JPH0117273B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention integrates a photoelectric conversion device that generates photovoltaic power by exciting electrons and holes with light irradiation with redox (reduction-oxidation reaction solution), thereby flattening the output, storing power, and even storing power at night. The aim is to reduce electricity usage, etc. BACKGROUND ART Conventional photoelectric conversion devices, particularly solar cells, can generate photovoltaic force by irradiation with light. However, this solar cell produces output only when it is irradiated with sunlight and is proportional to the intensity of the irradiation, so the output fluctuates greatly depending on whether it is sunny or cloudy. When installed on the roof of a general household, there are drawbacks such as no photovoltaic power being generated when illuminating at night, which is a major problem for practical use in civilian use. A method of using a secondary battery to compensate for these problems is known. However, secondary batteries have drawbacks such as being expensive and requiring separate installation locations. On the other hand, redox reactions are known. Typically, this involves irradiating an oxide semiconductor such as TiO ₂ in water with light, and using the electrons and holes generated on this surface to initiate a redox (oxidation-reduction) reaction or such a process. This is a general term for solutions that carry out reactions). In such conventional redox reactions, it has been considered an essential condition that the semiconductor electrode in contact with the redox solution be irradiated with light. In particular, the semiconductor used in this reaction, typically an oxide semiconductor such as titanium oxide, is irradiated with light to create an interface level between the semiconductor and the redox solution, and this level energetically bends the semiconductor surface and depletes it. This is based on the idea of using layer regions. However, this interface level is susceptible to change and especially deterioration due to the progress of the reaction between the semiconductor itself and the redox solution on the semiconductor surface, so even if the actual reaction is carried out by light irradiation, the reaction will be completed within 1 hour to 1 day. It was so bad that it virtually stopped. Furthermore, this photochemical reaction has the disadvantage that colored solutions cannot be used. In order to eliminate such drawbacks, the present invention has developed a non-single-crystal semiconductor having an amorphous or semi-amorphous structure to which hydrogen or halogen elements are added, which is produced at a low temperature of 200 to 300 degrees Celsius by a plasma vapor phase method. In addition, this semiconductor itself has one or more PIN or NIP junctions in a tandem structure (PINPIN junction or NIPNIP junction), and a third junction in contact with redox is used. The electrode surface has a cathode or an anode depending on the polarity of the N or P type semiconductor in contact with the conductive substrate, so that it can be determined only by electrochemical potential. Therefore, it is possible to completely eliminate the influence of so-called interface states. Further, in the conventional redox reaction, as shown in FIG. 1, the irradiated light 10 passes through the container 2 and travels through the solution 10, and is then irradiated onto the cathode or anode electrode 55. For this reason, the irradiation light 10
30-40% is reflected 60 at the container surface and the interface with the container solution, and approximately 60-70% travels through the solution. If this solution is translucent, e.g. water, it is especially important for short wavelengths.
Because it is extremely easy to absorb light in the 100-300 nm range,
As a result, only 5 to 10% of the short wavelength light necessary for the electrodes is irradiated. Furthermore, an additional 20 to 40% of the light is reflected at the surface of this electrode, so the portion of the irradiated light that actually contributes to the reaction is 300 nm or more.
