JPH0563950B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improving the efficiency of an amorphous silicon photoelectric conversion element. Currently, attempts are being made to improve the efficiency of amorphous silicon photoelectric conversion elements by various means, one of which is an attempt to increase the amount of light incident on the photoactive region. For this reason, a material (such a material is referred to as a window material) having an Eopt wider than the optical forbidden band (hereinafter referred to as Eopt) of the i-type amorphous silicon, which is the photoactive region, is used as a window material. Attempts have been made to form an element by arranging it on the incident side. As such window materials, amorphous silicon carbide (hereinafter referred to as a- _SiCx ) and amorphous silicon nitride (hereinafter referred to as a-SiNy), which are silicon with carbon and nitrogen introduced and bonded, have been considered.
Some p-type a-SiC _x doped with boron has been put into practical use. However, the above a-SiC _x and SiNy
are inherently difficult to conduct electricity, and when they are used as window materials, there is always a problem that the electrical conductivity decreases. Therefore, in order not to reduce the electrical conductivity, a-SiC _x
For a-SiNy, increase the values of x and y,
It was not possible to increase Eopt. ^For example, in a ^- _SiC Furthermore, since it is low, it acts as a resistance component in the photoelectric element, which is disadvantageous for improving efficiency. Therefore, even if Eopt is wider than this, the loss due to the increase in resistance will be greater than the benefit of capturing short wavelength light, and as a result, the overall photoelectric conversion efficiency will be lower than that of window materials with such a wide gap. On the contrary, the use of As a result of intensive studies from the above viewpoint, the present inventors found that Eopt increases in amorphous silicon (hereinafter amorphous silicon will be referred to as a-Si:H) formed by glow discharge decomposition using disilane gas. (Patent Application No. 57-134709) As a result of further investigation, p-type a-Si:H obtained by doping a-Si:H with a substance that imparts p-type conductivity type is
It has Eopt exceeding 1.70eV and its conductivity is
It exceeded 10 ^-4 S cm ^-1 . That is,
We thus demonstrated that disilane and p
The inventors have completed the present invention by discovering that p-type a-Si:H, which is formed by glow discharge using a material that imparts conductivity type, has properties suitable as a window material for photoelectric conversion elements. That is, the present invention provides a method for manufacturing a pin-type amorphous silicon photoconversion device including at least a p-type amorphous silicon layer and an i-type amorphous silicon layer, which comprises disilane and a p-type conductivity imparting substance. A mixed gas consisting of is introduced into the glow discharge chamber, and an energy of 10 kJ or less per unit mass of the disilane is applied to decompose the disilane by glow discharge to produce an optical forbidden band wider than the optical forbidden band of the i-type amorphous silicon layer. and decomposing the p-type amorphous silicon layer so that the formed p-type amorphous silicon layer is located on the light incident side. A method for manufacturing high-quality silicon photoelectric conversion elements. It provides: The present invention will be explained in detail below. In the pin-type amorphous silicon photoelectric conversion device of the present invention, at least this p-type amorphous silicon layer (a-Si:H) is heated by glow discharge to a mixed gas consisting of disilane and a p-type conductivity imparting substance. Formed by decomposition. In the present invention, disilane has the general formula SinH _2o+2
It corresponds to n=2 among the disilanes represented by, and has the chemical formula of Si ₂ H ₆ . Of course, disilane is preferably of high purity, but trisilane, tetrasilane, etc. that behave similarly to disilane in glow discharge (n = 3, 4 in the above general formula)
There is no problem with the fact that it is included. Furthermore, it does not matter if a small amount of monosilane is mixed in. Disilane can be produced by physical synthesis methods, such as by separating monosilane (n = 1 in the above general formula), which partially changes into disilane when it is silently discharged, or by chemical synthesis methods. In order to industrially produce photoelectric conversion elements in large quantities, it is practically convenient to use a chemical synthesis method (for example, a method such as reducing hexachlorodisilane) that can produce large quantities of photoelectric conversion elements of stable quality. In addition, the substance that imparts p-type conductivity is diborane (B ₂ H ₆ ), for example, and it is generally recommended to use it diluted with a diluent gas such as H ₂ or He for safety and control of doping amount. Preferable from above. The ratio of these gases to disilane is
It is 0.1 to 5 parts by volume per 100 parts by volume. In the present invention, an n layer other than a p-type layer or an i
The silicon layer to be formed is obtained by glow discharge decomposition using monosilane gas or any silane represented by the general formula SinH _2o+2 (n=1 to 3) as a raw material gas. Preferably, however, as shown in the reference example
A monosilane having an Eopt of 1.65 to 1.67 (n=1 in the above general formula) is used. When using disilane (also n = 2) or trisilane (also n = 3), give p-type a-Si::H an energy of 3 KJ/g-Si ₂ H ₆ or less as shown in the example. Just form it. In addition, as n-type conductivity imparting substances, PH ₃ (phosphine), AsH ₃ (arsine) are used.
etc. are used. In other words, compounds such as Sn and Ge can be added to these amorphous silicon layers.
In short, these amorphous substances can also be added. In short, it is sufficient that the Eopt of these amorphous materials is smaller than that of the p-type a-Si:H located on the light incident side. Therefore, when used in the prior art, a-Si:F:H, a-Si:Ge:H, a
-Si:Sn:H etc. can be used in the present invention without any problem. In the present invention, it is preferable that disilane, which is a raw material for forming p-type a-Si:H, and a p-type conductivity imparting substance are diluted and mixed with a diluent gas, but such diluent gas may include He, Ar, _H2 , etc. desirable. Since the reproducibility of photoelectric characteristics is improved when a diluent gas is used, it is thought that it probably has the role of reducing the influence of trace impurities and mitigating damage to the film caused by the prism. There is no particular limitation on the dilution ratio, but it is 5 to 5.
It is convenient for manufacturing that it is in the range of 20vol%,
The above effects are greatly exhibited. Of course, i-type a-Si:H or n-type a-
The use of a diluent gas during Si:H formation is also preferred for similar reasons. As described above, the p-type amorphous silicon layer of the present invention is formed by decomposing a mixed gas consisting of disilane, a p-type conductivity-imparting substance, and preferably a diluent gas by a commonly known glow discharge. It has an optical forbidden band wider than the optical forbidden band of the i-type amorphous silicon layer, and the photoelectric conversion element of the present invention has such a p-type amorphous silicon layer disposed on the light incident side. It is something. In order to arrange the p-type amorphous silicon layer of the pin-type photoelectric conversion element on the light incident side, as will be explained in detail later, (i) when using an opaque substrate such as stainless steel, it is necessary to From the substrate side: n type, I type, p type
A silicon layer may be formed in the order of the mold, a transparent electrode may be formed on the outside of the p-type silicon layer, and light may be incident on the transparent electrode side.Also, (ii) if a transparent substrate such as a glass substrate is used, In addition to the above, silicon layers may be formed in the order of p-type, i-type, and n-type from the substrate side, and the substrate side may be used as the light incident side. The present invention also provides a p-type amorphous silicon layer having a wider optical forbidden band width than that of the i-type amorphous silicon layer as described above, and a silicon photovoltaic layer used as the p-type layer of a pin-type amorphous silicon photoelectric conversion element. The present invention provides a method for manufacturing a conversion element, which comprises the above-mentioned disilane,
A mixed gas consisting of a p-type conductivity-imparting substance and preferably a diluent gas is supplied into a glow discharge chamber, and energy of 10 KJ or less per unit mass of disilane is applied and decomposed by glow discharge to form a p-type amorphous silicon layer, The decomposition is performed so that the p-type silicon layer is formed on the light incident side. In the present invention, the glow discharge energy given per unit mass of disilane is 10 KJ or less.
This is to maintain the Eopt of p-type a-Si:H greater than 1.70 eV to satisfy the performance as a window material. That is, as shown in the examples below,
Eopt changes depending on the glow discharge energy and becomes larger in the region where the energy is small, but as is clear from the similar reference example mentioned later, the Eopt of a-Si:H made from monosilane is about 1.65 to 1.67 eV, As mentioned above, by selecting the energy range for applying disilane as a raw material gas to 10KJ or less, the Eopt of p-type a-Si:H becomes i-type a-
The requirement of the present invention to make Eopt sufficiently larger than Si:H is fully satisfied. Further, the lower limit value of claw discharge energy may be any value that can form a stable glow discharge state, and it is preferable that this value changes depending on the conditions of the glow discharge equipment and the raw material gas used. For disilane alone or disilane diluted with diluent gas such as helium (He) or argon (Ar), it is 0.5 KJ/g-Si ₂ H ₆ or more, and for disilane diluted with hydrogen (H ₂ ) or Big 1.5KJ/g
−Si ₂ H ₆ or more. To summarize the above, in the present invention, p-type a-
The preferred range of glow discharge energy given to form Si:H is 0.5 to 10 KJ/g − Si ₂ H ₆
It is. If energy outside this range is supplied, the effects of the present invention can no longer be expected. i.e. 10
When applying energy exceeding KJ/g-Si ₂ H ₆ , Eopt becomes small as shown in the comparative example, and the performance as a window material is not exhibited, and 0.5KJ/g-
If the energy is lower than that of Si ₂ H ₆ , the discharge itself may not occur, or even if it does occur, the discharge will not be stable, and the formation of p-type a-Si:H itself becomes a problem. The glow discharge energy value per unit mass of disilane in the present invention is calculated by the following formula. Glow discharge energy value (J/g-Si ₂ H ₆ = applied glow discharge power / (raw material gas flow rate) × (average molecular weight / 22.4
) x weight fraction of disilane
() For example, when a power of 10 W is applied to 500 c.c./min of disilane (Si ₂ H ₆ ) diluted to 10% by volume with helium (He), the energy value is calculated as follows. Average molecular weight = (62.2184 x 0.1 + 4.0026 x 0.9) = 9.824 (g) The weight fraction of Si ₂ H ₆ is 62.2184 x 0.1 / 9.824 = 0.633
It is. Substituting these into the above equation (), the energy value per unit mass of disilane is 10/0.5/60×9.824/22.4×0.633=1732 [J/g−Si ₂ H ₆
] Now, if 10 ³ J is expressed as KJ, the above energy value can be expressed as approximately 1.7 KJ/g−Si ₂ H ₆ . In the present invention, it is preferable to increase the raw material gas flow rate when forming p-type a-Si:H.
In the above energy output formula (), the flow rate is in the denominator, and as the flow rate is increased, the glow discharge power that can be applied can be increased, and the allowable range of power variation is also increased, making discharge management easier. . Furthermore, as the flow rate increases, the rate of formation of a-Si:H also increases. In addition to these advantages, a favorable result is also obtained in that the variation in conductivity of p-type a-Si:H is reduced. It is difficult to specifically and unambiguously indicate a preferable flow rate range because the range varies depending on the shape of the a-Si:H forming equipment, capacity material, etc., but examples of preferable flow rates are shown in the example below. Ta. In the present invention, the temperature when forming p-type a-Si:H is maintained at 450°C or less, preferably from 100 to 400°C. When the glow discharge energies are equal, the lower the temperature, the larger the Eopt, but at temperatures lower than 100°C, a-Si:H film formation does not proceed effectively;
The object of the present invention cannot be achieved because the film peels off or yellow amorphous silicon powder is generated. Also, at temperatures exceeding 400℃, a-Si:
There is no problem in forming H, but as the temperature rises further, electrical properties such as Eopt deteriorate, and at such temperatures, problems with heat resistance of the substrate and electrodes become more prominent. That is, it is better to avoid forming a-Si:H at temperatures exceeding 400° C., since the efficiency of the photoelectric conversion element also decreases when the substrate is at a temperature where the electrodes develop defects due to heat. Furthermore, in the present invention, it is preferable to increase the pressure during formation of p-type a-Si:H to 1 to 10 Torr. By doing so, the photoelectric conversion efficiency can be further improved. The reason why the efficiency improves by increasing the pressure is unknown, but by increasing the pressure,
It is thought that because the mean free path of the plasma becomes small, the plasma does not directly damage the substrate, electrodes, a-Si:H, etc. There are no particular limitations on the material of the substrate and the materials of the first and second electrodes used in the present invention, and conventionally used materials can be usefully used. For example, the substrate may be insulating or conductive, transparent or opaque.
Specifically, a film or plate-shaped material made of glass, alumina, silicon, stainless steel, aluminum, molybdenum, heat-resistant polymer, or the like can be effectively used as the substrate. . Of course, transparent or light-transmitting materials must be used as the materials for the first and second electrodes on the light incident side, but there are no other restrictions. aluminum, molybdenum, nichrome,
Thin films or plates of ITO, tin oxide, stainless steel, etc. are effectively used as electrode materials. Next, regarding an embodiment of the present invention, a case where a transparent substrate is used will be described. A glass substrate provided with a transparent second electrode is placed in a reaction chamber capable of glow discharge, and heated and maintained at a temperature of 100 to 400°C under reduced pressure. A p-type conductivity-imparting substance, disilane, and diluent gas are introduced therein as raw materials, and glow discharge energy of 10 KJ or less per unit mass of disilane is applied to perform glow discharge at a pressure of 1 to 10 Torr. In this way, a layer of p-type a-Si:H is formed on the second electrode. Then, by introducing silane and a diluent gas, an i-type a-Si:H layer is formed on the p-type a-Si:H layer.
