JP2000357807A - Silicon-based thin-film photoelectric conversion device - Google Patents

Abstract

(57) Abstract: An object of the present invention is to increase the open-circuit voltage and the short-circuit current density of a silicon-based thin-film photoelectric conversion device, thereby improving the change efficiency. A back electrode (12), a one conductivity type layer (131) formed on the back electrode (12), a photoelectric conversion layer (132) made of a crystalline silicon-based thin film, and a reverse conductivity type layer (133). Silicon-based thin film photoelectric conversion unit (1)
3) and a transparent front electrode (15) formed on the photoelectric conversion unit (13). A passivation film (14) partially covering the underlayer (131) is formed between the one conductivity type layer (131) and the photoelectric conversion layer (132).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film photoelectric conversion device, and more particularly to improvement of performance such as conversion efficiency of a silicon-based thin-film photoelectric conversion device represented by a solar cell. In the specification of the present application, the terms “crystalline” and “microcrystal” also mean those partially including amorphous.

[0002]

2. Description of the Related Art In recent years, silicon-based thin-film photoelectric conversion devices using a thin film containing crystalline silicon such as polycrystalline silicon or microcrystalline silicon as a photoelectric conversion layer have been vigorously developed. These developments are mainly aimed at achieving both low cost and high performance of the photoelectric conversion device by forming a high-quality crystalline silicon thin film on an inexpensive substrate by a low-temperature process.

[0003] Such a silicon-based thin-film photoelectric conversion device generally includes a transparent front electrode provided on the light incident side, a silicon layer including a photoelectric conversion layer made of a one-conductivity-type layer and a crystalline silicon-based thin film, and a reverse-conductivity-type layer. A thin-film photoelectric conversion unit; and a back electrode provided on the side opposite to the front electrode with respect to the photoelectric conversion unit. Such silicon-based photoelectric conversion devices are expected to be applied not only to solar cells but also to various uses such as optical sensors.

It is known that the conversion efficiency of a silicon-based thin-film photoelectric conversion device is reduced due to various factors. For example, since the crystalline silicon-based photoelectric conversion layer has a small absorption coefficient with respect to light in a long wavelength region, when the photoelectric conversion layer is thin, it can sufficiently absorb light in a long wavelength region among incident light. And the amount of photoelectric conversion tends to decrease. In order to solve this, for example, a metal film having a high light reflectance is provided on the back side of the photoelectric conversion unit, and a surface unevenness (surface texture) structure is provided on the metal film. Light incident on the photoelectric conversion layer is irregularly reflected into the photoelectric conversion layer by the surface uneven structure, and light absorption by the photoelectric conversion layer is enhanced (light confinement effect). Such a surface uneven structure is
It may also be applied to the front electrode.

[0005]

Incidentally, in a photoelectric conversion device such as a silicon-based photoelectric conversion device, silicon atoms are excited in the photoelectric conversion layer by light incident through the front transparent electrode and the conductive type layer, so that the outermost is generated. It emits shell electrons and simultaneously generates holes. The generated holes and electrons are attracted to the respective conductive layers of the photoelectric conversion unit, and generate current.

However, a conductive type layer or a photoelectric conversion layer and a layer or a film adjacent thereto (for example, a back electrode or a conductive type layer)
At the interface with, there are relatively many impurities and defects, and at the interface, electrons are easily trapped by the impurities and defects and disappear. That is, the so-called diffusion length of the electrons is shortened, and the conversion efficiency is reduced. Conventionally, in silicon-based photoelectric conversion devices, little effort has been made to increase the diffusion length of electrons.

Accordingly, an object of the present invention is to increase the diffusion length of electrons generated by incident light in a silicon-based thin-film photoelectric conversion device, thereby improving photoelectric conversion efficiency.

