JPS59101879A - Thin film solar battery - Google Patents

Abstract

PURPOSE:To obtain a P-I-N type thin film solar battery wherein the forbidden band width of an I-layer is in the neighborhood of 1.4eV and that of a window layer is made as large as possible by changing the I-layer into an amorphous film with Si and Ge as the main constituent and the window layer into an amorphous film with Si and Ci as the main constituent. CONSTITUTION:An ITO film 2 is formed on a glass substrate 1 by vapor deposition, and amorphous films are formed thereon in the order of a P-layer 3, an I- layer 4, and an N-layer 5. The P-layer 3 is formed by the glow discharge decomposition of the mixed gas with an Si hydrogen compound such as SiH4 or an Si fluoride, hydrocarbon such as CH4, B2H6, etc., and the I-layer 4 by the mixed gas with an Si compound such as SiH4 and a Ge compound, respectively. The N- layer 5 can be formed by the mixed gas with SiH4 and PH3 in the same manner as a conventional solar battery. A photovoltage generated by the incidence of a light 7 can be led out from connection conductors 8 and 9 by providing a metallic electrode 6 on the N-layer 5. The forbidden band width of the P-layer 3 with Si and C as the main constituent increase as C-content increases.

Description

[Detailed description of the invention] Regarding.

In recent years, amorphous semiconductors have attracted attention as new electronic materials.
A typical example is amorphous silicon, which is patented as IG 1.
11. Application to ponds is underway. It has been known for a long time that amorphous silicon can be obtained by vacuum evaporation, but because it has many defects (mainly tank ring bonds where bonds between atoms are broken), its properties as a semiconductor are extremely poor. It was bad. However, monosilane (Si1(
4) Glow release of gas 1 (4) In the amorphous silicon deposited on the substrate by the decomposition method, the hydrogen taken into the film neutralizes (terminators) the dangling bonds, and moreover, the boron.

It was found that valence electrons could be controlled by adding phosphorus or the like. In addition to hydrogen, a halogen element such as fluorine can also be used as a terminator.

Amorphous silicon in which dangling bonds are terminated with hydrogen or the like is a semiconductor having a forbidden band width of about 1.7 eV. Considering a p-i-n type solar cell, it is desirable that the forbidden band width of the i-layer, which is the main current generation region, be smaller than 1.7 eV from the viewpoint of effective use of the solar cell. The ml diagram shows the relationship between the forbidden band width of the semiconductor constituting the active region of the solar cell and the theoretical efficiency of the solar cell.

As you will see, the highest value is obtained around 1.4 eV.

On the other hand, the layer on the light incident side has the advantage of improving light transmittance.
A large forbidden band width is desirable.

Therefore, in the present invention, the forbidden band width of the i layer is 1. An object of the present invention is to provide a p-i-n type thin-film solar cell in which the bandgap of the layer (window layer) on the light incident side is as large as possible, and the bandgap is around 4 eV.

This objective is achieved in that the window layer mainly consists of silicon and carbon, and the i-layer mainly consists of silicon and germanium.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a conceptual diagram of the structure of a thin film solar cell as an embodiment of the present invention. An ITO film 2 is formed on a glass substrate 1 by vapor deposition, and amorphous films are formed thereon in the order of 9 layers 3, 1 layer 4, and 0 layers 5. The 9th layer 3 is formed by glow discharge decomposition of a silicon hydride compound or silicon fluoride such as 8iH, a hydrocarbon such as CH, and a mixed gas such as B2H6, and the 1st layer 4 is formed by SiH.

These are formed by a mixed gas of a silicon compound and a Ge compound, respectively. 0 layer 5 is Si as in conventional solar cells.
It may be formed using a mixed gas of H, and PH3. 0
By providing a metal electrode 6 on layer 5, the photovoltaic force generated by the incidence of light 7 can be extracted from connecting conductors 8 and 9. The forbidden band width of the 9-layer 3 whose main components are 8i and C increases as the content of C increases, and when the atomic ratio of Si to C is 1:1, 2 e Vs O, 3:
When it is 0.7, it becomes 2.2 eV. However, it has been found that the technical difficulty in forming an amorphous film is that a value of 1.4 eV can be achieved when the C content is 20 to 40 atoms. Such a bandgap value can also be obtained when a terminator other than hydrogen, such as fluorine, is used.

As described above, the present invention provides a p-i-n type solar cell with an amorphous film mainly composed of 8i and Ge in the i-layer.
By forming the window layer from an amorphous film containing Si and C as main components, the i-layer can achieve the highest theoretical efficiency of 1.4 eV.
It is possible to obtain a near-ideal thin-film solar cell made of a semiconductor having a band gap of 2 eV or more, and the window layer being made of a semiconductor with good transparency and a band gap of 2 eV or more. Therefore, the effect obtained in improving the characteristics of solar cells is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the conversion efficiency of a solar cell and the forbidden band width of the constituent semiconductors, and FIG. 2 is a conceptual cross-sectional view of an embodiment of the present invention. l...Glass plate, 2...Transparent electrode, 3...5i (
C) p layer, 4-8i(Ge)i layer.

Claims (1)

[Claims] ]) In a device comprising an amorphous semiconductor thin film having a p-i-n structure, the p-layer or n-layer on the light incident side mainly consists of silicon and carbon, and one layer mainly consists of silicon and germanium. A thin film solar cell characterized by: