JP3244369B2 - Photovoltaic device with heterojunction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device,
In particular, for example, a heterojunction formed of crystalline silicon (single crystal or polycrystal) having the opposite conductivity type and amorphous silicon is used, and a collector electrode is formed on the amorphous silicon on the light incident side. It relates to the formed photovoltaic device.

[0002]

2. Description of the Related Art An example of a photovoltaic device having a heterojunction of this type is disclosed in, for example, Japanese Patent Laid-Open No. 4-130671 (H
01L 31/04) and JP-A-4-199750 (H
01L31 / 04). FIG. 4 shows a conventional photovoltaic device having a heterojunction. This photovoltaic device 1 has a heterojunction formed of n-type single-crystal silicon 2 and p-type amorphous silicon 3. And a transparent electrode 4 formed on the entire surface of the p-type amorphous silicon 3 on the light incident side. This transparent electrode 4 is made of, for example, ITO.
And combines current collection and anti-reflection. In addition,
Reference numeral 5 denotes a collector electrode, and reference numeral 6 denotes a back electrode.

[0003]

However, in the conventional photovoltaic device 1, an IT used as a transparent electrode is not used.
The refractive index of O is small, and a sufficient antireflection effect cannot be obtained,
Therefore, there is a limit in improving the efficiency. Therefore, it is conceivable to use TiO ₂ having an optimum refractive index as the transparent electrode and generally used as an antireflection film.
TiO ₂ has a high resistivity and cannot be used for a photovoltaic device having a heterojunction.

[0004] It is, therefore, a primary object of the present invention to provide a more efficient photovoltaic device having a heterojunction.

[0005]

According to the present invention, a heterojunction formed of crystalline silicon and amorphous silicon having opposite conductivity types is used, and a collector electrode is formed on the amorphous silicon on the light incident side. In the photovoltaic device, the collector electrode is formed directly on the amorphous silicon as a comb-like collector electrode, and an electrical contact substantially serving as a diode immediately below the collector electrode is formed.
A photovoltaic device, wherein a junction is formed and the distance between the fingers of the collector electrode is smaller than at least the diffusion length of minority carriers in crystalline silicon.

[0006]

For example, a comb-shaped collecting electrode having a bus bar and a finger extending therefrom is arranged on amorphous silicon, and the interval between the fingers of the collecting electrode is reduced. By making the interval between the collecting electrodes smaller than the diffusion length of minority carriers in crystalline silicon, current can be collected without using a transparent electrode. That is, since the resistivity of amorphous silicon is high,
The current flowing through the amorphous silicon is very small. Therefore, the amorphous silicon acts as an electrical junction substantially serving as a diode immediately below the collector electrode, and acts as a passivation layer for reducing surface recombination of crystalline silicon in a portion without the collector electrode. Therefore, the diode current of the photovoltaic device can be reduced, and the recombination on the surface of the crystalline silicon is reduced.

[0007]

According to the present invention, a more efficient photovoltaic device having a heterojunction can be obtained by merely devising the interval between the collecting electrodes. In addition, since the collector electrode does not need to have an anti-reflection function, an optimum anti-reflection layer can be selected as an anti-reflection layer formed as needed, and the efficiency can be further improved.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a photovoltaic device 10 according to the present embodiment has a HIT (Heterojunction with Intrinsic Thin-Layer).
yer) structure and includes the back electrode 12. Back electrode 1
2 is formed, for example, of aluminum to a thickness of, for example, 2 μm. On the back electrode 12, n-type single crystal silicon 1
4 are arranged. The resistivity of the n-type single crystal silicon 14 is 1
Ωcm, and its thickness is 300 μm. The diffusion length of minority carriers in n-type single crystal silicon 14 is approximately 300.
μm.

An i-type amorphous silicon 16 is formed on n-type single crystal silicon 14. The thickness of i-type amorphous silicon 16 is, for example, 50 to 300 °. By forming i-type amorphous silicon 16 on n-type single crystal silicon 14, recombination on the surface of n-type single crystal silicon 14 is prevented. Reduced. A p-type amorphous silicon 18 is formed on the i-type amorphous silicon 16. The p-type amorphous silicon 18 is 50
Formed at ~ 200 °.

A collector electrode 19 is formed on the p-type amorphous silicon 18.
Are formed directly . The collecting electrode 19 is specifically configured as, for example, a comb-shaped electrode shown in FIG. That is, the collector 19 includes a bus bar 19a and a number of fingers 20 extending therefrom.
i / Ag multilayer structure, and the fingers 20 are, for example, 5
It is formed as a fine electrode of μm width × 5 μm thickness. The distance D between the fingers 20 is set smaller than the diffusion length of minority carriers in the n-type single crystal silicon 14 (about 300 μm), and is set to, for example, 50 μm.

An anti-reflection layer 22 is formed on the p-type amorphous silicon 18. The antireflection layer 22 is made of MgF
_It is formed in a multilayer structure of ₂ / TiO ₂ , and is formed on the p-type amorphous silicon 18 except for a portion where the collector electrode 19 is formed.
Such a photovoltaic device 10 is manufactured as follows. First, in FIG. 3A, after the n-type single crystal silicon 14 is cleaned, the i-type amorphous silicon 16
And p-type amorphous silicon 18 are formed by, for example, a plasma CVD method. The p-type amorphous silicon 18 is obtained by mixing a source gas of B ₂ H ₆ (diborane): SiH ₄ (silane): H ₂ = 0.1: 5: 100 with 0.2
It is formed by applying the Torr, 30 mW / cm ² condition. Good conversion efficiency characteristics were exhibited when the formation condition of the p-type amorphous silicon 18 was a substrate temperature of about 120 ° C. and B ₂ H ₆ / SiH ₄ = 1 to 2%. The i-type amorphous silicon 16 is formed by supplying a source gas containing no dopant such as B ₂ H ₆ or PH ₃ (phosphine) and containing, for example, SiH ₄ .

