JPH046112B2 - - Google Patents

Description

[Detailed description of the invention]

〓Field of Industrial Application〓 The present invention relates to a photoelectric conversion device in which a coating mainly composed of a semiconductor is provided as at least a part of a counter electrode on an insulating or semi-insulating film on a semiconductor for photoelectric conversion. <Prior Art> Conventionally, as photoelectric conversion devices, semiconductor devices using a PN junction, semiconductor devices using a Schottky junction, and devices using a heterojunction have been known. Regarding devices using PN junctions,
A PN junction is provided near the light irradiation surface, and one charge is diffused to the counter electrode on the light irradiation surface side and the other to the electrode on the back surface to generate photovoltaic force. However, this bonding surface is 0.01 to 0.5 μm deeper than the interface.
Since it cannot be made shallow compared to the lifetime of the minority carrier, the holes and electrons generated by photoexcitation recombine and convert before reaching the counter electrode (hereinafter, the electrode provided on the light irradiation surface side is referred to as the counter electrode). It was not possible to increase efficiency. Furthermore, if this junction surface is made shallow, the diffusion resistance there increases, and the carrier cannot be taken out, so there has been a need to improve conversion efficiency by achieving both of these aspects. In addition, there is a conversion device using a Schottky junction in which the junction surface is made even shallower and has a thickness substantially equal to the thickness of the depletion layer. This converter is the first
As shown in Figure A, an electrode 4 is placed on the back surface of the semiconductor 1.
is provided for ohmic contact, and furthermore, a counter electrode 5 is provided as a semi-transparent shot electrode facing the irradiation light 13. In this case, apply natural oxide at the interface between the shot electrode and the semiconductor.
It is made to a thickness of 30 Å, and a shot barrier is provided as shown in Figure 1B by utilizing the interface states generated there and the work function of the shot electrode. That is, a shot electrode 5, a natural oxide 2, a depletion layer 3, a semiconductor 1, and a Fermi level 1.
1 is provided. In a similar category to this, MIS type photoelectric conversion devices are known. This is a silicon oxide film (20 to 30 Å) with a thickness of 600 to 700 to allow tunneling current.
This semiconductor is formed by thermal oxidation at a temperature of .degree. C., and electrodes made of platinum, aluminum, molybdenum, etc. are formed thereon. In addition, a heterojunction photoelectric conversion device (Figure 2) or PN using a transparent electrode made of tin oxide, indium oxide, or indium tin oxide (ITO) as a counter electrode.
In order to reduce the sheet resistance on the light irradiation surface of a photoelectric conversion device using a junction, a device using an oxide transparent electrode as a counter electrode (FIG. 3) is known. The photoelectric conversion device shown in FIG. 2 has an oxide transparent electrode 7 formed on a semiconductor 1 as shown in FIG. 2A. An example of the energy band structure is shown in FIG. 2B. That is, when ITO is used as the oxide transparent electrode 7, its energy band width is 3.7 eV, and the work function difference (φ _B ~
0.6 eV), and the silicon semiconductor 1 is bent upward by about 0.36 eV. However, this bending of the band is caused by the amount of natural oxide, and there has been a problem in that it varies widely depending on the manufacturing method and has poor controllability. 〓Problems to be Solved by the Invention〓 Among these, the problem with the Schottky type is that its natural oxide is extremely sensitive to the cleanliness of the semiconductor surface, and is also extremely susceptible to fluctuations depending on the method of forming the counter electrode. It was hot. For example, if this semiconductor device is
If left for a long time, the counter electrode 3 and the natural oxide 2 semiconductor 1 may react with each other and lose their shot characteristics. Also, in a heterojunction, as shown in Figure 2,
ITO7 is in contact with the semiconductor through the lower silicon oxide film that makes up this ITO, and since this oxide film has a thickness of 5 to 20 Å similar to natural oxide, tunneling current Holes generated by the light irradiation 13 reach the ITO 7 from the depletion layer through the oxide 2. However, since this thin oxide film is not artificially created, it also causes a 20-30% reduction in efficiency in high-temperature operation reliability tests at 150°C. This is because ITO and the semiconductor react at the interface, and local destruction occurs in this thin oxide film of low grade due to strong light irradiation, which apparently reduces the series resistance under the transparent electrode. As a result, it was found that there is also a deterioration mode in which the semiconductor depletion layer disappears. Furthermore, in the semiconductor device using the PIN junction shown in FIG. Recombination with electrons, which are majority carriers, impairs conversion efficiency and is an extremely serious drawback. In addition, a decrease in efficiency was observed in reliability tests, similar to the shottoki type and hetero type. An object of the present invention is to improve reliability by eliminating the generation of uncontrollable interfacial charges or insulators that increase series resistance in the depletion layer region, which is extremely sensitive to the conversion efficiency of a photoelectric conversion device. Furthermore, the purpose is to prevent minority carriers generated near the light irradiation surface from disappearing due to recombination. 〓Means for Solving the Problem〓 The present invention provides a photoelectric conversion device in which an insulating or semi-insulating film is provided on a semiconductor for photoelectric conversion with a thickness sufficient to allow tunneling current, and the film is provided in close contact with the insulating or semi-insulating film. By providing a film mainly composed of a semiconductor as at least a part of the counter electrode, it is possible to lengthen the lifetime of minority carriers on the light irradiated surface side and to reduce the substantial work function difference (difference in electron affinity). It is characterized by providing a photoelectric conversion device with a high open-circuit voltage with excellent controllability. In particular, the present invention is characterized in that an insulating or semi-insulating film having an energy band width larger than that of a semiconductor for photoelectric conversion is used. For example, when silicon nitride (Eg = 5.1eV) is used, due to its diffusion prevention effect against impurities and its small number of trap centers for holes, a highly impurity-doped semiconductor can be placed close to it as a counter electrode. It could be used as a part. In addition, as a semiconductor used for the counter electrode,
It is characterized in that it is made of substantially the same material as the semiconductor for photoelectric conversion and has a conductivity type opposite to that of the semiconductor for photoelectric conversion. In this specification, an example will be explained in which silicon and its nitride, carbide, and oxide semiconductors are used as _{semiconductors} . etc. In addition, although the semiconductor used for the counter electrode is mainly silicon in the examples, the same applies to semiconductors to which nitrogen and impurities or metals are added, or semiconductors to which carbon or oxygen is added instead of nitrogen. can. Examples of the present invention are shown below. Example 1 In FIG. 4A, a cross-sectional view B of the structure of this example shows that an N-type single crystal semiconductor is used as the semiconductor 20, which is a semiconductor for photoelectric conversion, and a P-type non-single crystal semiconductor is used as the counter electrode 23. The energy band diagram for the case is shown. Further, C is an energy band diagram when the conductivity type of the semiconductor for photoelectric conversion and the conductivity type of the semiconductor constituting the electrode are opposite to B. In drawing A, the semiconductor 20 is a single-crystal N type, and an electrode 21 is formed on the back surface of aluminum with a thickness of 1 to 1.5 μm by vacuum evaporation, and the upper surface is coated with hydrogen peroxide, ammonia, and pure water. Thorough pre-treatment cleaning was carried out. Plasma this board
Transfer to CVD equipment and maintain pressure at 0.1 to 1 Torr.
Helium gas containing 10% ammonia gas
50SCCM is introduced, high frequency output of 50W is applied, and the upper surface of the semiconductor 20 is plasma nitrided by heating to 400℃.
The insulating film 22 could be formed to a thickness of 20 Å. Due to the reducing atmosphere of plasma, natural
The oxide and oxide contaminants could be gettered, and extremely stable silicon nitride could be formed. Furthermore, 30 SCCM of silane gas containing diborane at a concentration of 0.1 to 1% is introduced onto this insulating film, the pressure is similarly set to 0.1 to 1 Torr, and a high frequency output of 50 W is applied to form a P-type non-single crystal semiconductor 23 with a thickness of 500 Å. Formed. The substrate temperature was 100 to 400°C, especially 300°C. In this semiconductor, the insulating film 22 is used to release holes, which are minority carriers, generated in the depletion layer to the counter electrode through the insulating film 22.
The thickness of the film is extremely important. If the thickness of the semiconductor forming the electrode is as thick as 1 to 10 .mu.m, the semiconductor portion will absorb the irradiated light, so a thickness of 0.5 .mu.m or less, particularly 1000 .ANG. or less, 5 to 500 .ANG. is sufficient. Since the insulating film is made of silicon nitride, the impurities in the semiconductor 23 do not diffuse to the photoelectric conversion semiconductor section due to its diffusion prevention effect, and play a major role in improving reliability. In addition to boron, the semiconductor 23 constituting the counter electrode may be made of beryllium, magnesium, barium, aluminum, or a lanthanum-based material, which is a metal with a small work function, to improve conductivity. In this example, aluminum is used. Furthermore, a comb-shaped auxiliary electrode was placed on the counter electrode by vacuum evaporation.
A thickness of 1 μm was formed to improve conductivity. Furthermore, SiO was formed as an antireflection film on top of this to form a photoelectric conversion device. The characteristics of the photoelectric conversion device thus produced are shown on the next page.