A Si:H layer is formed by glow discharge. Then n
A material that imparts conductivity to the mold, silane, and a diluent gas are introduced as raw materials, and the n-type a-
Forms a Si:H layer. Finally, a third electrode is formed to obtain the photoelectric conversion element of the present invention. Furthermore, in addition to the embodiments described above, a photoelectric conversion element in which light enters from the opposite side of the substrate is also possible. At this time, n-type, i-type, and p-type layers may be formed in this order from the substrate side, and a transparent second electrode may be formed on the p-type a-Si:H layer. The embodiment described above is a pin type A in one glow discharge chamber.
Although an example of forming -Si:H has been shown, it is of course possible to form these a-Si:H in separate, connected glow discharge chambers. In the present invention, the thickness of the p-type a-Si:H layer is 50 to 500 Å. Also, n-type a-
The thickness of the Si:H layer and i-type a-Si:H layer is 50 mm each.
~500 Å, approximately 3000-7500 Å. As described above, the present invention provides a novel photoelectric conversion element in which a new window material that can replace a-SiC _x etc. is formed without using carbon or _nitrogen . Since there is no need to use hydrocarbons as a raw material for formation, there is no need to deposit carbon inside the glow discharge chamber, eliminating the problem of its removal.Also, since hydrocarbons can be removed from the raw material gas, raw material management can be improved. Si to reduce complexity and further manage Eopt conductivity
It is no longer necessary to control the composition ratio of C and C, and the window material can be formed simply by using disilane as a raw material, which is an excellent effect. Hereinafter, the present invention will be explained in more detail with reference to Examples. Examples 1 to 9 (Measurement of Eopt of p-type amorphous silicon thin film) Capacitively coupled type with substrate heating means, evacuation means, gas introduction means, and a glow discharge chamber having parallel plate electrodes in which the substrate can be installed. A 7059 glass substrate manufactured by Corning was installed in the substrate installation section of a high-frequency plasma CVD ( Chemical Vapor Deposition ) device. While evacuating to 10 ⁻⁷ Torr or less using an oil diffusion pump, the substrate was heated so that the temperature of the substrate mounting portion (thin film formation temperature) became the value shown in Table 1.
Disilane diluted with He (dilution ratio Si ₂ H ₆ /He = 1/9)
and H ₂ diluted B ₂ H ₆ (dilution ratio B ₂ H ₆ /H ₂ = 1/99), and added the flow rate and glow discharge power shown in Table 1 to form a p-type amorphous silicon thin film. Formed. The flow rates of disilane and B ₂ H ₆ in Table 1 indicate the total flow rate including the diluent gas.
The thin film formation time was approximately 13 minutes and 40 seconds, and Eopt, which formed a thin film of approximately 5000 Å, measured the light absorption coefficient α of the thin film with a spectrophotometer, and then calculated (αhν) with respect to the energy of incident light (hν). ^1/2 was plotted, the straight line portion was extrapolated, and the value of the intercept with the hν axis was obtained.
The conductivity was measured by forming electrodes at intervals of 200 μm, applying a voltage between the electrodes, and measuring the current. As a reference example, disilane and monosilane are used at 25KJ/
The Eopt of the silicon thin films obtained by glow discharge with energy of g-Si ₂ H ₆ and 30 KJ/g-SiH ₄ were 1.75 eV and 1.64 eV, respectively. That is, the first
As shown in the table, the discharge energy is 10KJ/g-
By keeping Si ₂ H ₆ or less and appropriately selecting the formation temperature, the requirements of the present invention can be satisfied.

[Table] Examples 10 to 12 (Creation of photoelectric conversion elements and measurement of characteristics) Pin-type photoelectric conversion elements were formed using the plasma CVD apparatus used in Examples 1 to 9, and their characteristics were measured. In other words, a glass substrate with transparent electrodes is used.
It was installed in the CVD equipment. by oil diffusion pump
While evacuating to 10 ^-7 Torr or less, heating was carried out so that the formation temperature was 250°C. Disilane 50 c.c./min used in the previous example with a doping ratio (volume ratio of B ₂ H ₆ /Si ₂ H ₆ ) of 2%, B ₂ H ₆ 10 c.c. diluted to 0.1 vol% with H ₂ ./min and perform glow discharge for 30 seconds at a pressure of 2 Torr to give the p-type amorphous silicon thin film the glow discharge energy shown in Table 2 and give it approximately
A thickness of 100 Å was formed. For example, glow discharge power
At 2.5W, the discharge energy is approximately 1.7KJ/g−
Calculated as Si ₂ H ₆ . Next, after raising the formation temperature to 280°C, 500c.c./min of the disilane was added, and glow discharge energy of approximately 26KJ/g-Si ₂ H ₆ was added at a pressure of 5Torr to form an i-type amorphous silicon thin film for 2 minutes. It was formed to a thickness of approximately 4200 Å.
It was then diluted to 0.1 vol% with the disilane and _H2 .
PH ₃ was introduced at 50 c.c./min and 10 c.c./min, respectively, and the n-type amorphous silicon thin film was heated for about 40 seconds by glow discharge.
A thickness of 100 Å was formed. Next, a thin aluminum film was formed by vacuum evaporation to form a back electrode. For comparison, a photoelectric conversion element was fabricated under the same formation conditions as in the above example except that the energy used to form a p-type amorphous silicon thin film was different. . Table 2 shows the characteristics obtained when AMI light was irradiated from the substrate side using a solar simulator. In the example of the present invention, compared to the example for comparison, the open circuit voltage (Voc) is
It increased by 0.12V and reached 0.85~0.89V. Also, the short circuit current (Jsc) increased by 20-50% and reached 12.6mA/ ^cm2 . The photoelectric conversion efficiency showed an excellent value exceeding 6%. In particular, although the total formation time of the pin-type amorphous silicon thin film as in this example is 1/3 of a second, which is less than 1/10 of the time of the known technology,
The fact that the above conversion efficiency was achieved indicates that the effects of the present invention are significantly superior.

[Table] Example 13 This example differs from Examples 10 to 12 in that the i-type amorphous silicon thin film of the photoactive layer is formed using monosilane SiH ₄ as a raw material. A pin-type photoelectric conversion element was formed using the high-frequency plasma CVD apparatus used in the optical example. That is, after forming a transparent electrode on a glass substrate, it was installed in the CVD apparatus. The substrate was heated to a temperature of 260° C. while being evacuated to 10 ⁻⁷ Torr or less using an oil diffusion pump. disilane and B ₂ H ₆ used in the previous example with a doping ratio of 2%, respectively.
Flow rates of 50 c.c./min and 10 c.c./min were introduced. 8.6K
J/g-Si ₂ H ₆ discharge energy given, pressure 1.5 Torr
Discharge was performed for 30 seconds to form a p-type a-Si:H film. Next, SiH ₄ /H ₂ = 1/10 mixed gas 100c.c./min was added, and the energy was 80.4KJ/g-SiH ₆ , i-type a-
A Si:H film was formed for 25 minutes. Furthermore, the flow rate of the mixed gas used to form this i-layer was set to 50 c.c./mi, and _the pH
An n-type a-Si:H film was formed by introducing a mixed gas of H ₂ =0.1 vol % at 10 c.c./min. It took about 2 minutes to form the n-type a-Si:H film. The time required to form the p, i, n type a-Si film was 27 minutes and 30 seconds. next
The photoelectric characteristics obtained by depositing Al by vacuum evaporation and using it as the second electrode and irradiating AMI light from the substrate side are Voc = 0.87V, Jsc = 14.2mA/cm ² , FF = 0.62, and efficiency is 7.64. %, which was excellent. in this way
When SiH ₄ was used, the formation rate was slow, but excellent photoelectric conversion efficiency was obtained. As described above, the present invention provides a novel photoelectric conversion element in which a window material is formed without using carbon or nitrogen, and provides an excellent technique for manufacturing the same.

Claims (1)

[Claims] 1. A method for manufacturing a pin-type amorphous silicon photoelectric conversion element including at least a p-type amorphous silicon layer and an i-type amorphous silicon layer, the method comprising disilane and imparting a p-type conductivity type. A mixed gas consisting of the substance is introduced into a glow discharge chamber, energy of 10 kJ or less is applied per unit mass of the disilane, and the optical forbidden band of the i-type amorphous silicon layer is decomposed by glow discharge at a temperature of 100 to 400°C. forming a p-type amorphous silicon layer having an optical forbidden band width larger than 1.70 eV, which is wider than the width of the p-type amorphous silicon layer, and the formed p-type amorphous silicon layer is positioned on the light incident side. A method for manufacturing an amorphous silicon photoelectric conversion element, characterized in that the decomposition is carried out as follows. 2. The method for manufacturing a photoelectric conversion element according to claim 1, wherein disilane and a p-type conductivity imparting substance are diluted and mixed with a diluent gas.