JPH0558271B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generates photovoltaic force in a photoelectric conversion device by using light on the short wavelength side of continuous light such as sunlight, and also provides a photovoltaic device for generating photovoltaic power by using light on the short wavelength side of continuous light such as sunlight. The purpose of this is to allow light energy such as infrared light, which only acts on the photoelectric conversion device, to pass through the photoelectric conversion device without converting it into heat.

The present invention prevents incident light from being scattered and absorbed by impurities added into the semiconductor layer in the P- or N-type semiconductor layer on the light irradiation surface and converted into heat, which causes the photoelectric conversion device to generate heat. Therefore, the energy band width of the semiconductor layer on this irradiated surface is defined as an I-type semiconductor layer (a semiconductor layer having a substantially intrinsic conductivity type without the addition of impurities that determine the intrinsic or intentional conductivity type) (hereinafter referred to as I layer). In addition, light with energy (longer wavelength) smaller than the band width of the I layer can be transmitted through the I layer and also through the N or P type semiconductor layer provided on the back side. The purpose of this is to prevent heat generation in this area.

As described above, in a photoelectric conversion device having a PIN or NIP type structure, the present invention performs only photo-electrical conversion, and allows energy sources that cause heat generation such as light or infrared rays that can perform photo-thermal conversion to pass through as is. The purpose is to

Therefore, in addition to making the electrode on the side of the light irradiation surface transparent, which has been conventionally done, the present invention also makes the electrode provided on the back surface of the semiconductor transparent, instead of using a metal surface electrode. It is characterized by being used as a sex electrode.

Furthermore, the present invention utilizes infrared rays that have passed through the photoelectric conversion device to give thermal energy to the cooling section provided on the back side of the photoelectric conversion device, thereby preventing the temperature of the conversion device from rising, and using water as a photothermal conversion device using a heat pipe system. Instead of heating each part separately, it can be integrated without increasing the area irradiated with light, or by converting some of the sunlight into electricity and using some of it to heat water, the overall utilization rate can be increased to 40%. % or more.

An example of a vertical cross-sectional view of the conventional photoelectric conversion device 1 is shown in FIG. A comb-shaped electrode and an external lead-out electrode 4 are provided for the purpose of ensuring the safety, and a metal, such as aluminum, is provided on the entire surface as the back electrode 2 on the lower surface in order to reduce the sheet resistance on the back surface.

However, the metal electrode on the back side has the effect of reflecting the light back to the front side and doubling or more the optical path, so the thickness of the semiconductor can be reduced.
It can be reduced to about 1/2 of 100 to 200 μm, which is significant in materials such as single crystal silicon, which has a low light absorption coefficient. However, in non-single-crystalline semiconductors such as amorphous or semi-amorphous (a semi-crystalline semiconductor film with a microcrystalline structure having a size of 10 to 1000 Å), the thickness of the semiconductor may be as thin as 0.3 to 2 μm; Since its light absorption coefficient is also 10 times larger than that of a single crystal semiconductor, a back electrode with such a reflective effect is completely worthless.

However, conventionally, this non-single crystal semiconductor (hereinafter referred to as NSCS) is also provided with a metal electrode on the back surface, similar to single crystal semiconductors (hereinafter referred to as SCS), and its effect is to shield light (for example, infrared rays) on the irradiation side. It only has an effect (the effect of increasing the temperature of the semiconductor),
It was extremely inconvenient.

In order to prevent such drawbacks, the present invention is characterized in that the back surface of the photoelectric conversion device is also provided with a light-transmitting electrode in the same way as the light irradiation surface.

Furthermore, the present invention provides light-transmitting electrodes as described above on the irradiation surface and the back surface, thereby making it possible to reduce the amount of incident light.
It was possible to release 15 to 25% of the energy to the outside (externally in the direction of the back side) and prevent the photoelectric conversion device itself from generating heat.

