JP2522024B2 - Method for manufacturing photoelectric conversion element - Google Patents

Description

The present invention relates to a method for manufacturing a photoelectric conversion element using a single crystal semiconductor powder.

[Conventional technology]

In photoelectric conversion elements using semiconductors, various substances are used as semiconductors. When a thin-film semiconductor layer is used, amorphous Si is often used. However, when amorphous Si is used, the thickness of the thin film is 1μ.
Although it may be about m, since the apparatus is formed using a vacuum apparatus, the scale of the apparatus itself is large, the cost is high, and there is a serious problem of photodegradation in terms of reliability. When using single crystal Si as a semiconductor, there is no problem in terms of reliability and conversion efficiency. However, there is a problem that Si used as a material is as thick as 200 μm and is expensive.

Therefore, there is a demand for a photoelectric conversion element that can be manufactured at low cost in terms of both materials and processes. On the other hand, a photoelectric conversion element using powder of a single crystal semiconductor has been considered. The structure and manufacturing method will be described with reference to FIG.
First, for example, a Mo layer is formed as the diffusion preventing layer 5,
Next, as the back surface electrode 4, for example, an Al layer is formed. Then, a p-type single crystal Si powder 8 which is a crystal grain having a grain size of about 25 μm is mixed with the insulating material 7, and a paste formed by being dissolved in an organic substance is printed. A glass raw material is used as the insulating material 7, and polyvinyl alcohol or the like is used as the organic substance. Next, the substrate is put into a heating furnace and heated in an inert gas and a forming gas. Organic substances evaporate at around 200 ° C. When it is further heated to about 600 ° C., eutectic of Al and Si of the back surface electrode 4 starts, and a molten alloy of Al—Si is formed between the Si powder 8 and the electrode 4. When the temperature is further raised, the insulating material 7 melts and Al-Si
Cover the top of the alloy layer. Then, when the temperature is gradually lowered, the protrusion amount of the Al electrode 4 and the Si powder 8 from the Al-Si molten alloy becomes p ⁺ -type Si9, and an electrical contact with the back surface electrode 4 is formed. Next, the surface of the crystal grain is polished, and an ultrathin Al thin film is formed thereon as the light incident side electrode 10. This electrode is the opposite electrode to the back surface electrode 4 and at the same time the Si powder 8
Has the purpose of forming a Schottky junction with.

[Problems to be Solved by the Invention]

In such a photoelectric conversion element structure, a diode is formed by forming a Schottky junction so that photoelectric conversion can be performed. Therefore, the Si powder 8 and the Schottky junction can be formed as the electrode 10 on the light incident side. Since metal has to be used, the selection range of the electrode material is narrowed. Also, since metal is used as the electrode, the thickness of the electrode should be at least several in order to improve the electrical contact.
About 10Å is required, and the transmittance of light decreases and the reflectance also increases, and the substantial amount of incident light entering the photoelectric conversion layer formed in the Si powder 8 decreases, resulting in low output characteristics. There was a problem such as.

An object of the present invention is to provide a method for producing a low-cost photoelectric conversion element having high output characteristics by increasing the amount of incident light entering the semiconductor powder forming the photoelectric conversion layer from the light incident side electrode.

[Means for solving the problem]

In order to solve the above problems, the present invention, a step of densely arranging a single crystal semiconductor powder of the first conductivity type on the same plane,
On one side of the surface, the semiconductor powder is brought into contact with a thin film of a conductive material containing a doping impurity for the second conductivity type, and the semiconductor powder and the conductive material are alloyed by heating and then cooled. A step of forming a region of the second conductivity type in a part of the semiconductor powder to form a pn junction in the semiconductor powder, and a step of covering the other side of the semiconductor powder with a transparent electrode are provided. .

[Action]

In the above method, the conductive material containing the doping impurities is alloyed with the semiconductor powder and cooled to form a pn junction forming a photoelectric conversion layer in the semiconductor powder, and at the same time serve as one electrode of the photoelectric conversion element. The translucent electrode that covers the other side of the semiconductor powder can have higher transmittance and lower reflectance than the electrode that also serves as the Schottky junction formation, so that the amount of light incident on the photoelectric conversion layer increases and the output characteristics of the device improve. .

