JP2804608B2 - Photovoltaic device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photovoltaic device having a polycrystalline silicon thin film formed on a substrate.

[Conventional technology]

As a semiconductor thin film used for solar cells, sensors, etc.,
Amorphous silicon thin films and polycrystalline silicon thin films are widely used. Polycrystalline silicon has characteristics of higher mobility than amorphous silicon by about one to two digits, thermal stability, and high reliability.

However, polycrystalline silicon has a higher forming temperature than amorphous silicon. Therefore, for example, as shown in the article “Growth of polycrystalline Si thin films for solar cells by the liquid phase method” in the 50th Proceedings of the Society of Materials Science, p.567 (autumn 1989), monocrystalline silicon and cast polycrystalline At present, silicon is used as a substrate, and a polycrystalline silicon thin film is formed on the substrate by a liquid phase growth method.

[Problems to be solved by the invention]

As described above, since polycrystalline silicon has a high formation temperature, a single crystal silicon or the like having excellent heat resistance is used for a substrate to be used, and the substrate is expensive and costly. At present, a single-crystal silicon substrate of an 8-inch wafer is put to practical use for a semiconductor integrated circuit. However, this substrate is very expensive, and becomes extremely expensive when used for a solar cell or the like. Had been an obstacle.

Therefore, it is conceivable to use a ceramic substrate, quartz glass, or the like as a substrate, but the wettability between these substrates and a silicon layer formed by liquid phase growth is extremely poor, and a polycrystalline silicon layer cannot be formed on these substrates. Was.

Here, the wettability refers to the rate at which the material adheres to the surface of the substrate, and a material having an N of 90% or less represented by the following equation is defined as poor wettability.

N = material adhesion area / substrate area × 100 If this wettability is poor, a polycrystalline silicon thin film cannot be formed by the liquid phase growth method.

An object of the present invention is to provide a photovoltaic device capable of forming a polycrystalline silicon layer irrespective of the material of a substrate, in view of the above-mentioned conventional problems.

[Means for solving the problem]

According to the present invention, a buffer layer for improving the wettability of a substrate is formed on a heat-resistant substrate by plasma spraying, and a semiconductor thin film made of a polycrystalline silicon layer of one conductivity type is formed on the buffer layer by liquid phase growth. A semiconductor thin film of another conductivity type is formed on the semiconductor thin film.

Further, the buffer layer may be formed of a single layer or a multilayer of a silicon thin film, a silicide thin film, a cermet thin film, a silicon nitride thin film or a silicon carbide thin film.

[Action]

According to the present invention, a buffer layer having good wettability is formed on a substrate by plasma spraying. Thus, this buffer layer is reliably deposited on the substrate. The buffer layer and the polycrystalline silicon layer have extremely good wettability, and polycrystalline silicon is deposited on the buffer layer. Therefore, polycrystalline silicon can be formed on the substrate regardless of the material of the substrate.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention. In this figure, reference numeral 1 denotes a substrate made of translucent ceramic or quartz glass.

As described above, the substrate 1 has poor wettability. Therefore, in the present invention, in order to improve the wettability, the substrate 1
The buffer layer 2 is provided on the surface by plasma spraying. The buffer layer 2 is made of a material that improves the wettability with polycrystalline silicon. For example, a single layer or a multilayer film of a silicon thin film, a silicide thin film, a cermet thin film, a silicon nitride thin film, or a silicon carbide thin film is used.
Thin films of these materials have extremely good wettability with polycrystalline silicon. Since the buffer layer 2 is formed on the substrate 1 by plasma spraying, each of the above-described materials can be reliably deposited on the substrate 1.

On this buffer layer 2, ap ⁺ -type polycrystalline silicon thin film 3 is formed by a liquid phase growth method.

4 p was formed similarly by the liquid phase growth method on the p ⁺ -type polycrystalline silicon film 3 ^- type polycrystalline silicon thin film, 5 is p ^- is likewise formed by a liquid phase growth method on type polycrystalline silicon thin film 4 N ⁺ type polycrystalline silicon thin film.