However, further investigation revealed that short wavelength light, especially
For light with a wavelength of 600 nm or less (having a light energy of 2 eV or more), a semiconductor layer with a conductivity type of P or N type (hereinafter referred to as P or N layer) on the incident light surface side is formed with a thickness of 300 to 1000 Å. 40-60 when formed
% was absorbed and simply turned into thermal energy without being converted into electrical energy, causing the photoelectric conversion device itself to generate heat and contributing only to a decrease in conversion efficiency.

In order to prevent such a situation, the present invention is characterized in that a window effect is applied to the P or N layer so that the energy band width is wider than that of the I layer.

For this purpose, the present invention provides six C _1-x (0<x<1), Si ₃ N _4-x (0
<x<4) or SiO _2-x (0<x<2), and by selecting the X value, the
(620 nm) to 4.0 eV (310 nm), and was able to transmit irradiated light having optical energy below this band width.

By doing this, the amount of light that is absorbed by the P or N layer on the irradiated light surface and becomes heat is reduced to 20 to 10%.
We were able to reduce the heat generation of the photoelectric conversion device to 1/3 to 1/4.

Furthermore, the present invention has such a structure and the P of the irradiation light surface is
Or, in addition to making the N layer a window structure, a
It was found that N ⁺ or P ⁺ layers have a very negative effect. This is because if this N ⁺ or P ⁺ layer has an energy band width of 1.4 to 1.8 eV, the same as the I layer, the N or P type impurities added therein (e.g. phosphorus, boron) will cause light scattering. It's for a reason. For this reason, the fabrication is done with N or P on the back side.
Although the layer was formed casually with a thickness of about 2000 Å, the present invention is characterized in that the layer has a wider energy band width than the I layer, similar to the light irradiation surface.

That is, this N or P layer is
By setting the voltage to 2.0 to 4.0 eV as in the semiconductor layer, infrared rays with wavelengths of 700 nm or more that pass through this semiconductor layer can be reduced by 5.
It was possible to increase it by ~10 times. i.e. 20-30 of the incident light
%, the photoelectric conversion device generates heat due to impurity scattering in the N or P layer on the back electrode side, but the present invention reduces this heat generation to 3 to 7% by making the energy band width wide. was completed.

By doing this, on the incident light side, 40-60% of the light energy from sunlight on the irradiated surface and 20-30% on the back surface was converted into heat energy, but it is reduced to 10-10% on the irradiated surface. 20%, 3-7% on the back side,
The conventional light-to-heat conversion of 60 to 90% can be reduced to 15 to 30% even when taking into account the light-to-heat conversion in the I layer, and the difference in light energy is converted into light and is provided under the back electrode. Thermal energy can be absorbed and given to a light-to-heat conversion device such as a heat pipe, and the overall effective utilization rate of sunlight can be increased to 8 to 15% by the photoelectric conversion device of the present invention. The converter enabled effective utilization of 40 to 65%. Therefore, the overall effective utilization rate is 48-80% instead of the conventional 5-30%.
I was able to raise it to .

In particular, by preventing heat generation within the photoelectric conversion device by providing a P or N layer with a window effect on the irradiation surface and back surface, the conversion efficiency of the photoelectric conversion device itself can be increased from 5% to 12%.
It could be increased to ~15% under AM1, and the synergistic effect was quite remarkable.

Furthermore, the conduction of thermal energy is not transmitted as heat to the lower photothermal converter, but as radiant energy such as infrared rays is transmitted to the lower photothermal converter, which has a great effect, and the photothermal converter transfers thermal energy back to the photoelectric converter. I was able to prevent it from happening. That is, by providing a vacuum region between the photothermal conversion device and the photoelectric conversion device, heat transfer by conduction is prohibited, and heat transfer is performed by radiation.
As a result, both the photoelectric conversion device and the photothermal conversion device were able to operate effectively.

