JP2706352B2 - Photoelectric conversion device using compound semiconductor polycrystalline thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photoelectric conversion element using a compound semiconductor polycrystalline thin film.

[Prior Art] A conventional thin film photoelectric conversion element using a P-type compound semiconductor CuInSe ₂ as a light absorbing layer usually has a basic structure shown in FIG. In FIG. 3, reference numeral 6 denotes a substrate made of glass, ceramics, or the like, on which an electrode 7 made of molybdenum Mo, nickel Ni, or the like is formed. CuInSe ₂ is formed as the P-type semiconductor layer 8 on the electrode 7 by a physical vapor deposition method (multi-source vapor deposition method, sputtering method, or the like), a spray method, a plating method, or the like. Further, an n-type semiconductor layer 9 is formed on the P-type semiconductor layer 8 by the method described above. Cadmium sulfide CdS or cadmium sulfide CdS-zinc sulfide is used for the n-type semiconductor layer 9.
A ZnS solid solution is used. When a solid solution is used, its composition is usually uniform in the n-type semiconductor layer 9. The thicknesses of the P-type semiconductor layer 8 and the n-type semiconductor layer 9 depend on manufacturing conditions, but are generally 2.0 to 4.0 μm and 1.0 to 2.0 μm, respectively.
It is. On the n-type semiconductor layer 9, a mixed oxide of indium In and tin Sn (hereinafter referred to as ITO) or tin oxide SnO ₂ is formed by a method such as a vacuum evaporation method or a thermochemical evaporation method (hereinafter referred to as a thermal CVD method). Transparent electrode 10 is formed. Further, on the transparent electrode 10, a current collecting grid electrode 11 made of aluminum Al, gold Au, or the like is formed.

In the device having the structure shown in FIG.
The light enters from the side and is mainly absorbed in the P-type semiconductor layer 8. Electrons and holes are generated in the P-type semiconductor layer 8 which has absorbed light, but these are polarized by the internal electric field formed by the Pn junction, and the electrons are directed to the n-type semiconductor and the holes are directed to the P-type semiconductor. Each moves and is taken out to an external circuit through an electrode.

[Problems to be solved by the invention]

The photoelectric conversion device having the conventional basic configuration shown in FIG. 3 has the following problems.

(1) Thin films of CuInSe ₂ and cadmium sulfide CdS usually show strong orientation. Therefore, when a Pn junction is formed of CuInSe ₂ and cadmium sulfide CdS polycrystalline thin film, there is a difference between the respective plane distances, so local distortion occurs,
Many defects are generated near the Pn junction surface. Therefore, the light-generated electrons and holes are trapped by these defects and do not contribute to the current, so that the device characteristics are degraded.

(2) The n-type semiconductor layer is a light incident layer and has a function of transmitting light-generated electrons to the transparent electrode. Therefore, it is desirable that both the forbidden band width and the conductivity of the n-type semiconductor layer be large. Cadmium sulfide as n-type semiconductor layer
When CdS is used, zinc sulfide ZnS is usually dissolved in a solid solution to widen the forbidden band. However, in the case of this method, the forbidden band width increases with an increase in the amount of solid solution of zinc sulfide ZnS, but at the same time, the conductivity decreases. Therefore, when a film having a uniform composition is formed, both the forbidden band width and the conductivity cannot be increased.

The present invention has been made to solve the above problems, and has as its object to provide a photoelectric conversion element using a compound semiconductor polycrystalline thin film having good Pn characteristics.

[Means for solving the problem]

The photoelectric conversion element according to the present invention forms a window layer on the light incident side, and is formed of a cadmium sulfide CdS-zinc sulfide ZnS solid solution.
A n-type semiconductor layer, a transparent electrode bonded to one surface of the semiconductor layer on which light is incident, and a p-type semiconductor layer bonded to the other surface of the n-type semiconductor layer. The composition is characterized in that the composition thereof is inclined in the thickness direction so that the amount of solid solution of zinc ZnS is increased on the side close to the joint surface with the P-type semiconductor layer and becomes smaller as the joint surface approaches the joint surface with the transparent electrode.