Reference numeral 6 denotes a comb-shaped front electrode made of aluminum or the like provided on the n ⁺ -type polycrystalline silicon thin film 5, and reference numeral 7 denotes a back electrode that makes ohmic contact with a part of the p ⁺ -type polycrystalline silicon thin film 3.

Next, a manufacturing method of the present embodiment having such a configuration will be described.

FIG. 3 is a schematic diagram of a low-pressure plasma spraying apparatus used in the production of this embodiment, and FIG. 4 is a schematic diagram of a liquid phase growth apparatus.

First, the reduced pressure plasma spraying device will be briefly described.

In FIG. 3, reference numeral 11 denotes a vacuum vessel capable of maintaining a reduced pressure, and reference numeral 12 denotes a DC power supply for plasma spraying. This DC power supply is connected to cathodes 14a and 14b constituting a plasma spray gun 13.
Reference numeral 15 denotes a powder supply port for supplying a raw material powder of a semiconductor thin film to be formed, for example, silicon (Si) powder, silicon carbide (SiC) powder, silicon nitride (SiN) powder having a particle size of several μm to several tens μm. The raw material powder is melted by the heat of the DC plasma generated between the cathode 14a and the anode 14b. Reference numeral 16 denotes a spray gas inlet into which a spray gas, such as helium, argon, or hydrogen, for injecting a melt of the raw material powder from the plasma spray gun 13 as a fine-particle plasma jet 17 is introduced. Polycrystalline or microcrystalline silicon or silicon carbide based on the raw material powder on the substrate 1 opposed to the application gun 13.
The buffer layer 2 made of a thin film semiconductor such as silicon nitride is formed. Reference numerals 20 and 21 denote an atmospheric gas inlet and an exhaust port for introducing or exhausting an atmospheric gas into the vacuum vessel 11.

Next, the configuration of the liquid phase growth apparatus will be briefly described with reference to FIG.

In FIG. 4, reference numeral 30 denotes a high-purity carbon tray, on which the substrate 1 for liquid phase growth is held.

Reference numeral 31 denotes a boat made of high-purity carbon, and silicon tin (SiSn) is dissolved in a crucible 32 in the boat 31. Then, the substrate 1 held on the tray 30 is placed in contact with the surface of the SiSn solution 33 dissolved in the crucible 32 of the boat 31 made of high-purity carbon.

Subsequently, in a hydrogen atmosphere atmosphere, the crucible temperature is set to, for example, 1000 ° C., and the substrate 1 is set.
By lowering the temperature at a rate of 2 ° C. and the temperature of the crucible to 950 ° C., a polycrystalline silicon thin film of about 50 μm is formed on the substrate 1.

Next, a specific embodiment of the embodiment of the present invention shown in FIG. 1 will be further described according to a production example.

First, quartz glass or alumina (Al ₂ O ₃ ), aluminum nitride (AIN), yttria (Y ₂ O ₃ ), magnesia (M
A heat-resistant substrate 1 made of a ceramic such as gO) or zirconia (ZrO ₂ ) is placed in a plasma spraying apparatus. And
After evacuating the inside of the vacuum chamber 11 of the plasma spraying apparatus to about 10 ^-3 Torr, a mixed gas of argon and hydrogen is introduced at 1 to 10 slm from the spraying gas inlet 16, and the particle diameter is 10 to 44 from the powder supply port 15.
μm of silicon powder is introduced at 1 to 10 g / min.

Then, a power of 30 KW is applied from the DC power supply 12 to generate a plasma jet 17, thereby depositing a 400 μm thick buffer layer 2 made of a polycrystalline silicon thin film on the substrate 1. The deposition conditions at this time are as follows: pressure 1-10 Torr, substrate temperature
500-1000 ° C for 10 minutes.

Subsequently, the substrate 1 on which the buffer layer 2 is deposited is supported on a high-purity carbon tray 30 in an atmosphere of hydrogen at atmospheric pressure, and the surface of the SiSn solution 33 dissolved in the crucible 32 of the high-purity carbon boat 31 is The tray 30 is stopped so that the surface of the buffer layer 2 of the substrate 1 contacts the substrate 30. At this time, the SiSn solution 33 is mostly tin (Sn) based on the phase diagram. The silicon (Si) source is p-type single crystal silicon, and its specific resistance is 1 Ωcm or less.

Then, the substrate 1 is cooled at a temperature of 1 to 2 ° C./min from 1000 ° C. in an atmosphere of hydrogen at atmospheric pressure.
Then, a p ⁺ -type polycrystalline silicon layer 3 having a thickness of 50 μm is formed on the buffer layer 2 deposited on the substrate 1 by liquid phase growth.

Thereafter, the substrate 1 on which the polycrystalline silicon layer 3 has been formed is similarly supported on a high-purity carbon tray 30, and the SiSn solution 33 dissolved in the crucible 32 of the high-purity carbon boat 31.
The tray 30 is stopped so that the front surface and the surface of the substrate 1 are in contact with each other. At this time, most of the SiSn solution 33 is Sn based on the phase diagram. The silicon (Si) source is p-type single crystal silicon, and its specific resistance is 5 Ωcm or less.

In the same manner as described above, the substrate 1 is
The temperature is lowered from 1000 ° C. at 1-2 ° C./min.
When separated from the iSn solution 33, a p ^- type polycrystalline silicon layer 4 having a thickness of 100 μm is formed on the p ⁺ type polycrystalline silicon 3 deposited on the substrate 1 by liquid phase growth.

Thereafter, similarly, an n ⁺ -type polycrystalline silicon layer 5 is formed by a liquid phase growth method. At this time, the silicon (Si) source of the SiSn solution 33 is n-type single crystal silicon, and its specific resistance is 1 Ωcm or less.

In the same manner as described above, the substrate 1 is
The temperature is lowered at a rate of 1 to 2 ° C per minute from 1000 ° C.
When separated from the iSn solution 33, a 5 μm-thick n ⁺ -type polycrystalline silicon layer 5 is formed on the p ⁻ -type polycrystalline silicon layer 4 deposited on the substrate 1 by liquid phase growth.

Thereafter, an electrode layer in ohmic contact with each of the n ⁺ -type polycrystalline silicon layer 5 and the p ⁺ -type polycrystalline silicon layer 3 is provided by evaporating aluminum or the like, and is patterned, respectively, to form a comb-shaped front electrode 6 and a back electrode. Is formed to form the photovoltaic device according to the present invention.

In the above-described embodiment, the case where a silicon thin film is used as the buffer layer 2 has been described. However, a method of forming the buffer layer 2 using other materials will be described below.

First, a case where a silicide layer is used as the buffer layer 2 will be described.

TiSi ₂ , VSi ₂ , CrSi ₂ , FeSi
₂ , CoSi ₂ or NiSi ₂ powder having a particle size of 10 to 44 μm is used. The powder of these silicide materials is supplied from the powder supply port 15 of the plasma spraying apparatus shown in FIG.
Introduce ~ 10g.

Then, a power of 50 kw is applied from the DC power supply 12 to generate a plasma jet 17, and a thin 500 μm buffer layer 2 made of a silicide thin film is deposited on the substrate 1.

Next, a case where a cermet thin film is used as the buffer layer 2 will be described.

Cermet materials are WC-9% Co, WC-13% C
_{o, WC15% Co, Cr 3} C 2 -NiCr, Al 2 O 3 -Cr, or Al ₂ O ₃ -Mo
A powder having a particle size of -Cr of 10 to 44 µm is used. The powder of the cermet material is introduced at 1 to 10 g per minute from the powder supply port 15 in the same manner as described above.

Then, a power of 50 KW is applied from the DC power supply 12 to generate a plasma jet 17, and a thin film 500 μm buffer layer 2 made of a cermet thin film is deposited on the substrate 1.

Subsequently, a case where a silicon nitride thin film is used as the buffer layer 2 will be described.

As described above, 1 to 10 g of Si ₃ N ₄ powder having a particle size of 10 to 44 μm is introduced from the powder supply port 15 per minute.