In the present invention, amorphous (hereinafter referred to as AS) or semi-amorphous (hereinafter referred to as semi-amorphous or SAS), that is, a crystalline semiconductor with a small crystal size (less than 2.5 μm, especially one having a size of 10 to 1000 Å) Or, SAS consisting of a mixture of crystal and amorphous or amorphous has an energy band width of
1.4-1.8 eV, especially 1.6 eV, and were found to be particularly effective.

In FIG. 2, the horizontal axis shows the wavelength of reflected light, and the vertical axis shows the transmittance in a structure in which transparent electrodes are provided on the front and back surfaces.

As is clear from the drawing, NSCS (non-single crystal
Silicon semiconductors such as AS or SAS (non-single crystals including polycrystals with an energy band width of 1.4 eV or more)
In the present invention using the semiconductor, as shown in curve 5, the thickness of the semiconductor may be as extremely thin as 0.3 to 3 μn. It can be seen that more than 90% of the light is transmitted to the opposite side through the semiconductor and the transparent electrodes on its front and back surfaces. However, the SCS of curve 6
In a structure using (single-crystal silicon), the thickness of the semiconductor is 200 to 300 μm, so the transmittance is not very high even for infrared rays below the energy band width of 1.1 eV, and the light that cannot be transmitted is inside the semiconductor. Heat is accumulated in the semiconductor, and the temperature increase to lower the carrier mobility of the semiconductor is no longer effective.

Therefore, in NSCS, the fact that both the front and back surfaces of the present invention are translucent is extremely effective. Furthermore, the energy band width of NSCS is 1.4 to 2.0 eV, which is larger than the 1.1 eV of single crystal silicon, making it transparent to infrared rays. It is extremely preferable to have the properties because it not only increases the photoelectric conversion efficiency but also prevents the temperature of the semiconductor from rising.

Figure 3 shows the relative transmittance when a wide energy band width is provided for use in the P or N layer.
2.5eV7,8 and as an example of 2.0~4.0eV
This is shown at 3.5eV9. The horizontal axis shows SixC _1-x (0<
x<1), and is the optical energy width obtained by controlling the X value. Measurements were performed using a reflection type monochromator. Curves 7 and 11 are P
Or, it shows the relationship between transmittance and wavelength when no N-type impurity is added. Curves 8, 9, and 10 are P
It is obtained by simultaneously mixing boron as a mold impurity or phosphorus as an N-type impurity in SixC _1-x (0<x<1) with 0.1 to 5 mol% of diborane or phosphin.

Intrinsic semiconductors with no intentionally added impurities are
In the case of SAS, it had 1.6 eV, so in 17 it was possible to absorb light with a shorter wavelength as shown in curve 11 and generate electron-hole pairs. However, P- or N-type impurities with the same energy band width similarly exhibit 100% absorption on the short wavelength side, as shown in curve 10, so here, there are many recombination centers due to the impurity, and the electrons are excited. - Holes do not recombine in the same P or N layer and contribute to photoelectric conversion. In addition, even light on the long wavelength side smaller than Eg in the region 50 is reduced by 30 to 40%.
This also causes the temperature of the photoelectric conversion device itself to rise.

For this reason, the P or N layer was made to have a wide energy band width, and when Eg was set to 2.5 eV, curve 8 was obtained, and when Eg was set to 3.5 eV, curve 9 was obtained. These curves show that it is extremely important to have a wide Eg as the P or N layer provided on the irradiation surface side in order to obtain high transmittance in the 500 to 700 nm range where sunlight has strong energy.

Further, curves 8 and 9 have transmittances 20 to 35% higher in the infrared region of region 50 than curve 10 of Eg, which is the same as the I layer, so that infrared rays can be emitted to the outside.

These curves show the case where the P or N layer is 500 to 1000 Å thick, but if this thickness is halved or doubled, the transmittance will be doubled or halved, respectively.
Needless to say, it will become.

