JPH0645622A - Solar cell and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a crystal solar cell provided with a window layer effect without using a heterogeneous material by a method wherein porous silicon, of a second conductivity type, to be used as a light-incident layer is laminated on crystal silicon of a first conductivity type. CONSTITUTION:Impurities are introduced into the surface of a silicon wafer by a thermal diffusion operation, an ion implantation operation or the like, and a first crystal silicon layer 101c is formed. Then, the surface on the side into which the impurities have been introduced of the wafer is anodically formed in an HF solution, and a second porous crystal silicon layer 103c is formed. A transparent conductive film 105c and a collector electrode 105a are formed on it, an electrode 106c is formed on the rear and a solar cell is formed. Consequently, the crystal silicon layer 101c and the porous silicon layer 103c of an opposite conductivity type are formed on the surface of crystal silicon, the porous silicon layer 103c functions as a good window layer, and the solar cell whose photoelectric conversion efficiency is high can be manufactured. Consequently, a good-quality crystal solar cell provided with mass productivity can be put on the market.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell and a method of manufacturing the same, and more particularly to a crystalline solar cell which exhibits good characteristics at a low cost and a method of manufacturing the same.

[0002]

2. Description of the Related Art In various devices, solar cells are used as a driving energy source.

A solar cell uses a pn junction in its functional portion, and silicon is generally used as a semiconductor forming the pn junction. The forms of silicon used as a semiconductor include single crystal, polycrystalline and amorphous.
Amorphous silicon is considered to be advantageous in terms of large area and cost reduction, but single crystal silicon is preferable in terms of efficiency and stability of converting light energy into electromotive force, and thus low cost single crystal silicon. Solar cells are strongly desired.

High-efficiency solar cells made of single crystal silicon have been actively developed in recent years, and conversion efficiencies exceeding 20% have been realized (A.W. Blackers).
and M.D. A. Green, Applied Phy
sics Letters, vol. 48, p215,
1986; A. Sinton, Y .; Kwalk,
J. Y. Gand and R. M. Swanson, I
EEE Electron Device Letter
rs, vol. EDL-6, p567, 1986;
Saitoh, T .; Uematsu, Y .; Kida,
K. Matsukuma and K.M. Morita,
Proceedings of 19th IEEE P
photovoltaic Specialists C
onference, pl518, 1987).

In these high-efficiency solar cells, high-quality single crystal wafers are used and the IC manufacturing process is used to improve the performance. That is, these high-efficiency solar cells are characterized by using a high-quality FZ wafer, which has a long lifetime of minority carriers, as a substrate and suppress surface reflection of incident light to confine light inside the crystal, Introducing structures and processes that reduce the recombination loss of.

However, a complicated process and time are required to suppress the reflection of incident light to increase the capture rate and to reduce the recombination loss of generated carriers on the crystal surface.
There is a problem in mass production. Using high-priced, high-quality wafers also makes the transition to mass production difficult.

On the other hand, from the light absorption coefficient of single crystal silicon and the diffusion length of minority carriers, it has been shown that sufficient conversion efficiency can be obtained if the crystal thickness is 100 μm (E. Fabre and C. Belouet, Pr
ocedings of 15th IEEE Ph
autovoltaic Specialists Co
nference, p. 654, 1981). In reality, since the wafer has an excessive thickness, conversely, the generated minority carriers recombine while diffusing in the crystal and the photocurrent decreases.Therefore, attempts have been made to reduce the thickness of the silicon wafer of the substrate. However, since the mechanical strength is lost as the film thickness is reduced, the wafer itself cannot be made too thin.

Further, when the film is thinned, the required crystal diffusion length is equal to or more than the film thickness, and therefore it is not necessary to use an expensive FZ substrate. In addition, optical confinement effect and BSF (Back Surface Field)
d) It is possible to make the film thickness 10 to 50 μm by using the structure together, and there are advantages such as effective use of resources, weight reduction, and reduction of characteristic deterioration due to temperature rise of the solar cell due to infrared absorption. Occurs. However, heretofore, such a solar cell having a sufficiently thin film and high efficiency has not been realized.

On the other hand, in recent years, the use of polycrystalline silicon has been studied for the purpose of obtaining a low cost like amorphous silicon and a high energy conversion efficiency like single crystal silicon. However, the method proposed hitherto is very similar to the case of single crystal silicon, and it is difficult to make the thickness 0.3 mm or less in order to slice a massive polycrystal into a plate-like body and use this. Therefore, the thickness is more than necessary to fully absorb the amount of light, and in this respect, the material is not effectively used. That is, it is necessary to make the device sufficiently thin in order to reduce the cost. Recently, a method of forming a silicon sheet by a method of pouring molten silicon droplets into a mold has been proposed, but the thickness is at least 0.1.
The thickness is about mm to 0.2 mm, and the thickness is still insufficient as compared with the film thickness (20 to 50 μm) necessary for absorbing light as crystalline silicon.

Therefore, it has been proposed to try to achieve high energy conversion efficiency and cost reduction by separating (peeling) a thin film epitaxial layer grown on a single crystal silicon substrate from the substrate and using it in a solar cell. (M
ilnes, A .; G. and Feucht, D.M.
L. , "Peeled Film Technology"
ySolar Cells ”, IEEE Photov
oltaic Specialist Confere
nce, p. 338, 1975).

However, according to this method, an intermediate layer of SiGe is inserted between the single crystal silicon serving as a substrate and the growth epitaxial layer for heteroepitaxial growth, and this intermediate layer is further selectively melted to form a growth layer. Need to be peeled off. Generally, when heteroepitaxial growth is performed, defects are likely to be induced at the growth interface because the lattice constants are different. In addition, it cannot be said that it is advantageous in terms of process cost because different materials are used.

In addition, U.S.P. S. Pat. No. 4,81
No. 6,420, that is, a sheet-shaped crystal is formed on a crystal substrate through a mask material by selective epitaxial growth and lateral growth, and then separated from the substrate. It was shown that a thin crystalline solar cell was obtained by the manufacturing method.

However, in this method, the opening provided in the mask material is line-shaped, and in order to separate the sheet-shaped crystal grown by selective epitaxial growth and lateral growth from this line seed, the crystal cleavage is performed. When the shape of the line seed is larger than a certain size because it is mechanically peeled off, the area of contact with the substrate is large, so that the sheet crystal is damaged during the peeling. Especially when increasing the area of a solar cell, no matter how narrow the line width (actually around 1 μm), the line length is several mm.
The above method becomes practically difficult when the size is up to several cm or more.

In addition, SiO ₂ is used as a mask material.
An example in which a silicon thin film is grown by selective epitaxial growth and lateral growth at a substrate temperature of 00 ° C. is shown. At such a high temperature, the reaction between the growing silicon layer and SiO ₂ results in silicon layer / SiO ₂ A considerable stacking fault (plane defect) may be introduced on the silicon layer side near the interface. There is a problem that such a defect has a great adverse effect on the characteristics of the solar cell.

In a conventional solar cell using crystalline silicon, a pn junction is generally formed in the bulk, so that the p ⁺ layer (or n ⁺ layer) on the light incident side is naturally a silicon layer. However, it is more important that such a light-incident layer functions as a window layer rather than functioning as a power generation layer, and in this respect it is better to use a material having a smaller light absorption coefficient than silicon. It is advantageous.

Therefore, a method has been proposed in which a heterojunction is formed by depositing a different material, a-SiC, on the surface of crystalline silicon, rather than forming a pn junction in the bulk.