[Table] Furthermore, in a reliability test conducted at 150°C for 1000 hours, the deterioration of conversion efficiency was improved to within 5%. This example can also be said to be implemented using a semiconductor for the electrodes of a photoelectric conversion device using a Schottky junction. Furthermore, the present invention prevents minority carriers from recombining in the transition region by providing an insulating or semi-insulating layer between the P layer and the I layer of the PIN junction photoelectric conversion device, which completely blocks impurities. It can be said that there is. Example 2 FIG. 5A shows a longitudinal sectional view, and FIG. 5B shows an energy band diagram. FIG. 5 corresponds to FIG. 2. In Figure 2, the silicon oxide layer 8 is made of chemically unstable ITO.
It was generated due to the reaction between 7 and semiconductor 1. However, in this embodiment, the insulating layer uses silicon nitride, which is more stable than silicon oxide. Furthermore, a semiconductor layer 23 is formed thereon as part of the counter electrode. Furthermore, ITO is formed on top of it as before. This prevents the ITO layer from directly contacting the depletion layer. The photovoltaic power generation semiconductor 20 and the insulating or semi-insulating layer 22 were produced in exactly the same manner as in Example 1,
The ITO layer was formed to a thickness of about 1000 Å by sputtering. Example 3 FIG. 6 shows a longitudinal cross-sectional view A and an energy band diagram B of this example. A glass substrate 35 was used as the substrate, and aluminum was deposited to a thickness of 2000 Å on its upper surface by vacuum evaporation. A portion of this aluminum was then anodized to form alumina and used as the antireflection film 37.
On top of this, a 600 Å thick N-type non-single crystal semiconductor to which 10 links/cm ³ or more were added was formed in the same manner as in Example 3 to form a counter electrode 23. Furthermore, as in Example 1, about 20 Å of the upper surface of this semiconductor layer was plasma nitrided to provide an insulating film 22. After this, 50 sccm of helium gas containing 10% silane and phosphine mixed at 0.01 atm% with respect to silane and 0 to 10 sccm of ammonia were introduced as reaction gas, and the substrate temperature was 250℃ and the pressure was
The film was formed at 0.05 Torr for 20 minutes. At this time, by changing the amount of ammonia supplied so that the concentration of nitrogen is 50 to 0.01% with respect to silicon, the amount of nitrogen added is continuously changed from the widest to the narrowest energy band. Intrinsic non-single crystal semiconductors 34 and 33 were thus formed. Furthermore, a P-type semiconductor having an energy band width equal to or larger than that of this semiconductor layer was formed as a P-type non-single crystal semiconductor layer 32 using silane gas, ammonia gas, and diborane gas. It was formed by adding organic aluminum (trimethylaluminum) to degenerate the Fermi level. As a result, in this example, an open circuit voltage of 0.9 to 1V was obtained. <Effects> The present invention provides a photoelectric conversion device in which an insulating or semi-insulating film is made thick enough to allow tunneling current, and at least a part of a counter electrode provided in close proximity to the insulating or semi-insulating film is different from a semiconductor for photoelectric conversion. By providing a film whose main component is a semiconductor with a conductivity type, it is possible to lengthen the lifetime of minority carriers on the light irradiated surface side and to reduce the substantial work function difference (which can also be called a difference in electron affinity). The photoelectric conversion device has a high open-circuit voltage with excellent controllability, and has an extremely large effect of improving conversion efficiency. In particular, when silicon nitride (Eg = 5.1 eV) is used as an insulating or semi-insulating film, its diffusion prevention effect against impurities and its small number of trap centers for holes make it possible to create a highly impurity-doped semiconductor in close contact with silicon nitride (Eg = 5.1 eV). could be used as part of the counter electrode. As a result, the reliability of photoelectric conversion devices has been greatly improved compared to conventional ones. Furthermore, in the example, since the energy band of the semiconductor portion was made into a W-N structure closer to the light irradiation surface, the conversion efficiency could be further improved due to the self-bias effect. It goes without saying that the present invention is not limited only to the examples.

[Brief explanation of drawings]

1 to 3 show conventional embodiments. Fourth
The figure shows an embodiment of the present invention, and A is a longitudinal sectional view thereof;
B and C show the energy band diagram. FIG. 5 shows an embodiment of the present invention, A is a longitudinal sectional view thereof, B,
C shows its energy band diagram. FIG. 6 shows an embodiment of the present invention, A is a longitudinal sectional view thereof, and B is an energy band diagram thereof.

Claims (1)

[Scope of Claims] 1. In a photoelectric conversion device having a semiconductor for photoelectric conversion, an insulating or semi-insulating film, and a counter electrode, the insulating or semi-insulating film is provided on the semiconductor for photoelectric conversion, and the counter electrode The electrode is provided on an insulating or semi-insulating film, and the insulating or semi-insulating film has a thickness that allows tunneling current, and an energy band width that is similar to that of an insulating semiconductor for photoelectric conversion. or larger than the energy band width of the semiconductor for photoelectric conversion at a portion in contact with the semi-insulating film; 1. A photoelectric conversion device characterized in that the main component is a semiconductor made of the same material and of a different conductivity type, and further provided in contact with an insulating or semi-insulating film.