JPS634356B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a low-cost, large-area isotype-heterojunction photoelectric conversion element. The present invention is n
type mainly made of amorphous silicon,
The present invention relates to a method for manufacturing an isotype heterojunction type photoelectric conversion element of n-type tin oxide, and in particular to forming n-type tin oxide by a vacuum evaporation method. In general, isotype heterojunctions connect a second semiconductor with a wide band gap with the same conductivity type.
A good photoelectric conversion element can be obtained by forming a depletion layer or an inversion layer in the vicinity of the surface of the first semiconductor having a narrow band gap and in contact with the first semiconductor having a narrow band gap.
As shown in Figure 1, this condition is established in a junction where the conduction band (C ₂ ) or valence band (V ₂ ) of the second semiconductor with a wide band gap is the bandgap of the first semiconductor with a narrow band gap. This can be achieved by a combination of materials located at the level within the band (F ₀₁ ), and is conventionally implemented by forming a thin film of tin oxide on n-type crystalline silicon. Note that F ₀₂ is a forbidden band of the second semiconductor, the portion is a depletion layer or an inversion layer, and F is a Fermi level. As a method of making tin oxide, it is made on n-type single crystal silicon.
CVD method (chemical vapor deposition)
The photoelectric conversion efficiency was 15.4% (Yamanaka, Hayashi, Murayama; Proceedings of the 40th Japan Society of Applied Physics Conference, p. 450 (1979)), and 10.5% by electron beam evaporation (T.Feng, AKGhosh, C.
Fishman; Appl.Phys.Lett. 34 , 198 (1979)), 12.3% by spray method (T.Feng, AKGhosh, C.
Fishman; Appl. Phys. Lett. 35 , 266 (1979)). However, because it takes time and effort to create single crystal silicon, it has not been useful enough as a low-cost, large-area photoelectric conversion device. In recent years, amorphous silicon obtained by the glow discharge decomposition method of silane (SiH ₄ ) contains hydrogen, which significantly reduces the localized electronic state density, making it possible to control valence electrons by adding group or group impurities. So, p type/n
pn junction type or Schottky barrier type photoelectric conversion elements have been produced. This amorphous silicon can be produced at a much lower cost and in a larger area than single crystal silicon, making it extremely promising as a material for low-cost, large-area photoelectric conversion elements. This isotype heterojunction photoelectric conversion device in which n-type tin oxide (SnO ₂ ) is placed on n-type amorphous silicon was fabricated by a tin oxide sputtering method (Okamoto and Hamakawa; Applied Physics 47 , 872 (1978). )) However, the sputtering method had the problem that the film formation rate of tin oxide was not fast. The present invention eliminates these drawbacks by forming tin oxide (SnO ₂ ) on n-type amorphous silicon by vacuum evaporation, and achieves a maximum film formation rate of 1000 A/sec. is,
This method is extremely promising as a method for manufacturing low-cost, large-area photoelectric conversion elements. In addition, in vacuum evaporation of tin oxide, the angle (θ) between the vacuum evaporation particle beam and the perpendicular to the substrate surface
It has been discovered that the photoelectric conversion characteristics of a vacuum-deposited tin oxide (SnO ₂ ) amorphous silicon n-n isotype heterojunction photoelectric conversion element can be significantly changed by changing the . A detailed explanation will be given below with reference to the drawings. Amorphous silicon is usually formed by glow discharge decomposition of silane, but there are capacitive and inductive methods to generate glow discharge. In the inductive method, a high frequency application method is performed. In addition to silane, silicon raw materials used include silane chloride (SiH ₃ Cl), silane dichloride (SiH ₂ Cl ₂ ), silane trichloride (SiHCl ₃ ), silane bromide (SiH ₃ Br), and silane dichloride (SiH 2 Cl 2 ). Silicon oxide (SiF ₄ ) alone or a mixture containing at least one of these can be used. Also, silicon tetrachloride (SiCl ₄ ) in a hydrogen gas stream
A similar amorphous silicon film can be obtained by using. In addition, by adding methane (CH ₄ ), acetylene (C ₂ H ₂ ), carbon tetrafluoride (CF ₄ ), nitrogen (N ₂ ), oxygen (O ₂ ), etc. as introduced gases, it is possible to By introducing carbon, nitrogen, oxygen, etc., the film strength can be increased or the sensitive wavelength range can be changed. Furthermore, the fermi level of amorphous silicon can be adjusted by adding phosphine (PH ₃ ) and diborane (B ₂ H ₆ ). When creating an amorphous silicon film, the substrate heating temperature is preferably in the range of 50° to 350°C.
The temperature is between 150° and 250°C. Amorphous silicon films are made by forming a heavily doped n ⁺ layer, usually several hundred angstroms long, on a conductive substrate to improve ohmic contact, and then depositing n-type amorphous silicon on top of it.
The thickness is preferably 0.2 to 2.0 μm, preferably 0.5 to 1.0 μm. Furthermore, when a transparent substrate and a transparent electrode are used, the present invention can also include an element in which tin oxide, amorphous silicon, and a surface electrode are formed in this order on the transparent substrate and transparent electrode. It may also be carried out by sputtering silicon in a hydrogen gas stream or by plasma reactive deposition in hydrogen gas, or by ion implantation of hydrogen into silicon films prepared by various methods. Good too. As the substrate, metal plates such as stainless steel, aluminum, and copper, glass, and synthetic resins such as polyethylene terephthalate can be used. A conductive electrode made of metal or the like is used on an insulating substrate such as glass or synthetic resin. The second semiconductor is tin oxide or a semiconductor mixed with at least one of indium oxide and antimony oxide, and is heated by resistance heating