Also, in the drawing, the curves 7 and 11 of the I layer are 0.5 to 1 μm.
However, this may be changed to 0.3 to 3 μm. However, if it is made too thin, the amount of light absorbed by this semiconductor layer will decrease, and if it is made too thick, it will absorb infrared rays that should be transmitted, resulting in self-heating. was optimal.

4A and 4C show the basic vertical cross-sectional structure of the present invention.

That is, light 15 passes through a transparent substrate 45 such as glass.
is irradiated, and electrically conductive and transparent coatings 16 and 19 are provided on the glass using oxides of tin (Sn), indium (In), and antimony (Sb). The coating 16 is a light-transmitting electrode on the light irradiation surface side, and 19 is a light-transmitting back electrode. I-type semiconductor 20, P layer 22 on the light irradiation side, N layer on the back side
A layer 23 is provided.

As shown in FIG. 4B, the P and N layers are formed with a thickness of 50 to 1000 Å, the I layer is formed with a thickness of 0.5 to 1 μm, and the P and N layers 22 and 23 are formed with a voltage of 2.5 eV and 3.5 eV. Then, under AM1, the conversion efficiency is 8.0 to 10%, 12.0
~14% each.

As described above, the present invention photoelectrically converts light with a large Eg, and converts small light, especially infrared light, into
As a result, it was emitted to the outside from the back electrode. In this way, the temperature of the semiconductor itself was prevented from rising, and as a result, it was possible to improve the photoelectric conversion efficiency and achieve combination with a photothermal conversion device.

FIG. 4C shows a semiconductor device provided with a P(I) IN type (P-type semiconductor 22 - insulating or semi-insulating film 17 allowing tunneling current - substantially intrinsic semiconductor 1 - N-type semiconductor 23), 22, Transparent electrodes are formed closely on the front and back surfaces of 23 in the same manner as in FIG. 4A.

In the drawing, the substrate is provided with transparent glass as 15 on the back side of the semiconductor side.

FIG. 4D shows an energy band diagram of the photoelectric conversion device 1 of C with corresponding numbers.

In this vertical cross-sectional view, the insulating or semi-insulating film I layer is made of silicon carbide (SiC) or silicon nitride (Si ₃ N _{4 )} having a film thickness of 10 to 30 Å, and voids, pinholes, etc. at the joint surface of the P-I junction are formed. This prevents leakage from occurring at the bonding surface. By doing this, the film factor in the photoelectric conversion device was improved, and the film factor, which was 0.5 to 0.55 in FIG. 4A, was reduced to 0.7.
A conversion efficiency of up to 18% could be obtained under AM1 conditions, showing an improvement of ~0.75.

In the devices shown in Figures 4A and B, the translucent electrode is a comb-shaped electrode, and only the space between the combs is translucent, or it is a translucent electrode made of gold or aluminum with an extremely thin film of 20 to 50 Å. However, the idea is the same as that of the present invention. However, such a structure has drawbacks such as insufficient transmittance and delicate manufacturing, and is not necessarily suitable for large areas.

In the present invention, the atmosphere during light irradiation is 10
At room temperature of ~30°C, simply making it translucent has a great effect.

However, when the atmosphere is at a high temperature of 40 to 100 degrees Celsius, the thermal energy promotes a decrease in conversion efficiency. Therefore, another feature of the present invention is that a heat converter having a cooling mechanism is provided under the back electrode of the semiconductor using a heat pipe or the like.

A heat pipe is generally a system that takes heat energy from a low-temperature part and gives this heat energy to a high-temperature part.
An example is shown in USP 3875926 (Solar Thermal Energy Collection System).

In the present invention, such a photothermal conversion device can be provided adjacent to and below the transparent electrode on the back surface of the present invention.

By doing this, in series with sunlight
Short wavelength light with optical energy greater than Eg is first extracted into electrical energy by a photoelectric conversion device,
Further, long-wavelength light having a light energy smaller than Eg, such as infrared light, is transmitted through this photoelectric conversion device and the thermal energy is extracted by the photothermal conversion device below.