Then, a power of 50 kW is applied from the DC power supply 12 to generate a plasma jet 17, and a 500 μm thin film buffer layer 2 made of a silicon nitride thin film is deposited on the substrate 1.

Finally, a case where a silicon carbide thin film is used as the buffer layer 2 will be described.

As described above, 1 to 10 g of SiC powder having a particle size of 10 to 44 μm is introduced from the powder supply port 15 per minute.

Then, a power of 50 KW is applied from the DC power supply 12 to generate a plasma jet 17, and a thin 500 μm buffer layer 2 made of a silicon carbide thin film is deposited on the substrate 1.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a sectional view showing a second embodiment of the present invention. In this figure, reference numeral 1 denotes an insulating substrate made of ceramic or quartz glass.

Reference numeral 2 denotes a buffer layer formed on the surface of the substrate 1 by plasma spraying to improve wettability. As in the first embodiment, a material that improves the wettability with polycrystalline silicon is used for the buffer layer 2.

An n-type polycrystalline silicon thin film 40 is formed on buffer layer 2 by a liquid phase growth method.

Reference numeral 41 denotes a p-type polycrystalline silicon thin film similarly formed on the n-type polycrystalline silicon thin film 40 by a liquid phase growth method.

Reference numeral 42 denotes an amorphous silicon semiconductor layer formed on the p-type polycrystalline silicon thin film 41 by n-type i-type p-type formed by a plasma CVD method or the like.

43 denotes an IT formed on the entire surface of the amorphous silicon semiconductor layer 42
Transparent electrode made of O, etc., 44 is an extraction electrode of the surface electrode that contacts the transparent electrode 43, 45 is n-type polycrystalline silicon
The back surface extraction electrode that makes ohmic contact with 40.

Next, a production example of the second embodiment of the present invention will be further described.

First, a heat-resistant substrate 1 made of quartz glass or ceramic such as alumina (Al ₂ O ₃ ), aluminum nitride (AlN), yttria (Y ₂ O ₃ ), magnesia (MgO), zirconia (ZrO ₂ ) is plasma sprayed. Place in the device. After evacuating the inside of the vacuum chamber 11 of the plasma spraying apparatus to about 10 ⁻³ Torr, a mixed gas of argon and hydrogen is introduced at 1 to 10 slm from the spraying gas inlet 16, and a particle diameter of 10
A silicon nitride powder or a silicon carbide powder of ~ 44 µm is introduced at a rate of 1 to 10 g / min.

Then, a power of 30 KW is applied from the DC power supply 12 to generate a plasma jet 17, and a film thickness 40 of a polycrystalline silicon nitride thin film or a polycrystalline silicon carbide thin film is formed on the substrate 1.
A 0 μm buffer layer 2 is deposited. The deposition conditions at this time are as follows: pressure 1 to 10 Torr, substrate temperature 500 to 1000 ° C., time 10
Minutes.

Subsequently, in a hydrogen atmosphere, the substrate 1 supported on the high-purity carbon tray 30 is transferred to the high-purity carbon boat 31.
The tray 30 is stopped so that the surface of the SiSn solution 33 dissolved in the crucible is in contact with the surface of the substrate 1. At this time, SiSn solution
33 is mostly Sn based on the state diagram. The silicon (Si) source is n-type single crystal silicon, and its specific resistance is 1 Ωcm or less.

Then, the substrate 1 is cooled at a temperature of 1 to 2 ° C./min from 1000 ° C. in an atmosphere of hydrogen at atmospheric pressure.
Then, an n-type polycrystalline silicon layer 40 having a thickness of 50 μm is formed on the buffer layer 2 deposited on the substrate 1 by liquid phase growth.

Thereafter, the substrate 1 on which the polycrystalline silicon layer 40 is formed is similarly supported on a high-purity carbon tray 30, and the surface of the SiSn solution 33 dissolved in the crucible of the high-purity carbon boat 31 and the surface of the substrate 1 The tray 30 is stopped so that the tray contacts.
At this time, most of the SiSn solution 33 is Sn based on the phase diagram.
The silicon (Si) source is p-type single crystal silicon, and its specific resistance is 5 Ωcm.

In the same manner as described above, the substrate 1 is
The temperature is lowered at a rate of 1 to 2 ° C./min.
When separated from the solution 33, a 100 μm-thick p-type polycrystalline silicon layer 41 is formed on the n-type polycrystalline silicon 40 deposited on the substrate 1.
Are formed by liquid phase growth.

Thereafter, an amorphous silicon layer 42 in which an n-type i-type p-type amorphous silicon thin film is sequentially laminated on the p-type polycrystalline silicon layer 1 by a plasma CVD method is formed. The conditions for forming each amorphous silicon thin film are as follows.

n-type amorphous silicon maintains the substrate temperature at 200 ° C, RF
Output: 0.01 W / cm ² Pressure: 0.1 Torr, PH ₃ / Si as reaction gas
The reaction was performed for 5 minutes using H ₄ = 1%.

The i-type amorphous silicon was reacted for 1 hour using the same substrate temperature of 200 ° C., RF output of 0.01 W / cm ² , pressure of 0.1 Torr, and SiH ₄ = 30 SCCM as a reaction gas.

In the case of p-type amorphous silicon, the substrate temperature is also maintained at 200 ° C., the PF output is 0.01 W / cm ² , and the pressure is 0.1 Torr reaction gas.
The reaction was carried out for 5 minutes using B ₂ H ₆ / SiH ₄ = 0.1%.

Thereafter, a transparent electrode 43 made of ITO is formed on the amorphous silicon layer 42 by a sputtering method.

Then, by a vapor deposition method, an extraction electrode of the transparent electrode 43 made of aluminum or the like and the n-type polycrystalline silicon layer 40 are formed.
An electrode layer that makes ohmic contact with the electrode is provided, and each is patterned to form an extraction electrode 45 for the back electrode and an extraction electrode 44 for the front electrode, thereby forming the photovoltaic device according to the present invention.

In the above-described embodiment, the polycrystalline silicon nitride thin film or the polycrystalline silicon carbide thin film is used as the buffer layer 2. However, the method of forming the buffer layer using other materials is the same as in the above-described embodiment. Omitted.

〔The invention's effect〕

As described above, according to the present invention, since the buffer layer having good wettability is formed on the substrate by plasma spraying, polycrystalline silicon can be reliably deposited on the buffer layer. Therefore, since polycrystalline silicon can be formed regardless of the material of the substrate, the area of the photovoltaic device can be easily increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention, and FIG.
FIG. 5 is a sectional view showing a second embodiment of the present invention. FIG. 3 is a schematic view of a plasma spraying apparatus used in the present invention, and FIG. 4 is a schematic view of a liquid phase growth apparatus. 1 ... substrate, 2 ... buffer layer, 3 ... p ⁺ -type polycrystalline silicon layer, 4 ... p ^-- type polycrystalline silicon layer, 5 ... n ⁺ -type polycrystalline silicon layer, 40 ... ... n-type polycrystalline silicon layer Crystal silicon layer, 41: p-type polycrystalline silicon layer, 42: amorphous silicon layer, 43: transparent electrode.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-49420 (JP, A) JP-A-64-53475 (JP, A) JP-A-60-233818 (JP, A) JP-A-58-58 48418 (JP, A) JP-A-2-28315 (JP, A) JP-A-2-185021 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/04

Claims (2)

(57) [Claims] A buffer layer for improving the wettability of a substrate is formed on a heat-resistant substrate by plasma spraying. On the buffer layer, a semiconductor thin film made of a polycrystalline silicon layer of one conductivity type is formed by liquid phase growth. A photovoltaic device, wherein a semiconductor thin film of another conductivity type is formed on the semiconductor thin film. 2. The light according to claim 1, wherein the buffer layer is formed of a single layer or a multilayer of a silicon thin film, a silicide thin film, a cermet thin film, a silicon nitride thin film or a silicon carbide thin film. Electromotive device.