from a vapor deposition source of tin oxide or a mixture of indium oxide or antimony oxide. Vacuum evaporation or vacuum evaporation by electron beam and introduction of a small amount of oxygen, or reactive vacuum evaporation using oxygen introduction and plasma glow, or from a deposition source of tin or a mixture of tin and one of indium or antimony in an oxygen atmosphere. It is reactively vapor-deposited or reactively co-deposited. The thickness of this second semiconductor is at least 50 angstroms, with typical values ranging from 500 to 1000 angstroms. Further, the second semiconductor is not limited to a single layer, but may have a multilayer structure of two or more types with different compositions. The photoelectric conversion efficiency of the device may be dramatically improved by subjecting the device to heat treatment in an oxygen-containing atmosphere after depositing the second semiconductor. The temperature of heat treatment is 150℃ or higher and 400℃ or lower, preferably 250℃ or higher.
The temperature is 350°C or less, and the heat treatment time is 10 minutes or more and 5 hours or less. It has been found that the conversion efficiency of the photoelectric conversion element varies greatly depending on the angle (θ) between the perpendicular to the substrate surface and the direction of the evaporated particle flow during vacuum evaporation of tin oxide. When θ=0°, the resistance value of the attached tin oxide film is extremely large, 100KΩ・
cm or more, and even after heat treatment at 300°C for 3 hours, its resistance was 100Ω·cm, indicating that the photoelectric conversion efficiency of the device was extremely low. However, when θ exceeds 15°, the resistance value of tin oxide decreases rapidly, with a specific resistance of 0.1Ω・cm in the angle range of 30° to 60°.
The following can now be obtained, and it has come to show sufficient conversion efficiency as a photoelectric conversion element. As a method for producing tin oxide at high speed, it was confirmed that deposition speeds of several hundred A/sec can be easily achieved by vapor deposition of tin oxide by electron beam heating, and a deposition rate of 1000 A/sec is also possible. The n-n isotype heterojunction photoelectric conversion element of the present invention, which is a combination of amorphous silicon and a vacuum-deposited tin oxide film, can be formed over a large area at a faster deposition rate than ever before for both amorphous silicon and tin oxide films. It has been found that this manufacturing method is extremely promising for industrial use of low-cost, large-area photoelectric conversion elements. This will be described in detail below along with examples. Example 1 FIG. 3 is a cross-sectional view of a photoelectric conversion element manufactured according to this example, and the following description will be made with reference to this cross-sectional view. A substrate 1 of Corning type 7059 glass measuring 25 mm x 25 mm x 1 mm was placed in a first vacuum evaporator at a distance of 30 cm from the evaporation source, and the basic temperature remained at room temperature and the vacuum level was 5 x 10 ^-6 Torr. After evaporating 700 angstroms of aluminum by resistance heating, an alloy of nickel and chromium was formed without breaking the vacuum.
Deposit 300 angstroms. The glass on which the nickel chromium (NiCr)/aluminum (Al) layer 2 is vapor-deposited is used as a substrate for forming an amorphous silicon film. The second vacuum device for forming amorphous silicon film has a vacuum chamber of 45 mmφ x 20 cm, in which electrodes of 100 mmφ are placed 35 mm apart.
High frequency power can be applied between both electrodes. Attach the substrate to the anode side. The gas system of the device is shown in Figure 2. Set the substrate temperature to 300℃, and heat the vacuum chamber 6x.
After evacuation to 10 ^-6 Torr, 1 mol% of phosphine/silane-containing gas, the whole of which is 20% helium.
Introduce gas diluted to 0.12Torr.
The gas flow rate at this time was 30 c.c./min. Here, a high frequency of 13.56 MHz is applied at 10 W (0.13 W/cm ² ) to cause glow discharge for 4 minutes to form an n ⁺ -amorphous silicon layer 3 of 400 angstroms. Continue to use non-doped silane gas (20% helium dilution) to generate a glow discharge in the same way.
A 1 μm thick non-doped amorphous silicon layer 4 was formed over 50 minutes. The glass on which the amorphous silicon film was formed as described above is used as a substrate, and is attached to a substrate holder installed in a second vacuum device. This substrate holder is capable of rotating the substrate around a horizontal axis, and is set so that the vertical direction of the surface of the substrate forms an angle θ with a straight line connecting the evaporation source and the substrate. θ is
It is set in the range of 0° to 70°. The distance between the substrate and the evaporation source was 30 cm, and the substrate was heated to 200°C. Tin oxide (SnO ₂ , 99.999%) was used as the evaporation source, and heating was performed by an electron beam. Vacuum chamber is 8x
Exhausted to 10 ^-6 Torr. 2×10 ^-4 Torr during deposition
It became. A 0.1 μm thick tin oxide film 5 is formed by vapor deposition for 4 minutes through a mask in which 2 mm x 2 mm holes are lined up with 1 mm spacing between them. After evaporation, place 1mm in the center of the part where tin oxide was evaporated.
A silver paste of ×1 mm was applied to form the upper electrode 6.
This creates a cell with an effective area of 0.03 cm ² . The device formed by the method described above has both an open voltage short circuit current and a photoelectric conversion efficiency of 0. This element is placed in a constant temperature dryer and heat treated in an air atmosphere. Heat treatment temperatures below 200°C had little effect. After heat treatment at 300℃, as shown in Table 1, the open circuit voltage Voc and short circuit current
Isc and photoelectric conversion efficiency η increase. Here, when the element θ is different, the short circuit current and the photoelectric conversion rate are different.
Note that f·f in the table indicates a fill factor.