However, although conventional a-SiC is usually formed by the plasma CVD method, the doping efficiency is poor, it is difficult to make the conductivity 10 ⁻² S / cm or more, and ion damage from plasma is generated during formation. Is easily affected by the above and it is difficult to obtain a good a-SiC / silicon interface. For this reason, sufficiently satisfactory solar cell characteristics have not been realized.

In order to solve this point, ECR (Elec
tron Cyclotron Resonance)
Studies have been conducted to form a good heterojunction solar cell by depositing μc-SiC using the plasma method (Y.M.
atsumoto, G .; Hirata, H .; Takak
ura, H .; Okamoto and Y. Hamak
awa, Journal of App1ied Ph
ysics, 67 (1990) p. 6538). However, this method has a problem in that the apparatus is complicated and mass productivity is high.

On the other hand, if the window layer effect can be provided by silicon itself without using different materials, it is advantageous in terms of process.

[0020]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to provide a high-efficiency crystal solar cell which can be mass-produced and a method of manufacturing the same.

That is, an object of the solar cell of the present invention is to provide a solar cell having good characteristics by making the silicon layer itself have a window layer effect.

Further, a high quality solar cell is provided by using a thin single crystal semiconductor, and an inexpensive solar cell is provided by forming a high quality crystalline silicon layer on a metal substrate such as a SUS substrate. The purpose is to do.

Further, the present invention provides a method for manufacturing a thin film single crystal solar cell having good characteristics.

[0024]

The present invention has been completed as a result of earnest research by the present inventors in order to achieve the above object.

A first aspect of the present invention is a solar cell characterized in that a second conductive type porous silicon serving as a light incident layer is laminated on a first conductive type crystalline silicon. To do.

The second gist of the present invention resides in a solar cell characterized in that porous silicon is formed on the first crystalline silicon or metal substrate, and second crystalline silicon is further laminated thereon. .

The third gist of the present invention is i) the step of forming a porous layer on one surface of the first crystalline silicon by anodization, and ii) the second crystalline silicon on the porous layer. A solar cell, comprising: a forming step; iii) texturing the surface of the second crystalline silicon; and iv) forming a semiconductor junction on the surface of the second crystalline silicon. Exist in the manufacturing method.

Further, the fourth gist of the present invention is that i) a step of forming a porous layer on one surface of the first crystalline silicon by anodization, and ii) forming conditions at the end of the formation of the porous layer. Alternately, electropolishing to separate the porous layer from the first crystalline silicon; iii) fixing the porous layer to a metal substrate; and iv) crystal growth method on the metal substrate. A method for manufacturing a solar cell, comprising: a step of forming second crystalline silicon on the porous layer; and v) forming a semiconductor junction on the surface of the second crystalline silicon. To do.

[0029]

The structure of the solar cell of the present invention is shown in FIGS. 1 (a) and 1 (b).
2 and 3 and 4 show the respective manufacturing processes.

In FIGS. 1A and 2, 101a,
201 is crystalline silicon of the first conductivity type, 103a, 203
Is a second conductive type porous silicon layer, 104a, 204
Is a transparent conductive layer, 105a and 205 are collecting electrodes, and 106
Reference numerals a and 206 denote back surface electrodes, and 202 denotes a second conductivity type layer.

In FIG. 2, impurities are introduced into the surface of the silicon wafer by thermal diffusion or ion implantation,
A bond is formed (FIG. 2A). Next, the surface of the wafer on which impurities are introduced is made porous by anodization in an HF solution (Fig. 2 (b)), and a transparent conductive film and a collecting electrode are formed on the surface, and an electrode is formed on the back surface to form a solar cell. A battery is used (FIG. 2 (c)).

The light absorption coefficient of porous silicon is considerably smaller than that of crystalline silicon (H. Koyama).
and N.M. Koshida, Extended A
btracts of the l991 Inte
national Conference on S
Old State Devices and Ma
terials, Yokohama, 1991, pp.
314). Therefore, by forming a porous silicon layer having a conductivity type opposite to that of the crystalline silicon on the surface of the crystalline silicon, the porous silicon layer functions as a favorable window layer and a solar cell with high photoelectric conversion efficiency can be manufactured. Becomes

In FIG. 1 (b) and FIG. 3, 101b,
303 is a metal substrate, 102b and 302 are porous silicon layers, 103b and 304 are second crystalline silicon layers, and 104.
b and 305 are crystalline silicon of the opposite conductivity type to 103b and 304, 105b and 306 are transparent conductive films, 106b and 3
Reference numeral 07 is a collector electrode, and 301 is crystalline silicon.

In FIG. 3, the surface of the silicon wafer is exposed to H
In the F solution, it is made porous by anodization (Fig. 3 (a)),
At the end of the formation of the porous layer, the HF concentration in the solution is lowered to increase the formation current and the electropolishing mode is set to remove only the porosity near the porous layer / wafer interface by etching to separate the porous layer from the wafer. (FIG. 3B). Next, the separated porous layer is placed on the metal substrate and fixed (see FIG. 3).
(C)), a silicon layer is grown on the porous layer by epitaxial growth (FIG. 3 (d)), and a junction is formed on the surface of the silicon layer to obtain a solar cell (FIG. 3 (e),
(F)).

In FIGS. 1C and 4, 101c,
401 is first crystalline silicon, 102c and 402 are porous silicon layers, 103c and 403 are second crystalline silicon layers, 104c and 404 are crystalline silicon of opposite conductivity type to 103c and 403, and 105c and 405 are transparent conductive films. 1
06c and 406 are collector electrodes.

In FIG. 4, the surface of the silicon wafer is exposed to H
In the F solution, it is made porous by anodization (Fig. 4 (a)),
A silicon layer is laminated thereon by epitaxial growth, or a porous layer and another silicon wafer are attached to each other to grind and polish the silicon wafer into a thin film silicon layer (FIG. 4 (b)). A solar cell is formed by forming a junction after texturing (FIGS. 4C to 4E).

In FIGS. 3 and 4, the interface between the porous layer and the second crystalline silicon layer grown thereon is the surface of the silicon layer at the portion where holes are formed on the porous layer side as shown in FIG. Is in contact with air, and the reflection of light at this portion is larger than that when an oxide film is attached to the silicon surface. Therefore, light can be effectively confined between the porous layer and the surface of the silicon layer, and the light confinement effect can be further enhanced by controlling the diameter and number density of the holes on the porous surface. Therefore, the thickness of the silicon layer is 100μ
It can be m or less.

An anodizing method is preferably used for forming the porous layer of the present invention.

The formation of porous silicon by anodization requires holes for the anodic reaction, so that it is said that the p-type silicon in which holes are mainly present is used to make the porous (T. Unagami, J. Electrochem.
Soc. , Vol. 127, 476 (1980)). However, on the other hand, there is also a report that low resistance n-type silicon is made porous (RP Holmstrom a.
nd J. Y. Chi, Appl. Phys. Let
t. , Vol. 42, 386 (1983)), regardless of whether it is p-type or n-type, low resistance silicon can be used to make it porous.
Also, depending on the conductivity type, it can be made porous selectively.
IPOS (Full Isolation Por)
It is possible to make only the p-layer porous by performing anodization in a dark place like the ous Oxidized Silicon process.

The porous silicon obtained by anodizing the single crystal silicon has a thickness of several nm when observed with a transmission electron microscope.
Holes having a diameter of about the same are formed, and the density thereof is less than half that of single crystal silicon. Nevertheless, single crystallinity is maintained, and it is possible to grow an epitaxial layer on porous silicon by the LPCVD method or the like.

