JP2966908B2 - Photoelectric conversion element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photoelectric conversion element, and more particularly, to an amorphous silicon photoelectric conversion element having excellent photoelectric characteristics stably and with little deterioration.

(Background technology)

Amorphous silicon photoelectric conversion elements have already been put into practical use as low-power energy sources for driving calculators and watches. However, as an energy source with a large output, such as 0.1 W or more, as in solar power generation, it cannot be said that its performance and stability are sufficient.
Various studies have been conducted with the aim of improving performance. Actually, although some improvement has been seen due to the device structure as in the case of tandem solar cells, the photoelectric characteristics of practical solar cells have been reduced by about 20% after one year. That is the reality. The limitations of these performance improvements and the deterioration of the photoelectric characteristics are due to the plasma CVD method and the photo CVD method.
Method, the properties of the hydrogenated amorphous silicon film itself formed by a film forming method such as thermal CVD method, the present inventors,
The solution was proposed. That is, in the film forming step, amorphous silicon having a small amount of hydrogen is formed, and then the film is formed of a non-deposited reactive gas containing deuterium such as deuterium gas or deuterium fluoride gas. As a result of acidification of modification by forming a film by alternately repeating treatment in a discharge atmosphere, it has better optical characteristics with a narrower optical bandgap and almost changes in characteristics with light irradiation It has made it possible to obtain a thin film free of defects. Therefore, in this application,
By applying this new film formation method to the formation of a thicker second substantially intrinsic thin film, which is primarily for power generation,
This has led to the completion of a photoelectric conversion element having extremely improved performance and deterioration characteristics and excellent stability.

(Basic idea of the invention)

The performance of the current amorphous silicon photoelectric conversion device and its stability to light irradiation are largely limited by the properties of the substantially intrinsic thin film mainly used for power generation, particularly the amount of hydrogen and the hydrogen bonding state in the film. ing. So, at least,
A thicker second substantially intrinsic thin film was formed by controlling the amount of hydrogen, with a narrower optical bandgap than in the prior art, and by exhibiting good photoelectric and carrier-transport characteristics. That is, by forming a semiconductor thin film by 5 to 100 ° (hereinafter abbreviated as “film formation”) by a plasma CVD method or the like, and then exposing the semiconductor thin film to a discharge atmosphere containing deuterium, a second substantially thicker film is formed. When an intrinsic thin film was formed to produce a photoelectric conversion element, a high-performance element extremely stable to light irradiation was successfully obtained.

[Disclosure of the Invention]

That is, the present invention provides a method for forming a first electrode, a first conductive thin film, a thinner first substantially intrinsic thin film, a thicker second substantially intrinsic thin film, a second conductive film on a substrate. In the photoelectric conversion element formed in the order of the conductive thin film and the second electrode, at least the formation of the thicker second substantially intrinsic thin film is performed using disilane gas and deuterium gas, and combined hydrogen and / or A step of forming a semiconductor thin film having a deuterium content of 20 atomic% or less (hereinafter abbreviated as a film forming step) and a step of exposing the formed thin film to a discharge atmosphere containing deuterium (hereinafter abbreviated as a reforming step); Preferably, in the repetition of the film forming step and the modification step, the semiconductor thin film formed in one repetition is 5 to 100
It is formed to have a thickness of Å.

 Hereinafter, the present invention will be described in detail.

In the present invention, it is essential to form a thicker second substantially intrinsic thin film by repeating the film forming step and the modifying step, but of course, the other first conductive thin film, the thinner Even if both the first substantially intrinsic thin film and the second conductive thin film are formed by repeating the film forming step and the reforming step, the effects of the present invention are not hindered at all, but rather a preferable method. It is. The details of the repeated formation of the film formation step and the modification step will be described below.

In the present invention, the film forming step is not particularly limited. Specifically, it is a process of forming a film by a physical film forming method such as vacuum deposition, sputtering, or ion plating, or a chemical vapor deposition (CVD) method such as optical CVD or plasma CVD. The step is a step of generating a discharge containing a reactive gas containing deuterium in the thin film and exposing the thin film to an atmosphere of the discharge, thereby improving the properties of the semiconductor thin film.

