JPH0213938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a solar cell, and particularly to a solar cell with improved energy conversion efficiency.

<Prior Art> Solar cells are widely used as semiconductor devices that convert light energy into electrical energy. As shown in FIG. 4, conventionally used solar cells are made by, for example, diffusing n-type impurities into one main surface of a p-type silicon substrate 1 to form a PN junction 2, and forming a p-type layer 1.
A back electrode 4 and a front electrode 5 are formed on the n-type layer 3, respectively, for extracting the generated power. Note that the light-receiving surface side on which the surface electrode 5 is formed is covered with an anti-reflection film 6 in order to increase the utilization rate of the irradiated light.

Generally, a TiO ₂ film is used as the antireflection film 6, but the TiO ₂ film is formed as an insulating film.
The anti-reflection and surface protection functions are merely expected, and it is difficult to say that they are being used effectively.

<Object of the invention> The present invention eliminates the drawbacks of the above conventional solar cells,
The TiO ₂ film is improved to provide a solar cell with higher conversion efficiency.The TiO ₂ film covering the light-receiving surface is reduced to become n-type, and a hetero bond is formed with the silicon semiconductor substrate body. , increases the absorption rate of short wavelength light.

<Example> FIG. 1 is a sectional view of a solar cell showing an example according to the present invention. In the figure, as in the conventional device, n-type impurities are diffused into one main surface of a p-type silicon substrate 1 to form a PN junction 2. Next, an n-type TiO ₂ film 7 is formed on the p-type silicon substrate 1 so as to cover the surface of the diffused n-type layer 3 . The n-type TiO ₂
Membrane 7 was formed as an electrically insulating membrane.
It is produced by converting TiO ₂ into an n-type semiconductor.

That is, the silicon semiconductor substrate 1 on which the PN junction 2 has been formed is heated, and an insulating TiO 2 film 7 is first formed on the surface of the heated n-type layer 3 by CVD using a titanium compound such as isopropyl _titanate as a source. Form.

The electrically insulating TiO ₂ film 7 to be laminated on the surface of the n-type silicon substrate 3 can be produced by the CVD method as described above, or by applying a Ti-containing organic compound solution and forming TiO ₂ by a chemical reaction. A method for producing a film or a vapor deposition method can be used.
The TiO ₂ film laminated on the surface of the silicon substrate is
In the process of converting the TiO 2 film 7 formed by CVD into a type semiconductor, the TiO ₂ film 7 formed by CVD is converted from an insulating property to a semiconductor. The reduction treatment includes heat treatment in vacuum (approximately 700°C), heat treatment in reduced pressure hydrogen (approximately 1 Torr, approximately 700°C), heat treatment in normal pressure hydrogen, or heat treatment in hydrogen plasma (approximately 700°C).
1Torr, approximately 400℃), etc., and through this reduction treatment, oxygen in the TiO ₂ film is removed and becomes vacancies, converting the insulating TiO ₂ film into an n-type TiO ₂ semiconductor layer. . As a result, an n-TiO ₂ /n + -Si heterojunction is formed between the n ⁺ silicon layer 3 and the n-TiO 2 /n ⁺ -Si heterojunction.

On the surface of the converted n-type TiO ₂ layer 7', a light-receiving surface side electrode 8 is formed, for example, in a lattice shape, and the electric power generated between it and the back surface electrode 4 formed on the p-type silicon substrate 1 side is taken out. .

In the solar cell with the above structure, the incident light energy generates a photocurrent even at the n-TiO ₂ /n ⁺ p-Si heterojunction, whereas in the conventional silicon substrate, photocurrent was generated only at the n ⁺ p junction. The optical output current becomes larger compared to the structure. That is, as shown schematically in Fig. 2, the band gap of n-TiO ₂ is
3.20 eV, which is much larger than the silicon band gap of 1.106 eV shown in the conventional device structure shown in Figure 3, making it possible to effectively utilize short wavelength light with low sensitivity to silicon substrates. Therefore, it is possible to increase the short-circuit photocurrent.

In addition, the TiO ₂ film is converted into an n-type semiconductor, so it is negatively charged and has good conductivity, and its sheet resistance is reduced and the curvature factor in the current-voltage curve is significantly improved.

The TiO ₂ film functions as a semiconductor layer for heterojunction as described above, and also functions as an original antireflection film.

Although a silicon substrate was used as the semiconductor substrate in the above embodiment, semiconductor substrates with a band gap smaller than 3.20 eV, such as amorphous Si, GaAs, CdS, etc.
For solar cells using CdSe, ZnS, ZnSe, Ge, GaP, etc., on the light receiving surface side, as in the above example, an n-type
By depositing a TiO ₂ film, a solar cell with a heterojunction and high photoelectric conversion efficiency can be created.

<Effects> According to the present invention, by forming a solar cell by depositing an n-type TiO ₂ film on the light-receiving surface side of a semiconductor substrate equipped with a PN junction, short circuits can be prevented by simply adding a simple configuration. With the synergistic effect of increasing photocurrent and increasing curvature factor in the current-voltage curve,
Photoelectric conversion efficiency can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an element showing an embodiment of the present invention, FIG. 2 is a bandgap model diagram of the same embodiment, and FIG. 3 is a bandgap model diagram of a conventional element.
FIG. 4 is a sectional view of a conventional element. 1: p-type silicon substrate, 3: n-type silicon substrate, 7': n-type TiO ₂ film, 8: electrode.

Claims (1)

[Claims] 1. An n-type semiconductor layer with a smaller bandgap than TiO ₂ is formed on the surface, and between it and the p-type semiconductor substrate.
A semiconductor substrate formed by forming a PN junction, and an n formed on the surface of the above n-type semiconductor layer to form a heterojunction.
A solar cell comprising a type TiO ₂ film. 2. The solar cell according to claim 1, wherein the semiconductor substrate is made of silicon. 3. The solar cell according to claim 2, wherein the n-type TiO ₂ film is made n-type by reducing an insulating TiO ₂ film.