Even if polycrystalline silicon is used instead of single crystal silicon, a porous layer can be similarly obtained by anodization. A crystalline silicon layer can be grown thereon by the LPCVD method or the like (in this case, partial epitaxial growth corresponding to the size of the crystal grains of polycrystalline silicon is possible).

As described above, the present inventor has conducted repeated experiments and found that a favorable window layer can be formed by changing the conductivity type of the surface of crystalline silicon to form a porous silicon layer. The knowledge that the layer is separated from the wafer and adhered on the metal substrate to obtain an epitaxial layer on it, and the silicon formed on the porous silicon layer by controlling the size and number density of holes on the surface. The present invention has been completed based on the finding that the light confinement effect can be further enhanced in the layer. The experiment conducted by the present inventors will be described in detail below.

(Experiment 1) Formation of Porous Silicon A p-type (100) single crystal silicon wafer having a specific resistance of 0.01 Ωcm and a thickness of 500 μm was anodized in an HF aqueous solution. Table 1 shows anodization conditions.

[0044]

[Table 1] When the surface of the obtained porous silicon layer was observed with a transmission electron microscope, pores having an average diameter of about 6 nm were formed. Also, when the cross section of the porous silicon layer was observed with a high resolution scanning electron microscope, it was confirmed that minute holes were similarly formed in the direction perpendicular to the substrate.

Further, when the anodization time was extended under the conditions of Table 1 to increase the thickness of the porous silicon layer and the density was measured, the density of the porous silicon layer was 1.1 g / c.
It was found to be m ³ , which was about half that of single crystal silicon.

Further, the time for the anodization is increased to increase the thickness of the porous layer, and the current density is increased at the end of the anodization to separate the porous layer from the wafer by electrolytic etching. The absorption coefficient was measured. As a result, the light absorption coefficient of porous silicon is about ⅙, 900 for light with a wavelength of 500 nm compared to that of crystalline silicon.
It was about 1/5 the size of light having a wavelength of nm. (Experiment 2) Making the Impurity Introduction Layer Porous After introducing impurities into the surface of the wafer, the portion was made porous. 25 B was deposited on the surface of an n-type (100) single crystal silicon wafer having a specific resistance of 1 Ωcm and a thickness of 500 μm.
Perform 1 × 10 ¹⁵ cm ^-2 ion implantation with KeV, and
0 ℃, 1hour / 800 ℃, 30min / 550 ℃,
Continuous annealing was performed under the condition of 1 hur for activation of impurities and recovery of damage due to ion implantation to form a junction. The surface of the ion-implanted wafer is exposed to H
Anodization was performed in an F aqueous solution. Table 2 shows anodization conditions
Shown in. At this time, anodization was performed in the dark.

[0047]

[Table 2] When the cross section of the wafer surface after the chemical conversion was observed with a high resolution scanning electron microscope, it was observed that the same porous silicon layer as in Experiment 1 was formed. The thickness of the porous layer was about 200 nm. Further, when the distribution of B in the depth direction was examined by secondary ion mass spectrometry, the junction depth was about 200 nm, and it was confirmed that the porosification by anodization was completed in the p layer. .

(Experiment 3) Formation of Solar Cell A solar cell was produced using the single crystal wafer obtained in Experiment 2 on the surface of which a porous silicon layer was provided.

A transparent conductive film (IT0) also serving as an antireflection film and a grid-shaped collector electrode are vacuum-deposited on the surface of the porous layer, and a metal serving as an ohmic electrode is vacuumed on the surface of the wafer opposite to the porous layer. It vapor-deposited and produced the solar cell.
The solar cell AM1. 5 (100
mW / cm ²⁾ was subjected to measurement for the current - voltage characteristics under light irradiation (I-V characteristic), the open-circuit voltage 0.60V in cell area 6 cm ^2, short-circuit photoelectric current 36 mA / cm ^2, a fill factor 0. 74, the conversion efficiency was 15.9%, and a good crystalline solar cell with high conversion efficiency was obtained.

As a reference, in Experiment 2, when the junction was formed by ion implantation and the solar cell was not made porous, the open circuit voltage was 0.58 V and the short-circuit photocurrent was 34 mA.
/ Cm ² , fill factor 0.77, conversion efficiency 15.2%. As described above, it was confirmed that the use of the porous layer as the window layer improved the characteristics, in particular, increased the photocurrent.

The present invention completed based on the above experimental results relates to a crystalline solar cell obtained by forming regions of different conductivity types on a silicon wafer and making them porous as described above. It is a thing.

A feature of the present invention is that the porous layer is used as a light window layer and more light is supplied to the power generation layer.

(Experiment 4) Epitaxial growth method on porous silicon Epitaxial growth was performed on the porous silicon layer on the wafer formed in Experiment 1 by a normal low pressure CVD method (LPCVD method). SiH ₂ Cl ₂ was used as a raw material, and H ₂ was added as a carrier gas. Table 3 shows the growth conditions at this time.

[0054]

[Table 3] When the state of the crystal growth surface after the growth was observed with an optical microscope and a scanning electron microscope, a flat surface was obtained and the thickness of the epitaxial layer was about 50 μm. When the cross section of the growth layer was observed with a transmission electron microscope, it was confirmed that it was a single crystal epitaxial layer having good crystallinity.

(Experiment 5) Solar cell formation A solar cell was produced using the epitaxial silicon on the porous layer obtained in Experiments 1 and 4.

The surface of the epitaxial layer was anisotropically etched by immersing the substrate in a KOH aqueous solution to form a texture structure having a height between valleys and peaks of about several μm. Next, P is applied to the surface of the epitaxial layer provided with the texture structure with 50 Ke.
Ion implantation is performed at V, 1 ^× 10 ¹⁵ cm ⁻² , and 550
℃, 1hour / 800 ℃, 30min / 550 ℃, 1
Continuous annealing was performed under the condition of the hour, and activation of impurities and recovery of damage due to ion implantation were performed to form a junction. Finally, a grid-shaped collector electrode and a transparent conductive film that also serves as antireflection were vacuum-deposited on the surface of the epitaxial layer to fabricate a solar cell.

AMl. Of a solar cell using the epitaxial thin film thus grown on the porous layer. 5 (100
mW / cm ²⁾ under light irradiation current - Measurements for voltage characteristics (I-V characteristic), open at the cell area 6 cm ² Voltage 0.61 V, the short circuit photocurrent 35 mA / cm ^2, a fill factor 0. 76, the conversion efficiency was 16.2%, and a good crystalline solar cell with high conversion efficiency was obtained.

(Experiment 6) Porosity forming conditions and solar cell characteristics The pore size and number density of the porous layer were changed by changing the anodizing conditions to check the correlation with the solar cell characteristics.

First, the formation current during the anodization of the substrate wafer was changed. Under the conditions shown in Table 1 of Experiment 1, the current density was 5
varied from mA / cm ² until 125 mA / cm ² was observed how the holes of the porous layer surface with high resolution scanning electron microscope.

As a result, it was found that the size of the holes increased as the current density increased, but the number density of the holes did not change (Table 4).

[0061]

[Table 4] Further, in the above, when the substrate wafer was formed similarly with the specific resistance of 1 Ω · cm, the number density increased, and when the current density was 3 mA / cm ² , the hole diameter was 2.5 nm and the number density was 2 × 1.
A value of 0 ¹² / cm ² was obtained. Thus, the diameter and number density of the holes on the surface of the porous layer can be controlled by changing the chemical conversion conditions.

Next, a solar cell was formed on the porous layer produced above in the same manner as in Experiments 4 and 5, and changes in the characteristics were measured. Table 5 shows the substrate wafer with a specific resistance of 0.01 Ω · cm
The change of the photocurrent of a solar cell when changing the formation current density using (p type) is shown.

