JPH05235389A - Photovoltaic device - Google Patents

Abstract

PURPOSE:To provide a high-performance photovoltaic device where the surface of a rear electrode is formed into a rugged face having ruggedness of spherical shape and optimum size. CONSTITUTION:On a photovoltaic device having an insulating substrate 1, a rear electrode 2, amorphous semiconductors 3-5, and a transparent electrode 6, which are piled up on the substrate 1 one after another, the rear electrode 2 comprises a polycrystalline germanium layer formed by etching treatment after amorphous germanium doped with an n-type dopant is grown in a solid phase.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to photovoltaic devices.

[0002]

2. Description of the Related Art Generally, a photovoltaic device includes, for example, an insulating substrate such as glass, a back electrode laminated on the substrate in order, and an amorphous semiconductor laminated in the order nip.
Those having a transparent electrode are known.

As the back electrode, silver or the like having a high light reflectance occupies the mainstream, and as the amorphous semiconductors laminated in the order of n-ip or p-i-n, amorphous silicon, amorphous silicon carbide, Amorphous silicon germanium or the like is used. Further, as the transparent electrode, tin oxide (SnO ₃ ) and indium oxide (In ₂
O ₅ ), yttrium tungsten oxide (IT
O), zinc oxide (ZnO) and the like are used.

In this conventional photovoltaic device, in order to improve the conversion efficiency, the back electrode is formed by, for example, vapor deposition, sputtering, etc., so that the surface of the back electrode has an uneven surface having fine unevenness, a so-called texture structure. In order to utilize the so-called light confinement effect, light is scattered on the surface of the back surface electrode and the optical path length of the reflected light of the back surface electrode that transmits the amorphous semiconductor is lengthened.

[0005]

If the size of the unevenness of the back electrode is too small, the amount of scattered light on the surface of the back electrode is reduced, and the effect of light confinement becomes too low, which is not preferable. On the contrary, if the size of the back electrode is too large, the total reflectance of the back electrode becomes too low and the output is rather lowered, which is not preferable.

Further, as the shape of the unevenness, a hemispherical shape is most preferable because an appropriate total reflectance can be obtained and uniform scattering can be obtained.

However, in the conventional method of forming the back electrode, the size of the unevenness on the surface of the back electrode is controlled by controlling the parameters such as the sputtering temperature, and the shape of the unevenness of the surface is formed in a hemispherical shape. It is extremely difficult to do so. It is an object of the present invention to provide a photovoltaic device in which hemispherical irregularities of optimal size are formed on the surface of a back electrode.

[0008]

A photovoltaic device having an insulating substrate, a back electrode laminated on the substrate, an nip type amorphous semiconductor, and a transparent electrode. Polycrystalline germanium layer (hereinafter, abbreviated as poly-Ge layer), which is obtained by performing solid phase growth of amorphous germanium (hereinafter, abbreviated as a-Ge) to which an electrode is added with n-type dopant, is etched. It is characterized by being formed by.

[0009]

When a-Ge doped with an n-type dopant is annealed and solid-phase grown, a poly-Ge layer is obtained.

When this poly-Ge layer is subjected to an etching treatment using an acid solution, hemispherical fine irregularities are densely formed on the surface.

The size of the irregularities can be controlled to any size depending on the processing conditions for forming a-Ge, for example, the forming temperature and the etching conditions, such as temperature and time.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The photovoltaic device according to the embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in the schematic view of FIG. 1, this photovoltaic device comprises a substrate 1 made of glass (trade name: Corning 7059), a back electrode 2 laminated on the substrate 1, an n-type amorphous semiconductor. The layer 3, the i-type amorphous semiconductor layer 4, the p-type amorphous semiconductor layer 5, the transparent electrode 6, and the metal electrode 7 for current collection are provided.

As shown in the schematic diagram of FIG. 2, the back surface electrode 2 is annealed after forming an a-Ge layer 2o having a thickness of about 5000Å by a plasma CVD method under a hydrogen dilution condition of about 9 times. Then, so-called solid phase growth for polycrystallizing the amorphous layer is performed, and thereafter, the film is formed by immersing in an acid solution and etching.

Table 1 shows conditions for forming the a-Ge layer 2o by the plasma CVD method.

[0016]

[Table 1]

The substrate temperature was 290 ° C. in Example a, 310 ° C. in Example b, 330 ° C. in Example c, and 350 ° C. in Example d.

The reason why phosphine (PH ₃ ) is added to the reaction gas is to promote the solid phase growth and to increase the conductivity of the back electrode 2.

As shown in Table 2, the annealing treatment conditions were an annealing temperature of 350 ° C., an annealing atmosphere of nitrogen (N ₂ ) atmosphere, and an annealing time of 2 hours.

