JPS61180487A - Amorphous silicon solar cell - Google Patents

Abstract

PURPOSE:To reduce the reflection factor of incident light and to improve the transducing efficiency of the solar cell, by providing with a light-transmitting insulator film having a refractive index different from that of the light- transmitting insulator substrate, between the substrate and a light-transmitting conductive film. CONSTITUTION:After a light-transmitting insulator film 1 is evaporated on a light-transmitting insulator substrate 5, an In2O3-SnO2 (ITO) film 2 is formed as a light-transmitting conductive film by a sputtering apparatus. Using plasma CVD, on the ITO film 2 a P-type amorphous silicon film 31, I-type amorphous silicon film 32, and N-type amorphous silicon film 33 are sequentially deposited. As a final step, an Al electrode 4 is evaporated on the N-type silicon film 33. The refractive index of the insulator film 1 is made larger than that of the substrate 5. Thus, the reflection factor of incident light can be decreased to improve the transducing efficiency of the solar cell.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to antireflection of amorphous silicon solar cells.

(Prior art) Conventional amorphous silicon solar cells are made of In2O3-
It has a structure in which a p-type amorphous silicon layer, an i-type amorphous silicon layer, and an n-type amorphous silicon are sequentially laminated on a glass substrate with a transparent electrode such as 3nO, and finally a back electrode is deposited.

(Problems to be Solved by the Invention) In the conventional solar cells mentioned above, generally 20 to 40% of the incident light
is reflected and results in a loss of incident energy, so
It is desired to reduce the reflectance. Conventionally, the Inz03 3nOg (hereinafter referred to as ITO) film that constitutes the transparent electrode has a refractive index of about 2 and has an antireflection function against incident light, so the ITO film thickness has been adjusted to reduce the reflectance. Studies have been made to reduce the reflectance, but a sufficient reflectance reduction effect has not been obtained. Also, ITO is p
It is in contact with the amorphous silicon layer and needs to function as an electrode, so if the film thickness is changed to reduce the reflectance, for example, if the film thickness is made thinner, the electrical resistance will increase and the solar cell may reduce the conversion efficiency.

Therefore, in view of the above points, the present invention aims to reduce the reflectance of incident light and improve the conversion efficiency of a solar cell.

(Means for Solving the Problems) In order to achieve the above-mentioned technical problem, the present invention provides a solar cell comprising a transparent conductive film and a pin-type amorphous silicon layer laminated on a transparent insulating substrate. In the battery, a technical means is provided in which a light-transmitting insulating film having a different refractive index with respect to the light-transmitting insulating substrate and the light-transmitting conductive film is provided between the light-transmitting insulating substrate and the light-transmitting conductive film. adopt.

(Function) By adopting the above technical means, the incident light to the solar cell is refracted when passing through the transparent insulating substrate, the transparent insulating film, and the transparent conductive film in order, resulting in pin-type amorphous light. reaches the crystalline silicon layer, is photoelectrically converted by the pin-type amorphous silicon layer,
An electromotive force is generated at both ends of the pin type amorphous silicon layer.

Here, the refractive index of the light-transmitting insulating film is different from that of the light-transmitting insulating substrate and the light-transmitting conductive wire film, so the difference in refractive index causes the light to emit more light than in the case without the light-transmitting insulating film. Interference increases and reflectance in the visible range decreases. Therefore, the amount of incident light absorbed by the solar cell increases, and the amount of photoelectric conversion increases. Moreover, since there is no current-carrying relationship with the light-transmitting insulating film and the pin-type amorphous silicon layer, the conductivity will not be reduced. Furthermore, since the transparent conductive film is thin, the amount of attenuation of light when passing through this portion is also very small.

(Effects of the Invention) Therefore, the solar cell of the present invention as a whole has improved conversion efficiency compared to the conventional solar cell, and can effectively utilize light energy.

In addition, since the reflectance of light is reduced, the anti-glare effect is large.
It is very effective in practice.

(Example) Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 shows a cross-sectional view of the solar cell of the present invention. A first embodiment of the present invention will be described below using this figure. In FIG. 1, reference numeral 5 indicates a refractive index of 1, which is an example of a translucent insulating substrate.
．． A transparent glass substrate No. 53 is used, and an M g F z film 1 having a refractive index of 1.36, which is an example of a transparent insulating film, is deposited thereon to a thickness of 1103 nm using an electron beam evaporation apparatus. Next, using a sputtering device, InzOi SnO, which is an example of a transparent conductive film, was formed using In-3n metal as a target.
□A transparent electrode (ITO) 2 is formed to a thickness of about 60 nm.

The refractive index of this ITO film 2 was 1.85. Next, Mg
F, the glass substrate 5 on which the film 1 and the IT○ film 2 are formed is set in a plasma CVD apparatus, and the p-type amorphous silicon film 31 (refractive index 2.64) is coated with the ITO film 2 under the following conditions.
deposit on top of.