[0063]

[Table 5] As the formation current increases, so does the photocurrent of the solar cell. In the case where a substrate wafer having a specific resistance of 1 Ω · cm and a porous layer formed with a formation current of 3 mA / cm ² under the conditions shown in Table 1, the solar cell produced had a photocurrent of 34 mA / cm ² . These results are due to the fact that the light reflection from the holed portion on the porous layer side increases at the interface between the porous layer and the epitaxial silicon layer, and the optical confinement is effectively performed in the epitaxial silicon layer. is there.

As a reference, when a solar cell was manufactured on a substrate wafer having a specific resistance of 0.01 Ω · cm in the same manner as in Experiments 4 and 7 (without a porous layer), the photocurrent was 32 mA /
It was cm ² .

The present invention, which has been completed based on the results of Experiments 1 and 4 to 6 described above, forms a porous layer on a wafer and a silicon layer on the porous layer as described above. The present invention relates to a crystalline solar cell obtained and a method for manufacturing the same. A feature of the present invention is that a porous layer is used as a light reflecting layer and a high quality wafer such as an FZ wafer is not required.

(Experiment 7) Separation of Porous Layer and Fixation on Metal Substrate In Experiment 1, the time was extended under the conditions of Table 1 to form a porous layer of about 100 μm, and in the formation aqueous solution at the end of the formation of the porous layer. When the HF concentration of was reduced to about 1% and the formation current density was increased to 150 mA / cm ² to enter the electropolishing mode, the formed porous layer was separated from the wafer.

The separated porous layer was placed on a Cr substrate having a thickness of 1 mm and adhered thereto, and then annealed at a temperature of 1100 ° C. for 2 hours in an N ₂ atmosphere to perform bonding. The layer was affixed to a Cr substrate.

[0068] When the interfacial sticking porous layer / Cr substrate was cross-sectional observation with a transmission electron microscope, CrSi ₂ in the interface
It was confirmed that the silicide layer of was formed.

(Experiment 8) Formation of Solar Cell Based on the results obtained in Experiments 1, 4, and 7, a solar cell was produced using epitaxial silicon on a metal substrate / porous layer.

Epitaxial growth was performed on the porous silicon layer on the Cr substrate obtained in Experiment 7 by the ordinary LPCVD method under the conditions shown in Table 3.

50 Ke on the surface of the epitaxial layer
Ion implantation was performed at V, 1 × 10 ¹⁵ cm ^-2 and 550
℃, 1hour / 800 ℃, 30min / 550 ℃, 1
Continuous annealing was performed under the condition of the hour, and activation of impurities and recovery of damage due to ion implantation were performed to form a junction. Finally, a transparent conductive film also serving as an antireflection film and a grid-shaped collector electrode were vacuum-deposited on the surface of the epitaxial layer to fabricate a solar cell.

AMl. Of the solar cell using the epitaxial thin film thus grown on the porous layer. 5 (100
mW / cm ²⁾ was subjected to measurement for the current - voltage characteristics under light irradiation (I-V characteristic), the open-circuit voltage 0.52V in cell area 6 cm ^2, short-circuit photocurrent 31 mA / cm ^2, a fill factor 0. 73, the conversion efficiency was 11.8%, and a good crystalline solar cell was obtained.

As described above, the present invention completed based on the results of Experiments 1 and 4 to 6 described above forms a porous layer on a wafer and separates (separates) the porous layer from the wafer. )
The present invention relates to a thin film crystal solar cell obtained by using an epitaxial layer fixed on a metal substrate and grown on the porous layer, and a manufacturing method thereof.

The characteristics of the present invention are that the characteristics equivalent to those of the epitaxial layer on the wafer can be obtained by using the epitaxial layer on the porous layer, and the wafer forming the porous layer can be reused. That is, it is advantageous.

A hydrofluoric acid solution is used in the anodization method for forming the porous silicon layer used in the present invention.
When the F concentration is 10% or more, it can be made porous. The amount of electric current applied during anodization is appropriately determined depending on the HF concentration, the desired thickness of the porous layer, the state of the surface of the porous layer, etc., but it is generally several mA / cm ² to several tens mA / cm ² . The range is appropriate.

Further, by adding an alcohol such as ethyl alcohol to the HF solution, the bubbles of the reaction product gas generated during the anodization can be removed from the reaction surface without instantaneously stirring, and the porous silicon can be uniformly and efficiently produced. Can be formed. The amount of alcohol to be added is appropriately determined depending on the HF concentration, the desired film thickness of the porous layer or the surface state of the porous layer, and it is necessary to carefully determine so that the HF concentration does not become too low.

The conductivity type of the surface layer of the wafer to be made porous may be p-type or n-type, but in the case of p-type in particular, anodization is performed in the dark to automatically complete the formation. It is possible.

On the contrary, in the case of electropolishing for the purpose of separating the porous layer from the wafer after forming the porous layer, the HF concentration is set to several% or less and the formation current is 100 mA / cm 2.
Must be ² or more.

LPCVD is an epitaxial growth method used for forming a silicon layer on a porous layer in the present invention.
Method, sputtering method, plasma CVD method, photo CVD method or liquid phase growth method.

For example, as the source gas used in the vapor phase growth method such as the LPCVD method, the plasma CVD method or the photo CVD method, SiH ₂ Cl ₂ , SiCl ₄ , SiHC is used.
Representative examples include silanes such as l ₃ , SiH ₄ , Si ₂ H ₆ , SiH ₂ F ₂ , and Si ₂ F ₆ and halogenated silanes.

H ₂ is added as a carrier gas or in addition to the above-mentioned source gas for the purpose of obtaining a reducing atmosphere for promoting crystal growth. The ratio of the amounts of the raw material gas and hydrogen is appropriately determined according to the formation method, the type of the raw material gas and the formation conditions, and is preferably 1: 1.
0 or more and 1: 1000 or less (introduction flow rate ratio) is appropriate,
More preferably, the ratio is 1:20 or more and 1: 800 or less.

When the liquid phase growth method is used, Si is dissolved in a solvent such as Ga, In, Sb, Bi or Sn in an atmosphere of H ₂ or N ₂ and the solvent is gradually cooled or a temperature difference is set in the solvent. Epitaxial growth is performed by turning on. When Sn is used as the solvent, the obtained crystal is electrically neutral, and the conductivity type can be determined at a desired doping concentration by appropriately adding a desired impurity after or during the growth.

The temperature and pressure in the epitaxial growth method used in the present invention vary depending on the forming method, the type of the raw material gas used, the flow rate ratio of the raw material gas and H _2, and the like. In the general LPCVD method, a temperature of 600 ° C or higher and 1250 ° C or lower is suitable, and more preferably 650 ° C or higher and 1200 ° C.
It is desirable to be controlled below. In the case of the liquid phase growth method, it depends on the kind of the solvent, but when Sn is used, it is desirable to control the temperature to 850 ° C. or higher and 1050 ° C. or lower. Further, in a low temperature process such as plasma CVD method, the temperature is generally 200 ° C. or higher 60
0 ° C or lower is suitable, and more preferably 200 ° C or higher and 5
It is desirable to control the temperature below 00 ° C.

Similarly, the pressure is about 10 ^-2 Torr.
〜760 Torr is suitable, more preferably 10 ^-1
A range of Torr to 760 Torr is desirable.

In the solar cell of the present invention, as the metal substrate material for fixing the porous silicon layer, any metal having good conductivity and forming a compound such as silicon and a silicide is used. , Cr and alloys thereof. Of course, any other material may be used as long as the metal having the above-mentioned properties is attached to the surface thereof, and thus an inexpensive substrate other than the metal can be used. The thickness of the silicide layer is not particularly limited, but is preferably 0.01 to 0.2 μm.

As another method of forming a silicon layer on the porous layer in the present invention, another surface of the silicon wafer is superposed on the surface of the porous layer and bonded by heat treatment, and then the silicon wafer is ground. It can also be obtained by making it thinner. The heat treatment condition at this time is 1 in N ₂ atmosphere.
30 minutes to several hours is suitable at 000 ° C or higher.

In the solar cell of the present invention, the texture treatment formed on the surface of the silicon layer for the purpose of reducing the reflection loss of incident light is performed using hydrazine, NaOH, KOH or the like. The height of the textured pyramid is suitably in the range of several μm to several tens of μm.

The depth of the junction formed in the solar cell of the present invention depends on the amount of impurities to be introduced, but is not more than 0.
The range of 05 to 3 μm is suitable, and the range of 0.1 to 1 μm is preferable.

[0089]

EXAMPLES Hereinafter, the method for forming a desired solar cell according to the present invention will be described in more detail, but the present invention is not limited to these examples.

Example 1 As described above, Experiments 1 to 3
A porous silicon / single crystal silicon solar cell was manufactured by the process shown in FIG.

On the surface of a 500 μm thick n-type (100) silicon wafer (ρ = 1 Ωcm), BCl ₃ was used as a diffusion source to thermally diffuse B at a temperature of 950 ° C. to form a p ⁺ layer,
A junction depth of about 0.5 μm was obtained.

The dead layer formed on the surface of the p ⁺ layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm (FIG. 2 (a)).

Next, the surface of the p ⁺ layer was anodized in an HF aqueous solution under the conditions shown in Table 2 in the dark to form a porous silicon layer on the wafer (FIG. 2 (b)).

Finally, EB (Electron Beam)
ITO transparent conductive film (82 nm) / collector electrode (Ti / Pd / Ag (400 nm / 200 nm / 1 μ) by vapor deposition
m)) on the porous layer and Ti / Cr as the back electrode.
(400 nm / 1 μm) was formed on each back surface of the wafer (FIG. 2C).

Thus obtained porous silicon /
Crystalline silicon solar cells AMl. 5 (100 mW
/ Cm ² ) It was measured for IV characteristics under light irradiation, and when the cell area was 6 cm ² , the open circuit voltage was 0.61 V, the short circuit photocurrent was 36.4 mA / cm ² , and the fill factor was 0.76.
An energy conversion efficiency of 16.9% was obtained.

As described above, by using the porous silicon layer formed on single crystal silicon as the window layer, a thin film crystal solar cell exhibiting good characteristics could be manufactured.

Example 2 In the same manner as in Example 1, a solar cell was prepared by forming a porous layer on the surface of a textured wafer.

A 500 μm thick n-type (100) silicon wafer (ρ = 3 Ωcm) was dipped in a hydrazine aqueous solution at 110 ° C. and 60% concentration for 10 minutes to form a textured structure having irregularities of about several μm on the surface of the wafer.

Next, thermal diffusion of B was performed on the textured surface using BCl ₃ as a diffusion source at a temperature of 950 ° C. to obtain p ⁺
A layer was formed to obtain a junction depth of about 0.5 μm. The dead layer formed on the surface of the p + layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm. The surface of the p ⁺ layer was anodized in an HF aqueous solution under the conditions shown in Table 2 in the dark to form a porous silicon layer on the textured wafer. After that, P is 50 KeV, 1x by ion implantation on the back surface of the wafer.
Ion implantation is performed at 10 ^l5 cm ^-2 and 550 ° C for 1 h.
continuous annealing at our / 750 ° C., 2 hours for n ⁺
Layers were formed.

Further, EB (Electron Beam)
ITO transparent conductive film (82 nm) / collector electrode (Ti / Pd / Ag (400 nm / 200 nm / 1 μ) by vapor deposition
m)) on the porous layer and Ti / Cr as the back electrode.
(400 nm / 1 μm) was formed on each back surface of the wafer.

Regarding the crystalline silicon solar cell obtained as described above, AMl. When the IV characteristics were measured under 5 (100 mW / cm ² ) light irradiation, the open area voltage was 0.62 V and the short-circuit photocurrent was 36.5 m when the cell area was 6 cm ^2.
A / cm ² and a fill factor of 0.76 were obtained, and an energy conversion efficiency of 17.2% was obtained.

(Example 3) In the same manner as in Examples 1 and 2,
Porous silicon / polycrystalline silicon thin film solar cells were prepared using polycrystalline silicon wafers.

A 500 μm thick n-type polycrystalline silicon wafer (ρ = 2 Ωcm; crystal grain size of several mm to several tens of mm) was immersed in a boiling 1% aqueous NaOH solution for about 5 minutes to texture the surface of the silicon layer. Then, B was thermally diffused on the textured surface using BCl ₃ as a diffusion source at a temperature of 950 ° C. to form a p ⁺ layer, and a junction depth of about 0.5 μm was obtained. The formed dead layer on the surface of the p ⁺ layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm. HF on the surface of p ⁺ layer
Anodization was performed in an aqueous solution in the dark under the conditions shown in Table 2 to form a porous silicon layer on the textured polycrystalline wafer. After that, P is ion-implanted on the back surface of the wafer at 50 KeV and 1 × 10 ¹⁵ cm ^-2 , and 550 ° C., 1 hour / 750 ° C., 2 hours.
Continuous annealing was performed at r to form an n ⁺ layer.

Further, EB (Electron Beam)
IT0 transparent conductive film (82 nm) / collecting electrode (Ti / Pd / Ag (400 nm / 200 nm / 1μ)
m)) on the porous layer and Ti / Cr as the back electrode.
(400 nm / 1 μm) was formed on each back surface of the wafer.

Thus obtained porous silicon /
Regarding polycrystalline silicon solar cells AMl. 5 (100 m
W / cm ² ) The IV characteristics under light irradiation were measured, and when the cell area was 6 cm ² , the open voltage was 0.58 V, the short-circuit photocurrent was 35.8 mA / cm ² , the fill factor was 0.75, and the energy conversion efficiency was 15.6% was obtained.

As a reference, the short-circuit photocurrent of the solar cell when the p ⁺ layer was not made porous was 30.5.
It was mA / cm ² .

As described above, a crystalline solar cell exhibiting excellent characteristics could be manufactured by using the structure in which the porous layer was formed on the polycrystalline silicon wafer.

(Embodiment 4) In the same manner as in Embodiment 1, n ⁺
A porous silicon / single crystal silicon solar cell having a / p / p ⁺ structure was produced.

On the surface of a 500 μm thick p-type (100) silicon wafer (ρ = 1 Ωcm), PO n ₃ was used as a diffusion source to thermally diffuse P at a temperature of 900 ° C. to form an n ⁺ layer. Got the junction depth of. N ⁺ formed
The dead layer on the layer surface was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm.

Next, the surface of the n ⁺ layer was anodized in a HF aqueous solution under the conditions of Table 6 under light irradiation to form a porous silicon layer on the wafer.

[0111]

[Table 6] Finally, on the porous layer, EB (Electron Bea
m) ITO transparent conductive film (82 nm) / collector electrode (Ti / Pd / Ag (400 nm / 200 nm / 1μ) by vapor deposition
m)), and an Al paste was printed on the back surface of the wafer as a back surface electrode and annealed to form ap ⁺ layer between the back surface electrode and the wafer by an alloying reaction.