[0020]

[Table 2]

The etching was performed using a mixed solution of 0.15 mol potassium chromate aqueous solution (K ₂ Cr ₂ O ₇ / H ₂ O) and 49% hydrogen fluoride aqueous solution (HF / H ₂ O). By this etching, hemispherical unevenness 2a as shown in FIG. 3 is densely formed on the surface of the back electrode 2 made of the poly-Ge layer.

In each of Examples a to d, the etching treatment time was set to 0.5 seconds or 1.0 seconds.

As shown in the characteristic diagram of FIG. 4, hemispherical irregularities 2
The diameter of a reaches a maximum of about 1000Å or about 3000Å when the formation temperature of a-Ge is 330 ° C, and increases at a lower temperature corresponding to the increase of a-Ge formation temperature and at a higher temperature, a-Ge. Corresponding to an increase in the formation temperature of Further, when the etching treatment time is 1 second or less, the diameter of the hemispherical unevenness 2a becomes larger as the etching treatment time becomes longer.

Even if the processing time was increased to 1 second or longer, the entire thick film was thinned, and the grain size of the irregularities 2a on the surface was almost the same as in the case of 1 second.

The N-type amorphous semiconductor layer 3, the I-type amorphous semiconductor layer 4, and the P-type amorphous semiconductor layer 5 are formed by a known plasma CVD method, and the transparent electrode 6 is formed by a sputtering method. The current collecting metal electrode 7 is formed by a vacuum deposition method.

When the solar cell characteristics of the above Examples a to d were determined, the results shown in Table 3 were obtained.

[0027]

[Table 3]

In Example a. F. Is extremely low because the crystallinity of the poly-Ge layer is insufficient and does not function sufficiently as the back electrode 2.

In Examples a and b, I
The low sc is due to small irregularities and insufficient light confinement.

In Example d, since the formation temperature of a-Ge was high, delicate crystal grains were generated before the solid phase growth, which hinders the solid phase growth and causes uneven grains formed during etching. The system diameter becomes smaller (see FIG. 3). Therefore, in comparison with Example c in which the grain size of the unevenness is maximum, Example d is used.
Output current is low.

In Example c, the crystallinity of the poly-Ge layer is sufficient and the poly-Ge layer functions sufficiently as the back electrode. Further, since the size of the unevenness is optimized and the light is confined effectively, the maximum output is obtained.

The absolute value of the current in each example is low because the reflection component of the back electrode 2 cannot be used.

In another embodiment of the present invention, the back electrode 2
Of poly-Ge formed in the same manner as in Example c above.
It is composed of a layer and a silver (Ag) layer having a thickness of about 500Å formed thereon by a sputtering method. The other structure of this embodiment is the same as that of the above-mentioned embodiment c.

The solar cell characteristics of this example are shown in Table 4 as c / A.
It is shown in column g.

As a comparative example, substrate temperature 3 on stainless steel
The back surface electrode is composed of a first silver layer having a film thickness of 350Å formed by vapor deposition at 50 ° C, and a second silver layer having a film thickness of 500Å formed by vapor deposition after lowering the substrate temperature to 150 ° C. The other configurations were the same as those in Example c.

The solar cell characteristics of this comparative example are as shown in Table 4
It is shown in column g.

[0037]

[Table 4]

From Table 4, it can be seen that the photovoltaic device according to another embodiment of the present invention has an open circuit voltage Voc, an output current Isc, an F.V.
F. It can be seen that the performance is higher than that of the comparative example in any characteristics such as efficiency and efficiency Eff.

[0039]

As described above, according to the present invention,
The surface of the back electrode can be formed into an uneven surface having hemispherical unevenness, and the size of the unevenness can be precisely controlled by controlling the a-Ge forming conditions and etching conditions.

As a result, it is possible to form the unevenness having the optimum shape and size and obtain a photovoltaic device having higher performance than the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of the present invention.

FIG. 2 is a schematic view showing a formation state of a-Ge.

FIG. 3 is a schematic view showing a state of a poly-Ge layer after etching treatment.

FIG. 4 is a characteristic diagram showing the etching treatment time dependency of the relationship between the a-Ge formation temperature and the diameter of the hemispherical irregularities.

[Explanation of symbols]

 1 substrate 2 back surface electrode 3 n-type amorphous semiconductor layer 4 i-type amorphous semiconductor layer 5 p-type amorphous semiconductor layer 6 transparent electrode

Claims (1)

[Claims] 1. An insulating substrate, a back electrode laminated on the substrate, and an amorphous semiconductor laminated in the order of n-i-p,
A photovoltaic device having a transparent electrode, wherein the back electrode has a polycrystalline germanium layer which is etched after solid-phase growth of amorphous germanium doped with an n-type dopant. ..