JPH073876B2 - Photovoltaic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a photovoltaic device in which a plurality of unit power generation elements are stacked.

(B) Prior art As disclosed in Japanese Patent Laid-Open No. 55-125680, pin, pn ^- n
A photovoltaic device having a so-called tandem structure, in which unit power generating elements having semiconductor junctions such as ⁺ are stacked in a double, triple or more layers, is already known. Such a tandem structure photovoltaic device can absorb the transmitted light without contributing to power generation in the unit power generation element in the front stage when viewed from the light incident side, and can absorb the light in the unit power generation element in the rear stage. The photoelectric conversion efficiency can be increased. Moreover, if the optical bandgap (Egopt) of the photoactive layer that mainly generates photocarriers when light is incident, such as the i-type layer or the n ⁻ type layer of each unit power generation element, is adjusted, each unit power generation element It is possible to shift the photosensitivity peak wavelength in the photosensitivity and further increase the photoelectric conversion efficiency.

The photo carriers of electrons and holes generated in the photoactive layer are
The electrons move toward the n-type layer and the holes move toward the p-type layer and are collected by the junction electric field created by the p-type layer and the n-type layer sandwiching the photoactive layer. It is taken out.
Therefore, actually contributes to the power generation i-type layer and n In the unit power generating element ^- or is not at all doped impurities as type layer, the junction field not only photoactive layer slightly doped The impurity layer for forming is indispensable.

However, the impurity layer indispensable for forming the junction electric field is interposed in the light incident path like the photoactive layer, and as a result, when the light absorption in the impurity layer increases, the light reaches the photoactive layer. The rate is reduced, and the photoelectric conversion efficiency is significantly reduced.

JP-A-57-95677, JP-A-57-104276, and JP-A-57-136377 disclose that in a photovoltaic device including one unitary power generating element, light is incident on a photoactive layer. In the window layer, the impurity layer disposed on the front side, that is, a so-called window layer is made of a wide bandgap material such as amorphous silicon carbide having a wider optical bandgap Egopt than the photoactive layer or amorphous silicon nitride. A technique for reducing light absorption is disclosed.

Therefore, if the effect of reducing the light absorption of such a wide band gap material is applied to the impurity layer for forming the junction electric field that hardly contributes to power generation in the tandem structure, the light absorption in the impurity layer can be minimized. The photoelectric conversion efficiency can be increased by decreasing the amount.

However, the contact interface where the unitary power generating elements are adjacent to each other has a reverse junction, and the interface junction property is poor and causes a voltage drop. Therefore, even if a wide band gap material is used in order to reduce the light absorption in the interface impurity layer, the interface bondability is deteriorated, and as a result, the photoelectric conversion efficiency cannot be significantly increased.

(C) Problems to be Solved by the Invention The photovoltaic device of the present invention has a so-called tandem structure in which a plurality of unit power generation elements are stacked as described above, and has an impurity layer for forming a junction electric field that hardly contributes to power generation. By using a wide band gap material, it is possible to reduce light absorption as much as possible, but it is intended to solve the problem of voltage drop.

(D) Means for Solving the Problems In order to solve the above problems, the photovoltaic device of the present invention comprises:
The impurity layer arranged at the contact interface between adjacent unit power generation elements is composed of a layer of a wide band gap amorphous silicon alloy of one conductivity type and opposite conductivity type, which has a wider optical band gap than the amorphous silicon. A layer of non-single crystal silicon having a conductivity type is interposed between these impurity layers.

(E) Action As described above, by arranging the layers of wide bandgap amorphous silicon alloys of one conductivity type and reverse conductivity type at the contact interfaces of the adjacent unit power generating elements, each layer is a light source in the unit power generating element of the preceding stage. The incident light that is not absorbed by the active layer is transmitted to the unitary power generating element in the subsequent stage, and the non-single-crystal silicon sandwiched by the amorphous silicon alloy improves the interfacial bondability.

(F) Example FIG. 1 is a schematic sectional view showing the basic structure of the photovoltaic device of the present invention. ITO, SnO _{2 is provided on} one main surface of a transparent and insulating substrate (1) such as glass. After forming the light-receiving surface electrode (2) of a translucent conductive oxide (TCO) typified by, for example, each of the first and second unit power generating elements (SC ₁ ) (SC ₂ ) is the first unitary power generation element (SC ₁ )
Are sequentially stacked in contact with the light-receiving surface electrode (2). Then, Al, Ag, Al / Ti, Al / Ti are formed on the back surface of the _second unit power generation element (SC ₂ ) which is the exposed surface when viewed from the light incident direction.
A back electrode (3) having a single-layer or three-layer structure of Ag, TCO / Ag, TCO / Al, TCO / Al / Ti, etc. is connected.

Each of the first and second unit power generating elements (SC ₁ ) (SC ₂ ) is mainly composed of amorphous silicon (a-Si)
A silicon compound gas such as H ₄ , SiH ₄ , SiH ₄ + SiF ₄ , and Si ₂ H ₆ is used as a main raw material gas, and B ₂ for controlling p-type and n-type valence electrons is appropriately used.
Impurity gas such as H ₆ and PH ₃ and C for wide band gap
It is formed by plasma decomposition with a raw material gas to which a wide band gap gas such as H ₄ , C ₂ H ₆ , C ₂ H ₂ , NH ₃ , and NO is added, or photolysis using a low-pressure mercury lamp. And
Each unit power generation element (SC ₁ ) (SC ₂ ) is composed of a non-doped i-type layer formed in a state that does not contain any impurity gas for controlling valence electrons or a slightly doped layer containing slightly impurities. photoactive layer as a (4 ₁₎ (4 _2), the photoactive layer (4 ₁₎ (4 ₂₎ so as to generate a junction field that promotes movement of the optical carriers is formed in the photoactive layer (4 ₁ ) (4 ₂ ) sandwiched between p-type and n-type impurity layers (5d ₁₁ ) (5d ₁₂ ) (5d
₂₁ ) (5d ₂₂ ), and, when viewed from the light incident side, pin / pi
It has a tandem structure of n or nip / nip.

Thus, the feature of the present invention is that the impurity layer (5d ₁₂ ) arranged at the n / p or p / n contact interface of the first and second unit power generating elements (SC ₁ ) (SC ₂ ) adjacent to each other. (5d ₂₁ ) is shown in Fig. 2 (a).
As shown in, the first unit power generation element (SC ₁ ) side is connected to the first layer (5d
_12w ) and the second layer (5d _12n ), or as shown in FIG. 2 (b), the second unit power generating element (SC ₂ ) side is connected to the second layer (5d).
_12n ) and the third layer (5d _21w ), or the second layer
As shown in Figure (c), both are the first layer (5d _12w ), the second layer (5d _12n ), the third layer (5d _21n ′) and the fourth layer (5d _21w ′).
In addition to the two-layer structure of
-Type or n-type conductivity type non-single-crystal silicon layers such as amorphous silicon or microcrystalline silicon (μc-Si) (5d _12n ′), (5d _21n ), (5d _12n ), (5d _21n ′)
A wide bandgap amorphous silicon alloy layer (5d _12w ) (5d ₂₁ ), (5d ₁₂ ), (5d ₁₂ ) (5) having an optical bandgap wider than the amorphous silicon of the _first i-type layer (i ₁ ) above.
d _21w ), (5d _12w ) (5d ₂₁ ′) and sandwich structure. The wide bandgap amorphous silicon alloy is an amorphous silicon carbide (a-S) having an optical bandgap of about 1.8 eV or more.
i _1-x C _x ), amorphous silicon nitride (a-Si
_1-x N _x ), amorphous silicon oxide (a-Si _1-x
O _x ), amorphous silicon oxynitride (a-
Si _1-2x N _x O _x ), etc., and one or two of them are selected and used. Among various combinations of wide band gap materials, a combination of n-type a-Si _1-x N _x and p-type a-Si _1-x C _x , a p-type a-Si _1-x N _{x x} and n-type a-
Combination with Si _1-x C _x , p-type a-Si _1-2x N _x O _x and n-type a-Si
Combination with _1-x C _x , or n-type a-Si _1-x N _x and p-type a-Si
Combination of _1-2x N _x O _x is preferable.

Table 1 below shows the basic characteristics (initial values) of the photovoltaic device, which are the open circuit voltage Voc (V), short circuit current Isc (mA), fill factor FF (%), and photoelectric conversion efficiency η (%) of the present invention. Irradiation intensity for artificially irradiating the sunbeam (AM-1) immediately below the equator between the embodiment of FIG.
This is a summary of the actual measurement values measured using a 0 mW / cm ² solar simulator.

The photovoltaic devices used for such measurement are all viewed from the light incident side, the glass substrate (1) / TCO light receiving surface electrode (2) / pin junction type first unit power generating element (SC ₁ ) / pin It is a tandem structure of the junction type second unit power generation element (SC ₂ ) / Al back electrode (3),
At the contact interface between the first unit power generating element (SC ₁ ) and the second unit power generating element (SC ₂ ), the impurity layer (5d ₁₂ ) of the first unit power generating element (SC ₁ ) is n-type, and a− First layer of Si _1-x N _x (5d _12w ).
And the second layer (5d _12n ) of a-Si or μc-Si, the two layers are the impurity layers (5) of the second unit power generating element (SC ₂ ).
In d ₂₁ ), p-type a-Si _1-x C _x was arranged, respectively. And
The impurity layer (5d ₁₂ ) of the first unit power generating element (SC ₁ ) and the impurity layer (5d of the second unit power generating element (SC ₂ ) that form the contact interface
Only the composition of ₂₁ ) was made variable, and the other constituents had the same specifications for both the examples and comparative examples. First and second unitary power generation element (SC ₁₎ (SC ₂₎ is disclosed in JP-A-56-114387, the unit power generating element (SC ₁₎ mainly comprising the amorphous silicon (SC ₂₎ A general three-chamber separation type plasma CVD method was used as a manufacturing method. Table 2 shows the plasma CVD conditions in Examples 1 and 2 and
Table 3 shows the structure manufactured under the conditions.