Visible and infrared light up to 1100nm, and a total of 10~300~350nm with TiO ₂ electrode (Eg = 3.5eV)
Only 20% effective. For this reason, it has a major drawback in that only 0.1 to 0.2% of the total incident light, such as sunlight, can be effectively utilized. In addition, when the redox solution used in the present invention is a colored redox solution such as bipyridine containing iron, chromium, etc., it is completely impossible to cause a photochemical reaction. The present invention aims to eliminate this drawback, and its first feature is that the electrode layer of the semiconductor that performs the redox reaction and the surface of the semiconductor that is irradiated with light are separated and provided on opposite sides of each other. This does not require light irradiation on the reaction surface itself for the redox reaction, and only the electrons or holes generated by light irradiation and the potential (monopolar characteristic) at the electrode surface of the third electrode for redox are important. , or rather the PIN
In the semiconductor that constitutes the junction, the intrinsic semiconductor (the I layer to which no impurities are actively added) generates electrons and holes, and the holes and electrons generated in the P and N layers on the upper and lower surfaces are transferred to the first and second layers, respectively. This is based on the idea that it is important to make all the functions independent, such as the internal electric field in the semiconductor that promotes the movement of No. 3 to the electrode, and to improve its controllability and efficiency. FIG. 1 shows an outline of a conventionally known method for generating hydrogen and oxygen through a reaction using water as a redox solution. An example is JP-A-54-4582 or App1.Phys.Lett Vol. 29 No. 6, 15 (1976) 338~
340 shown. The present invention compensates for these drawbacks. An overview of Figure 1 is shown. Glass container 2 containing redox solution 3 and water
An anode 55 and a cathode 54 are provided, and the surface of the anode is made of a semiconductor coated with titanium oxide. Further, light, particularly sunlight 10, is applied, and as a result, oxygen is generated on the anode side and released from 44 to the outside. Further, hydrogen is generated from the cathode 54 side and released from the cathode 43. This causes an electrochemical reaction to occur due to the current flowing through the load 25. As is clear from this drawing, in the past, when a semiconductor was used for a redox reaction, it was not possible to directly extract electricity from the semiconductor. Furthermore, it has been impossible to control and extract the necessary amount of electrical energy from this semiconductor and store it as a by-product for effective use of unnecessary electrical energy. The present invention not only allows effective redox reactions as described above, but also enables three types of reactions: photo-electrical conversion and photo-redox (electricity storage, discharge) reactions. Therefore, when there is no sunlight, it is possible to extract electrical energy and cause the surplus to undergo a redox reaction, and at night, it is also possible to re-react the stored reaction products and extract electrical energy again. This is an all-time, all-weather photoelectric conversion device. The present invention is further characterized in that the solar cell system is provided on the main surface that is irradiated with light, and a redox system that has an integrated power storage effect is provided on the back surface. Furthermore, the redox system also provides a plant system capable of charging and discharging that has the function of a regenerative fuel cell. That is, a photovoltaic force is generated by a non-single-crystal semiconductor having a PIN or NIP junction on the upper surface of a conductive substrate, such as a titanium, stainless steel, or aluminum substrate constituting the first electrode. ITO (a mixture of indium oxide and tin oxide), conductive titanium oxide, a multilayer film of conductive titanium oxide and indium oxide, and other light-transmitting materials that constitute the second electrode provided on the light-irradiated surface of this semiconductor It is taken out to the outside through a second electrode constituted by a conductive film and an auxiliary electrode provided in a comb shape on the conductive film. On the other hand, on the opposite side of the conductive substrate, which is electrically continuous with the semiconductor layer consisting of the N or P layer below the semiconductor, there is a third electrode provided selectively or on the entire surface, which is in contact with the redox solution and is connected to the redox. Provide electrons or holes. Even if the third electrode is made of the same electrode material as the first electrode, if it acts as an anode or a cathode, the first and third electrodes may be made of the same material. In particular, when the cathode is made of stainless steel, a cathode electrode may be provided on its upper surface. Furthermore, to prevent an increase in series resistance at this third electrode, this electrode should be
It is important to make it extremely thin, with a resistance of 1Ω or less. In other words, the semiconductor on the substrate, which is the first electrode, is P
Alternatively, in the case of the N type, the redox electrodes are also provided with third electrodes that are aligned so that the polarity is such that the electric charges generated in the semiconductor layer are easily imparted to the redox system, that is, the anode or the cathode. Furthermore, this redox solution includes non-aqueous solutions and aqueous solutions. In particular, when water is used in water-soluble redox, hydrogen is generated on the cathode side where the semiconductor contacts the redox with the N layer, and oxygen is generated on the P layer side, which is the anode electrode side where the semiconductor receives holes or emits electrons. Occur. For this reason, non-single crystal semiconductors that have an energy band width of 1.3 to 2.0 eV with high photoelectric conversion efficiency and constitute PIN junctions, especially amorphous or lattice-strained semiconductors in which hydrogen or halogen elements are added to neutralize recombination centers. It was possible to separate and generate oxygen and hydrogen by integrating it with a photoelectric conversion device using a semi-amorphous semiconductor with microcrystallinity of 5 to 100 Å. Furthermore, the present invention has a significant difference compared to the conventionally known redox system using a platinum-titanium oxide semiconductor electrode system. In other words, the energy band width of conventionally known titanium oxide is 3.2 eV.
