JPH04252080A - Photoelectric conversion device - Google Patents

Abstract

PURPOSE:To provide a sufficiently reliable photoelectric conversion device of a structure wherein a rectifying contact between photoelectric conversion layers is dissolved and a photoelectric conversion factor is sufficiently improved. CONSTITUTION:This device is a photoelectric conversion device 1 characterizing a structure wherein in a tandem constitution formed by superposing a plurality of photoelectric conversion layers 2, which respectively have a semiconductor thin film to make a photoelectric conversion the light of a wavelength to be set on a condition of L<=1/alpha(lambda), on each other, layers 3 having an ohmic property are respectively provided between the layers 2. (provided that, the lambda...the wavelength of incident light, the alpha(lambda)... the absorption factor of a semiconductor thin film to the light of a wavelength lambda and L... a carrier absorption length).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called tandem type photoelectric conversion device in which a plurality of photoelectric conversion layers are stacked one on top of the other.

0002

[Prior art] As a tandem type photoelectric conversion device,
As shown in FIG. 6, the inventors first developed a tandem-type photoelectric conversion device in which a plurality of photoelectric conversion layers having semiconductor thin films that photoelectrically convert light with a wavelength of L≦1/α(λ) are stacked one on top of the other. (Patent Application No. 1-044123).

In the photoelectric conversion device shown in FIG. 6, a lower electrode 51 such as Ni-Cr or Al is formed on the surface of an insulating substrate 50, and amorphous silicon (a-
Photoelectric conversion layers 52, 53, and 54 each having a semiconductor thin film made of Si) or the like and satisfying the relationship L≦1/α(λ) are laminated. That is, in each of the photoelectric conversion layers 52 to 54, a first conductivity type impurity semiconductor layer (e.g., p layer) 61, a semiconductor layer with a relatively low valence electron control impurity concentration (e.g., i layer: a semiconductor for performing photoelectric conversion of the present invention) thin film) 62, and a second (reverse) conductivity type impurity semiconductor layer (for example, n layer) 63
are stacked in this order. A transparent electrode 55 made of In2O3 or the like is formed on the surface of the uppermost third photoelectric conversion layer 54.

[0004] This photoelectric conversion device has a relatively good photoelectric conversion rate and has a high degree of freedom in design since problems such as a decrease in photoelectric conversion rate, connection loss, and dead space caused by the carrier collection length L are eliminated. It has the advantage of being wide, resistant to photodegradation, and highly reliable.

[0005]

Although the photoelectric conversion device shown in FIG. 6 has many advantages, it cannot be said that the photoelectric conversion rate has been sufficiently improved. In this photoelectric conversion device, the impurity concentration of the p-layer to n-layer is not very high (
Doping gas is approximately 0.25% of the flow rate of silane gas)
Therefore, as shown by the broken line in Fig. 5, there is a bending strain G in the IV characteristic.
occurs, and the photoelectric conversion rate deteriorates accordingly. This is because a rectifying contact is formed between each of the photoelectric conversion layers 52 to 54, and as shown in the equivalent circuit diagram of FIG. 10, a parasitic diode D is interposed between each of the photoelectric conversion layers 52 to 54. This is because FIG. 8 shows an energy band explanatory diagram corresponding to FIG. 7, which is an explanatory diagram of the semiconductor layer structure of the photoelectric conversion device of FIG. 6. As seen in this energy band explanatory diagram, recombination of electron-hole pairs due to the tunnel effect does not occur at the pn junction.

If the impurity concentration of both the adjacent p-layer and n-layer is increased, recombination of electron-hole pairs occurs at the pn junction due to the tunnel effect, as shown in the energy band diagram in FIG. The rectifying contact can be eliminated, but in this case, the amount of ineffective light absorbed by semiconductor layers other than the i-layer increases, making it impossible to improve the photoelectric conversion rate, and also causing the following problems. .

In order to form the photoelectric conversion layers 52 to 54, all necessary semiconductor films are laminated and then subjected to a photolithography process to form a predetermined pattern by wet etching. It is difficult to be etched compared to a semiconductor layer, and as shown in FIG. 11(a), a situation occurs in which the high impurity concentration p layer protrudes from the side surfaces of the photoelectric conversion layers 52 to 54, and the subsequently formed transparent electrode 55 is As shown in b), it tends to be interrupted and becomes less reliable.

In view of the above circumstances, it is an object of the present invention to sufficiently improve the photoelectric conversion rate in the photoelectric conversion device by eliminating the rectifying contact between each photoelectric conversion layer without reducing reliability. .

[0009]

[Means for Solving the Problems] In order to solve the above problems, in the photoelectric conversion device according to the present invention, L≦1/α(λ
) In a structure in which a plurality of photoelectric conversion layers each having a semiconductor thin film that photoelectrically converts light having a wavelength of 1 is stacked, a layer having ohmic properties is provided between the photoelectric conversion layers. However, λ, α(λ), and L are as follows.

λ... Wavelength of incident light α (λ)... Absorption coefficient of semiconductor thin film for light with wavelength λ L... Carrier collection length Layer with ohmic property (electrical resistance between adjacent photoelectric conversion layers Examples of the layer (which makes the contact ohmic) include a layer that can recombine most of the electron-hole pairs injected into this layer, as claimed in claim 2. There is a microcrystalline silicon (μC-Si) layer as in item 3. In addition, as claimed in claim 4, the layer having ohmic properties (hereinafter referred to as "ohmic layer") has a large number of energy levels in the forbidden band, and is capable of absorbing injected electrons.
There are also layers that can capture most of the hole pairs at the energy level, and specifically, amorphous silicon (a-Si) that does not contain hydrogen or has a low hydrogen content,
) There are layers. Other examples of the ohmic layer include various metal layers made of chromium and aluminum, and transparent conductive layers made of ITO and the like.

The photoelectric conversion layer includes a first conductivity type impurity semiconductor layer (for example, a p-type a-Si layer), a semiconductor layer with a relatively low valence electron control impurity concentration (for example, an i-type a-Si layer: the photoelectric conversion layer of the present invention), Examples include a pin type photoelectric conversion layer having a photovoltaic function, in which a semiconductor thin film that performs conversion) and a second conductivity type impurity semiconductor layer (for example, an n-type a-Si layer) are laminated in this order. The number of photoelectric conversion layers stacked is usually 3 or more, preferably 5 or more.

It should be noted that if the thickness of the i-type a-Si layer, which is a semiconductor thin film that performs photoelectric conversion in each photoelectric conversion layer, is less than or equal to the carrier collection length L, or if the total thickness d of all the i-type a-Si layers is When the number of laminated photoelectric conversion layers is n, L<d<nL or the number of laminated photoelectric conversion layers is 1/[α(λ)・L] or more, a higher photoelectric conversion rate can be obtained. achievable.

[0013]

[Function] In the photoelectric conversion device of the present invention, each semiconductor thin film that performs photoelectric conversion in a plurality of photoelectric conversion layers has L≦
Even if it is 1/α(λ), the decrease in photoelectric conversion rate caused by the carrier collection length L can be eliminated by reducing the thickness of each semiconductor thin film. The thin semiconductor film is thin, allowing light to pass through it easily, but the transmitted light is absorbed by the underlying semiconductor thin film and contributes to photoelectric conversion. In addition, a thin semiconductor film is less susceptible to photodeterioration and has high reliability. Even if there are multiple photoelectric conversion layers, the stacked tandem structure reduces connection loss and dead space.

Furthermore, in the case of the photoelectric conversion device of the present invention,
Since an ohmic layer is provided between each photoelectric conversion layer, rectifying contacts can be eliminated and parasitic diodes can be eliminated without providing a semiconductor layer with a high impurity concentration in the photoelectric conversion layer. Therefore, I shown by the solid line in FIG.
As seen in the -V characteristic curve, bending distortion is eliminated, the maximum power that can be taken out is increased, and the photoelectric conversion rate is sufficiently improved, and at the same time, the electrodes are not interrupted and reliability does not deteriorate.

When the ohmic layer is a μC-Si layer, as shown in FIG. 3, it is thought that ohmic properties are ensured by recombination of electron-hole pairs injected into the μC-Si layer. In the case of a μC-Si layer, the resistivity of the layer itself can also be easily reduced. When the ohmic layer is an a-Si layer that does not contain hydrogen or has a low hydrogen content, as shown in Figure 4, there are many energy levels E1 ... En ... in the forbidden band, and the a-Si layer It is thought that ohmic properties are ensured by capturing the injected electron-hole pairs in the energy levels E1 . . . En .

[0016] The ohmic layer of μC-Si or a-Si is
When the photoelectric conversion layer is made of a-Si, the ohmic layer can be continuously formed using the same device when forming the photoelectric conversion layer, and can be patterned using the same etchant.
It becomes very easy to manufacture.