In the present invention, the film forming step of forming a thin film and the modification step are repeated, and the thickness of the semiconductor thin film formed by one repetition is set to 5 to 100 °, preferably 10 to 80 °, more preferably 30 to 80 °. To 50 ° is an essential requirement, and other film forming conditions do not particularly hinder the effects of the present invention.

 An effective physical film forming method will be described below.

First, in the case of forming a substantially intrinsic thin film, silicon, silicon carbide, silicon nitride, silicon-germanium alloy (or composite powder) are used as starting materials for film formation.
Elements, compounds, and alloys such as a silicon-tin alloy (or a plurality of powders) can be used effectively. In addition, elements, compounds, and alloys such as carbon, germanium, and tin can also be used. The film forming conditions are not particularly limited except for reducing the amounts of bound hydrogen and deuterium. The film forming conditions are selected so that the amount of bound hydrogen and / or deuterium in the semiconductor thin film is 20 at% or less, and preferably 10 at% or less. Excessive amounts of bound hydrogen and / or deuterium, exceeding 20%, have no effect of exposing to a discharge atmosphere containing deuterium. Of course, as long as these conditions are satisfied, the film can be formed in an atmosphere of an inert gas, hydrogen, deuterium, hydrocarbon, fluorine, oxygen gas, or the like. As a specific condition, the gas flow rate is 1 to 100 scc.
m and the reaction pressure are in the range of 0.001 mtorr to 10 mtorr, and the film forming conditions such as flow rate, pressure and power are appropriately selected according to the film forming speed. The film formation temperature is controlled by controlling the substrate temperature. Although the temperature range is not basically limited, it is preferable to set the temperature in accordance with the reforming step. Specifically, it is selected in a temperature range of 500 ° C. or less.

On the other hand, in the case of forming a conductive thin film, the first conductive thin film and the second conductive thin film have different conductivity types. For example, if the first conductivity type is p-type, the second conductivity type is n-type. It goes without saying that the reverse is also possible. The p-type conductivity can be imparted by using a compound containing a group III element (for example, boron) as a starting material, or by forming a film in an atmosphere of diborane, boron halide, trimethylboron gas, or the like. In order to impart n-type conductivity, a compound containing a group V element (for example, phosphorus) as a starting material, or phosphine, arsine,
The film formation can be performed in an atmosphere of a phosphorus halide, an arsenic halide, an alkyl phosphorus, an alkyl arsenic gas or the like.

 Next, specific examples of the effective CVD method will be described below.

First, in the case of forming a substantially intrinsic thin film, a general formula, Si _n H _{2n + 2} , Si _n D _{2n + 2} , Si _n H _{((2n + 2) -m )} Monosilane, disilane represented by D _m (n and m are natural numbers)
A silane compound such as trisilane or tetrasilane, fluorinated silane, organic silane, hydrocarbon, or the like is used. Also,
A gas such as hydrogen, deuterium, fluorine, chlorine, helium, argon, neon, or nitrogen may be introduced together with the source gas. When these gases are used, it is effective to use them in the range of 0.01 to 100% (volume ratio) with respect to the raw material gas. Is what is done.

