JPH06101575B2 - 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 generating 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.
Accordingly, the unit power generation contributes i-type layer actually generation In the element and n ^- or impurities as type layer is not at all Dove, the junction field not only photoactive layer slightly Dove The impurity layer for forming is indispensable.

However, like the impurity layer and the photoactive layer, which are indispensable for forming a junction electric field, they are interposed in the light incident path as a result, and 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.

On the other hand, in a photovoltaic device mainly composed of amorphous silicon, it has been known that the photoelectric conversion efficiency thereof is lowered when it is irradiated with strong light for a long time. In recent years, research for increasing the photoelectric conversion efficiency has been performed. And research for reducing deterioration over time are being conducted in parallel. That is, even if the initial increase in the photoelectric conversion efficiency can be achieved, the increase in the photoelectric conversion efficiency is canceled if the deterioration over time is significant, and conversely, after a long time, the photoelectric conversion efficiency of the conventional structure may be lowered. .

(C) Problems to be Solved by the Invention In the photovoltaic and electric power device of the present invention, in a so-called tandem structure in which a plurality of unit power generating elements are laminated as described above, an impurity layer for forming a junction electric field that hardly contributes to power generation. By using a wide bandgap material, the light absorption in (1) is reduced as much as possible and the deterioration over time is suppressed.

(D) Means for Solving the Problems In order to solve the above problems, the photovoltaic device of the present invention uses a p-type amorphous silicon oxide as an impurity layer arranged at a contact interface between adjacent unit power generating elements. It is characterized by using nitride and n-type amorphous silicon carbide.

(E) Action As described above, by arranging the wide band gap material of p-type amorphous silicon oxynitride and n-type amorphous silicon carbide at the contact interface between adjacent unit power generation elements, the amorphous silicon oxynitride Each layer of amorphous silicon carbide transmits incident light that has not been absorbed by the photoactive layer in the unit power generation element in the previous stage to the unit power generation element in the subsequent stage, and effectively acts against deterioration over time.

(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 , SiF ₄ , SiH ₄ + SiF ₄ , 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-dove i-type layer formed without containing the impurity gas for controlling the valence electrons or a slightly dry layer containing a slight amount of 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 or n-type impurity layers (5d ₁₁ ) (5d ₁₂ ),
(5d ₂₁ ) (5d ₂₂ ), and when viewed from the light incident side, pi
It has a tandem structure of n / pin 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. As (5d ₂₁ ), n-type amorphous silicon carbide (a-Si _1-X C _X ) and p-type amorphous silicon oxynitride (a-Si) are selected from combinations of several kinds of wide band gap materials.
_1-2X N _X O _X ).

Table 1 below shows the structure of the present invention with respect to the basic characteristics (initial values) of the photovoltaic device, which are the open circuit voltage Voc (V), the short circuit current Isc (mA), the fill factor FF (%), and the photoelectric conversion efficiency η (%). Example and the comparative example of the conventional structure
This is a summary of the actual measurement values measured by using a solar simulator with an irradiation intensity of 100 mW / cm ² that artificially irradiates -1).

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 the second Each of the unit power generation elements (SC ₂ ) (5d ₂₁ ) was a p-type. Then, the impurity layer (5) of the first unit power generation element (SC ₁ ) constituting the contact interface is formed.
Only the composition of d ₁₂ ) and the impurity layer (5d ₂₁ ) of the second unit power generating element (SC ₂ ) was made variable, and the other constituents were made common specifications in both the example and the comparative example. 1st and 2nd unit power generation element (SC
₁ ) (SC ₂ ) is a unit power generating element (SC) mainly composed of the amorphous silicon disclosed in JP-A-56-114387.
₁ ) (SC ₂ ) was manufactured using the general three-chamber separation plasma CVD method. Plasma C in this embodiment
Table 2 shows the VD conditions, and Table 3 shows the structure produced under such CVD conditions.

Common conditions Power supply: 13.56MHz high frequency power supply SiH ₄ Gas flow rate: 5-10 (SCCM) Gas pressure: 0.3-0.5 (Torr) On the other hand, Comparative Example 1 which is a comparison target is the first unit instead of the interface impurity layer (5d ₂₁ ) of a-Si _0.9 N _0.05 O _0.05 of the second unit power generating element (SC ₂ ) in the example. The power generation element (SC ₁ ) has the same a-Si _0.9 C _0.1 as the impurity layers (5d ₁₁ ) and (5d ₁₂ ) of the power generation element (Comparative Example 2).
_0.9 C _0.1 n-type interface impurity layer (5d ₁₂ ) or a-Si _0.9 N
_0.05 O _0.05 a-Si instead of p-type interface impurity layer (5d ₂₁ ).
_In the configuration using _0.9 N _0.1 . Table 4 shows the configurations of the bonding interfaces having different configurations.

The a-Si _1-2X NxOx and a-Si _1-X N of each of the examples and comparative examples
The content of N, O or C in _X , a-Si _1-X C _X is adjusted as described above so that the optical bandgap Egopt is about 2.0 (eV) wider than a-Si.