[0008]

Means for Solving the Problems As a result of repeated studies to solve the above-mentioned problems, the present inventors have found that between the conductive type layer and the back surface electrode or between the conductive type layer and the silicon type thin film photoelectric conversion unit. It has been found that the intended purpose can be achieved by forming a passivation film partially covering (partially exposing) the underlying layer between the photoelectric conversion layer and the photoelectric conversion layer.

That is, according to the present invention, a back electrode,
A silicon-based thin-film photoelectric conversion unit that is provided on the front side of the back electrode and includes a one-conductivity-type layer, a photoelectric conversion layer made of a crystalline silicon-based thin film, and a reverse-conductivity-type layer; And a front transparent electrode,
Provided is a silicon-based thin-film photoelectric conversion device including a passivation film partially covering an underlayer between the back electrode and the one conductivity type layer or between the one conductivity type layer and the photoelectric conversion layer. Is done.

In the silicon-based thin-film photoelectric conversion device, the back electrode preferably includes a light-reflective metal film and a transparent conductive oxide film provided on the front surface thereof.

The silicon-based thin-film photoelectric conversion device may further include a passivation film partially covering the underlayer between the front electrode and the opposite conductivity type layer or between the opposite conductivity type layer and the photoelectric conversion layer. Can be.

In the present invention, the passivation film is
It is preferable to include silicon oxide or silicon nitride.

In this specification, the light incident side is called a front surface, and the opposite side is called a back surface. In the passivation film, the base layer refers to a layer or a film provided below the passivation film and in contact with the passivation film.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. The same parts are denoted by the same reference symbols throughout the drawings.

FIG. 1 is a schematic sectional view schematically showing a silicon-based thin-film photoelectric conversion device according to a first embodiment of the present invention. The photoelectric conversion device illustrated in FIG. 1 includes a silicon-based thin film photoelectric conversion unit having a so-called nip structure, and light enters from a side opposite to a substrate.

Referring to FIG. 1, a silicon-based thin-film photoelectric conversion device 10 includes a back electrode 12 and an n-type
Thin-film photoelectric conversion unit 13 including a p-type layer 133 having a conductivity type opposite to that of the n-type layer 131, the crystalline thin-film silicon-based photoelectric conversion layer 132, and the n-type layer; A passivation film 14 is provided between and the photoelectric conversion layer 132.

The substrate 11 can be made of a metal such as stainless steel, an organic film, ceramics, low-melting-point inexpensive glass, or the like.

In FIG. 1, the back electrode 12 is preferably formed of a light-reflective metal film 121 provided on the substrate 11 and a transparent conductive oxide film 122 formed thereon.
As a composite film including a two-layer structure.

The light-reflective metal film 121 has a thickness of 500 to 120.
It preferably has a high reflectance of 95% or more for light having a wavelength in the range of 0 nm. The light-reflective metal film 121 is formed of one selected from silver (Ag), gold (Au), aluminum (Al), copper (Cu), and platinum (Pt) or an alloy containing the same. Preferably, it can be formed as one or more layers. It is particularly preferable that at least the surface region of the light reflective metal film 121 is formed of a silver-based metal material made of silver or a silver alloy.

The light-reflective metal film 121 can be formed on the substrate 11 by a vapor deposition method such as vacuum evaporation or sputtering. For example, the Ag layer 121 having high light reflectivity can be formed on the glass substrate 11 by a vacuum evaporation method at a substrate temperature in the range of 100 to 330 ° C, more preferably 200 to 300 ° C.

In the present invention, the light-reflective metal film 121 is used.
Although the surface may have a flat surface, it has been found that the short-circuit current density can be further improved by having a surface uneven structure (surface texture structure) as shown in FIG. The concavo-convex structure on the upper surface of the light-reflective metal film 121 is formed by processing the surface of the substrate 11 into a concavo-convex structure in advance by etching or the like, and transmitting the concavo-convex structure to the upper surface of itself. Membrane 121
Can be obtained by forming Or,
After depositing a transparent conductive oxide film (not shown) having an uneven surface on the substrate 11, forming a thin light-reflective metal film 121 capable of transmitting the uneven structure to the upper surface of itself. Can also be obtained by

The difference in height of the unevenness in the surface uneven structure of the light-reflective metal film 121 is preferably in the range of 0.01 to 2 μm, and the pitch of the unevenness is preferably larger than the height difference and 25 times or less. More preferably, it is within the range of 4 to 20 times. In addition, such a surface uneven structure can be measured by a TEM (transmission electron microscope) photograph of a cross section of the light-reflective metal film 121 or a surface observation by an AFM (atomic force microscope).

In the surface uneven structure of the light-reflective metal film 121, if the height difference between the unevenness is too large with respect to the pitch, the angle between the concave portion and the convex portion becomes sharp, and the silicon-based photoelectric conversion unit deposited on the silicon photoelectric conversion unit The formation of the semiconductor junction does not work well, which causes a decrease in the open-circuit voltage and the manufacturing yield of the finally obtained photoelectric conversion device. That is, the light reflective metal film 12
There is an optimum value for the height difference and the pitch of the unevenness in the surface uneven structure of No. 1, and by giving a sufficient interval pitch to the unevenness of the unevenness to loosen the angle between the concave portion and the convex portion, a high opening is achieved. It has been found that an end voltage is obtained. That is, by using the light-reflective metal film 121 having a surface uneven structure including a height difference and a pitch as defined in the present invention, the light confinement effect can be achieved without lowering the open-end voltage and lowering the production yield. And a high-performance photoelectric conversion device can be obtained.

The transparent conductive oxide film 122 provided on the light-reflective metal film 121 may be a single layer or a multilayer. The transparent conductive oxide film 122 is made of indium.
It is preferably formed of at least one or more transparent conductive oxide materials selected from tin oxide (ITO), tin oxide (SnO ₂ ), zinc oxide (ZnO), and the like. Are more preferred.
It is particularly preferable that at least the surface region of the transparent conductive oxide film 122 which is in contact with the photoelectric conversion unit contains zinc oxide as a main component. The average crystal grain size of the transparent conductive oxide film 122 disposed adjacent to the photoelectric conversion unit 11 is preferably 100 nm or more. It is preferable to form the transparent conductive oxide film 122 by using the method described above. Note that the thickness of the transparent conductive oxide film 122 containing zinc oxide as a main component is preferably in the range of 50 nm to 1 μm, and the specific resistance thereof is preferably 1.5 × 10 ⁻³ Ωcm or less. preferable.

Incidentally, such a surface uneven structure can be measured by a TEM (transmission electron microscope) photograph of the cross section of the transparent conductive oxide film 122 or a surface observation by an AFM (atomic force microscope).

The silicon-based photoelectric conversion unit 13 formed on the back electrode 12 includes an n-type layer 131, a crystalline silicon-based thin-film photoelectric conversion layer 132, and a p-type layer 133.
All the semiconductor layers included in the photoelectric conversion unit 13 are subjected to plasma CV under a condition of a base temperature of 400 ° C. or less.
It can be deposited by D method. Plasma CVD
The method is generally well-known parallel plate type RF.
RF whose frequency is 150MHz or less, in addition to plasma CVD
C using high-frequency power supply from band to VHF band
VD can also be used.

N-type layer 131 formed on back electrode 12
For example, an n-type silicon-based thin layer doped with an n-type impurity such as phosphorus or nitrogen can be used. The material of the n-type layer 131 is not only amorphous silicon but also alloy materials such as amorphous silicon carbide and amorphous silicon germanium, and also polycrystalline or microcrystalline partially containing amorphous. Of silicon or its alloy material can also be used. If desired, by irradiating the deposited n-type layer 131 with a pulsed laser beam, the crystallization fraction and the carrier concentration due to the conductivity type determining impurity atoms can be controlled.