[0017]

[Embodiments] Hereinafter, embodiments of the photoelectric conversion device according to the present invention will be described. FIG. 1 shows an example of the basic configuration of a photoelectric conversion device of the present invention, and FIG. 2 shows an equivalent circuit of this photoelectric conversion device. The photoelectric conversion device 1 has five a-Si pin type photoelectric conversion layers 2 having a photovoltaic function (Fig. 1,
2, only three are shown for convenience), and are provided between the transparent upper electrode 4 and the lower electrode 5. Not only light but also transparent upper electrode 4
It comes in from the side. All i layers of each photoelectric conversion layer 2 are L≦1
It is a semiconductor thin film that photoelectrically converts light with a wavelength of /α(λ). The thickness of each of the p, i, and n semiconductor layers in the photoelectric conversion layer 2 is usually about 5000 Å or less for the i layer, and 500 Å or less for the n layer and p layer, each of which is 1/10 or less of the i layer.
It is about the following. For the p-layer and n-layer, silane gas is used.
．． An example is an impurity semiconductor layer formed by adding a doping gas (for example, phosphine in the case of n-type, and diborane in the case of p-type) at a flow rate of about 25% to 1% or less.

As described above, the ohmic layer 3 is provided between each photoelectric conversion layer 2, and the photoelectric conversion rate is improved. The ohmic layer 3 includes a μC-Si layer and an a-Si layer that does not contain hydrogen or has a low hydrogen content, and is formed by vacuum evaporation, sputtering, plasma CVD, or the like. The a-Si layer containing no or low hydrogen content can be formed by, for example, forming a film by plasma CVD using silane gas without hydrogen compensation. In the case of μC-Si layer, usually n-type μC-S
Although it is an i-layer, in the case of an a-Si layer, it may be of any conductivity type, and may be an i-type.

The present invention is not limited to the above embodiments. For example, another example may be one in which n and p are reversed in FIG.

[0020]

[Effects of the Invention] As described above, the photoelectric conversion device of the present invention has an ohmic layer between each photoelectric conversion layer to eliminate rectifying contact, so that the photoelectric conversion rate is sufficiently improved. It has become a very useful device with sufficient reliability. In addition, in the photoelectric conversion device according to claims 3 and 5, the ohmic layer is made of μC-Si or a-Si.
It has the advantage of being easy to manufacture.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a configuration example of a photoelectric conversion device of the present invention.

FIG. 2 is an equivalent circuit diagram of the photoelectric conversion device of FIG. 1.

[Fig. 3] The photoelectric conversion device of Fig. 1 (the ohmic layer is μC-
FIG. 3 is an energy band explanatory diagram (in the case of a Si layer).

FIG. 4 shows the photoelectric conversion device in FIG. 1 (the ohmic layer is a-S
FIG. 3 is an explanatory diagram of energy bands (in the case of an i-layer).

FIG. 5 is a graph showing IV characteristics of a photoelectric conversion device of the present invention and a conventional photoelectric conversion device.

FIG. 6 is a cross-sectional view showing the configuration of a conventional photoelectric conversion device.

FIG. 7 is an explanatory diagram of a semiconductor layer structure of a conventional photoelectric conversion device.

FIG. 8 is an explanatory diagram of energy bands of an example of a conventional photoelectric conversion device.

FIG. 9 is an explanatory diagram of energy bands of another example of a conventional photoelectric conversion device.

10 is an equivalent circuit diagram of the photoelectric conversion device of FIG. 6. FIG.

FIG. 11 is an explanatory diagram of the manufacturing process of a conventional photoelectric conversion device.

[Explanation of symbols]

1... Photoelectric conversion device 2... Photoelectric conversion layer 3...Ohmic layer 4...Transparent upper electrode 5...Lower electrode

Claims (5)

[Claims] [Claim 1] A photoelectric conversion device in which a plurality of photoelectric conversion layers having semiconductor thin films that photoelectrically convert light with a wavelength satisfying L≦1/α(λ) are stacked, which has ohmic properties between the photoelectric conversion layers. A photoelectric conversion device characterized by being provided with a layer. However, λ... Wavelength of incident light α (λ)... Absorption coefficient of semiconductor thin film for light with wavelength λ L... Carrier collection length 2. The photoelectric conversion device according to claim 1, wherein the layer having ohmic properties is a layer capable of recombining most of the electron-hole pairs injected into this layer. 3. The photoelectric conversion device according to claim 2, wherein the layer having ohmic properties is a microcrystalline silicon layer. 4. The layer having ohmic properties has many energy levels in the forbidden band, and the injected electrons and
2. The photoelectric conversion device according to claim 1, wherein the layer is capable of trapping most of the hole pairs in the energy level. 5. The photoelectric conversion device according to claim 4, wherein the layer having ohmic properties is an amorphous silicon layer containing no hydrogen or a low hydrogen content.