JPH0552673B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to increasing the efficiency of silicon photoelectric conversion elements. Attempts have been made to improve the efficiency of silicon photoelectric conversion elements by various means. One of these is an attempt to increase the amount of light incident on the photoactive region. That is,
The element is formed by disposing a material having a wide optical forbidden band (hereinafter referred to as Eopt) on the light incident side. Such thin film materials with low incident light loss are called window materials. With conventional techniques, it has been difficult to form such window materials using only silicon raw materials. Therefore, amorphous silicon carbide (hereinafter referred to as a-SiCx) and amorphous silicon nitride (hereinafter referred to as a-SiNy), in which carbon and nitrogen are introduced into silicon, have been considered as wide gap windows, and boron-doped P-type a-SiCx is partially used as a window material for heterojunctions. However, (i)a-
SiCx and a-SiNy are inherently difficult to conduct electricity, and when they are used as window materials, problems arise due to low electrical conductivity. In order not to reduce electrical conductivity, a
-In SiCx and a-SiNy, increasing the amount of C and N added, that is, increasing the values of x and y.
It was not possible to increase Eopt. For example, for P-type a-SiCx, it is said that adjusting Eopt to 1.9 to 2.0 eV is optimal in terms of balance with electrical conductivity, but the electrical conductivity at this time is approximately 10 ^-7 s. -cm ^-1 is still low, and acts as a resistance component in photoelectric conversion elements such as solar cells, which is disadvantageous for improving efficiency. (ii) Furthermore, a carbon source must be used as a raw material for a-SiCx formation. As a result, carbon is deposited inside the glow discharge chamber, and a new problem arises in that the deposited carbon must be removed. Since the above-mentioned electrical conductivity is greatly affected by the carbon content, the composition and control of the silicon raw material and the carbon raw material must be strictly controlled, which complicates the process. The present invention has been made in view of these points, and its purpose is to provide an n-type, high conductivity and wide Eopt.
An object of the present invention is to provide a photoelectric conversion element formed using a silicon thin film suitable as a window material and a method for manufacturing the same. As a result of intensive studies from the above viewpoint, the present inventors found that a silicon thin film formed by glow discharge electrolysis using disilane gas has an increased Eopt (Japanese Patent Application No. 134709/1982), and also found a method for forming a thin film. As a result of our investigation, we found that when adding an n-type conductivity imparting substance to the disilane gas, the conductivity must be at least 1×10 ^-3 s·cm ^-1 or higher, and a high one is 1 s·cm ^-1 and It was discovered that a silicon thin film having Eopt of 1.80 eV, with a wide one exceeding 2.0 eV, having properties suitable as a window material could be obtained, and by using the thin film as a window material, the photoelectric conversion element of the present invention was completed. The inventors also discovered that a silicon thin film having the above characteristics could be obtained more accurately by performing the glow discharge decomposition operation at a specific film formation rate, and completed the method for forming the device of the present invention. That is, the present invention provides a method for manufacturing a pin-type silicon photoelectric conversion element consisting of a p-type silicon layer, an i-type silicon layer, and an n-type silicon layer, which comprises: A mixed gas consisting of a conductivity type imparting substance and a diluting gas is introduced into the glow discharge chamber, and a gas of 50 kJ or more per unit mass of disilane is introduced into the glow discharge chamber.
It is decomposed by glow discharge with energy of 500 kJ or less applied, and the formation rate of the thin film on the substrate is 2 Å/2.
n with an optical bandgap exceeding 1.80eV and conductivity of 1x10 ^-3 s cm ^-1 or more while keeping it below sec
1. A method for manufacturing a silicon photoelectric conversion element, characterized in that (ii) the formed n-type silicon layer is disposed on a light incident side. It provides: Hereinafter, the constituent elements of the present invention will be explained in detail. In the pin type silicon photoelectric conversion element of the present invention,
At least this n-type silicon layer is made of disilane, n
It is formed by decomposing a gas mixture consisting of a conductivity-imparting material and a diluent gas by glow discharge. Here, disilane refers to a polysilane compound represented by the general formula Si _o H _2o+2 where n=2. Of course, it is preferable that disilane be of high purity, but there is nothing wrong with including trisilane, tetrasilane, etc. (n = 3, 4 in the general formula), which behave in the same way as disilane in glow discharge. be. Further, a small amount of monosilane (n=1) may be mixed. Disilane can be synthesized by a physical synthesis method in which monosilane is partially converted into disilane through silent discharge, but from the point of view of industrially producing solar cells, it is preferable to use a chemical method that can produce a large quantity of stable quality. It is preferable to use a method of synthesis (for example, a method of reducing hexachlorodisilane). The silicon thin film to constitute the p-layer or i-layer other than the n-layer can be obtained by glow discharge decomposition using monosilica gas as a raw material gas by a normal method. Of course, there is nothing to prevent the disilane used to form the n-layer of the present invention from also being used as a raw material gas for the p-layer and i-layer structures. Note that trisilane, tetrasilane, etc. may of course be contained. Further, the n-type conductivity imparting substance is, for example, PH ₃
It is a group V element compound such as (phosphine) and AsH ₃ (arsine), and is usually used diluted with H ₂ or He. The ratio of these substances to disilane is 0.1 to 5 parts by volume per 100 parts by volume of disilane. In addition, B ₂ H ₆ (diborane) or the like is used as the p-type conductivity imparting substance. As diluting gas for diluting disilane etc., H ₂ ,
He, Ne, Ar, etc. are used. The total amount of diluent gas used for disilane is per part by volume of disilane.
10 parts by volume or more. In addition, for an n-type conductive substance, the substance 1
10 to 1000 parts by volume of diluent gas are used. As described above, the n-type silicon layer of the invention, which is formed by decomposing a gas mixture consisting of disilane, n-type conductivity, a conductivity-imparting substance, and a diluent gas, by an ordinary glow discharge that is well known per se, has an optical energy exceeding 1.80 eV. Although it can have a forbidden band width and a conductivity of 1×10 ^-3 s·cm ^-1 or more, the present invention uses this as the n layer of a pin type silicon photoelectric conversion element, and
The n-type silicon layer is placed on the light incident side. In order to place the n-type silicon layer of the pin-type photoelectric conversion element on the side where light enters, as will be detailed later, (i) If an opaque substrate such as stainless steel is used, (ii) forming silicon layers in the order of p-type, i-type, and n-type, forming a transparent electrode on the outside of the n-type silicon layer, and making the transparent electrode side the light incident side; When using a transparent substrate, in addition to the above, from the substrate side, n-type,
The silicon layers may be formed in the order of i-type and p-type, and the substrate side may be set as the light incident side. The n-type silicon layer of the present invention is probably an n-type hydrogen-containing amorphous silicon thin film that partially contains a microcrystalline state. However, it has been known that an n-type hydrogen-containing amorphous silicon thin film containing a microcrystalline state can be obtained only from monosilane (SiH ₄ ) as a raw material, but its optical forbidden band is at most 1.80 eV. Therefore, it should be clearly distinguished from the silicon thin film of the present invention. The present invention also provides an n-type silicon layer with a wide optical bandgap and high conductivity as described above.
The present invention provides a method for manufacturing a silicon photoelectric conversion element as an n-type layer of a type silicon photoelectric conversion element, which comprises supplying a mixed gas consisting of the above-mentioned disilane, an n-type conductivity imparting substance, and a diluting gas into a glow discharge chamber. However, when forming a thin film on the substrate by decomposing it by glow discharge, (i) the formation rate of the thin film is kept within a specific range of 2 Å/sec or less, and the formed n-type silicon layer is exposed to light. It is placed on the side. When the formation rate of the thin film is increased beyond the above 2 Å/sec, Eopt becomes narrower or the conductivity becomes lower, as shown in Examples and Comparative Examples below.