However, the conditions in parentheses of the layers 5d _12n are the conditions for only the second embodiment, and the other conditions are common to both the first and second embodiments.

Common conditions Power supply: 13.56MHz high frequency power supply SiH ₄ Gas flow rate: 10 (SCCM) Gas pressure: 0.3 to 0.5 (Torr) However, the layer 5d _12n in parentheses is the configuration of only the second embodiment, and the other is common to both the first and second embodiments.

On the other hand, the structures of the interface impurity layers (5d ₁₂ ) (5d ₂₁ ) of Comparative Examples 1 and 2 which are comparison targets are as shown in Table 4 below.

Thus, as the impurity layers (5d _12w ) (5d ₂₁ ) at the junction interface between the first and second unit power generating elements (SC ₁ ) (SC ₂ ), the same wide bandgap material a-Si _{1- x} N _x, a-Si
Despite being composed of _1-x C _x , a-Si or μc-S
The open-circuit voltage Voc is improved by interposing the i layer (5d ₁₂ ) between the two, and the a-Si or μc-Si
Even if the layer (5d _12n ) was provided, a numerical value almost the same as the short circuit current Isc of Comparative Example 2 was obtained, and as a result, the photoelectric conversion efficiency was increased.

On the other hand, the deterioration over time was measured for the examples and comparative examples having the above-mentioned constitution. The deterioration test is AM- of 500 mW / cm ² which is 5 times the intensity of 100 mV / cm ² of the sunlight directly below the equator.
A photodegradation test for measuring the photoelectric conversion efficiency when irradiated with one light for 5 hours and a heat deterioration test for determining deterioration with respect to the initial value of the photoelectric conversion efficiency after 200 hours at 50 ° C. were individually performed. The results are shown in Table 5.

As a result of such light deterioration and heat deterioration tests, the structure of this embodiment is a-
It was found that it is also effective for the photodegradation and heat degradation peculiar to the power generation element mainly composed of Si.

(G) Effect of the Invention As is apparent from the above description, the present invention is constituted by a wide band gap amorphous silicon alloy layer as an impurity layer arranged at the contact interface between adjacent unit power generating elements, and the impurity layers are formed between these impurity layers. Since a non-single-crystal silicon layer having a conductivity type is interposed, it is possible to reduce the light absorption in the interface impurity layer and improve the interface bondability at the same time, and to lower the voltage. Therefore, the amount of current can be increased and the photoelectric conversion efficiency can be increased.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of the basic structure of the photovoltaic device of the present invention, and FIGS. 2 (a) to 2 (c) are schematic cross-sectional views of various embodiments of the photovoltaic device of the present invention. Each one is shown. (1) ... Substrate, (4 ₁ ) (4 ₂ ) ... Photoactive layer, (5d ₁₁ ) (5d
₁₂ ) (5d ₂₁ ) (5d ₂₂ ) ... impurity layer, (5d _12w ) ... first
Layer, (5d _12n ) (5d _21n ) ... second layer, (5d _21n ′) ... third
Layer, (5d _21w ') ... 4th layer.

Claims (8)

[Claims] 1. A photovoltaic device comprising a plurality of unitary power generating elements mainly composed of amorphous silicon, wherein an impurity layer disposed at a contact interface between adjacent unitary power generating elements comprises:
Wider optical bandgap than the amorphous silicon,
Photovoltaic characterized by comprising a layer of a wide bandgap amorphous silicon alloy of one conductivity type and an opposite conductivity type, and a layer of non-single-crystal silicon having a conductivity type interposed between these impurity layers. apparatus. 2. The photovoltaic device according to claim 1, wherein the non-single crystal silicon layer having a conductivity type is one conductivity type amorphous silicon or microcrystalline silicon. 3. One-conductivity-type and opposite-conductivity-type amorphous silicon, wherein the non-single-crystal silicon layers having the conductivity type are arranged so as to be in contact with the wide-band-gap amorphous silicon alloy layers having the same conductivity type, respectively. Alternatively, the photovoltaic device according to claim 1, which is microcrystalline silicon. 4. The photovoltaic device according to claim 1, wherein at least one of the wide band gap amorphous silicon alloys is an amorphous silicon car band. 5. The method according to claim 1, wherein at least one of the wide band gap amorphous silicon alloys is amorphous silicon nitride.
The photovoltaic device according to any one of items 1 to 3. 6. The photovoltaic device according to claim 1, wherein at least one of the wide band gap amorphous silicon alloys is amorphous silicon oxide. 7. The photovoltaic device according to claim 1, wherein at least one of the wide band gap amorphous silicon alloys is amorphous silicon oxynitride. 8. The photovoltaic device according to claim 1, wherein the compositions of the one conductivity type and the opposite conductivity type wide band gap amorphous silicon alloys are different from each other.