The film forming conditions are not particularly limited, as in the case of the physical film forming method, except that the amount of bound hydrogen and / or deuterium is reduced to a specific amount or less. The film forming conditions are selected so that the amount of bound hydrogen and / or deuterium in the semiconductor thin film is 20 at% or less, and preferably 10 at% or less. Specific conditions are disclosed below. Optical CVD
Is formed by decomposing a source gas using an ultraviolet light source having a wavelength of 350 nm or less, such as a low-pressure mercury lamp, a deuterium lamp, or a rare gas lamp. The conditions for film formation are as follows:
100sccm, reaction pressure 15mtorr ~ atmospheric pressure, substrate temperature 200 ~ 600
° C, heat resistance of the substrate, deposition time considered from the deposition rate,
Taking into account the plasma processing temperature of the post-processing and the like, more preferably, it is appropriately selected in the range of 300 to 500 ° C. The plasma CVD will be specifically described below. As a discharge method, a method such as a high-frequency discharge, a DC discharge, a microwave discharge, and an ECR discharge can be effectively used. A flow rate of the raw material gas of 1 to 900 sccm, a reaction pressure of 0.001 mtorr to atmospheric pressure, and a power of 1 mW / cm ^{2 to} 10 W / cm ² are sufficient. These film forming conditions are appropriately changed according to the film forming speed and the discharge method. The substrate temperature is from 200 to 600C, more preferably from 300 to 500C.

On the other hand, in the case of forming a conductive thin film, the first conductive thin film and the second conductive thin film have different conductivity types, as in the physical film forming method. For example, if the first conductivity type is p-type, the second conductivity type is n-type. It goes without saying that the reverse is also possible. In order to impart p-type conductivity, a film can be formed by adding siborane, boron halide, trimethylboron gas, or the like to a source gas. In order to impart n-type conductivity, a film can be formed by adding phosphine, arsine, phosphorus halide, arsenic halide, alkyl phosphorus, alkyl arsenic gas, or the like to a source gas.

In the present invention, the reforming step is a step of introducing a reactive gas containing deuterium into the reforming chamber to generate a discharge, and exposing the thin film formed in the film forming step to this discharge atmosphere.

As a method of generating a discharge, a high-frequency discharge, a DC discharge, a microwave discharge, an ECR discharge, or the like can be effectively used. The reactive gas containing deuterium is deuterium, a fluorine compound, or the like, and deuterium gas, deuterium fluoride gas, or the like can be used effectively. Also, a mixture of these gases and a mixture of these gases with hydrogen gas, hydrogen fluoride gas, fluorine gas, nitrogen trifluoride, carbon tetrafluoride, or the like may be used. Deuterium in the mixed gas is at least 1% or more, preferably 10% or more, more preferably 50% or more, and more preferably 80% or more. The specific conditions of the reforming step will be disclosed below. The discharge is performed at a discharge power of 1 to 500 W, a flow rate of a reactive gas containing deuterium of 5 to 500 sccm, a pressure of 0.001 mtorr to
It is generated and maintained in the range of atmospheric pressure. The temperature condition in the reforming step is controlled by the temperature of the substrate. This substrate temperature is the same as or lower than the substrate temperature in the film forming step, and is from room temperature to 600 ° C., preferably 200 to 500 ° C.

In one film forming step, the film is formed to a thickness of 5 to 100 °, preferably 10 to 80 °, more preferably 30 to 50 °. If the film thickness is too thin, it may be crystallized, so that an amorphous thin film cannot be excessively thin. The time required for one cycle is not particularly limited, but is not more than 1000 seconds and several seconds or more. It is preferable that the time to shift from the film forming step to the reforming step and the time to shift from the reforming step to the film forming step be as short as possible.
This time depends on the shape and size of the apparatus, the evacuation system, and the like. Specifically, it can be shortened within one second.

Although there is no particular limitation on a forming apparatus for carrying out the present invention, for example, as shown in FIG. 2, a substrate insertion chamber 1, a first conductive thin film forming chamber 2, a thicker second substantially second chamber The chamber comprises an intrinsic thin film forming chamber 3, a second conductive thin film forming chamber 4, and a second electrode forming chamber 5. The plasma CVD method can be applied to all except the substrate inserting chamber and the electrode forming chamber.

The material of the substrate and the electrode used in the present invention is not particularly limited, and conventionally used substances are effectively used.
For example, the substrate may have any of insulating or conductive, transparent, and opaque properties. Basically, a film or plate-like material formed of a substance such as glass, alumina, silicon, stainless steel, aluminum, molybdenum, chromium, or a heat-resistant polymer can be effectively used. As the electrode material, a transparent or transparent material must of course be used on the light incident side, but there is no other practical limitation. It can be appropriately selected from metals such as aluminum, silver, chromium, titanium, nickel-chromium, gold and platinum and metal oxides such as tin oxide, zinc oxide and indium oxide.
The configuration of the photoelectric conversion element obtained in the present invention is shown in FIG. 1, but the thickness of each constituent layer is not particularly limited.
The well-known photoelectric conversion conventionally used, except that the thickness of the thicker second substantially intrinsic thin film must naturally be greater than the thickness of the thin film formed in one cycle. The thickness of the element can be used as it is. For example, a thicker second substantially intrinsic thin film thickness of about 500-50,000 mm can be used.

Example 1 An experiment was performed using the apparatus shown in FIG. The apparatus comprises a substrate insertion chamber, a first conductive thin film formation chamber, a thicker second substantially intrinsic thin film formation chamber, a second conductive thin film formation chamber, and a second electrode formation chamber. Except for the chamber and the electrode forming chamber, all the chambers to which the plasma CVD method can be applied were used. FIG. 1 shows the structure of the photoelectric conversion element obtained here. The glass substrate 1 on which the tin oxide thin film was formed as the first electrode 2 was heated in a vacuum in the substrate insertion chamber and transferred to the first conductive thin film forming chamber. In order to impart p-type conductivity to the first conductive thin film 3, disilane / dimethylsilane / diborane / hydrogen is used as a raw material gas in 5 / 1.5 / 0.01.
At a pressure of 0.2 Torr, a forming temperature of 250 ° C., and a high frequency power of 1 W, a p-type amorphous silicon carbide film having a thickness of about 100 A was formed. Then, stop supplying diborane,
The ratio of dimethylsilane / disilane was reduced from 1/5 to 0, and the pressure was 0.1 Torr, the formation temperature was 275 ° C, and the high frequency power was 1 W.
Thinner first substantially intrinsic thin film 4 150 mm thick 4
Was formed. The substrate was then transferred to a thicker second substantially intrinsic film deposition chamber. A thicker second substantially intrinsic thin film 5 is first prepared by forming disilane 2scc
m, deuterium 50sccm, reaction pressure 0.25Torr, high frequency power 15W,
After setting the substrate temperature to 300 ° C and forming a Si thin film of about 40 ° C, without stopping the discharge, immediately stop the supply of disilane, deuterium 50sccm, pressure 0.25Torr, high frequency power 15
The W thin film was exposed to the Si thin film at a substrate temperature of 400 ° C. for 10 seconds during discharge. After the reforming, disilane was introduced again at 2 sccm, and a film forming process was performed.
The reforming step was repeated under the same conditions. Formation was performed up to about 6000 ° by repeating 150 times. Next, it was transferred to the second conductive thin film forming chamber. In order to impart n-type conductivity, disilane / phosphine / hydrogen is introduced into the second conductive thin film 6 at a ratio of 10 / 0.01 / 100 at a ratio of 10 / 0.01 / 100 at a pressure of 0.2 Torr and a forming temperature of 250 ° C. Then, an n-type microcrystalline silicon film having a thickness of about 500 ° was formed at an RF power of 80 W. Then, it was transferred to a second electrode forming chamber and formed as a second electrode of an aluminum film by vacuum evaporation.

The photoelectric characteristics of the amorphous silicon photoelectric conversion device thus obtained were measured by irradiating light of AM-1.5, 100 mW / cm ² with a solar simulator. As a result, the photoelectric conversion efficiency
13.0%, short-circuit photocurrent 18.87mA / cm ² , open-end voltage 0.902V,
It showed excellent performance with fill factor 0.766. In addition, to study the photostability of this amorphous solar cell, AM-1.5, 100
Light of mW / cm ² was continuously irradiated for 20 hours, and a change in photoelectric conversion efficiency was observed. The change in the photoelectric conversion efficiency after 20 hours with respect to the initial photoelectric conversion efficiency was 1% or less, which proved that the photoelectric conversion element was extremely stable.

[Comparative Example 1] In Example 1, in forming a thicker second substantially intrinsic thin film, after forming a Si thin film, it was formed to a thickness of 6000 mm without going through a reforming step, and a photoelectric conversion element was formed. Was prepared. The performance of the photoelectric conversion element obtained by this method is as follows:
The photoelectric conversion efficiency was 11.9%, the short-circuit photocurrent was 17.27 mA / cm ² , the open-circuit voltage was 0.910 V, and the fill factor was 0.756, which was lower than the performance shown in Example 1. Also, when the photostability was measured, the rate of change in photoelectric conversion efficiency showed a change of about 10%, and although this was slightly improved compared to the normal one using no deuterium, reliability was still lacking. It is a characteristic. This comparative example shows that a reforming step of exposing to a deuterium atmosphere is essential, and that the effects of the present invention cannot be fully exhibited without this.

Comparative Example 2 In Example 1, hydrogen was used instead of deuterium in forming a second substantially intrinsic thin film having a greater thickness.
A photoelectric conversion element was manufactured. The performance of the photoelectric conversion device obtained by this method was as follows: photoelectric conversion efficiency 12.8%, short-circuit photocurrent 18.7%
0 mA / cm ² , open-end voltage of 0.900 V, and fill factor of 0.760. Although the performance was slightly inferior to that of Example 1, it showed excellent performance. When the light stability was measured, the rate of change in photoelectric conversion efficiency was as follows. A change of about 5% was shown. Although this rate of change is much better than the conventional rate, it is considerably inferior to the example of the present invention, indicating the effect of the addition of deuterium.

〔The invention's effect〕

As is evident from the above Examples and Comparative Examples, at least a thicker second substantially intrinsic thin film was treated in a discharge atmosphere containing deuterium in the reforming step, with a single repeated film thickness of 5 to 100 °, The fabricated photoelectric conversion element is
The thin film had much better photoelectric characteristics than the photoelectric conversion element produced without performing the reforming step, and the stability to light irradiation, which is essentially a problem, was greatly improved. Therefore, it is possible to provide a technology that enables high conversion efficiency and high reliability required for the power solar cell of the present invention, and it is a very useful invention for the energy industry.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of the configuration of a photoelectric conversion element obtained according to the present invention. FIG. 2 is a schematic view showing an example of a preferred apparatus for forming the element of the present invention.
In FIG. 2, 1... A substrate insertion chamber, 2... A first conductive thin film forming chamber, 3... A thicker second substantially intrinsic thin film forming chamber, 4. Forming chamber, 5: Second electrode forming chamber, 6: Substrate removal chamber, 7: Substrate, 8 ...
... discharge power application electrode, 9 ... substrate heating electrode, 10 ... metal mask, 11 ... evaporation source, 12 ... vacuum evacuation line, 13 ...
... Source gas introduction line, 14 ... Three-way switching valve, 15
…… Gate valve

Continuation of the front page (56) References JP-A-63-304673 (JP, A) JP-A-2-155225 (JP, A) JP-A-61-218177 (JP, A) JP-A-61-222113 (JP, A) , A) JP-A-62-51210 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/04

Claims (1)

(57) [Claims] 1. A first electrode, a first conductive thin film, a thinner first substantially intrinsic thin film, a thicker second substantially intrinsic thin film, a second conductive film on a substrate. In the photoelectric conversion element formed in the order of the thin film and the second electrode, at least the formation of the thicker second substantially intrinsic thin film is performed using disilane gas and deuterium gas, The step of forming a semiconductor thin film having a hydrogen content of 20 atomic% or less and the step of exposing the formed thin film to a discharge atmosphere containing deuterium are performed repeatedly, and the thickness of the semiconductor thin film formed in one repetition is reduced. A photoelectric conversion element characterized by having a size of 5 to 100 mm.