Thus, a-Si _1-X C having the same optical bandgap Egopt as the impurity layers (5d ₁₂ ) (5d ₂₁ ) at the junction interface of the first and second unit power generating elements (SC ₁ ) (SC ₂ ) _When composed of _X , a-Si _1-X N _X , it is a n-type layer rather than composed of the same material.
-Si _1-X C _X and a-Si _1-2X N _X O _X as a p-type layer
The improvement of the basic characteristics in the photovoltaic device was observed when using the.

On the other hand, the deterioration over time was measured for the examples and comparative examples having the above-mentioned constitution. The deterioration test was conducted with an AM- of 500 mW / cm ² which is five times as strong as the light intensity of 100 mW / cm ² of the sun rays just below the equator.
A photo-deterioration test that measures the photoelectric conversion efficiency when irradiated with 1 light for 5 hours and obtains the deterioration rate with respect to the initial value, and a heat deterioration test that obtains the deterioration rate with respect to the initial value of the photoelectric conversion efficiency after 200 ° C. 50 hours have passed. Each was applied individually. The results are shown in Table 5.

As described above, it was found that the examples of the present invention are superior to the comparative examples 1 and 2 not only in the basic characteristics of the photovoltaic devices but also in deterioration over time due to light and / or heat.

FIG. 2 shows the relationship between the carbon content (x) of the n-type interface impurity layer (5d ₁₂ ) and the photoelectric conversion efficiency (η) in the first unit power generating element (SC ₁ ) of the example of the present invention and Comparative Example 1. X = 0,0.
02, 0.03, 0.05, 0.1, 0.2, 0.3, 0.5 were investigated. In this measurement, as the p-type interface impurity layer (5d ₂₁ ) of the second unit power generation element (SC ₂ ), this example was a-Si _0.9 N _0.05 O _0.05 and Comparative example 1 as shown in Table 4.
A-Si _0.9 C _0.1 fixed ratio film was used. From this measurement result, even if the carbon content (x) in the n-type interface impurity layer (5d ₁₂ ) was changed, a-Si ₁ was obtained as the p-type interface impurity layer (5d ₂₁ ) with the same content. It can be seen that the photoelectric conversion efficiency (η) of the example of the present invention using _-2X N _X O _X is higher than that of Comparative example 1 using a-Si _{1 -X} C _X.

On the other hand, the second unit power generating element (SC
₂ ) Nitrogen and oxygen content (x) and carbon content (x) of the p-type interface impurity layer (5d ₂₁ ) and photoelectric conversion efficiency (η)
The relationship is shown in FIG. In such measurement, as the n-type interface impurity layer (5d ₁₂ ) of the first unit power generating element (SC ₁ ), as shown in Table 4, in both the present Example and Comparative Example 1, a
A fixed ratio film of -Si _0.9 C _0.1 was used in common. From this measurement result, even if the nitrogen and oxygen contents (x) in the p-type interface impurity layer (5d ₂₁ ) were varied, the Egop in such contents was changed.
If the carbon content (x) is such that t is almost equal, p
The photoelectric conversion efficiency (η) of the example of the present invention using a-Si _1-2X N _X O _X as the type interface impurity layer (5d ₂₁ ) is higher than that of Comparative example 1 using a-Si _1-X C _X. Was confirmed.

Although the tandem structure of two unit power generating elements has been described in the above embodiment, the present invention is applicable to a tandem structure of three or more unit power generating elements.

(G) Effect of the Invention As is clear from the above description, the photovoltaic device of the present invention includes an n-type amorphous silicon carbide and a p-type amorphous silicon oxynitride arranged at the contact interface between adjacent unit power generation elements. Each impurity layer transmits incident light that was not absorbed by the photoactive layer in the unit power generation element in the previous stage to the unit power generation element in the subsequent stage, and also acts effectively against deterioration over time, so that the junction hardly contributes to power generation. Light absorption in the impurity layer for forming an electric field can be reduced as much as possible, and the photoelectric conversion efficiency can be increased in combination with the suppression of deterioration over time.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one embodiment of the photovoltaic device of the present invention, and FIG. 2 is an n-type interface impurity layer (a-Si _1-X C _X ) of the embodiment of the present invention and Comparative Example 1. FIG. 3 is a characteristic diagram showing the relationship between the carbon content and the photoelectric conversion efficiency in FIG. 3, and FIG. 3 is a p-type interface impurity layer (a-Si _1-2X N _X O _X : a-Si) of Example of the present invention and Comparative Example 1.
FIG. 3 is a characteristic diagram showing the relationship between the nitrogen and oxygen content or the carbon content in _1-X C _X ) and the photoelectric conversion efficiency. (1) ... substrate, (2) ... light-receiving surface electrode, (3) .... back electrode (4 ₁₎ (4 ₂₎ ...... photoactive layer, (5d ₁₁₎ (5d ₁₂₎
(5d ₂₁ ) (5d ₂₂ ) ... Impurity layer, (SC ₁ ) ... 1st unit power generation element, (SC ₂ ) ... 2nd unit power generation element.

Claims (1)

[Claims] 1. A photovoltaic device in which a plurality of unit power generation elements mainly composed of amorphous silicon are stacked, and a p-type amorphous silicon oxynitride is used as an impurity layer arranged at a contact interface between adjacent unit power generation elements. A photovoltaic device comprising a nitride and an n-type amorphous silicon carbide.