Therefore, among the irradiated light, only the ultraviolet rays can effectively create electron-hole pairs and separate them. For this reason, the efficiency is extremely low for continuous light centered around 500 nm, such as sunlight. Moreover, its production requires high temperature and high energy of 600 to 800°C. On the other hand, in the present invention, Eg (energy band width) is set to 1.0.
Another feature is that non-single-crystal silicon, silicon carbide, and germanium silicide with Eg of 1.3 to 2.0 eV are used in the active region that generates electrons and holes with irradiation light. That is, among these silicon, especially amorphous or semi-amorphous silicon having a microcrystalline structure in the short range of 5 to 100 Å,
Silane, SiF ₄ , etc. 200-300% by plasma vapor phase method
Because Eg is produced at a low temperature of 1.4 to 1.9 eV, the light absorption coefficient for light, especially sunlight, at short wavelengths of 3500 to 5000 Å is 10% lower than that of single crystal silicon (Eg 1.1 eV).
The efficiency on the short wavelength side is ~30 times greater. In addition, the I layer (intrinsic or substantially intrinsic conductivity type) in the PIN junction of the present invention has a light absorption coefficient of 20 on the short wavelength side.
Since it is twice as large as single crystal silicon, its thickness can be reduced.
0.3 to 1 μm, typically _0.5 μm;
x1) In particular, the optical energy band width of x = 0.2 to 0.7 is 1.8 to 2.8 eV, and the I layer is typically 1.3 to 2.0 eV.
The heterojunction was set wider than 1.6 to 1.8 eV. By adopting such a structure, the irradiated light is not absorbed by the redox solution etc. in the photoelectric conversion device.
By irradiating a semiconductor that has a PIN junction, a conversion efficiency of 5 to 15% can be obtained, for example as a solar cell, and by providing the most ideal third electrode as an electrode for redox, this electric energy can be used for photoelectric conversion. It has become possible to control redox reactions independently and accurately. Furthermore, in the present invention, the following materials can be used without regard to the fact that the third electrode in close contact with the redox is a semiconductor. Namely, the anode material is tin oxide, antimony oxide, titanium oxide, iron oxide, silicon carbide, carbon, tin oxide, or titanium oxide added with antimony oxide, and the cathode material is silicon carbide, platinum tungsten, stainless steel, carbon, indium oxide, or indium oxide. It was made of titanium oxide or the like to which indium was added. Especially when using semiconductor as electrode material,
To use it as an anode, use a P-type semiconductor to make it easier to generate holes (easier to accept electrons).