Gas used: 10% Si Ha / Ht 30SC
CM10% CH4/B2 70SCC
M500 ppm B2 Hb /H230SCCM
Pressure: 1.2 Torr
Power: 2QW Substrate temperature: 250°C Film thickness: 20nm Next, an i-type amorphous silicon film 32 (refractive index 4.
35) is deposited on the p-type silicon film 31. The conditions at that time are as follows.

Gas used: 10% Si H4/Hz 60SCC
M pressure: 0.9 Torr voltage
Force = 35 v Substrate temperature = 250° C. Film thickness: 500 nm Next, an n-type amorphous silicon film 33 is deposited on the i-type silicon film 32 . The conditions are as follows.

Gas used: 10% SI Ha / Hz 35SC
CM500 ppm PH3/HE 35SCCM Pressure: 1. OTorr power
: 160 W Substrate temperature: 250° C. Film thickness: 30 nm As a result, a pin type amorphous silicon layer 3 shown in FIG. 1 is formed.

Finally, A! The electrode 4 is attached to the n-type silicon film 33 at 110
It is deposited to a thickness of 0 nm using an electron beam evaporator.

With this configuration, a solar cell as shown in FIG. 1 is completed.

In the pin-type amorphous silicon layer 3, the i-type silicon layer 32 is responsible for photoelectric conversion, and the p-type silicon layer 31 and the n-type 9937 layer 33 have many defect levels and therefore hardly contribute to photoelectric conversion. The film thicknesses of the p-type silicon layer 31 and the n-type 9937 layer 33 need to be selected to be as thin as possible so as to be sufficient to maintain the diffusion potential and to suppress a decrease in the FF of the solar cell due to an increase in resistance and light absorption. On the other hand, the thicker the i-type silicon layer 32 is, the more light it can absorb; however, if it is too thick, a region with a weak electric field will occur, causing an increase in series resistance and a decrease in carrier collection efficiency. It is necessary to take these factors into consideration for optimization.

The film thickness of the transparent electrode 2 is determined according to the antireflection condition (nd = λ/4)
determined to satisfy. A thick film is advantageous because it reduces resistance, but it is not preferable because it causes problems in the amount of light transmitted and cost. Therefore, in the present invention, it is set to 60 nm.

Next, the operation of the solar cell having the above configuration will be explained.

In the above battery, a glass substrate 5. When light is incident on the amorphous silicon film 3 through MgF2° and the transparent electrode 2, a photoelectromotive voltage is generated between the transparent electrode 2 and the A1 electrode 4.

According to measurements carried out by the present inventors, this solar cell had an open circuit voltage of 0.83 mm and a short circuit current of 13.5 mA/cm2 under sunlight AMI. It exhibited excellent characteristics with FF=0.62 and photoelectric conversion efficiency η=6.92%.

Curve a in FIG. 2 shows the results of measuring the reflection characteristics of the solar cell of this first example. Note that the horizontal axis in FIG. 2 indicates the wavelength of incident light, and the vertical axis indicates the reflectance of the solar cell with respect to the incident light.

As can be seen from FIG. 2, the solar cell of this example has a minimal peak of reflectance when the wavelength of incident light is around 560 nm. In this example, when the wavelength of the incident light was 560 nm, the reflectance was 3%. In other words, of the incident light at this wavelength, 9
This means that 7% was absorbed by the solar cells. Moreover, since the amorphous silicon of this example has a characteristic that the conversion efficiency is high in the visible region, extremely efficient photoelectric conversion is possible.

Furthermore, it is known that the specific luminous efficiency of the human eye peaks at a wavelength of 560 nm, so if the solar cell of this example is used as a power source for various devices, the user will experience glare. It can be used without any problems. In particular, when used as a power source for automobile equipment, it has a large anti-glare effect on the driver, so it can improve safety when driving the car.

Figure 3 shows MgF, wavelength 40 when the film thickness of film 1 is changed.
Average reflectance from 0 nm to 800 nm is shown.

From this figure 3, even if the thickness of MgF film 1 changes, 4
It can be seen that the average reflectance from 00 nm to 800 nm hardly changes. However, if we consider the attenuation of light,
It is preferable that the film thickness be as thin as possible. In this first example, the average reflectance was 13% because the MgF film thickness was 1103 nm.

Next, a first comparative example with respect to the first example will be described. In this example, in the solar cell shown in FIG.
F. The characteristics of a solar cell without film 1 were investigated. According to it, this solar cell has an open circuit voltage o, s ov, and a short circuit current of 13.3 mA/cm under sunlight AMI.
, FF-0,62, photoelectric conversion efficiency η=6.60% characteristics.

Further, in FIG. 2, a curve shows the reflectance of the solar cell of this example with respect to the wavelength of incident light.

It can be seen that the reflectance of this example at a wavelength of 560 nm is 8%, which is higher than that of the first example described above. As can be seen from FIG. 2, the reflectance of the first example is lower than that of the first comparative example in the wavelength range of about 450 nm to 750 nm.

Note that the average reflectance of the first comparative example at 400 to 800 nm was 8%. However, the reflectance at 560 nm is the first
Since it is larger than that of the example, the conversion efficiency is lower than that of the first example.