As the crystalline silicon-based photoelectric conversion layer 132 formed on the n-type layer 131, a non-doped genuine semiconductor polycrystalline silicon thin film, a microcrystalline silicon film having a volume crystallization fraction of 80% or more, or a trace amount A silicon-based thin film material having a weak p-type or weak n-type and sufficiently having a photoelectric conversion function can be used. However, the photoelectric conversion layer 132 is not limited thereto, and may be formed using an alloy material such as silicon carbide or silicon germanium.

The thickness of the photoelectric conversion layer 132 is equal to 0.1.
The thickness is preferably in the range of 5 to 20 μm, which is a necessary and sufficient film thickness as a crystalline silicon-based thin film photoelectric conversion layer. Further, since the crystalline silicon-based thin-film photoelectric conversion layer 132 is formed at a low temperature of 400 ° C. or lower, the crystalline silicon-based thin film photoelectric conversion layer 132 contains a large number of hydrogen atoms that terminate or inactivate defects in crystal grain boundaries or grains, and the hydrogen content is Preferably it is in the range of 1 to 30 atomic%. Furthermore, many of the crystal grains contained in the crystalline silicon-based thin-film photoelectric conversion layer 132 extend in a columnar manner from the underlayer and grow upward, and have a (110) preferential crystal orientation plane parallel to the film surface. The intensity ratio of the (111) diffraction peak to the (220) diffraction peak in the X-ray diffraction is preferably 0.2 or less.

The p formed on the crystalline photoelectric conversion layer 132
As the mold layer 133, for example, a p-type silicon-based thin film doped with a p-type impurity such as boron or aluminum can be used. In addition, as a material of the p-type layer 133, an alloy material such as amorphous silicon carbide or amorphous silicon germanium may be used in addition to amorphous silicon, and polycrystalline or partially amorphous is included. Microcrystalline silicon or its alloy material can also be used.

Here, the photoelectric conversion unit 13 to be deposited is
A surface texture structure including fine irregularities is formed on the upper surface 13A. This is due to the fact that the crystalline photoelectric conversion layer 132 included in the photoelectric conversion unit 13 naturally forms an uneven texture structure at the time of deposition thereof, whereby the upper surface 13A of the photoelectric conversion unit 13 has a wide wavelength range. A fine surface uneven texture structure more suitable for scattering incident light is obtained, and the light confinement effect in the photoelectric conversion device is also increased.

Now, according to the present invention, the back electrode 12 (more specifically, the transparent conductive oxide film 122) and the n-type layer 13
1, a passivation film 14 is formed so as to partially cover (partially expose) the underlying layer (in this example, the n-type layer 131). This passivation film 14 is preferably formed of silicon oxide (SiO _x ) or silicon nitride (SiN _x ). Such a passivation film is formed by a sputtering method, an evaporation method,
It can be formed by a known vapor deposition method such as a CVD method. For example, as a CVD method for depositing silicon oxide, a CVD method using a gas containing silane and oxygen can be exemplified. In addition, as a CVD method for depositing silicon nitride, CVD using a gas containing silane or silicon tetrachloride and ammonia is used.
The method can be illustrated.

The passivation film 14 is an n-type layer 131
The n-type layer is partially covered in order to secure the bonding between the n-type layer and the photoelectric conversion layer 132. For example, the n-type layer can be formed in a lattice pattern, a mesh pattern, or the like. The passivation film 14 having such a shape can be formed by using a mask having a shape corresponding to the shape at the time of vapor deposition. Note that the passivation film 14 made of silicon oxide is formed in an oxygen gas atmosphere by n
It can also be formed by selectively irradiating the mold layer 131 with a laser.

Since the passivation film 14 is preferably transparent, it is particularly preferable that the thickness of the passivation film 14 is 10 to 300 nm when it is made of silicon nitride.

Although the present invention is not limited by theory, by forming the passivation film 14 in this manner, the diffusion length of electrons in the photoelectric conversion layer 132 is increased, thereby shortening the short-circuit current density of the photoelectric conversion device. It is believed that the photoelectric conversion efficiency is improved because the open-circuit voltage is increased.

The transparent front electrode 15 formed on the photoelectric conversion unit 13 preferably includes one or more layers selected from ITO, SnO ₂ and ZnO.

Further, as a grid electrode on the transparent front electrode 15, a comb-shaped metal electrode preferably containing at least one or more metals selected from Al, Ag, Au, Cu and Pt, or a layer of an alloy thereof. 16 are formed.

In a preferred embodiment of the present invention, the p-type layer 1
33 and the transparent electrode 15, the passivation film 14
A second passivation film 17 similar to that described above is further formed. The second passivation film 17 also partially covers the underlying layer (p-type layer in this example). By further forming the second passivation film 17,
Conversion efficiency is further improved.

The silicon-based thin-film photoelectric conversion device 1 shown in FIG.
At 0, the light hν to be photoelectrically converted is emitted from the transparent front electrode 15 side.

FIG. 2 is a schematic sectional view schematically showing a silicon-based thin film photoelectric conversion device according to a second embodiment of the present invention. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the detailed description thereof will be omitted from the following description.

The silicon-based thin-film photoelectric conversion device 2 shown in FIG.
0 indicates that the passivation film 14 has n as in FIG.
It is provided not between the mold layer 131 and the photoelectric conversion layer 132 but between the back electrode 12 and the n-type layer 131 and that the back electrode 12 is constituted only by the light-reflective metal film 121. Except for this, it has the same structure as the photoelectric conversion device shown in FIG. In the photoelectric conversion device 20 shown in FIG. 2, the passivation film 14 is formed by partially forming the light-reflective metal film 121 in order to secure the connection between the base (the light-reflective metal film 121 in this example) and the n-type layer 131. It is formed so as to cover.

Although the embodiments of the present invention have been described with reference to FIGS. 1 and 2, the present invention is not limited to them. For example, the passivation film of the present invention can be applied to a photoelectric conversion device having a so-called pin type photoelectric conversion unit. In that case, a light-transmitting substrate is used as a substrate, a front electrode corresponding to the front electrode 15 is formed thereon, and a p-type layer corresponding to the p-type layer 133 and a photoelectric conversion layer 132 A conversion layer and an n-type layer corresponding to the n-type layer 131 are sequentially deposited, and a back electrode corresponding to the back electrode 12 (in this case, the transparent conductive oxide film 12).
First, a transparent conductive oxide film corresponding to 2 is formed first, and then a light-reflective metal film corresponding to the light-reflective metal film 121 is formed. A conversion device can be manufactured. In that case, a comb-shaped electrode is unnecessary. In the photoelectric conversion device having such a structure, the passivation film of the present invention is formed between the n-type layer and the back electrode or between the n-type layer and the photoelectric conversion layer.

[0043]

The present invention will be described below with reference to examples.

Example 1 In this example, a silicon-based thin film photoelectric conversion device having the structure shown in FIG. 1 was manufactured.

That is, first, a 300-nm-thick silver film 121 was deposited on the glass substrate 11 by vacuum evaporation.
Next, a zinc oxide layer 122 was deposited by an RF sputtering method using a zinc oxide target. The sputtering conditions at this time were as follows: Ar sputtering gas, 3 × 10 ⁻³
The pressure was Torr, the RF power density was 850 mW / cm ² , and the substrate temperature was 300 ° C. Obtained Zn
The O film 122 has an average particle size of 180 μm and 8.7 × 10
It had a specific resistance of ^-4 Ωcm.

Next, on the zinc oxide layer 122, a one-conductivity-type layer (n-type layer) 131 constituting the photoelectric conversion unit 13 was formed by a plasma CVD method, and then a passivation film 14 was formed. This passivation film 14 is made of Si
O ₂ was formed to a thickness of 30 nm at a substrate temperature of 200 ° C. by electron gun evaporation. At that time, using a mesh pattern having a vent pattern of 2mm square, the line width of each 2mm Kakuma in the mesh pattern, the line width for the base contact after SiO ₂ deposition (width between the SiO ₂ corner region) 0 .
It was 5 mm.

Next, a non-doped crystalline silicon-based photoelectric conversion layer 132 and a reverse conductivity type layer (p-type layer) 133 were formed on the passivation film 14 by a plasma CVD method. Non-doped crystalline silicon-based photoelectric conversion layer 132
Was formed to a thickness of 3.0 μm by RF plasma CVD at a base temperature of 300 ° C. In the crystalline photoelectric conversion layer 132, the hydrogen content determined by secondary ion mass spectrometry was 2.3 atomic%, and the intensity ratio of the (111) diffraction peak to the (220) diffraction peak in X-ray diffraction was 0%. 0.084.

Next, an ITO layer 14 was formed on the photoelectric conversion unit 13 as a front electrode, and a comb-shaped silver electrode 15 for extracting current was formed thereon.

The incident light h is applied to the photoelectric conversion device thus obtained.
When the output characteristics were measured by irradiating a light of AM 1.5 with a light amount of 100 mW / cm ² as ν, the open-circuit voltage was set to 0.
The short-circuit current density was 65 mA / cm ² , the fill factor was 77%, and the conversion efficiency was 13%.

Comparative Example 1 Example 1 was repeated except that no passivation film was formed.
In the same manner as in the above, a photoelectric conversion device was manufactured.

The incident light hν is applied to the obtained photoelectric conversion device.
100 mW / cm of AM1.5 light ^TwoIrradiate with the amount of light
When the output characteristics were measured, the open-circuit voltage was 0.55 V,
Short-circuit current density is 25.2 mA / cm^Two, The fill factor is 78
%, And the conversion efficiency was 10.8%.

Example 2 In this example, a silicon-based thin-film photoelectric conversion device having the structure shown in FIG. 2 was manufactured.

That is, a photoelectric conversion device was manufactured in the same manner as in Example 1 except that the passivation film 14 was formed on the silver electrode 121.

The incident light hν is applied to the obtained photoelectric conversion device.
100 mW / cm of AM1.5 light ^TwoIrradiate with the amount of light
When the output characteristics were measured, the open-circuit voltage was 0.6 V,
The fault current density is 26mA / cm^Two, The fill factor is 77.5
%, And the conversion efficiency was 12%.

[0055]

As described above, according to the present invention, the open-end voltage and the short-circuit current density of the silicon-based thin film photoelectric conversion device can be increased, and the change efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a crystalline silicon-based thin film photoelectric conversion device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating an amorphous / crystalline tandem silicon-based thin film photoelectric conversion device according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Substrate 12 ... Back surface electrode 13 ... Photoelectric conversion unit 14 ... Passivation film 15 ... Front electrode 16 ... Comb-shaped metal electrode 17 ... Second passivation film 121 ... Light reflective metal film 122 ... Transparent conductive oxide film 131 ... One conductivity type layer 132: photoelectric conversion layer 133: reverse conductivity type layer

Claims (4)

[Claims] A silicon-based thin-film photoelectric conversion unit provided on a front surface side of the back electrode and including a one-conductivity-type layer, a crystalline silicon-based thin film, and a reverse-conductivity-type layer; A front transparent electrode provided on the front side of the photoelectric conversion unit, and partially covering an underlayer between the back electrode and the one conductivity type layer or between the one conductivity type layer and the photoelectric conversion layer. A silicon-based thin-film photoelectric conversion device comprising a passivation film. 2. The silicon-based thin-film photoelectric conversion device according to claim 1, wherein the back electrode includes a light-reflective metal film and a transparent conductive oxide film provided on the front surface thereof. 3. The silicon-based thin-film photoelectric conversion device according to claim 1, further comprising a passivation film partially covering the underlayer between the front electrode and the opposite conductivity type layer. 4. The silicon-based thin-film photoelectric conversion device according to claim 1, wherein said passivation film contains silicon oxide or silicon nitride.