The porous silicon thus obtained /
Crystalline silicon solar cells AMl. 5 (100 mW
/ Cm ² ) The IV characteristics under irradiation with light were measured, and when the cell area was 6 cm ² , the open voltage was 0.61 V, the short-circuit photocurrent was 36.8 mA / cm ² , and the fill factor was 0.75.
An energy conversion efficiency of 16.8% was obtained.

As described above, according to the present invention, it was shown that a good solar cell can be manufactured by using the porous silicon layer formed on the wafer as the window layer.

Example 5 As described above, Experiments 1 and 4
A porous / epitaxial silicon thin film solar cell was produced by the process shown in FIG.

A 500 μm thick p-type (100) silicon wafer (ρ = 0.01 Ω · cm) was anodized in an HF aqueous solution under the conditions shown in Table 7 to form a porous silicon layer on the wafer (FIG. 4). (A)).

[0116]

[Table 7] Epitaxial growth was performed on the surface of the porous silicon layer by a normal LPCVD apparatus under the formation conditions shown in Table 3 so that the film thickness of the silicon layer was about 50 μm (FIG. 4B).

The surface of the epitaxial silicon layer formed by immersing the substrate in a boiling 1% aqueous solution of NaOH for about 5 minutes was textured (FIG. 4 (c)). Next, POCl ₃ is used as a diffusion source on the surface of the epitaxial layer to form 900
Thermal diffusion of P is performed at a temperature of ℃ to form an n ⁺ layer,
A junction depth of about μm was obtained. The formed dead layer on the surface of the n ⁺ layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm (FIG. 4 (d)).

Finally, EB (Electron Beam)
Current collecting electrode (Ti / Pd / Ag (400 nm /
200 nm / 1 μm)) / ITO transparent conductive film (82n
m) was formed on the n ⁺ layer (FIG. 4E).

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristic was measured under irradiation with 5 (100 mW / cm ² ) light, the open area voltage was 0.62 V and the short circuit photocurrent was 37.4 when the cell area was 6 cm ^2.
It was mA / cm ² and a fill factor of 0.77, and an energy conversion efficiency of 17.9% was obtained.

Using the epitaxial layer thus formed on the porous layer, a thin film crystal solar cell exhibiting high conversion efficiency could be manufactured.

(Embodiment 6) In the same manner as in Embodiment 5, p ⁺ n
A thin crystalline solar cell was produced. N-type (1
00) HF silicon wafer (ρ = 0.01Ω · cm)
Anodization was performed in an aqueous solution under the conditions shown in Table 7 to form a porous silicon layer on the wafer.

An epitaxial silicon layer was grown on the porous layer to a thickness of about 100 μm by the LPCVD apparatus under the formation conditions shown in Table 3 with a growth time of 120 minutes. Wafer 11
Soak for 10 minutes in 0 ° C, 60% aqueous hydrazine solution,
The surface of the epitaxial layer was textured.

Then, BCl ₃ is thermally diffused at a temperature of 950 ° C. using BCl ₃ as a diffusion source on the surface of the epitaxial layer to obtain p ^+.
A layer was formed to obtain a junction depth of about 0.5 μm. After the wet oxidation, the dud layer on the surface of the formed p ⁺ layer was removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm.

Further, the surface of the epitaxial layer is thinly oxidized by dry oxidation (-10 nm), the oxide film is etched into a fine grid shape by the photolithography method, and a collector electrode (Ti / Pd) is formed on the oxide film by a metal mask.
/ Ag (400 nm / 200 nm / 1 μm)) was deposited. Finally, an ITO transparent conductive film (82n
m) was formed.

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristics were measured under 5 (100 mW / cm ² ) light irradiation, the open area voltage was 0.65 V and the short circuit photocurrent was 37.5 at a cell area of 6 cm ^2.
mA / cm ² and a fill factor of 0.76 were obtained, and an energy conversion efficiency of 18.5% was obtained.

Example 7 A porous / silicon thin-film solar cell was produced using a polycrystalline silicon wafer in the same manner as in Examples 5 and 6.

500 μm thick p-type polycrystalline silicon wafer (ρ = 0.02 Ω · cm; crystal grain size of several mm to several tens of mm)
Was anodized in a HF aqueous solution under the conditions shown in Table 8 to form a porous silicon layer on the wafer.

[0128]

[Table 8] A silicon film was grown on the surface of the porous silicon layer by a normal LPCVD apparatus under the formation conditions shown in Table 3 with a growth time of 120 minutes to a thickness of about 100 μm. The crystal grain size of the silicon layer at this time was several mm to several tens of mm, and the crystallinity of the substrate was maintained.

The surface of the silicon layer was textured by immersing the substrate in a boiling 1% aqueous solution of NaOH for about 5 minutes, and then thermal diffusion of P was performed on the surface of the epitaxial layer at a temperature of 900 ° C. using POCl ₃ as a diffusion source. Then, an n ⁺ layer was formed to obtain a junction depth of about 0.5 μm. N formed
The dead layer on the ⁺ layer surface was wet-oxidized and then removed by etching to obtain a junction depth with an appropriate surface concentration of about 0.2 μm.

Further, the surface of the silicon layer is thinly oxidized by dry oxidation (~ 10 nm), the oxide film is etched into a fine grid shape by a photolithography method, and a collector electrode (Ti / Pd / Ag
(400 nm / 200 nm / 1 μm)) was deposited. Finally, an ITO transparent conductive film (82 nm) was formed thereon.

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. 5 (100mW / cm ²⁾ was measured for the I-V characteristic under irradiation with light, open-circuit voltage 0.603V in cell area 6 cm ^2, short-circuit photoelectric current 34.
It became ² mA / cm ² and a fill factor of 0.76, and an energy conversion efficiency of 15.7% was obtained.

Thus, a thin film crystal solar cell exhibiting high conversion efficiency could be manufactured by using the silicon layer formed on the porous layer of polycrystalline silicon.

(Embodiment 8) n ⁺ as shown in FIG.
A p-type thin film crystal solar cell was produced using a liquid phase growth method.

In the same manner as in Example 5, a 500 μm thick p-type (100) silicon wafer (ρ = 0.01 Ω · cm) was anodized in an aqueous HF solution under the conditions shown in Table 7, and porous silicon was formed on the wafer. Layers were formed.

Epitaxial growth was performed by the liquid phase growth method under the conditions shown in Table 9 to grow an epitaxial layer of about 45 μm. At this time, Sn was used as a solvent, and S
After Si was dissolved in n to saturate it, gradual cooling was started, and when it reached a certain degree of supersaturation, the surface of the porous layer of the wafer was dipped in an Sn solution and grown for a predetermined time.

[0136]

[Table 9] The substrate is soaked in a boiling 1% aqueous NaOH solution for about 5 minutes to texture the surface of the silicon layer, and then POCl ₃ is used as a diffusion source on the surface of the epitaxial layer for 900 minutes.
Thermal diffusion of P is performed at a temperature of ℃ to form an n ⁺ layer,
A junction depth of about μm was obtained. The formed dead layer on the surface of the n + layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm.

Finally, EB (Electron Beam)
Collection electrode (Ti / Pd / Ag (40 nm / 2
0 nm / 1 μm)) / ITO transparent conductive film (82 nm) was formed on the n ⁺ layer.

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristics were measured under irradiation with 5 (100 mW / cm ² ) light, the open circuit voltage was 0.59 V and the short-circuit photocurrent was 36.6 at a cell area of 1 cm ^2.
It became mA / cm ² and a fill factor of 0.75, and an energy conversion efficiency of 16.2% was obtained.