FIG. 5 is a perspective view showing an example in which a heat pipe is integrally provided in the photoelectric conversion device of the present invention.

In the drawing, an upper electrode 16 for sunlight 15,
Semiconductor 1, lower electrode 19, external connection terminals 34, 3
It's more familiar than 5.

The cooling water passes through the heat pipe 30 from 32 to 33
is released. In the drawing, three heat pipes are arranged in parallel. However, these may be connected in series, and the hot water 33 may be passed through another heat pipe again to improve the conversion efficiency.
In this case, the efficiency of the photothermal conversion device can generally be increased by using a liquid such as alcohol or Fluorinert and then using water with a large heat capacity in the next step.

In FIG. 5, the photoelectric conversion device serves as the antireflection film of the heat pipe, and from this point of view as well, the integration of the photoelectric conversion device for transmitting infrared light and the photothermal conversion device such as the heat pipe is preferable.

As is clear from the above description, the present invention is a photoelectric conversion device in which a light-transmitting electrode and a P and N layer are used not only for the electrode on the light irradiation surface side but also for the back surface, which has a wider energy band than the I layer. have a width,
In particular, the temperature of this photoelectric conversion device itself is prevented from increasing due to light having an energy of 1.6 eV or less, especially infrared light, and thermal energy including this infrared light is transferred to a thermoelectric conversion device for cooling provided in contact with this back electrode side. The purpose is to connect the device in series to the light. As a result, we were able to increase the overall conversion efficiency to 70-90% through photo-electrical and photo-thermal conversion on the same irradiation surface side.

The present invention is characterized in that a photoelectric conversion device using an amorphous or semi-amorphous silicon semiconductor and a light-to-heat conversion device using a heat pipe are integrated. As a result, the short wavelength light generates electricity, and the long wavelength light generates heat, so in order to create a vacuum between the photoelectric conversion device and the light-to-thermal conversion device and insulate it, the temperature rise in this device section is suppressed. prevention and ultimately increase photoelectric conversion efficiency,
It also takes advantage of the synergistic effect of using the wasted light in photothermal conversion to generate heat.

As a result, we were able to create an extremely effective solar energy conversion device that utilizes the limited roof area of a typical home to use part of the sunlight to generate electricity and the other part to heat water. The present invention is based on patent application No. 55-181463, 55- filed by the inventor.
It should be noted that this is a further development of the photoelectric conversion device of No. 181464 (filed on Dec. 22, 2015).

[Brief explanation of drawings]

FIG. 1 shows a longitudinal cross-sectional view of a conventional photoelectric conversion device. FIG. 2 shows the characteristics of transmitted light with respect to wavelength obtained by the photoelectric conversion device of the present invention. FIG. 3 shows the relationship between wavelength and relative transmittance of the I layer, P layer, and N layer used in the photoelectric conversion device of the present invention. Figure 4A,
C shows a photoelectric conversion device of the present invention, and B and D show energy band diagrams corresponding to A and C, respectively. FIG. 5 shows an embodiment of a photoelectric conversion device in which a photoelectric conversion device and a photothermal conversion device of the present invention are integrated.

Claims (1)

[Scope of Claims] 1. A semiconductor device that generates photovoltaic force by light irradiation and has transparent electrodes on the light irradiation surface and the back surface,
and a heat pipe that generates heat by irradiation with light, the heat pipes being vacuum insulated from each other, and a part of the light transmitted through the semiconductor layer of the semiconductor device being used for heat generation in the heat pipe. A photoelectric conversion device characterized by: 2. In claim 1, the semiconductor device has a PIN or NIP type structure, and the P-type semiconductor layer and the N-type semiconductor layer have a wider energy band width than the I-type semiconductor layer, A photoelectric conversion device characterized in that the electrodes in close contact with the P-type semiconductor layer and the N-type semiconductor layer are both transparent electrodes.