarkable, the light confinement effect can be increased by optimizing the height difference of the uneven surface as the surface texture structure, and the photoelectric conversion efficiency can be increased. Can be improved.

When the light absorption in the transparent conductive oxide layer is small, for example, when the transmittance of light at a long wavelength (wavelength of 1000 nm) exceeds 80%, the transparent conductive oxide layer and the p-type When the height difference of the uneven surface at the interface with the silicon layer is 0.5 μm or less, a light confinement effect that contributes to an improvement in photoelectric conversion efficiency can be obtained.

Further, the interface between the n-type silicon layer and the electrode layer preferably includes an uneven surface having a height difference within a range of 0.1 μm or more and 0.5 μm or less.

At the interface between the n-type silicon layer and the electrode layer, in the long wavelength region having a wavelength of 600 nm or more,
It does not contribute to photoelectric conversion, that is, the absorption of parasitic light is small. Therefore, the light confinement effect can be obtained by optimizing the range of the height difference of the uneven surface at the interface between the transparent conductive oxide layer and the p-type silicon layer to 0.1 μm or more and 0.5 μm or less, The photoelectric conversion efficiency can be improved.

<1 of many crystal grains contained in the photoelectric conversion layer
10> direction is 15 ° with respect to the direction of the thickness of the photoelectric conversion layer.
It is preferable that they are shifted within the following angle range.

The photoelectric conversion layer has a volume crystallization fraction of 8
Preferably, it is made of 0% or more of polycrystalline silicon and has a hydrogen content of 0.1 to 30 atomic%.

[0016] The electrode layer preferably includes a buffer layer formed on the n-type silicon layer and a metal layer formed on the buffer layer.

Preferably, the buffer layer contains zinc oxide and the metal layer contains silver. Further, in the thin-film photoelectric conversion device of the present invention, it is preferable that the photoelectric conversion unit includes first and second photoelectric conversion units. A first photoelectric conversion unit comprising: a p-type silicon layer; an i-type amorphous photoelectric conversion layer made of substantially amorphous silicon formed on the p-type silicon layer; An n-type silicon layer formed on the photoelectric conversion layer. The second photoelectric conversion unit includes a p-type silicon layer, an i-type polycrystalline photoelectric conversion layer substantially formed of polycrystalline silicon formed on the p-type silicon layer, and a polycrystalline photoelectric conversion layer. N formed above
Mold silicon layer.

As described above, by employing the configuration of a so-called tandem thin film photoelectric conversion device, a high open-circuit voltage can be obtained, and the photoelectric conversion efficiency can be further improved.

In the case where the above-described configuration of the tandem thin-film photoelectric conversion device is adopted, the photoelectric conversion unit includes a first photoelectric conversion unit and a second photoelectric conversion unit which are sequentially formed on the transparent conductive oxide layer. It is preferred to include

As described above, by forming an amorphous photoelectric conversion unit and a polycrystalline photoelectric conversion unit in this order from the surface of the glass substrate on which light is incident, short-wavelength light can be transmitted through the amorphous photoelectric conversion layer. Since the polycrystalline photoelectric conversion layer can efficiently absorb light and long-wavelength light, the photoelectric conversion efficiency can be significantly improved.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic sectional view schematically showing a thin film photoelectric conversion device according to one embodiment of the present invention. The thin-film photoelectric conversion device shown in FIG. 1 includes a transparent conductive oxide layer 2, a polycrystalline photoelectric conversion unit 3, a buffer layer 4 as a back electrode layer, and a metal layer 5 is included.

The transparent conductive oxide layer 2 is made of, for example, Sn
It is made of O ₂ (tin oxide) and is formed as a transparent electrode. The thickness of the transparent conductive oxide layer 2 is 500 nm to
It is in the range of 1 μm. The light transmittance (or light absorption) of the transparent conductive oxide layer 2 can be appropriately adjusted by changing the formation temperature in the sputtering method. Further, by appropriately adjusting the sputtering conditions, a texture structure including fine irregularities on the free surface 2S of the transparent conductive oxide layer 2 can be formed. These uneven surfaces can be formed so as to have a height difference within a range of 0.1 to 0.5 μm.