The purpose of the present invention cannot be achieved. The rate of thin film formation can vary depending on various factors such as the shape of the discharge equipment, electrode structure, distance between electrodes, formation temperature, formation pressure, and gas flow direction, but especially the flow rate (supply amount) of disilane. By changing the parameters of the amount of glow discharge energy and the amount of glow discharge energy, the formation rate correspondingly changes greatly, and it is usually difficult to effectively control the formation rate within an optimal range in conjunction with this. However, the present inventors have determined that "glow discharge energy per unit mass of disilane supplied" [KJ/
By focusing on the factor ``g-Si ₂ H ₆ '' and using this factor as a parameter, we found that the thin film formation rate and the disilane supply amount (flow rate) are uniquely correlated. is 10KJ/g-Si ₂ H ₆
In the above case, that is, per unit mass of disilane,
We discovered the important fact that when glow discharge is performed by applying a discharge energy of 10 KJ or more, the rate of thin film formation is almost unaffected by the glow discharge energy and changes depending only on the flow rate of disilane. be. Based on this fact, the optimum supply amount of disilane can be easily determined as follows.
That is, it is sufficient to apply glow discharge energy of 10 KJ or more per unit mass of disilane and measure each thin film formation rate for each amount of disilane supplied. The glow discharge energy per unit mass of disilane in the present invention is calculated using the following formula. Glow discharge energy (J/g-
Si ₂ H ₆ ) Applied glow discharge power / (raw material gas flow rate) × (average molecular weight / 22.4) × 1 weight fraction of disilane () For example, (i) Disilane (Si diluted to 10 vol% with helium (He)) ₂ H ₆ ) 0.02/min, (ii) phosphine (PH ₃ ) diluted to 1 vol% with hydrogen (H ₂ ).
0.002/min, (iii) H ₂ 0.06/min to the mixed raw material.
The energy when applying a glow discharge power of 100 W is calculated as follows. Raw material gas flow rate = 0.02 + 0.002 + 0.06 = 0.082 (/min) Average molecular weight of raw material gas = {(62.2 x 2/82) + (4 x 18/82) +
(31×0.02/82)+(2×61.98/82)≒3.914(gr) Weight fraction of disilane (62.2×2/82)/3.914
≒0.388Substituting these into the above formula (), energy per unit mass of disilane = 100
/0.082/60×3.914/22.4×0.388=162×103 [J/ ^g
−Si ₂ H ₆ ] Now, if 10 ³ J is expressed as KJ, the energy is
It can be expressed as 162KJ/g-Si ₂ H ₆ . In the present invention, the value of glow discharge energy per unit mass of disilane calculated by the above method is at least 10 KJ/g-Si ₂ H ₆ or more, preferably 50 to 500 KJ/g-Si ₂ H ₆ is added to form a thin film. form. If a large amount of energy exceeding 500KJ/g-Si ₂ H ₆ is applied, the balance between the raw material gas and the discharge is likely to become unstable, making it difficult to form a stable thin film, and adding more energy than necessary is itself an economic problem. In addition to leading to losses, a large and expensive glow discharge power supply must be installed. on the other hand,
Although the thin film obtained by applying a glow discharge energy of less than 50 KJ/g-Si ₂ H ₆ tends to have a slightly lower conductivity, it can sufficiently achieve the object of the present invention. In the present invention, the temperature for forming the thin film must be selected appropriately, but a range of 100 to 400°C is usually preferred. Eopt becomes large at low formation temperatures, but at 100℃
If the temperature is lower than that, the formation of a silicon thin film will not proceed effectively and the film will peel off or yellow amorphous silicon powder will be generated, making it impossible to achieve the object of the present invention. In addition, increasing the formation temperature improves the conductivity.