Next, as shown in FIG. 3B, a resist 24 is formed on the amorphous silicon 18 so that a pattern 2 for the collector electrode 19, that is, the finger 20 is formed.
0 'is formed. The resist 24 is formed by using an ultraviolet-sensitive method, a pattern coating type method by screen printing, or the like. Then, as shown in FIG. 3C, after the collector electrode 19, that is, the finger 20 is formed, the resist 2 is formed.
4 is peeled off. The removal of the resist 24 is performed by, for example, lift-off using vapor deposition.

Then, as shown in FIG. 3D, a collector electrode 19, that is, a finger 2 is formed on the p-type amorphous silicon 18.
Except for the portion where 0 is formed, the insulating antireflection layer 22 is formed. The antireflection layer 22 is formed by, for example, sputtering, CVD, or vapor deposition.
When the anti-reflection layer 22 using a multi-layer coating of MgF ₂ / TiO ₂ is formed by MgF _2, for example evaporation, is formed on the TiO _2, for example by sputtering.

Then, as shown in FIG. 3E, a back electrode 12 is formed on the entire lower surface of the n-type single crystal silicon 14, for example, by vapor deposition. The photovoltaic device 10 of this embodiment thus obtained is a photovoltaic device that converts light energy incident from the antireflection layer 22 into electric energy. In the photovoltaic device 10 of this embodiment, by setting the distance D between the fingers 20 of the collector electrode 19 to be smaller than the diffusion length of the minority carrier in the n-type single crystal silicon 14, current can be collected without using a transparent full-surface electrode. Is possible. That is, the resistivity of the p-type amorphous silicon 18 is high, and the current flowing through the p-type amorphous silicon 18 is very small as shown by an arrow a in FIG. Therefore, the p-type amorphous silicon 18 acts as an electrical junction that substantially serves as a diode immediately below the collector electrode 19, that is, the finger 20. Therefore, the junction area is the same as the bottom area of the collector, the diode current is small, and the open voltage Voc is large. Further, the p-type amorphous silicon 18 functions as a passivation layer for reducing surface recombination of the n-type single-crystal silicon 14 in a portion of the collector electrode 19 where the finger 20 is not provided, that is, in a light incident portion.

In this embodiment, reflection is performed separately from the collecting electrode 19.
Since the anti-reflection layer 22 can be formed,
The degree of freedom increases. Therefore, the Ti used in the Examples
O_TwoAnti-reflection layer 22 for reflecting light as shown in FIG.
Can be selected, and the efficiency can be further improved. However, anti-reflection
The layer 22 may be formed also on the collector 19. This
Thus, in the photovoltaic device 10 of the above-described embodiment,
Compared to the heterojunction photovoltaic device of
0mV higher, short circuit current is 1mA / cm ^TwoGet bigger,
Overall, the conversion efficiency was improved by 6%.

In the above embodiment, the HIT structure including the n-type single crystal silicon 14, the i-type amorphous silicon 16 and the p-type amorphous silicon 18 is used. May not be required. As a method for forming the collector electrode 19, there is an electrolytic plating method other than the lift-off method. In addition, there is a method in which an electrode is vapor-deposited on the entire surface before the resist 24 is formed, and then the resist is formed, a pattern is formed, and then etching is performed to form the collector electrode 19.

The anti-reflection layer 22 is made of TiO.
_2, ZnS, ZnSe, and that of the refractive index of 2-3, such as CdS or _{Bi 2 O 3, MgF 2,} CaF 2, LiF,
A combination with NaF or SiO _{2 having} a refractive index of ≦ 1.5 can also be used. Also, the back electrode 12
Aluminum was deposited at 2μm thick in the entire lower surface for example of Al n-type single-crystalline silicon 14 as, for improving the reflectivity of the back surface electrode 12, ITO, high film and reflectance, such as ZnO or SiO ₂ The back electrode 12 may be formed by laminating a film such as Ag or Au on the entire lower surface or a part of the n-type single crystal silicon 14.

[Brief description of the drawings]

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

FIG. 2 is an illustrative view showing one example of a collector electrode of the embodiment in FIG. 1;

FIG. 3 is an illustrative view showing a manufacturing step of the embodiment in FIG. 1;

FIG. 4 is a sectional view showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Photovoltaic device 12 ... Back surface electrode 14 ... N-type single crystal silicon 16 ... I-type amorphous silicon 18 ... P-type amorphous silicon 19 ... Collecting electrode 20 ... Fingers 22 ... Anti-reflection film

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-48-43284 (JP, A) JP-A-4-130671 (JP, A) JP-A-58-96777 (JP, A) JP-A-59-96777 172779 (JP, A) JP-A-4-298081 (JP, A) JP-A-3-131070 (JP, A) JP-A-61-2374 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (2)

(57) [Claims] 1. A photovoltaic device using a heterojunction formed of crystalline silicon and amorphous silicon having opposite conductivity types and forming a collector electrode on the amorphous silicon on the light incident side. The method according to claim 1, wherein the collector electrode is a comb-like collector electrode on the amorphous silicon.
And a diode directly under the collector.
A photovoltaic device, wherein an electrical junction to be formed is formed and the distance between the fingers of the collecting electrode is made at least smaller than the diffusion length of minority carriers in the crystalline silicon. 2. The photovoltaic device according to claim 1, further comprising an antireflection layer for preventing reflection of light formed on the amorphous silicon between at least the fingers of the collector electrode.