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 (a) to 1 (e) in which parts common to those in FIG. Since a heating step is performed as a subsequent step, the diffusion prevention layer 5 is formed on the insulating substrate 1 using a ceramic such as alumina silicate glass, quartz glass, or alumina as an insulating material to prevent impurity diffusion from the substrate. (Figure a). As the diffusion prevention layer 5, a silicon dioxide film, a silicon nitride film, a Mo or Ni film which is a refractory metal, or the like is used. Next, an Al film is laminated as the back electrode 4 on the diffusion prevention layer 5 by, for example, vapor deposition (FIG. B). Separately, an n-type single crystal Si powder 2 which is a crystal grain having a grain size of about 25 μm is mixed with an insulating material 7 and dissolved in an organic substance to form a paste, and this paste is printed on the Al film 4 ( Figure c). A glass raw material is used as the insulating material 7, and polyvinyl alcohol or the like is used as the organic substance. Next, the substrate is put into a heating furnace and heated in an inert gas and a forming gas. 200 ° C
The organic substance evaporates first by heating for about 600 ° C
At around ℃, eutectic of Al and Si of the backside electrode 4 starts,
An Al—Si alloy is formed between the Si powder 8 and the electrode 4. When the temperature is further raised, the insulating material 7 melts and covers the Al-Si alloy. This plays a role of preventing a short circuit between the light incident side electrode 3 and the back surface electrode 4. After that, when the temperature is gradually lowered, Al diffuses into Si as a dopant in the melting portion of the Si powder 8 and the alloy layer, so that the p-type Si layer 6 is formed during solidification (Fig. D). . Therefore, a pn junction is formed in the n-type Si powder 2. Then, the surface of the crystal grain is polished to form the light incident side electrode 3. (Fig. E). As the light incident side electrode 3, ITO or SnO ₂ thin film which is a transparent conductive material is used. When an ITO or SnO ₂ thin film is used, the reflectance can be controlled by the thin film, and the reflectance can be minimized by forming a thin film having a thickness of about 700Å, for example.

As another embodiment of the present invention, the substrate is not an insulative one, but a refractory metal, for example. A metal plate such as Mo or Ni may be used. In this case, the diffusion prevention layer 5 may not be formed. Furthermore, the solar cell characteristics of the present invention were evaluated. In the conventional method, an Al film is formed as a light incident window to a thickness of about 50Å, and in the present invention, ITO is used as a light incident window at about 700Å.
Formed to a thickness of. As a result, the short-circuit photocurrent is 12
What was the output of mA / cm ² is in the present invention improves the 15 mA / cm ^2, it was possible to improve the conversion efficiency.

In the above examples, n-type Si powder was used as the single crystal semiconductor powder, but p-type powder may be used, and in this case Sn-Sb alloy or the like may be used as the back electrode.

〔The invention's effect〕

According to the present invention, the photoelectric conversion layer of the photoelectric conversion element using the single crystal semiconductor powder does not depend on the conventional Schottky junction with the light incident side electrode, but is formed in the powder by alloying with the back electrode. Since it is formed by bonding, it is possible to adopt a transparent electrode that is effective in terms of transmittance and reflectance as the light incident side electrode, and the output characteristics are improved without increasing the number of manufacturing steps compared with the conventional method. It has become possible to manufacture low-cost photoelectric conversion elements.

[Brief description of drawings]

FIG. 1 is a sectional view sequentially showing the manufacturing process of a photoelectric conversion element according to an embodiment of the present invention, and FIG. 2 is a sectional view of a photoelectric conversion element using a conventional single crystal semiconductor powder. 1: Insulating substrate, 2: n-type Si powder, 3: light incident side electrode, 4: back electrode, 5: diffusion prevention layer, 6: p-type Si layer, 7: insulating material.

Claims (1)

(57) [Claims] 1. A step of densely arranging single crystal semiconductor powders of the first conductivity type on the same plane, and a conductive material containing a doping impurity for the second conductivity type in the semiconductor powder on one side of the surface. The step of contacting the thin film and the step of heating to alloy the semiconductor powder with the conductive material and then cooling to form a region of the second conductivity type in a part of the semiconductor powder to form a pn junction in the semiconductor powder. And a step of covering the other side of the semiconductor powder with a transparent electrode, the method for producing a photoelectric conversion element.