The polycrystalline photoelectric conversion unit 3 can be formed by a plasma CVD method. The photoelectric conversion unit 3 includes a p-type silicon layer 3p and an i-type photoelectric conversion layer 3i.
And the n-type silicon layer 3n are sequentially formed of the transparent conductive oxide layer 2
Is deposited by a plasma CVD method. The i-type photoelectric conversion layer 3i is substantially made of polycrystalline silicon. Here, “substantially polycrystal” means not only a complete polycrystal, but also a polycrystal containing a small amount of amorphous. For example, i-type photoelectric conversion layer 3i
Can be formed of polycrystalline silicon having a volume crystallization fraction of 80% or more. As plasma CVD conditions, for example,
Conditions selected from a range of a pressure of 0.01 to 5 Torr and a temperature of 50 to 550 ° C. can be adopted. The p-type silicon layer 3p is deposited by a plasma CVD method using a mixed gas containing diborane, silane and hydrogen.
Next, the i-type photoelectric conversion layer 3 which is a substantially intrinsic semiconductor
i is deposited by a plasma CVD method using a mixed gas of silane gas and hydrogen containing no conductive impurities.
Further, the n-type silicon layer 3n is made of, for example, phosphine,
Plasma CV using mixed gas containing silane and hydrogen
It can be formed by Method D.

The <110> direction of many crystal grains contained in the thus-formed substantially polycrystalline photoelectric conversion layer 3i is within a range of about 15 ° or less with respect to the thickness direction of the photoelectric conversion layer. And is substantially parallel to the thickness direction of the photoelectric conversion layer.

The polycrystalline photoelectric conversion unit 3 is about 0.5 to
It is grown to an average thickness in the range of 20 μm. p
The free surface of the type silicon layer 3p includes a fine uneven surface corresponding to the interface 2S with the underlying transparent conductive oxide layer 2. i
The free surface of the n-type photoelectric conversion layer 3i is also the n-type silicon layer 3n.
Also has a surface texture structure including a fine uneven surface. Free surface 3S including these uneven surfaces
Includes a V-shaped groove or pyramid, and the photoelectric conversion unit 3
Has a height difference within a range of 0.1 μm or more and 0.5 μm or less within a range smaller than 平均 of the average thickness.

In the polycrystalline photoelectric conversion unit 3 as shown in FIG. 1, light enters in the direction shown by the arrow, is refracted at the interface 2S, enters obliquely, and further enters the interface 2S.
Causes multiple reflections between the interface and the interface 3S. For this reason, the effective optical length is increased, and a large amount of light absorption can be obtained despite the thin film. The unevenness density and height difference at the interface 3S can be controlled by adjusting the plasma CVD conditions (temperature, pressure, gas flow rate, high frequency power, etc.) of the polycrystalline i-type photoelectric conversion layer 3i. Thereby, it is also possible to select the wavelength of the light scattered preferentially in the photoelectric conversion unit 3. In other words, by preferentially scattering long-wavelength light in the polycrystalline photoelectric conversion unit 3, the amount of light absorbed particularly for long-wavelength light can be increased.
As will be described later, in the photoelectric conversion device of the present invention, a surface texture structure suitable for increasing the amount of light absorption for long-wavelength light in consideration of light absorption in the thick transparent conductive oxide layer 2 is also taken into consideration. Can be obtained.

A back electrode layer is formed on the polycrystalline photoelectric conversion unit 3. The back electrode layer includes a buffer layer 4 and a metal layer 5. The buffer layer 4 acts to reduce the recombination of carriers and acts to enhance the effect of confining the reflected light from the metal layer 5 in the photoelectric conversion unit 3. As the buffer layer 4, a transparent conductive material such as zinc oxide (ZnO) and indium oxide (In) is used.
₂ O ₃ ), tin oxide (SnO ₂ ) and cadmium oxide (C
dO), or at least one of a light-transmitting semiconductor substance, iron oxide (Fe ₂ O ₃ ), titanium oxide (TiO), zinc selenide (ZnSe), and zinc sulfide (ZnS). , Preferably zinc oxide (Zn
O) is used.

The metal layer 5 can be formed by a sputtering method. For example, using a silver (Ag) target, argon (A) at a pressure of 0.1 to 50 mTorr is used.
r) It can be formed using RF (high frequency) discharge in gas. In addition, as a target, in addition to silver (Ag), gold (Au), copper (Cu), aluminum (Al), platinum (Pt), or an alloy containing at least one of them can also be used.

The free surfaces of the buffer layer 4 and the metal layer 5 include a fine uneven surface corresponding to the interface 3S with the underlying photoelectric conversion unit 3.

FIG. 2 shows the transmission characteristics of three types of transparent conductive oxide layers a, b, and c in which the transmittance of light is appropriately adjusted by changing the temperature at which the transparent conductive oxide layer 2 is formed. It is a graph. In this graph, the transparent conductive oxide layer a shows a transmittance of 80% or less at a long wavelength (wavelength of 1000 nm), and the other transparent conductive oxide layers b and c
Is 80% or more transmittance for long wavelength (1000nm wavelength)
Shown in FIG.

FIG. 3 shows the state of the interface 2S between the transparent conductive oxide layer 2 and the p-type silicon layer 3p (see FIG. 1) using the transparent conductive oxide layer a shown in FIG. 4 is a graph showing the external quantum efficiency (no unit) of the photoelectric conversion device obtained by variously changing the height difference (depth) of the uneven surface. As is clear from FIG. 3, the transparent conductive oxide layer a1 having a height difference of 0.5 μm on the uneven surface has a thickness of 600 nm.
In contrast, the spectral sensitivity is deteriorated in a long-wavelength region exceeding the above range. On the other hand, the transparent conductive oxide layer a2 having a height difference of 0.2 μm and the transparent conductive oxide layer a3 having a height of 0.1 μm
It can be seen that the spectral sensitivity in the long wavelength region exceeding 0 nm is good. As a result, when light absorption in the transparent conductive oxide layer is remarkable, for example, when the light transmittance is 80% or less (curve a in FIG. 2), the transparent conductive oxide layer 2 and the p-type silicon layer 3p It can be seen that good spectral sensitivity can be obtained at the interface 2S if the height difference between the uneven surfaces is 0.2 μm or less.

FIG. 4 shows a case where the light absorption of the transparent conductive oxide layer in FIG.
In the case where the light transmittance of the transparent conductive oxide layer 2 is 80% or more (curves b and c in FIG. 2), the height difference of the uneven surface at the interface 2S between the transparent conductive oxide layer 2 and the p-type silicon layer 3p is changed. This shows the result of examining the external quantum efficiency of the thin-film photoelectric conversion device. As is apparent from FIG. 4, when the height difference of the uneven surface is 0.8 μm, the spectral sensitivity is deteriorated as shown by the curve c2 when the transparent conductive oxide layer c has a height difference of 0.8 μm. Is 0.5 μm, the curve c1
As shown by, the spectral sensitivity is good. Further, in the case of the transparent conductive oxide layer b having a height difference of 0.2 μm on the uneven surface,
Good spectral sensitivity is obtained as shown by the curve b. From this, when the absorption of the transparent conductive oxide layer is small,
It can be seen that good spectral sensitivity can be obtained if the height difference of the uneven surface is 0.5 μm or less.

As an example of a thin film photoelectric conversion device having the structure shown in FIG. 1, a transparent conductive oxide layer 2 made of tin oxide is formed on a glass substrate 1 to a thickness of 900 nm, and a thickness of 150 nm is formed thereon. P-type silicon layer 3p, polycrystalline i-type photoelectric conversion layer 3i containing 10 atomic% of hydrogen and having a thickness of 2 μm, n-type silicon layer 3n having a thickness of 250 °, and oxidation having a thickness of 80 nm as buffer layer 4 A silver layer having a thickness of 300 nm was sequentially formed as a zinc film and a metal layer 5. In the photoelectric conversion device thus formed, a short-circuit current of 25 mA, a current
An open circuit voltage of 53 V and a conversion efficiency of 10% were obtained.

FIG. 5 is a schematic sectional view schematically showing a thin-film photoelectric conversion device according to another embodiment of the present invention.
The photoelectric converter of FIG. 5 is similar to that of FIG.
An amorphous photoelectric conversion unit 6 is formed between the transparent conductive oxide layer 2 and the p-type silicon layer 3p of the polycrystalline photoelectric conversion unit 3. The amorphous photoelectric conversion unit 6
p-type silicon layer 6p and amorphous i-type photoelectric conversion layer 6i
And an n-type silicon layer 6n. That is, the thin-film photoelectric conversion device shown in FIG. 5 is a thin-film photoelectric conversion device of the type in which light is incident from the surface of the glass substrate 1 in the direction of the arrow.
Is a tandem-type thin-film photoelectric conversion device in which is laminated.
In the amorphous photoelectric conversion unit 6, the n-type silicon layer 6
n, the substantially intrinsic i-type silicon layer 6i and the p-type silicon layer 6p each contain amorphous silicon.

As an example, a transparent conductive oxide layer 2, a polycrystalline photoelectric conversion unit 3, a buffer layer 4, and a metal layer 5 are formed as in the example of the photoelectric conversion device shown in FIG. The amorphous photoelectric conversion unit 6 has a film thickness of 1
50 ° p-type amorphous silicon layer 6p, film thickness 0.25μ
Thus, an m-type amorphous i-type silicon layer 6i and a 250-nm-thick amorphous n-type silicon layer 6n were formed. The tandem-type thin-film photoelectric conversion device formed as described above has the following features.
2.5 mA short circuit current, 1.35 V open circuit voltage and 1
It had a conversion efficiency of 3%. That is, as compared with the thin film photoelectric conversion device of FIG. 1, the short-circuit current is reduced in the tandem thin film photoelectric conversion device of FIG. 5, but a high open-circuit voltage can be obtained, and light of a short wavelength can be converted into an amorphous photoelectric conversion device. Conversion unit 6
It can be seen that the photoelectric conversion efficiency can be remarkably improved because the polycrystalline photoelectric conversion unit 4 can efficiently absorb light of a long wavelength and absorb light of a long wavelength.

The embodiments and examples disclosed above are illustrative in all respects and should not be considered as limiting. The scope of the present invention is defined by the terms of the claims, rather than the embodiments described above, and is to be construed as including any modifications and variations within the scope and meaning equivalent to the terms of the claims. .

[0037]

As described above, according to the present invention, an optimized surface texture structure with an improved light absorption coefficient, particularly in a long wavelength region, is provided in a glass surface incident type photoelectric conversion device. Provided with the thin-film photoelectric conversion device. Therefore, a large short-circuit current and a high open-circuit voltage can be obtained in a glass surface incident type thin film photoelectric conversion device, and a high photoelectric conversion efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a thin-film photoelectric conversion device according to one embodiment of the present invention.

FIG. 2 is a graph showing different light transmittances by changing the formation temperature of the transparent conductive oxide layer 2 in FIG.

FIG. 3 shows the external quantum efficiency of the thin-film photoelectric conversion device when the light transmittance of the transparent conductive oxide layer is 80% or less at a long wavelength (1000 nm) when the height difference of the uneven surface is changed. It is a graph shown.

FIG. 4 shows the external quantum efficiency of the thin-film photoelectric conversion device when the light transmittance of the transparent conductive oxide layer is 80% or more at a long wavelength (1000 nm) and the height difference of the uneven surface is changed. It is a graph shown.

FIG. 5 is a schematic sectional view showing a thin-film photoelectric conversion device according to another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 glass substrate 2 transparent conductive oxide layer 3 p-type silicon layer 3 i i-type photoelectric conversion layer 3 n n-type silicon layer 4 buffer layer 5 metal layer

Claims (9)

[Claims] 1. A glass substrate having first and second main surfaces, a transparent conductive oxide layer formed on a first main surface of the glass substrate, and a transparent conductive oxide layer Comprising a photoelectric conversion unit formed thereon, and an electrode layer formed on the photoelectric conversion unit, the photoelectric conversion unit comprising: a p-type silicon layer formed on the transparent conductive oxide layer; An i-type photoelectric conversion layer substantially made of polycrystalline silicon formed on the p-type silicon layer; and an n-type silicon layer formed on the photoelectric conversion layer. In a thin film photoelectric conversion device of a type in which light is incident from a second main surface, an interface between the transparent conductive oxide layer and the p-type silicon layer is in a range of 0.1 μm or more and 0.5 μm or less. Thin-film photoelectric conversion including uneven surface with height difference Location. 2. The thin-film photoelectric conversion device according to claim 1, wherein an interface between the transparent conductive oxide layer and the p-type silicon layer includes an uneven surface having a height difference within a range of 0.2 μm or less. . 3. The thin film according to claim 1, wherein an interface between the n-type silicon layer and the electrode layer includes an uneven surface having a height difference within a range of 0.1 μm or more and 0.5 μm or less. Photoelectric conversion device. 4. The method according to claim 1, wherein the <110> direction of many crystal grains included in the photoelectric conversion layer is shifted within an angle range of 15 ° or less with respect to the thickness direction of the photoelectric conversion layer. The thin-film photoelectric conversion device according to any one of the above. 5. The photoelectric conversion layer has a volume crystallization fraction of 8
The thin-film photoelectric conversion device according to any one of claims 1 to 4, wherein the thin-film photoelectric conversion device is made of 0% or more of polycrystalline silicon and has a hydrogen content of 0.1 to 30 atomic%. 6. The electrode according to claim 1, wherein the electrode layer includes a buffer layer formed on the n-type silicon layer, and a metal layer formed on the buffer layer. The thin-film photoelectric conversion device as described in the above. 7. The thin-film photoelectric conversion device according to claim 6, wherein the buffer layer contains zinc oxide, and the metal layer contains silver. 8. The photoelectric conversion unit includes first and second photoelectric conversion units, wherein the first photoelectric conversion unit is formed on a p-type silicon layer and substantially on the p-type silicon layer. An i-type amorphous photoelectric conversion layer made of amorphous silicon; and an n-type silicon layer formed on the amorphous photoelectric conversion layer, wherein the second photoelectric conversion unit is p-type silicon. A layer, an i-type polycrystalline photoelectric conversion layer substantially made of polycrystalline silicon formed on the p-type silicon layer, and an n-type silicon layer formed on the polycrystalline photoelectric conversion layer. The thin-film photoelectric conversion device according to any one of claims 1 to 7, comprising: 9. The photoelectric conversion unit according to claim 8, wherein the photoelectric conversion unit includes the first photoelectric conversion unit and the second photoelectric conversion unit sequentially formed on the transparent conductive oxide layer. Thin film photoelectric conversion device.