Next, a second comparative example will be explained. In this example, in a solar cell with a pin heterojunction structure similar to that of the first example, the light-transmitting insulating film 1 has a refractive index of 1.63, which is larger than that of the transparent glass substrate 5. A solar cell is made of an Al103 film with a thickness of 86 nm.

This solar cell has an open circuit voltage of 0.
72V, short circuit current 7.5mA/cm2. FF-0,66
, the photoelectric conversion efficiency η=3.6%.

In addition, in FIG. 2, curve C shows the reflectance of the solar cell of this example with respect to the wavelength of incident light, and the wavelength is approximately 44
Between 0 nm and 790 nm, the first example and the first example
It can be seen that the reflectance is higher than that of the comparative example.

Note that the reflectance of the solar cell in this example at a wavelength of 560 nm is 1
2%, and the average reflectance at a wavelength of 400 nm to 800 nm was 14%. In addition, A It z is shown in Fig. 4.
The average reflectance at an incident wavelength of 400 nm to 800 nm of the solar cell in the second comparative example when the Oy film thickness is changed is shown.

As can be seen from these measurement results, especially regarding anti-reflection of amorphous silicon solar cells, transparent insulating films l,
Transparent electrode 2. The refractive index and film thickness of p-type amorphous silicon [31] are problematic. Among these, the refractive index of the transparent insulating film 1 is important, and the inventors have confirmed that the reflectance can be reduced by using a transparent insulating film with a smaller refractive index than the glass substrate 5. .

According to the present inventor, the reason for this is inferred as follows.

In other words, Inz on -5no which is an example of the transparent electrode 2
Since the refractive index of the second transparent glass substrate 5 is larger than that of the transparent glass substrate 5, the second
As in the comparative example, when the refractive index of the light-transmitting insulating film 1 is made larger than that of the transparent glass substrate 5, the difference between the refractive index of the light-transmitting insulating film 1 and the refractive index of the transparent electrode 2 becomes smaller. However, according to the first embodiment, since the refractive index of the transparent insulating film 1 is smaller than that of the transparent glass substrate 5, the difference in refractive index between the transparent insulating film 1 and the transparent electrode 2 becomes large. It is thought that the interference of light is promoted and the reflectance is reduced.

Next, a second embodiment of the present invention will be described.

In this example, in a pin-type heterojunction structure solar cell similar to that of the first example, the transparent insulating film 1 has a refractive index of 1.24, which is smaller than MgF2. Ca with a film thickness of 113 nm
Assume that the solar cell is F.

This solar cell has an open circuit voltage of 0.
81V, short circuit current 13.4mA/cm2. FF = 0
．． 63, exhibited a photoelectric conversion efficiency of η=6.84%.

Also, in Fig. 2, the curve shows the reflectance of the solar cell of this example with respect to the wavelength of incident light! and the wavelength is 560n
The reflectance at m was 1.8%. However, the wavelength is 56
When it goes beyond 0nm, it suddenly becomes larger, and in the end it's the wavelength40
The average reflectance between 0 nm and 8 Q Onm is 12%.

In addition, FIG. 5 shows the incident light wavelength of 400 nm to 800 nm of the solar cell in the second example when the film thickness of CaF is changed.
Average reflectance in nm is shown.

In the above embodiment, the transparent insulating film 1 was created by vapor deposition, but there is no problem even if it is created by sputtering or ion blating as long as the refractive index is lower than that of the glass substrate 5 and it is transparent. There isn't.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the solar cell of the present invention, FIG. 2 is a characteristic diagram of the present invention and a comparative example showing changes in reflectance with respect to the wavelength of incident light, and FIG. 3 is a transparent diagram of the first embodiment of the present invention. FIG. 4 is a characteristic diagram showing the change in average reflectance for the light-transmitting insulating film of the second comparative example, and FIG. 5 is a characteristic diagram showing the change in average reflectance for the light-transmitting insulating film of the second comparative example. FIG. 3 is a characteristic diagram showing changes in average reflectance for an example translucent insulating film. 1... Transparent insulating film, 2... Transparent conductive film, 3...
・Amorphous silicon layer, 31...p-type amorphous silicon layer, 32...n-type amorphous silicon layer, 33...n-type amorphous silicon layer, 4...i back electrode, 5...translucent property Insulated substrate. Representative Patent Attorney Takashi Okabe Fig. 2 3fL table (nm) Fig. 3 MgF2,1gil (nm) Fig. 5 0 100 200 :100
400CAF2 ch medium)'Il-(nm) Figure 4

Claims (2)

[Claims] (1) In a solar cell formed by laminating a transparent conductive film and a pin-type amorphous silicon layer on a transparent insulating substrate, the above-mentioned An amorphous silicon solar cell characterized in that a transparent insulating film having a different refractive index is provided to a transparent insulating substrate and the transparent conductive film. (2) The refractive index of the light-transmitting insulating film is smaller than the refractive index of the light-transmitting insulating substrate, and the refractive index of the light-transmitting conductive film is larger than the refractive index of the light-transmitting insulating substrate. An amorphous silicon solar cell according to claim 1, characterized in that: