JP2704565B2 - Photoelectric conversion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device, and more particularly to a tandem type photoelectric conversion device applicable to a solar cell, a photosensor, a fluorescent lamp cell and the like.

[0002]

2. Description of the Related Art Various types of photoelectric sensing devices using a non-single-crystal silicon semiconductor layer have been known, but at present, the physical properties of the non-single-crystal silicon semiconductor layer have not been sufficiently elucidated.

A photoelectric conversion device using a non-single-crystal semiconductor absorbs light in the visible light region more than a photoelectric conversion device using a single-crystal semiconductor and a photoelectric conversion device using a polycrystalline semiconductor. Attention has been paid to its excellent photoelectric conversion efficiency under lighting.

A photoelectric conversion device using a non-single-crystal semiconductor is usually formed by decomposing and activating a silicon hydride gas such as silane or disilane in a plasma CVD device, and laminating a thin film on a substrate. You. Therefore, although various configurations have been proposed, a single cell in which a P-type semiconductor layer, an I-type semiconductor layer, and an N-type semiconductor layer are stacked, and a plurality of P-type semiconductor layers, I-type semiconductor layers, and N-type semiconductor layers are stacked. Tandem cells.

[0005] Among them, tandem cells have been attracting attention as a technique for increasing the efficiency because the material can be freely designed in accordance with the spectral sensitivity characteristics of the semiconductor itself for effective use of light.
FIG. 2 shows a representative example of this tandem photoelectric conversion device.
FIG. 2 has a low energy bandgap, eg, a-
A with a high energy band gap with a SiPIN device
2 shows a two-layer vertical series connection element (hereinafter referred to as a two-layer tandem cell) made using a SiPIN element.

In the figure, 1 is a conductive substrate, 2 is a P-type a
-Si layer, 3 is an I-type a-SiGe layer, 4 is an N-type a-Si
Layer, 5 is a P-type a-Si layer, 6 is an I-type a-Si layer, 7 is N
The type a-Si layer 8 is a transparent electrode.

In these device structures, light of a longer wavelength is collected by a photoelectric conversion device having a low energy band gap, and light of a shorter wavelength is collected by a photoelectric conversion device having a high energy band gap. It was intended to collect light, and to improve the photoelectric conversion efficiency by effectively utilizing light.

[0008]

It is known that a photoelectric conversion device using a non-single-crystal semiconductor as described above deteriorates with respect to light. That is, it is known that the efficiency of photoelectric conversion is reduced in accordance with the irradiation time due to light irradiated in actual use, and that the conversion efficiency is reduced by up to 30% or more by light irradiation for 1000 hours. I have. This is a major obstacle to the spread of photoelectric conversion devices using a non-single-crystal semiconductor layer, and it has been desired to improve the reliability of the light.

[0009]

Means for Solving the Problems The present invention solves the above-mentioned problems, and more particularly, a tandem-type cell for reducing a decrease in photoelectric conversion efficiency with respect to light. That is, a photoelectric conversion device having a tandem structure in which a plurality of photoelectric conversion devices are stacked over a substrate, wherein one I-type semiconductor layer included in the photoelectric conversion device is compared with another I-type semiconductor layer. Therefore, it has a narrow energy band gap, and this I-type semiconductor layer is provided on the light incident side. It has also been found that, at this time, when the thickness of the I-type semiconductor layer on the light incident side is smaller than the thickness of the other I-type semiconductor layers, the degree of deterioration with respect to light is reduced. This thickness is a thickness of 200 to 2000 °, and when the thickness is further increased, the conversion efficiency as a photoelectric conversion device decreases. Conversely, if the thickness is less than this range, the effect of preventing deterioration with respect to light is reduced. This is probably because the semiconductor film is not formed uniformly. Therefore, particularly preferably 300 to 100
The range of 0 ° was good.

Another method for solving this problem is a photoelectric conversion device having a tandem structure in which a plurality of photoelectric conversion devices are stacked on a substrate, wherein one of the photoelectric conversion devices included in the photoelectric conversion device is included. The I-type semiconductor layer has a lower hydrogen content than other I-type semiconductor layers, and is characterized in that the I-type semiconductor layer is provided on the light incident side. About 200-2000 similarly about thickness
The thickness range of Å, particularly preferably the range of 300 to 1000 良, was good. Techniques for reducing the amount of hydrogen include performing thermal annealing after forming a semiconductor film and reducing the amount of hydrogen during film formation, but are not particularly limited to a film forming method.

Still another method for solving the problem is a photoelectric conversion device having a tandem structure in which a plurality of photoelectric conversion devices are stacked on a substrate, wherein one of the photoelectric conversion devices included in the photoelectric conversion device is included. The I-type semiconductor layer is composed of a semi-amorphous semiconductor and is provided on the light incident side, and the other I-type semiconductor layer is composed of an amorphous semiconductor. In this case, the thickness range of 300 to 2500 ° was good.

When the semi-amorphous semiconductor is used, the thickness of the I-type semiconductor layer can be increased because the absorption coefficient for light is smaller than that of the amorphous semiconductor. Therefore, when a semiconductor film is formed by the plasma CVD method, the allowable range in the process technology is widened.

The semiconductor layer usable in the present invention includes a non-single-crystal silicon semiconductor, a semi-amorphous semiconductor, a silicon germanium semiconductor, a dehydrogenated non-single-crystal silicon semiconductor, a polycrystalline silicon semiconductor, and a crystallization-treated silicon semiconductor. Etc. are applicable.

The semi-amorphous semiconductor film of the present invention is LP
It can be obtained by performing a thermal crystallization treatment after forming a film by a CVD method, a sputtering method, a PCVD method, or the like.

That is, when a single-crystal silicon semiconductor is used as a target in the sputtering method and sputtering is performed with a mixed gas of hydrogen and argon, atomic silicon is separated from the target by sputtering (impact) of heavy atoms of argon, and the target is formed. While flying on a substrate having a surface, a cluster of tens to hundreds of thousands of atoms solidified at the same time leaves the target as a cluster and flies to the surface to be formed.

During the flight, hydrogen combines with the dangling bonds of silicon in the outer periphery of the cluster and forms a region having a relatively high order on the surface on which the cluster is formed.

That is, a mixture of pure amorphous silicon and clusters having high order and having Si—H bonds in the periphery is formed on the surface on which the film is formed. 450 ° C ~
By the heat treatment in a non-oxidizing gas at 700 ° C., the Si—H bonds around the cluster react with other Si—H bonds,
Create a Si-Si bond.

However, at the same time that the bonds are pulling together, the highly ordered clusters tend to shift to a more ordered state, ie crystallization. However, between adjacent clusters, Si-Si bonded to each other pulls between the clusters. As a result, the crystal has lattice distortion and the crystal peak in laser Raman is 52% of the single crystal.
It is measured shifted from 0 cm ^-1 to the lower wave number side.

Further, since the Si-Si bond between the clusters anchors (connects) each other, the energy band in each cluster may be electrically connected to each other via the anchoring portion. Therefore, it is fundamentally different from polycrystalline silicon in which a crystal grain boundary acts as a carrier barrier, and has a carrier mobility of 10 to ²⁰⁰ cm ² / VS.
ec can be obtained.

That is, as in the present invention, a semi-amorphous material based on such a definition can be expected to have a state in which although it has apparent crystallinity, there is substantially no crystal grain boundary.

Of course, instead of the intermediate temperature annealing of 450 ° C. to 700 ° C. in the case of a silicon semiconductor, when performing crystallization accompanied by crystal growth of 1000 ° C. or more, the crystal growth causes Breaks out at the grain boundaries and creates a barrier. This is a material having the same crystal and grain boundaries as a single crystal.

When the degree of anchoring between clusters in the semiconductor is increased, the carrier mobility is further increased. For this purpose, the amount of oxygen in this film is reduced by 7 ×
When it is set to 10 ¹⁹ cm ^−3, preferably 1 × 10 ¹⁹ cm ⁻³ or less, crystallization can be performed at a temperature lower than 600 ° C., and high carrier mobility can be obtained.

In the present invention, in order to solve the above-mentioned problems, the present invention is constituted singly or in combination of respective techniques. For example, in a tandem cell, when the I-type semiconductor layer on the light incident side is a dehydrogenated a-Si semiconductor and the other is a normal a-Si semiconductor, the dehydrogenated a-Si semiconductor is used.
Has a narrower energy band than ordinary a-Si semiconductors. At this time, the dehydrogenated a-Si semiconductor may have a semi-amorphous structure.

The semiconductor layers other than the I-type semiconductor layer constituting the tandem cell do not need to be particularly limited in their characteristics, and any semiconductor layer can be used. However, due to limitations in manufacturing technology, it is advantageous to form the individual PIN semiconductor layers from the same material in terms of manufacturing steps, costs, and the like.

[0025]

The present invention having the above-described structure is effective in preventing a decrease in the photoelectric conversion efficiency of the photoelectric conversion device with respect to light, and is provided with a conventional tandem for effective use of light. The problems, configurations and effects to be solved are different. That is, the energy band gap of the I-type semiconductor layer on the light incident side is reduced, the amount of hydrogen is reduced, a semi-amorphous semiconductor is used, and the like.
This is completely different from the conventional technical idea.

As a photoelectric conversion device to which the present invention can be applied, not only a two-layer tandem but also a three-layer or four-layer tandem-type photoelectric conversion device can be applied. Further, the present invention can be similarly applied to a photoelectric conversion device having an integrated structure in which individual photoelectric conversion devices are connected in series.

[0027]

Embodiment 1 FIG. 1A is a schematic view of a photoelectric conversion device of this embodiment. 1.1 mm thick glass substrate 1 as substrate
0 was used. On this upper surface, a tin oxide light-transmitting conductive film is formed as a first electrode 11. Plasma C
A P-type semiconductor SixC _1-x (0 <X <1 about 200 ° thick) 12-I-type silicon semiconductor (600 ° thick) 13-N-type microcrystalline silicon semiconductor 14 doped with hydrogen by a VD method is known in the art. And the first photoelectric conversion device 15 was formed.

After this step, an ultra-high pressure mercury lamp (output 5K)
W) wavelength light of 600 nm or more is cut by a filter,
The first photoelectric conversion device 15 was irradiated with a wavelength of 250 to 600 nm. This irradiation light is condensed by a cylindrical quartz lens, and is received as a slit-like strong light having a width of 3 mm and a length of 10 cm on the surface to be irradiated. ~ 50
cm / min). The substrate temperature is from room temperature to 400 ° C., for example, 21
0 ° C. Then, the crystallinity of the N-type microcrystalline semiconductor in the first photoelectric conversion device was obtained, and a crystallized layer could be grown in a columnar (columnar) shape in the I-type semiconductor. This crystallization is due to SixC _1-x (0 <X <
Blocked here because of 1).

Next, on this N-type semiconductor 14, a P-type semiconductor (SixC _1-x 0 <X <1 average thickness 100 °) 16
The hydrogen-added I-type silicon semiconductor 17 (thickness 3000)
Å) (The impurities such as boron and oxygen are each 1 atomic% or less.) A second photoelectric conversion device 19 made of an N-type microcrystalline semiconductor 18 (400 Å in thickness) is formed. Then, Ag and Cr were formed to a thickness of 3000 ° as reflective electrodes 20 ′ on the upper surface thereof to complete a tandem-type photoelectric conversion device.

As a result, since the I-type semiconductor layer of the second photoelectric conversion device mainly has an amorphous structure, hydrogen is reduced to 1%.
0 to 20 atomic%, and the optical energy bandwidth is 1.7
1.8 eV. On the other hand, the I-type semiconductor of the first photoelectric conversion device mainly has a polycrystalline structure, and can have an optical Eg of 1.4 to 1.6 eV, and the difference of Eg is 0.15 to 0. .4 eV. Fig. 1 shows an example of the corresponding energy band diagram.
It is shown in (B).

The fabricated photoelectric conversion device (area: 1.05 c
The characteristic of m ² ) is that the open circuit voltage is 1.69 V and the short circuit current is 7.
The photoelectric conversion efficiency was 9.26% with a fill factor of 7A / cm ² and a fill factor of 74.6%. FIG. 3 shows the IV characteristics of this photoelectric conversion device.

Further, for this photoelectric conversion device, AM
FIG. 4 shows the result of measuring the degree of photodeterioration upon irradiation with 1.5 (100 nW / cm ² ) light for a long time. FIG. 4 shows, for comparison, the degree of light deterioration of the conventional single cell and the state of deterioration of the photoelectric conversion device in which the thickness of the I-type semiconductor layer on the light incident side of the tandem cell of the present invention is changed. Curve 21
Is the data of the present embodiment, and curve 22 indicates that the thickness of the I-type semiconductor layer on the light incident side of the tandem cell of the present invention is 1000 °.
, And a curve 23 indicates data in the case of a conventional photoelectric conversion device. Obviously, in the case of the present invention, deterioration with respect to light is small. Further, it can be seen that the degree of deterioration is further reduced when the thickness of the I-type semiconductor layer on the light incident side is reduced.

[0033]

Embodiment 2 FIG. 5 shows a photoelectric conversion device according to this embodiment. A glass substrate 10 having a thickness of 1.1 mm was used as a substrate. On this upper surface, a tin oxide light-transmitting conductive film is formed as a first electrode 11. On this upper surface, a P-type semiconductor 12 having a thickness of about 200 ° -I-type semiconductor (thickness 500 °) 1 is formed by sputtering.
A 3-N-type semiconductor 14 was formed, and a first photoelectric conversion device was provided.

The conditions for the formation are such that the back pressure before sputtering is 1 ×
The test was performed at a pressure of 10 ⁻⁵ Pa or less, using single crystal silicon as a target, and in an atmosphere in which hydrogen was mixed with 20 to 80% of argon. For example, argon was 20% and hydrogen was 80%. The film formation temperature was 150 ° C., the frequency was 13.56 MHz, and the sputter output was 400 to 800 W. The pressure was 0.5 Pa. Also, the impurities that determine the P-type and N-type conductivity types have been doped in the target.

The coatings formed by these methods are:
Oxygen is 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³
The concentration is preferably ¹⁹ cm ⁻³ or less. When the silicon film is crystallized in such a range,
This is because the degree of crystallization can be promoted.

For example, as an impurity concentration in SIMS (Secondary Ion Mass Spectroscopy), oxygen is 8 × 10 ¹⁸ c
m ⁻³ , 3 × 10 ¹⁶ cm ⁻³ of carbon, and 4% of hydrogen.
× 10 ²⁰ cm ⁻³ and silicon 4 × 10 ²² cm ^−3.
Was 1 atomic%.

Thus, the amorphous silicon film is
After manufacturing to a thickness of 2,000 mm to 2 μm, for example, 1 μm,
Medium-temperature heat treatment was performed in a non-oxide atmosphere at a temperature of 50 to 700 ° C. for 12 to 70 hours. For example, it was kept at a temperature of 600 ° C. in a nitrogen or hydrogen atmosphere.

Since a silicon oxide film in an amorphous state is formed on the surface of the substrate below the silicon film, no specific nucleus is present in the silicon film by this heat treatment, and the entire silicon film is annealed uniformly. That is, it has an amorphous structure at the time of film formation, and hydrogen is simply mixed therein.

By this annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film exhibits a crystalline state. In particular, a region having a relatively high order at the time of forming a silicon film is particularly likely to be crystallized to be in a crystalline state. However, since the silicon existing between these regions is bonded to each other, silicon mutually pulls each other. When the crystal is measured by laser Raman spectroscopy, a peak shifted from the single crystal silicon peak 522 cm ⁻¹ to a lower frequency side is observed. Calculated from the half width, the apparent particle size is 50 to 500 °, which is like a microcrystal. However, in actuality, there are a large number of regions having high crystallinity and a cluster structure. It was possible to form a film having a semi-amorphous structure in which silicon mutually bonded (anchored) each other.

As a result, the coating exhibits a state substantially free of grain boundaries (GB). Carriers can easily move from one cluster to another through the anchored locations between the clusters, so-called GB
Carrier mobility higher than that of polycrystalline silicon that clearly exists. That is, hole mobility (μh) = 10 to 200 cm
² / Vsec, electron mobility (μe) = 15 to 300 cm
² / Vsec is obtained. Similarly, the carrier diffusion length is several μm to several tens μm, which is equivalent to or larger than that of the polycrystalline semiconductor.

On the other hand, when the film is polycrystallized by high-temperature annealing at a temperature of 900 to 1200 ° C. instead of annealing at a medium temperature as described above, segregation of impurities in the film occurs due to solid phase growth from nuclei. GB has many impurities such as oxygen, carbon, and nitrogen, and has high mobility in the crystal.
In this case, a barrier is formed, and the movement of carriers there is hindered. And as a result, 10 cm ² / Vs
Actually, it is difficult to obtain a mobility higher than ec.

That is, in the embodiment of the present invention, as described above, a silicon semiconductor having a semi-amorphous structure is used.

Next, chromium silicide 25 is formed as a transparent electrode between the second photoelectric conversion device and the first photoelectric conversion device. This electrode allows plasma C between the N-type semiconductor of the first photoelectric conversion device and the P-type semiconductor layer of the second photoelectric conversion device.
It is possible to prevent impurities from being mixed during film formation by the VD method, and to efficiently flow generated power.

Next, a P-type semiconductor (SixC _1-x 0 <X <1 average thickness 100 °) ₁ is formed on the transparent electrode 25.
6-I-type silicon semiconductor 17 doped with hydrogen (thickness 300
0 [deg.]) (Impurities such as boron and oxygen are each 1 atomic% or less). A second photoelectric conversion device 19 made of an N-type microcrystalline semiconductor 18 (thickness 400 [deg.]) Is formed. Then, Ag and Cr were formed to a thickness of 3000 ° as reflective electrodes 20 ′ on the upper surface thereof to complete a tandem-type photoelectric conversion device.

The fabricated photoelectric conversion device (area: 1.05 c
The characteristic of m ² ) is that the open-circuit voltage is 1.60 V and the short-circuit current is 7.
7A / cm ² , fill factor of 75.6%, photoelectric conversion efficiency of 9.31%, and degradation rate against light of 100 hours A
It was 4.6% by irradiation with M1.5.

In this embodiment, oxygen, carbon,
Since the nitrogen concentration was reduced, the reliability against heat and the long-term reliability were improved.

[0047]

According to the structure of the present invention, the rate of decrease in the photoelectric conversion efficiency of the photoelectric conversion device due to irradiation with light is significantly reduced as compared with the conventional case. As a result, the reliability has been improved, and practical use has been approached.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of a photoelectric conversion device of the present invention.

FIG. 2 shows a schematic diagram of a conventional photoelectric conversion device.

FIG. 3 shows IV characteristics of the photoelectric conversion device of the present invention.

FIG. 4 shows measurement results of light degradation.

FIG. 5 shows another embodiment of the present invention.

[Explanation of symbols]

 10 substrate 13 I-type semiconductor layer 15 first photoelectric conversion device 19 second photoelectric conversion device 25 chrome silicide

Claims (2)

(57) [Claims] 1. A photoelectric conversion device having a tandem structure in which a plurality of photoelectric conversion devices are stacked on a substrate, I-type semiconductor layer of one contained in one of the photoelectric conversion device, imaging
Composed of crystalline semiconductor and provided on the light incident side
The other I-type semiconductor layers are composed of amorphous semiconductors.
A photoelectric conversion device characterized by being formed . 2. The semiconductor having crystallinity according to claim 1.
The I-type semiconductor layer having a thickness of 300 to 2500 degrees .