If the temperature is increased too much above 400°C, Eopt will decrease, so in the present invention, it is preferable to form a thin film at 400°C or lower. Furthermore, at temperatures exceeding 400°C, problems such as heat resistance of photoelectric conversion element substrates and electrodes, and damage caused by plasma during glow discharge become more prominent. That is, if defects occur in the substrate or electrodes, the photoelectric conversion efficiency will naturally decrease, so it is better to avoid forming an n-type silicon film at a temperature exceeding 400°C. In addition, although the relationship between the thin film formation temperature and Eopt is shown in the example below, Eopt increases as the formation temperature decreases.
increases, and in this example it becomes 2.0 eV at 150°C. On the other hand, the conductivity shows that although it decreases slightly, it still maintains a high value of 9.1×10 ^-2 s·cm ^-1 even at 150°C. Next, a more specific embodiment of manufacturing the silicon photoelectric conversion element of the present invention will be described. First, a case will be described in which an opaque stainless steel substrate is used as the substrate. A stainless steel substrate, which also serves as a first 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 mixed gas of a P-type conductivity imparting substance, silane, and diluent gas is introduced therein, and glow discharge is performed to form a P-type silicon layer on the first electrode. An i-type silicon layer is then formed on the p-type silicon layer by introducing silane and diluent gas. Next, an n-type silicon layer is formed by the method of the present invention. That is, a mixed gas consisting of disilane, an n-type conductivity imparting substance, and a diluent gas is introduced so that the formation rate of the n-type silicon layer is 2 Å/sec or less, the formation temperature is 100 to 400°C, and the formation pressure is 0.5 to 5 Torr. , an n-type silicon layer is formed by glow discharge under conditions of glow discharge energy of 50 to 500 KJ/g-Si ₂ H ₆ . Finally, a second transparent electrode is formed to obtain the photoelectric conversion element of the present invention. Furthermore, when using a transparent substrate such as a glass substrate, in addition to the embodiment described above,
It is possible to form a photoelectric conversion element having a structure in which the substrate side is the light incident side by forming silicon layers in the order of type, i type, and p type. In the above, the thicknesses of the p-type and i-type silicon layers are 50 to 500 Å and 3000 to 7500 Å, respectively,
Further, the thickness of the n-type silicon layer used is 50 to 500 Å. Note that when forming the n-type silicon layer, it is preferable to increase the flow rate of the diluent gas in the above embodiment. This is because an increase in the flow rate of the diluent gas improves the conductivity of the n-type silicon layer, leading to an improvement in photoelectric conversion efficiency. There are no particular restrictions on the material of the substrate and the materials of the first and second electrodes, and conventionally used materials can be usefully used. For example, (i) the substrate may be insulating or conductive, transparent or opaque. Specifically, a film or plate-shaped material made of a substance such as glass, alumina, silicon, stainless steel, aluminum, molybdenum, or a heat-resistant polymer can be effectively used as the substrate. Further, (ii) as the first and second electrode materials, transparent or light-transmitting materials must be used on the light incident side, but there are no other restrictions. It is useful as a thin film and electrode material for aluminum, molybdenum, nichrome, ITO, tin oxide, stainless steel, etc. The above implementation mode is based on one glow discharge chamber.
An example of forming a type photoelectric conversion element was shown, but these
Of course, the pin-type silicon layers can also be formed in separate glow discharge chambers that are connected to each other. As described above, the present invention provides a novel photoelectric conversion element having an n-type silicon layer formed without using carbon or nitrogen as a window material, and provides an excellent technology in its manufacturing method. be. The device of the present invention is particularly suitable as a solar cell. The present invention will be described in more detail with reference to Examples below, but these are merely illustrative and do not limit the technical scope of the present invention (Article 70 of the Patent Law). Example 1 The substrate of a capacitively coupled high-frequency plasma CVD ( C hemical V apor D position) apparatus having a glow discharge chamber having a substrate heating means, evacuation means, gas introduction means, and parallel plate electrodes in which the substrate can be installed. A glass substrate with electrodes made of ITO was installed in the installation area. The substrate was heated to a temperature (formation temperature) of 250°C while evacuation was performed to below 10 ^-7 Torr using an oil diffusion pump. Disilane diluted with He (dilution ratio Si ₂ H ₆ /He = 1/9), diluted with H ₂
B ₂ H ₆ (dilution ratio B ₂ H ₆ /H ₂ = 1/999), respectively.
Introduced at a flow rate of 50 c.c./min, 10 c.c./min, and a pressure of 1 Torr.
Glow discharge was performed for 30 seconds to form a p-type silicon layer. Next, add 500% of the He diluted disilane.
A flow rate of cc/min was introduced, and an i-type silicon layer was formed with a blow discharge energy of about 17 KJ/g-Si ₂ H ₆ at a pressure of 5 Torr. The time required to form the i-type silicon layer was 2 minutes. Then the He diluted disilane, H ₂
Three types of gases, PH ₃ (dilution ratio PH ₃ /H ₂ = 1/99) and H ₂ , were diluted at 20 c.c./min, 2 c.c./min and
A flow rate of 60c.c./min is introduced into the glow discharge chamber to increase the pressure.
Adjusted to 1Torr. Glow discharge power 130W, that is, glow discharge energy approximately 210KJ/g-
Glow discharge was performed using Si ₂ H ₆ for 1 minute and 40 seconds to form an n-type silicon layer. Next, by electron beam evaporation
ITO was vapor-deposited to make a transparent electrode. The characteristics were measured by irradiating AMI light from the n-type silicon layer side using a solar simulator. The result is Voc=0.87V, Isc
=13.7mA/ ^cm2 , FF=0.586, photoelectric conversion efficiency 6.98
% and silicon alone, it was extremely excellent. Example 2 In Example 1, only the formation temperature of the n-type silicon layer was changed to 150°C. The characteristics of the resulting device are Voc = 0.89V, Isc = 14.1mA/cm ² , FF
= 0.562, and the photoelectric conversion efficiency was even better, 7.05%. Examples 3 to 7 High frequency plasma CVD used in Example 1
An n-type silicon layer was formed on a Corning 7059 glass substrate using the same equipment as in Example 1, except that the formation temperature was changed. The formation temperature and the characteristics of the obtained n-type silicon film are summarized in Table 1.

[Table] Comparative Example 1 In Example 1, the flow rates of disilane, PH ₃ and diluent gas were increased so that the formation rate of the n-type silicon layer was 5 Å/sec. The characteristics of the resulting device are Voc = 0.83V, Isc = 6.2mA/cm ² ,
FF=0.62, photoelectric conversion efficiency was 3.19%, and Isc and photoelectric conversion efficiency decreased considerably. Comparative Example 2 In Example 2, as in Comparative Example 1, the formation rate of the n-type silicon layer was set to 5 Å/sec. The characteristics of the obtained device are Voc = 0.85V, Isc = 9.8mA/cm ² ,
FF=0.43, photoelectric conversion efficiency was 3.58%, and the FF decreased significantly.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a pin-type silicon photoelectric conversion device consisting of a p-type silicon layer, an i-type silicon layer, and an n-type silicon layer, comprising: (i) at least the n-type silicon layer formed of disilane, n-type silicon A mixed gas consisting of a conductivity type imparting substance and a diluting gas is introduced into the glow discharge chamber, and a gas of 50 kJ or more per unit mass of disilane is introduced into the glow discharge chamber.
It is decomposed by glow discharge with energy of 500 kJ or less applied, and the formation rate of the thin film on the substrate is 2 Å/2.
n with an optical bandgap exceeding 1.80eV and conductivity of 1x10 ^-3 s cm ^-1 or more while keeping it below sec
1. A method for manufacturing a silicon photoelectric conversion element, characterized in that (ii) the formed n-type silicon layer is disposed on a light incident side. 2. The silicon photoelectric conversion element according to claim 1, which suppresses the formation rate of the n-type silicon layer thin film to 2 Å/sec or less by controlling the supply amount of disilane in the mixed gas introduced into the glow discharge chamber. Production method.