Further, it is preferable to use an N-type semiconductor doped with phosphorus or arsenic for the cathode to facilitate electron emission. When using metal, it is preferable to use a material with a large work function for the cathode, especially φ _M =3.5 eV or more. Regarding the photoelectric conversion device having the above-mentioned heterojunction, the patent application filed by the present inventor is U.S. Patent Publication No. 4254429 (corresponding Japanese Patent Application No. 53-83467,
83468 S53.7.8 application) U.S. Patent Publication No. 4239554 (corresponding Japanese patent application No. 53-86867, 86868 S53.7.17 application)
The details are shown in. Furthermore, if we create a tandem structure by stacking two or more PIN junctions, the voltage can be reduced to 0.7
It was more preferable because it could be set to 1.5 to 1.8V rather than 1.0V. Examples of the present invention will be shown below with reference to the drawings. Embodiment 1 FIG. 2 shows a non-single crystal semiconductor 12 having a PIN junction according to the present invention, in which a P-type semiconductor layer 14 is provided on a first electrode 30, an I-type semiconductor layer 15, an N-type semiconductor layer 1
6 is provided, and 9 is provided as a counter electrode on the N-type semiconductor layer. Further, the electrode 9 and the auxiliary electrode 23 opposing the light irradiation 10 constitute a second electrode, and the external lead terminal 8 drives the load 11 through the switch 17. On the other hand, the first electrode 30 is provided with a third electrode 24 for redox in close proximity thereto, and the electrode 28 constitutes a fourth electrode with an auxiliary electrode 29 serving as its substrate. In order to mechanically protect the 12 surfaces of the photoelectric conversion semiconductor, a translucent holder (e.g. tempered glass) is used.
21 and a translucent filler 20, such as Seaflex, is provided therebetween. The peripheral area of this semiconductor device was reinforced and insulated at 22 with epoxy or polyimide resin to maintain redox resistance and mechanical strength. When distributing water, the redox solution 3 does not require the ion conversion membrane 64, and generates oxygen at the anode and hydrogen at the cathode more efficiently than the water supplies 41 and 42, and releases them from 43 and 44, respectively. . In order to cause this redox reaction, the switch 19 may be turned on. In other words, the switch 17 can be used to drive the load 11 to obtain electrical energy, and the switch 19 can be used to decompose water. As a result, we were able to obtain a conversion efficiency of 7 to 15% as a solar cell, and also succeeded in generating oxygen and hydrogen without adding any external electricity. In particular, the third electrode 24 is made extremely thin, with a thickness of 50 to 300 Å.
Providing iron oxide (αFe ₂ O ₃ ) on the first substrate electrode,
When the other fourth electrode is made of platinum or graphite, a saturation current of 120 mA/cm ² can be obtained. Therefore, a short circuit current of 10 mA/cm ² can be obtained by light irradiation of AM1 (100 mW/cm ² ), which is 1.5 to 3%, which is 10 times higher than the energy conversion efficiency of 0.2 to 0.4% shown in Figure 1. was able to obtain. Similar values of 1.7 to 2.6% could be obtained when titanium oxide was provided as the third electrode using the attached method. Example 2 In this example, a non-aqueous solution was used as the redox solution. For this reason, in FIG. 2, an ion exchange membrane 24 is provided, an anode 24, a cathode 2
8 to prevent the charged solutions from mixing. Propylene carbonate is used as a non-aqueous solvent for this redox.

[Formula] (hereinafter simply referred to as PPK) or acetonitrile (CH ₃ -
CN) is an anhydride, which is a typical stable non-toxic solvent with little electrode reaction. Bipyridine (bpy) or its compounds such as 4,4(CH)bpy (hereinafter simply referred to as bipyridine) or 1,
10Phenanthroline (phen) or 4.7−
Compounds such as (C ₆ H ₄ SO ₃ )phen ^2- (simply referred to as phenanphroline) were used. In particular, the following materials using Fe, Ru, or O ₅ as solvents were used. That is, Fe (bipyridine) ²⁺ ₃ , (C10 ₄ ) ^2- ₂ (simply referred to as FBP) Fe (phenanthroline) ²⁺ ₃ , (C10 ₄ ) ^2- ₂ Ru (bipyridine) ²⁺ ₃ , (C10 ₄ ) ^2- ₂ (Simply referred to as RBP) Ru (phenanthroline) ²⁺ ₃ , (C10 ₄ ) ^2- ₂ RBP is particularly superior in terms of physical properties, but FBP, which is a low-cost, non-toxic and non-polluting material, is practically preferable. It was hot. By using such a material as a redox, it was possible to carry out a redox reaction, that is, FBP ²⁺ FBP ³⁺ +e ^- anode FBP ²⁺ + e ^- FBP ¹⁺ cathode, where → charge, ← discharge. As a cathode, CBP ³⁺ +e ^- CBP ²⁺ However, as shown in CBP represents bipyridine of chromium, a ligand of chromium may be used as a solvent. When performing this charging, the switch 19 was turned on. In addition, when discharging the accumulated energy, the switch 18 was turned on and the load 11 was used to cause the reverse reaction. Further, when the signal is simply used as an output of a photoelectric conversion device, the switch 17 may be turned on. Furthermore, since the battery is charged by light irradiation, the flattened voltage can be discharged at the same time by turning on the switch 17 and then turning on the switch 18. By doing so, it was possible to extract optical energy at a smoothed voltage in the circuit system. In the drawing, the redox solution is further filled into ports 4 and 5, so the supply ports are 41 and 42, and the discharge ports 43 and 44.
may be provided to increase the output. The rest of FIG. 2 is the same as in the first embodiment. By doing this, the output efficiency of charging and discharging light energy is 0.5 to 0.5, which was previously shown.
We were able to obtain 5 to 10%, which is 5 to 10 times more than 1%. Embodiment 3 This embodiment, whose system is shown in FIG. 3, is an example of a plant in which the redox system of Embodiment 2 is enlarged. In the drawing, the redox solution is filled in 4 and 5 as shown in Example 2, and the light irradiation 10
The redox is added to each tank 48, 53 and circulated by pumps 46, 45, and the electrical output is passed through the DA converter and temperature riser 49 to the external power system 51, 52. Supplied by In this system, when there is no light irradiation and there is surplus power 51, the redox system 4,
5 can now be charged. From the above, this embodiment uses the same plasma to evaporate and release electrical energy for photo-electrical conversion, and to store and release excess power using a redox system. This was made possible for the first time because the use of water-insoluble redox prevented the solution from deteriorating, electrode reactions, and dissolution of the electrode into the redox solution. Therefore, storage of electrical energy of 1 to 100 MWH,
Emission is also possible, and was made possible for the first time by a redox system integrated into the back side of the photoelectric conversion device. As is clear from the above description, the present invention provides a structure for a photoelectric conversion device that can integrate a photoelectric conversion device and a redox reaction, and its practical effect is that of a so-called small scale. It has become extremely effective in converting energy for general households and even for entire towns, and is considered to be extremely important from an industrial perspective.

[Brief explanation of drawings]

FIG. 1 shows a semiconductor device for redox reaction using a conventional semiconductor device. FIG. 2 shows an outline of the semiconductor device of the present invention. FIG. 3 shows a redox power generation system using the semiconductor device shown in FIG.

Claims (1)

[Claims] 1. A non-single crystal semiconductor having at least one PIN junction is provided on the light irradiation surface side of a first electrode made of a conductive substrate, and a second electrode is provided on the light irradiation surface side of the semiconductor. an anode or A third electrode acting as a cathode is provided, and a redox solution is provided between the third electrode and the fourth electrode to generate a photovoltaic force in the semiconductor between the first and second electrodes, and to generate a photovoltaic force in the semiconductor between the first and second electrodes. A photoelectric conversion device characterized in that a redox reaction is caused through a third electrode by an electromotive force. 2. A photoelectric conversion device according to claim 1, further comprising a light-transmitting second electrode laminated on a semiconductor layer having N or P type conductivity above the semiconductor. 3. The photoelectric conversion device according to claim 1, wherein the fourth electrode in contact with the redox solution is made of an electrode material having a polarity opposite to that of the third electrode.