【table】
Measured with 〓
〃 No.6 is 〃 65mW
/ ^cm2 〓
(Note 2) Area is 0.03cm ²
Example 2 After performing the vapor deposition of tin oxide in the same manner as in Example 1, heat treatment was performed at 300°C for 3 hours, and then gold was vapor-deposited at 200A on the tin oxide. As shown in Table 2, f.
f. has been improved.

[Table] Example 3 Tin oxide was deposited in the same manner as in Example 1 (film thickness
500A), heat treated at 300°C for 1 hour, and then treated with indium in the same way as tin oxide.
Deposited Tein Oxide at 1000A, 300A in air
The characteristics of the device heat-treated at ℃ for 1 hour are: incident light 58mW/cm ² , effective area 0.03cm ² , Voc = 0.35V,
Isc = 220μA, ff = 0.22, η = 1.0%. Example 4 After forming an amorphous silicon film in the same manner as in Example 1, a tin oxide film was formed by reactive vapor deposition as described below. In addition to the configuration described in Example 1, a counter electrode is installed in the second vacuum device so that an electric field is applied in a direction perpendicular to the straight line connecting the evaporation source and the substrate. The electrode area was 100 mm x 100 mm, and the distance between the electrodes was 8 cm. During vapor deposition, after reducing the back pressure to 8×10 ^-6 Torr or less, oxygen gas was
10 ^-4 Torr is introduced and a high frequency discharge of 10W (0.1W/cm ² ) is generated. The vapor deposition heat source is the same as in Example 1.
The tin oxide film obtained by this method does not require heat treatment. Example 5 A device was manufactured using a method different from Example 1 except that the substrate was not heated (at room temperature) during film formation of tin oxide. Open circuit voltage Voc, short circuit current before heat treatment
Both Isc and photoelectric conversion efficiency η were 0, but the results shown in Table 3 were obtained by heat treatment at 300° C. for 1 hour.

[Table] Example 6 This is the same as Example 1, but some of the conditions for forming the amorphous silicon film are different, as described below. The diluent gas is argon, the substrate is heated to 230°C, and a 1 μm thick film is formed in 30 minutes. Other conditions are the same as in Example 1. After 500A tin oxide deposition and heat treatment at 300℃ for 15 minutes, the following properties were obtained. The effective area of the element is 0.15cm ² ,
The irradiation light intensity was 74 mW/cm ² . Open circuit voltage 0.46V, short circuit current 0.70mA, fill factor
0.40, photoelectric conversion efficiency 1.2% Example 7 Using the device obtained in Example 1, tin oxide vapor deposition,
After heat treatment, 500 Å of indium tein oxide (ITO) or antimony doped tin oxide (Sbdope SnO ₂ ) was deposited on it by electron beam evaporation in the same manner as non-doped tin oxide, and then it was heated in air at 300°C. After 1 hour of heat treatment,
Surface resistance becomes extremely small. (See Table 4)

【table】 [Brief explanation of the drawing]

Figure 1 is the energy band diagram of the photoelectric conversion element, Figure 2 is the energy band diagram of the photoelectric conversion element.
The figure is a diagram for explaining the gas system of the vacuum evaporation apparatus used in the present invention, and FIG. 3 is a sectional view of an example of a photoelectric conversion element manufactured by the method of the present invention. In the figure, 1 is the substrate, 2 is the NiCr/Al layer, and 3 is the substrate.
is an n ⁺ -amorphous silicon layer, 4 is a non-doped amorphous silicon layer, 5 is a tin oxide layer,
6 is an electrode.

Claims (1)

[Claims] 1. A manufacturing method for forming an isotype heterojunction photoelectric conversion element consisting of a first semiconductor mainly composed of amorphous silicon and a second semiconductor mainly composed of tin oxide, using the above-mentioned tin oxide by vacuum evaporation method. In the vacuum evaporation method described above, vapor deposition is performed so that the angle between the tin oxide vacuum evaporated particle beam and the perpendicular to the surface of the support is in the range of 30° to 60°, and then at a temperature of 150°C to 400°C for 10 A method for producing an isotype/heterojunction type photoelectric conversion element, characterized in that heat treatment is performed for at least 5 minutes.