Example 9 A silicon thin film solar cell was produced by bonding porous silicon and a silicon wafer together.

A 500 μm thick p-type single crystal silicon wafer A (ρ = 0.01 Ω · cm) was anodized in an HF aqueous solution under the conditions shown in Table 7 to form a porous silicon layer on the wafer.

A p-type single crystal silicon wafer B of ρ = 5 Ω · cm was superposed on the surface of the porous silicon layer, and heat treatment was performed in an N ₂ atmosphere at 1050 ° C. for 2 hours to perform bonding.

Of the bonded substrates, the wafer B was ground by grinding to leave a residual film thickness of 100 μm.

The surface of the silicon layer which has been soaked in a boiling 1% aqueous NaOH solution for about 5 minutes and ground is textured, and then POCl ₃ is used as a diffusion source on the surface of the silicon layer to thermally diffuse P at a temperature of 900 ° C. Then, an n ⁺ layer was formed to obtain a junction depth of about 0.5 μm. N ⁺ formed
The dead layer on the layer surface was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm. Further, the surface of the silicon layer is thinly oxidized by dry oxidation (~ 10 nm), the photolithography method is used to etch the oxide film into a fine grid shape, and a metal mask is formed on the oxide film (Ti / Pd / Ag).
(400 nm / 200 nm / 1 μm)) was deposited. Finally, an lTO transparent conductive film (82 nm) was formed thereon.

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristics were measured under 5 (100 mW / cm ² ) light irradiation, the open circuit voltage was 0.67 V and the short circuit photocurrent was 38.1 when the cell area was 6 cm ^2.
It became mA / cm ² and a fill factor of 0.77, and an energy conversion efficiency of 19.7% was obtained.

As described above, a thin film crystal solar cell exhibiting high conversion efficiency could be manufactured by using the silicon layer formed by bonding on the porous layer of polycrystalline silicon.

As described above, according to the present invention, it is shown that a high-efficiency solar cell can be manufactured by a simpler process than before using a silicon layer formed on porous silicon formed on a wafer. It was

Example 10 As described above, Experiment 1,
A metal substrate / porous layer / epitaxial silicon thin film solar cell was produced by the process shown in FIG. 3 in the same manner as 4, 7, and 8.

A 500 μm thick p-type (100) silicon wafer (ρ = 0.01 Ωcm) was anodized in an HF aqueous solution under the conditions shown in Table 10 to form a porous silicon layer on the wafer (FIG. 3 (a). )).

[0149]

[Table 10] At the end of formation of the porous silicon layer, the HF concentration of the chemical conversion solution was lowered to 1% and the chemical conversion current was increased to 100 mA / cm ² to separate the porous layer from the wafer (FIG. 3).
(B)).

The separated porous layer was placed on a SUS substrate on which Cr was vapor-deposited to have a thickness of 100 nm and adhered thereto, and then annealed at 1100 ° C. for 2 hours in an N ₂ atmosphere to fix the layer (FIG. 3).
(C)). Then, on top of the adhered porous layer, normal LPC
Under the formation conditions shown in Table 3, the VD apparatus was used to extend the growth time to grow an epitaxial silicon layer to about 100 μm (FIG. 3 (d)).

Next, on the surface of the epitaxial layer, POCl ₃
N as a diffusion source by performing thermal diffusion of P at a temperature of 900 ° C.
^{A +} layer was formed to obtain a junction depth of about 0.5 μm. The formed dead layer on the surface of the n ⁺ layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm (FIG. 3 (e)).

Finally, EB (Electron Bea)
m) collector electrode (Ti / Pd / Ag (400n
m / 200 nm / 1 μm)) / ITO transparent conductive film (82
nm) was formed on the n ⁺ layer (FIG. 3 (f)).

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristics were measured under 5 (100 mW / cm ² ) light irradiation, the open circuit voltage was 0.52 V and the short circuit photocurrent was 33.8 when the cell area was 6 cm ^2.
It became mA / cm ² and a fill factor of 0.75, and an energy conversion efficiency of 13.2% was obtained.

As described above, a thin film crystal solar cell exhibiting excellent characteristics could be manufactured by using the epitaxial layer formed on the metal substrate / porous layer.

(Embodiment 11) As in Embodiment 10, p
^{A +} n thin crystalline solar cell was produced. H-type 500 μm thick n-type (100) silicon wafer (ρ = 0.01 Ωcm)
Anodization was performed in a F aqueous solution under the conditions of Table 10 under light irradiation to form a porous silicon layer on the wafer.

At the end of formation of the porous silicon layer, the HF concentration of the chemical conversion solution was reduced to 1% and the conversion current was 100 mA.
/ Cm ² and the porous layer was separated from the wafer.
The separated porous layer was placed on a SUS substrate on which Mo was vapor-deposited to a thickness of 100 nm and adhered thereto, and then, at 1100 ° C. in an N ₂ atmosphere.
It was annealed for a period of time and fixed. An LPCVD apparatus was used to grow the epitaxial silicon layer on the porous layer to a thickness of about 80 μm under the formation conditions shown in Table 3 while extending the growth time. After growth, the surface of the epitaxial silicon layer was textured with a 60% strength aqueous hydrazine solution.

Next, BCl ₃ is thermally diffused on the surface of the epitaxial layer at a temperature of 950 ° C. using BCl ₃ as a diffusion source to p ^+.
A layer was formed to obtain a junction depth of about 0.5 μm. The formed dead layer on the surface of the p ⁺ layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm. Current collector electrode (Ti / P
d / Ag (400 nm / 200 nm / 1 μm) is vapor-deposited, and finally an ITO transparent conductive film (820 n
m) was formed.

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristics were measured under irradiation with 5 (100 mW / cm ² ) light, the open area voltage was 0.53 V and the short-circuit photocurrent was 35.5 when the cell area was 6 cm ^2.
It was mA / cm ² and a fill factor of 0.74, and an energy conversion efficiency of 13.9% was obtained.

Example 12 A metal / porous / silicon thin film solar cell was prepared using a polycrystalline silicon wafer in the same manner as in Examples 10 and 11.

500 μm thick p-type polycrystalline silicon wafer (ρ = 0.02 Ω · cm; crystal grain size of several mm to several tens of mm)
Was subjected to anodization in an HF aqueous solution under the conditions shown in Table 11 to form a porous silicon layer on the wafer.

[0161]

[Table 11] When the formation of the porous silicon layer was completed, the HF concentration of the chemical conversion aqueous solution was dropped to 1% and the chemical conversion current was increased to 200 mA / cm ² to separate the porous layer from the polycrystalline wafer. The separated porous layer was placed on a SUS substrate on which Cr was vapor-deposited to a thickness of 100 nm and adhered thereto, and then annealed in a N ₂ atmosphere at 1100 ° C. for 2 hours to be fixed.

Next, ordinary LPC was applied to the surface of the adhered porous layer.
A silicon film is grown with a VD apparatus under the formation conditions shown in Table 3 for a long time to form a silicon film having a thickness of about 100 μm.
And The crystal grain size of the silicon layer at this time was several mm to several tens of mm, and the crystallinity of the substrate was maintained.

The surface of the silicon layer was textured by immersing the substrate in a boiling 1% aqueous solution of NaOH for about 5 minutes, and then thermal diffusion of P was performed on the surface of the epitaxial layer at a temperature of 900 ° C. using POCl ₃ as a diffusion source. Then, an n ⁺ layer was formed to obtain a junction depth of about 0.5 μm. N formed
The dead layer on the ⁺ layer surface was wet-oxidized and then removed by etching to obtain a junction depth with an appropriate surface concentration of about 0.2 μm. Finally, the collector electrode (Ti / Pd / Ag (40
0 nm / 200 nm / 1 μm)) and an ITO transparent conductive film (820 nm).

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristics were measured under 5 (100 mW / cm ² ) light irradiation, the open area voltage was 0.51 V and the short circuit photocurrent was 33.2 when the cell area was 6 cm ^2.
It became mA / cm ² and a fill factor of 0.73, and an energy conversion efficiency of 12.4% was obtained. As described above, a thin-film crystal solar cell exhibiting good characteristics as in the case of single-crystal silicon could be manufactured by using a porous layer of polycrystalline silicon.

(Embodiment 13) n as shown in FIG.
^{+ A} p-type thin film crystal solar cell was produced using a liquid phase epitaxy method. In the same manner as in Example 10, p-type (10
0) A silicon wafer (ρ = 0.01 Ωcm) was anodized in an HF aqueous solution under the conditions shown in Table 10 to form a porous silicon layer on the wafer.

At the end of formation of the porous silicon layer, the HF concentration of the chemical conversion solution was reduced to 1% and the conversion current was 100 mA.
/ Cm ² and the porous layer was separated from the wafer.
After the separated porous layer was adhered Place the Ti on SUS substrate was 100nm deposition, 1100 ° C. in a N ₂ atmosphere 2
It was annealed for a period of time and fixed. Next, epitaxial growth was performed on the surface of the adhered porous layer by the liquid phase growth method under the conditions shown in Table 9 to grow the epitaxial layer to about 45 μm.

At this time, Sn was used as a solvent, and Si was previously dissolved in Sn to saturate before growth, and then gradual cooling was started. When a certain degree of supersaturation was reached, the surface of the porous layer was Sn. It was immersed in the solution and grown for a predetermined time.

Next, on the surface of the epitaxial layer, POCl ₃
N as a diffusion source by performing thermal diffusion of P at a temperature of 900 ° C.
^{A +} layer was formed to obtain a junction depth of about 0.5 μm. The formed dead layer on the surface of the n ⁺ layer was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm.

Finally, EB (Electron Bea)
m) Current collector electrode (Ti / Pd / Ag (40 nm
/ 20 nm / 1 μm)) / ITO transparent conductive film (820n
m) was formed on the n ⁺ layer.

Regarding the thin film crystalline silicon solar cell thus obtained, AMl. When the IV characteristics were measured under 5 (100 mW / cm ² ) light irradiation, the open circuit voltage was 0.53 V and the short circuit photocurrent was 31.7 when the cell area was 1 cm ^2.
It was mA / cm ² and a fill factor of 0.76, and an energy conversion efficiency of 12.8% was obtained.

As described above, according to the present invention, the porous silicon formed on the wafer is separated from the wafer and fixed on the metal substrate, and the silicon layer formed on the porous layer is used. It has been shown that good solar cells are produced.

[0172]

As described above, according to the invention of claim 1, a crystalline solar cell having a window layer effect can be obtained without using different kinds of materials, whereby a high-quality crystalline solar cell with mass productivity can be obtained. Can now be offered to the market.

According to the fifth and sixth aspects of the present invention, it is possible to form a crystalline thin film solar cell having a high photoelectric conversion efficiency, and particularly by using a metal substrate, a crystalline thin film solar cell exhibiting good characteristics can be manufactured at low cost. It is now possible to provide.

Further, according to the inventions of claims 15 and 16, it has become possible to provide a mass-produced, inexpensive, high-quality thin solar cell to the market.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a solar cell of the present invention.

FIG. 2 is a diagram illustrating a manufacturing process of the solar cell of the present invention.

FIG. 3 is a diagram illustrating a manufacturing process of the solar cell of the present invention.

FIG. 4 is a diagram illustrating a manufacturing process of the solar cell of the present invention.

FIG. 5 is a diagram illustrating light reflection at an interface between a porous layer and a silicon layer.

[Explanation of symbols]

101a, 201 crystalline silicon 101b, 303 metal substrate 101c, 401 first crystalline silicon 103a, 102b, 102c, 203, 302, 40
2 Porous silicon layers 103b, 103c, 303, 304 Second crystalline silicon 104b, 104c, 305, 405 Silicon layers of opposite conductivity type to the second crystalline silicon 104a, 105b, 105c, 204, 306, 40
5 Transparent conductive layers 105a, 106b, 106c, 205, 307, 40
6 Current collecting electrodes 106a, 206 Back electrode 202 Silicon layer of opposite conductivity type to crystalline silicon (101a)

Claims (20)

[Claims] 1. A solar cell comprising a first conductive type crystalline silicon and a second conductive type porous silicon serving as a light-incident layer laminated on the first conductive type crystalline silicon. 2. The solar cell according to claim 1, wherein the first conductivity type is p-type and the second conductivity type is n-type. 3. The solar cell according to claim 1, wherein the first conductivity type crystalline silicon is single crystalline silicon. 4. The solar cell according to claim 1, wherein the crystalline silicon of the first conductivity type is polycrystalline silicon. 5. A solar cell comprising: a first crystalline silicon or a metal substrate on which porous silicon is further laminated; and a second crystalline silicon laminated on the porous silicon. 6. The solar cell according to claim 5, wherein the second crystalline silicon is single crystalline silicon. 7. The solar cell according to claim 6, wherein the first crystalline silicon is single crystalline silicon or polycrystalline silicon. 8. The solar cell according to claim 5, wherein the second crystalline silicon is polycrystalline silicon. 9. The solar cell according to claim 8, wherein the first crystalline silicon is polycrystalline silicon. 10. The solar cell according to claim 5, wherein the second crystalline silicon is an epitaxial layer formed on the porous silicon. 11. The film thickness of the second crystalline silicon is 1
It is 0 micrometer or more and 100 micrometers or less, The solar cell of any one of Claim 5 thru | or 10 characterized by the above-mentioned. 12. The solar cell according to claim 5, wherein a semiconductor junction is provided on the surface of the second crystalline silicon. 13. The specific resistance of the second crystalline silicon is
5. The method according to claim 5, wherein the distance is 0.1 cm or less.
2. The solar cell according to any one of 2. 14. The surface of the second crystalline silicon has a textured structure.
The solar cell according to any one of 3 above. 15. A step of: i) forming a porous layer on one surface of the first crystalline silicon by anodization; ii) forming a second crystalline silicon on the porous layer; iii) A method of manufacturing a solar cell, comprising: texturing the surface of the second crystalline silicon; and iv) forming a semiconductor junction on the surface of the second crystalline silicon. 16. A step of: i) forming a porous layer on one side surface of the first crystalline silicon by anodization; and ii) electrolytic polishing under different forming conditions at the end of the formation of the porous layer. A step of separating a porous layer from the first crystalline silicon, iii) a step of fixing the porous layer to a metal substrate, and iv) a second step on the porous layer on the metal substrate by a crystal growth method. And a step of forming a semiconductor junction on the surface of the second crystalline silicon, the method for manufacturing a solar cell. 17. The method of manufacturing a solar cell according to claim 15, wherein the first crystalline silicon is a single crystalline silicon wafer. 18. The method for manufacturing a solar cell according to claim 15, wherein the first crystalline silicon is a polycrystalline silicon wafer. 19. The method for manufacturing a solar cell according to claim 15, wherein the second crystalline silicon is obtained by forming epitaxial silicon on the porous layer. 20. The method for manufacturing a solar cell according to claim 15, wherein the second crystalline silicon is obtained by bonding the porous layer and a single crystalline silicon wafer.