[Action]

In the above, the amount of solid solution of zinc sulfide ZnS in the vicinity of the junction surface between the n-type semiconductor layer and the p-type semiconductor layer is adjusted, so that the difference in plane spacing between the p-type semiconductor layer and the n-type semiconductor layer becomes small, and the lattice matching becomes Due to the improved properties, local distortion is reduced. As a result, the number of defects generated near the Pn junction interface decreases, the number of electrons and holes generated by light, which are captured by these defects, decreases, and the current taken out to an external circuit increases.

Further, in forming the n-type semiconductor layer, the amount of solid solution of zinc sulfide ZnS decreases as approaching the bonding surface with the transparent electrode, so that the conductivity increases with the inclination of the composition. As a result, the internal resistance of the element decreases, and electrons generated inside the semiconductor layer efficiently flow to the transparent electrode.

As described above, in the conversion element of the present invention, a good Pn junction is formed, and electrons and holes generated by light in the semiconductor are efficiently extracted to an external circuit. Therefore, an increase in short-circuit current and fill factor is expected. Can be.

〔Example〕

 One embodiment of the present invention is shown in FIG.

In this embodiment shown in FIG. 1, a substrate 1 made of glass, a transparent electrode 2 formed on the substrate 1 and made of tin oxide SnO _{2 and} having a thickness of 2000 °, and a solid solution of zinc sulfide ZnS formed on the transparent electrode 2 are formed. The dissolution amount decreases as approaching the bonding surface with the transparent electrode 2, and the n-type semiconductor layer 3 made of cadmium sulfide CdS and zinc sulfide ZnS is formed on the n-type semiconductor layer 3, and the copper Cu, indium In and selenium Se— A P-type semiconductor layer 4 made of a copper-Cu alloy,
And a metal electrode 5 made of molybdenum M _o thickness 0.5μm is formed on the P-type semiconductor layer 4.

 The forming procedure of the present embodiment will be described below.

First, on a substrate 1 made of glass, a thickness 2
A transparent electrode 2 made of tin oxide SnO _{2 of} 000 ° is formed. The glass substrate 1 on which the transparent electrode 2 was formed was subjected to ultrasonic cleaning in acetone, methanol and pure water sequentially, and then dried.

N-type semiconductor layer 3 and P formed on transparent electrode 2
The mold semiconductor layer 4 was formed by a high frequency sputtering method, which is one of the physical vapor deposition methods. Regarding the formation of the n-type semiconductor layer 3, the glass substrate 1 with
The substrate 1 was evacuated to 5.0 × 10 ⁻⁷ Torr and heated to a predetermined temperature, and argon was introduced into the chamber to adjust the flow rate so that the pressure became 5.0 × 10 ⁻³ Torr. adjust. Subsequently, the shutter was closed to form plasma in order to keep a state between the target from which atoms evaporate and the substrate 1 were cut off, and the target surface was cleaned for about 5 minutes. Next, after setting the high-frequency power to a predetermined value, the shutter was opened and sputtering was performed for a predetermined time to form an n-type semiconductor layer 3. The n-type semiconductor layer 3 is a cadmium sulfide CdS sintered body (purity 99.99%, diameter 101.6 mm, thickness 5 mm)
And sintered zinc sulfide ZnS (purity 99.99%, diameter 101.6m
m, a thickness of 5 mm) as a target and by simultaneously sputtering while rotating the substrate 1. At this time, the high-frequency power applied to the electrodes of both targets was controlled in accordance with the film formation time, and the solid solution amount of zinc sulfide ZnS in the thickness direction in the n-type semiconductor layer 3 was changed to P-type as shown in FIG. It was changed so that it was larger on the side closer to the bonding surface with the semiconductor layer 4 and smaller as it came closer to the bonding surface with the transparent electrode 2. Considering the consistency of the spacing between CuInSe ₂ forming the P-type semiconductor layer 4 and the solid solution amount of zinc sulfide ZnS near the bonding surface (d = 0 in FIG. 2) with the P-type semiconductor layer 4 5-1
It is considered that about 0% is appropriate. In order to reduce the internal resistance of the element, the amount of solid solution of zinc sulfide ZnS near the bonding surface (d = d _{1 in} FIG. 2) with the transparent electrode 2 is 1 to 3.
% Is considered appropriate.

Subsequent to the n-type semiconductor layer 3, a P-type semiconductor layer 4 was similarly formed by a high frequency sputtering method. The formation procedure is the same as that of the n-type semiconductor layer 3, but in the case of the P-type semiconductor layer 4, copper Cu (purity 99.99%) and indium In (purity 99.99%).
%) And selenium Se-copper Cu alloy (copper 20% by weight) as targets, and the composition was controlled by adjusting the respective high-frequency currents.

In this embodiment, the n-type semiconductor layer 3 and the p-type semiconductor layer 4
The substrate temperature and the film thickness at the time of forming were respectively as follows.

Molybdenum M with a thickness of 0.5 μm following the P-type semiconductor layer 4
The metal electrode 5 made of o was formed by a high frequency sputtering method.

For comparative evaluation with the device of the present embodiment, a conventional device in which the solid solution amount of zinc sulfide ZnS in the n-type semiconductor layer 3 was made uniform and the film forming conditions other than the n-type semiconductor layer 3 were the same as in the present embodiment. The simulated sunlight (spectral AM
1.5, irradiation intensity of 100 mW · cm ⁻² ), and the device characteristics were evaluated. As a result, it was confirmed that the device in which the composition of the n-type semiconductor layer 3 of this example was graded increased the short-circuit current and the fill factor by 10 to 20% as compared with the conventional device in which the composition was uniform. .

In the above description, the composition near the junction surface of the n-type semiconductor layer 3 with the p-type semiconductor layer 4 is adjusted and lattice matching is improved, so that local distortion is reduced as compared with the conventional device. As a result, generation of a defect serving as a center for capturing electrons and holes is suppressed.

In addition, since the n-type semiconductor layer 3 gradually reduces the solid solution amount of zinc sulfide ZnS from the bonding surface with the P-type semiconductor layer 4 toward the bonding surface with the transparent electrode 2, the conductivity of the n-type semiconductor layer 3 increases with the inclination of the composition. Increase. As a result, the internal resistance of the device decreases.

As described above, in the photoelectric conversion element of this embodiment, good Pn
Since a junction is formed and electrons and holes generated by light in the semiconductor are efficiently extracted to an external circuit, an increase in short-circuit current and fill factor can be expected.

〔The invention's effect〕

In the photoelectric conversion element of the present invention, for an n-type semiconductor layer in which a P-type semiconductor layer is joined to one surface and a transparent electrode is joined to the other surface, the solid solution amount of zinc sulfide ZnS is determined for the P-type semiconductor layer. By inclining the composition in the thickness direction so that it increases near and decreases near the transparent electrode, the occurrence of defects near the Pn junction surface is suppressed, the conductivity near the transparent electrode is increased, and Electrons and holes generated by light can be efficiently extracted to an external circuit, and a short-circuit current and a fill factor can be increased.

[Brief description of the drawings]

FIG. 1 is an explanatory view of one embodiment of the present invention, FIG. 2 is an explanatory view of a change in the amount of solid solution of zinc sulfide ZnS in the n-type semiconductor layer of the one embodiment, and FIG. FIG. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Transparent electrode, 3 ... N-type semiconductor layer, 4 ... P-type semiconductor layer, 5 ... Metal electrode.

Claims (1)

(57) [Claims] Cadmium sulfide Cd is formed on a light incident side window layer.
An n-type semiconductor layer made of a solid solution of S-zinc sulfide ZnS, a transparent electrode bonded to one surface of the semiconductor layer on which light is incident, and a P-type semiconductor layer bonded to the other surface of the n-type semiconductor The solid solution amount of zinc sulfide ZnS in the n-type semiconductor layer is P
Using a compound semiconductor polycrystalline thin film, characterized in that its composition is inclined in the thickness direction so that it increases on the side close to the junction with the type semiconductor layer and decreases toward the junction with the transparent electrode. Conversion element.